1
Forestry
ENERGYPlantation&Biofuel
s
2
By Javed Iqbal
ENERGY PLANTATION AND BIO-FUELS 3(2-1)
Objective:
To develop understanding regarding the prospects and possibilities of raising bioenergy plantations,
bio-fuel production, and conversion technologies.
Course Outlines:
Theory
Introduction and advantages of energy plantations. Global overview of energy and biomass
consumption patterns. Energy and biomass consumption patterns in Pakistan. Environmental
impacts of biomass energy.
Basic concepts of forest production ecology; the biomass production potential of a forest ecosystem;
production of energy wood at special short-rotation plantations; use of residual biomass from
traditional forestry operations for energy; harvesting and transportation logistics of energy wood
production.
A brief introduction to bio-energy conversion technologies; utilization of bio-energy with reference
to the global carbon cycle and climatic change, especially with regard to CO 2 emissions and carbon
storage; and the role of bio-energy in Pakistan and other countries, especially its potential for the
development of rural areas.
Assessment of bio-energy programs in Pakistan. Power generation from energy plantation, biomass
gasification-producer gas. High Density Energy Plantations (HDEP).Land and biomass availability for
sustainable bio energy.
Bio-fuels introduction, Tree Born Oils (TBO‘s), potentials and advantages, bio-diesel transesterification, Important bio-fuel species and their silvicultural management.
Overview of the markets for wood biomass for energy production globally and within the Pakistan
this includes the supply, quantity, demand, and consumption as well as consumer market aspects.
Fundamentals of the policies that have impacts on the supply and consumption of the energy wood;
wood based fuels; and/ or bio-energy and bio-fuels‘ markets
Need for research and development on environment friendly and socio economically relevant
technologies. Energy from plants-problems and prospects. Petro-crops. Criteria for evaluation of
different species for energy plantation.
Advanced energy technologies in the production of bio-fuels
Practical:
Identification of important fuel woods and petro-crops. Study of different properties of bio fuels used
in Pakistan. Determination of calorific value, moisture and ash content in biomass. Study of energy
consumption pattern in rural and urban areas through survey. Visit to nearby Bio-energy units.
Suggested Readings
1. Donald L. Klass. 2010. Biomass for Renewable Energy, Fuels, and Chemicals. Amazon Publishers
2. Snelder, D.J. & Lasco. R. 2008. Small Holder Tree Growing for Rural Development and
Environmental Services. Springer Publisher.
3. Kumar V. 1999. Nursery and Plantation Practice in Forestry. Scientific Publications.
4. Luna RK. 1989. Plantation Forestry in India. International Book Distributors.
5. Chaturvedi AN. 1994. Technology of Forest Nurseries. Khanna Bandhu
6. William, B. R. & Gowen. 1994. Forest Resources and Wood based biomass. Oxford and IBH New
Delhi.
3
CHAPTER NO. 01
INTRODUCTION TO ENERGY PLANTATION
Globally, woodfuels are the main and often the only accessible energy sources for over two billion people,
including the poorest segments of rural and sub-urban populations. Forest resources can be placed into
two categories: industrial wood and fuelwood (USDA Forest Service 1989). Industrial wood is all
merchantable wood, also known as roundwood, which is utilized for lumber, timber, pulp and paper, and
other commercial products. Fuelwood is roundwood that is used for fuel plus forest residues. Forest
residues can in turn be broken down into three groupings: slash from final fellings, slash and small trees
from thinning and cleanings, and un-merchantable wood (EUBIA 2007).
1.1 ENERGY PLANTATION
Technically speaking, energy plantation means growing select species of trees and shrubs which are
harvestable in a comparably shorter time and are specifically meant for fuel.
Energy plantation is the practice of planting trees, purely for their use as fuel. Terrestrial biomass i.e., the
wood plants has been used since long time to generate fire for cooking and other purposes. In recent
years, to meet the demand of energy, plantation of energy plants has been re-emphasized.
According to a report, if fuel/fire wood plants were not raised rapidly, by 2,000 AD more than 250 millions
people would not be able to manage fuels for cooking purpose and, therefore, they would be forced to
burn animal dung which, however, depends on availability of animals and agricultural crop residues
(Anonymous, 1980 c). Same situation occur in past few years which make the human to think about the
alternative uses of energy resources.
The fuel wood may be used either directly in wood burning stoves and boilers or processed into
methanol, ethanol and producer gas. These plantations help provide wood either for cooking in homes
or for industrial use, so as to satisfy local energy needs in a decentralised manner. The energy
plantations provide almost inexhaustible renewable sources (with total time constant of 3-8 years only
for each cycle) of energy which are essentially local and independent of unreliable and finite sources
of fuel . The attractive features of energy plantations are: (a) heat content of wood is similar to that of
coal, (b) wood is low in sulphur and not likely to pollute the atmosphere, (c) ash from burnt wood is a
valuable fertiliser, (d) utilisation of erosion prone land for raising these plantations helps to reduce wind
and water erosion, thereby minimising hazards from floods, siltation, and loss of nitrogen and minerals
from soil and (e) help in rural employment generation - it is estimated that an hectare of energy
plantation is estimated to provide employment for at least seven persons regularly. Selection of
multipurpose species provides a number of by-products like oils, organic compounds, fruits, edible leaves,
forage for livestock, etc. Data collected from Forest Department (India) reveals that annual woody
biomass available is in the range 11.9 to 21 t/ha/yr. An energy forest raised at Hosalli village in Tumkur
district to support a wood gasifier plant has annual yield of 6 t/ha/yr.
1.1.1 Status of Forest and Fuelwood
India is the biggest fuel wood producing country in the world, but the per capita fuel wood production is
very low i.e. 290 m2/head. Mitchell (1979) estimated that the need of fire wood for cooking purpose in
India is 0.8 kg per capita per day. But this value does not hold good for cold areas where firewood is also
required for keeping houses warm.
Energy plays a pivotal role in socio-economic development by raising standard of living. Biomass has been
used as an energy source for thousands of years by the humankind. Traditional fuels like firewood, dung
and crop residues currently contribute a major share in meeting the everyday energy requirements of
rural and low-income urban households in Pakistan. An average biomass using household consumes
2325 kg of firewood or 1480 kg of dung or 1160 kg of crop residues per annum. There are good prospects
for using biogas energy in rural areas through a network of community biogas plants. Development of
fuel-efficient cook stoves is a modest effort to help conserve biomass energy at domestic level. PCRET has
so far installed 60,000 energy-conserving, improved cooking stoves all over the country, which are 12–
28% efficient. E-10 gasoline pilot project and research on biodiesel production are underway. Sugarcane
bagasse can potentially be used to generate 2000 MW of electric power. Attention is now being given to
the use of municipal and industrial waste for power generation. The government is financing many
4
projects related to biomass energy development in the country, but still lot more efforts are needed for
harnessing full potential and taking maximum benefit out of this important renewable energy resource.
In Pakistan, conditions of hills are quite different from that of plains. The villagers hardly get fire-wood
plants, as they have to go in interior of forest and collect wood-falls. Even they have very limited right to
fell trees and therefore, they depend on wood, falls and loppings of minor tree branches. If one talks
about to meet their needs by making available technologies developed for plains, it is not feasible. For
example, they cannot be motivated to use solar cooker, because of being solely traditional to which
religious factors have been associated. Even gobar gas plant cannot be useful in hills, because of
prevailing low temperature in mountain belt. Therefore, the search for renewable source of energy is
highly desirable for survival of population in hills and for reducing the pressure on forests.
About 200 billion tonnes of carbon per year is fixed photosynthetically into the terrestrial and aquatic
biomass. This amount of biomass contains 3,000 billion giga (109) jules energy every year. It has been
estimated that at present, only one seventh of the World's total energy comes from biomass and a large
amount of it remains untapped.
In view of getting maximum biomass, afforestation and forest management systems will have to be
developed. These must include social forestry, silviculture (short-rotation forestry) tree-use systems,
coppicing system, drought, salt-, pollutant - resistant plantations and high density energy plantations
(HDEP). HDEP is the practice of planting trees at close spacing. This leads to rapid growth of trees due to
struggle for survival. It provides quick and high returns, and opportunities for permanent income and
employment.
Therefore, annual plants should be grown to meet the demand of energy. Keeping in view the climatic
and edaphic factors, plantation of deciduous trees should be encouraged, as their growth is faster than
the coniferous ones. The species to be planted should have the following characters:
(i) Fast growth, (ii) Stress resistance, (iii) Less palatable to cattle and other animals, (iv) Early propagable,
(v) High caloric value, (vi) Absence of deleterious volatiles when smokes come out, (vii) High yield of
biomass, and (viii) Disease/pest resistant.
1.1.2 Social Forestry
Plantation through social forestry has been much emphasized by the Government to meet the demand of
fuel and fodder in the rural areas. It will certainly decrease the gradually increasing pressure on the
forests. This includes planting trees along road sides, canals, railway lines and waste lands in villages.
Some of important plants are: Acacia nilotica, Albizia lebbek, A. procera, Anthocephalus chinensis,
Azadirachta indica, Bauhinia variegata, Butea monosperma, Cassia fistula, Dalbergia sissoo, Eucalyptus
globulus, E. citriodora, Ficus glomerata, Lagerstroemia speciosa, Madhuca indica, Morus alba, Populus
ciliata, P. nigra, Terminalia arjuna, Toona ciliata, Salix alba and S. tetrasperma.
1.1.2.1 Silviculture Energy Farms (Short Rotation Forestry)
Silviculture energy farms employ techniques more similar to agriculture than forestry. The chief objective
of energy plantation is to produce biomass from the selected trees and shrub species in the shortest
possible time (generally 5-10 yrs) and at the minimal cost, so as to satisfy local energy needs in the
decentralized manner. This would certainly relieve the pressure on the consumption of fossil fuel like
kerosene and prevent the destruction of plant cover which is one of the primary components of the life
support system (Khoshoo, 1988).
1.1.2.2 Advantages of Short Rotation Management
Jahn (1982) has discussed the following advantages from short rotation management from production of
fuel biomass :
(i) High yield per unit of land area,
(ii) Smaller land requirements for given biomass output,
(iii) Shorter time span from initial stand establishment to harvestable crop,
(iv) Increased labor efficiency through mechanization and other methods similar to those used in
agriculture,
(v) Ability of most short rotation species to regenerate by coppicing; and
(vi) Ability to take advantages of cultural and genetic advances quickly.
Therefore, production of plant-based renewable energy is a part of the dynamic agro-botany-forestry
system and the need is to integrate both modern biology and culture in agriculture (Khoshoo, 1988, p.
356).
5
1.2 ADVANTAGES OF ENERGY PLANTATIONS.
1.2.1 Biomass Energy and its Benefits
Biomass is a substantial renewable resource that can be used as a fuel for producing electricity and other
forms of energy. Biomass feedstock, or energy sources, are any organic matter available on a renewable
basis for conversion to energy. Agricultural crops and residues, industrial wood and logging residues, farm
animal wastes, and the organic portion of municipal waste are all biomass feedstock.
Biomass fuels, also known as biofuels, may be solid, liquid, or gas and are derived from biomass
feedstock. Biofuel technologies can efficiently transform the energy in biomass into transportation,
heating, and electricity generating fuels.
Biomass is a proven option for electricity generation. Biomass used in today's power plants includes wood
residues, agricultural/farm residues, food processing residues (such as nut shells), and methane gas from
landfills. In the future, farms cultivating energy crops, such as trees and grasses, could significantly
expand the supply of biomass feedstock. Currently, there are over 7000 megawatts of biomass power
capacity installed at more than 350 plants in the U.S. (DOE, NREL, 1998). These plants are owned by a
diverse range of producers including the pulp and paper industry, wood manufacturing industry, electric
utilities, and independent power producers.
(a) Economic Benefits
Economic activity associated with biomass currently supports about 66,000 jobs in the U.S., most of which
are in rural regions. It is predicted that by the year 2010, over 13,000 megawatts of biomass power could
be installed, with over 40 percent of the fuel supplied from 4 million acres of energy crops and the
remainder from biomass residues (DOE, NREL, 1998). This would support over 170,000 U.S. jobs and
could significantly benefit rural economies.
Use of biofuels can reduce dependence on out-of-state and foreign energy sources, keeping energy
dollars invested in Ohio's economy. Biomass energy crops can be a profitable alternative for farmers,
which will complement, not compete with, existing crops and provide an additional source of income for
the agricultural industry. Biomass energy crops may be grown on currently underutilized agricultural land.
In addition to rural jobs, expanded biomass power deployment can create high skill, high value job
opportunities for utility, power equipment, and agricultural equipment industries.
(b) Environmental Benefits
 Biomass fuels produce virtually no sulfur emissions, and help mitigate acid rain.
 Biomass fuels "recycle" atmospheric carbon, minimizing global warming impacts since zero "net"
carbon dioxide is emitted during biomass combustion, i.e. the amount of carbon dioxide emitted
is equal to the amount absorbed from the atmosphere during the biomass growth phase.
 The recycling of biomass wastes mitigates the need to create new landfills and extends the life of
existing landfills.
 Biomass combustion produces less ash than coal, and reduces ash disposal costs and landfill
space requirements. The biomass ash can also be used as a soil amendment in farm land.
 Perennial energy crops (grasses and trees) have distinctly lower environmental impacts than
conventional farm crops. Energy crops require less fertilization and herbicides and provide
greater vegetative cover throughout the year, providing protection against soil erosion and
watershed quality deterioration, as well as improved wildlife cover.
 Landfill gas-to-energy projects turn methane emissions from landfills into useful energy.
1.2 GLOBAL OVERVIEW OF ENERGY AND BIOMASS CONSUMPTION PATTERNS.
World Energy Consumption refers to the total energy used by all of human civilization.
Typically measured per-year, it involves all energy harnessed from every energy source we use, applied
towards humanity's endeavors across every industrial and technological sector, across every country.
Being the power source metric of civilization, World Energy Consumption has deep implications for
humanity's social-economic-political sphere.
Institutions such as the International Energy Agency (IEA), the U.S. Energy Information
Administration (EIA), and the European Environment Agency record and publish energy data periodically.
Improved data and understanding of World Energy Consumption may reveal systemic trends and
6
patterns, which could help frame current energy issues and encourage movement towards collectively
useful solutions.
According to IEA (2012) the climate goal of limiting warming to 2 °C is becoming more difficult and costly
with each year that passes. If action is not taken before 2017, all the allowable CO2 emissions would be
locked-in by energy infrastructure existing in 2017. Fossil fuels are dominant in the global energy mix,
supported by $523 billion subsidies in 2011, up almost 30% on 2010 and six times more than subsidies to
renewable.
Fossil energy use increased most in 2000-2008. In October 2012 IEA wrote last decade ca half of the
increased energy use is coal, growing faster than all renewable energy. Since Chernobyl disaster in 1986
investments in nuclear power have been small.
Trend
Energy use (TWh)
According to IEA data from 1990 to 2008,
Fossil Nuclear Renewable Total
the average energy use per person
increased 10% while world population 1990
83,374 6,113 13,082
102,569
increased 27%. Regional energy use also
94,493 7,857 15,337
117,687
grew from 1990 to 2008: the Middle East 2000
increased by 170%, China by 146%, India by 2008
117,076 8,283 18,492
143,851
91%, Africa by 70%, Latin America by 66%,
Change 2000-2008 22,583 426
3,155
26,164
the USA by 20%, the EU-27 block by 7%, and
world overall grew by 39%.
In 2008, total worldwide energy consumption was 474 exajoules (474×1018 J=132,000 TWh). This is
equivalent to an average power use of 15 terawatts (1.504×1013 W).The potential for renewable energy
is: solar energy 1600 EJ (444,000 TWh), wind power 600 EJ (167,000 TWh), geothermal energy 500 EJ
(139,000 TWh), biomass250 EJ (70,000 TWh), hydropower 50 EJ (14,000 TWh) and ocean energy 1 EJ (280
TWh).
Energy consumption in the G20 increased by more than 5% in 2010 after a slight decline of 2009. In 2009,
world energy consumption decreased for the first time in 30 years, by −1.1% (equivalent to 130
Megatonnes of oil), as a result of the financial and economic crisis, which reduced world GDP by 0.6% in
2009.
This evolution is the result of two contrasting trends: Energy consumption growth remained vigorous in
several developing countries, specifically in Asia (+4%). Conversely, in OECD, consumption was severely
cut by 4.7% in 2009 and was thus almost down to its 2000 levels. In North America, Europe and the CIS,
consumptions shrank by 4.5%, 5% and 8.5% respectively due to the slowdown in economic activity. China
became the world's largest energy consumer (18% of the total) since its consumption surged by 8%
during 2009 (up from 4% in 2008). Oil remained the largest energy source (33%) despite the fact that its
share has been decreasing over time. Coal posted a growing role in the world's energy consumption: in
2009, it accounted for 27% of the total.
Most energy is used in the country of origin, since it is cheaper to transport final products than raw
materials. In 2008 the share export of the total energy production by fuel was: oil 50% (1,952/3,941 Mt),
gas 25% (800/3,149 bcm), hard coal 14% (793/5,845 Mt) and electricity 1% (269/20,181 TWh).
Most of the world's energy resources are from the conversion of the sun's rays to other energy forms
after being incident upon the planet. Some of that energy has been preserved as fossil energy, some is
directly or indirectly usable; for example, via wind, hydro- or wave power. The amount of energy is
measured by satellite to be roughly 1368 watts per square meter, though it fluctuates by about 6.9%
during the year due to the Earth's varying distance from the sun. This value is the total rate of solar
energy received by the planet; about half, 89 PW, reaches the Earth's surface.
The estimates of remaining non-renewable worldwide energy resources vary, with the remaining fossil
fuels totaling an estimated 0.4 YJ (1 YJ = 1024J) and the available nuclear fuel such as uranium exceeding
2.5 YJ. Fossil fuels range from 0.6 to 3 YJ if estimates of reserves of methane clathrates are accurate and
become technically extractable. The total energy flux from the sun is 3.8 YJ/yr, dwarfing all nonrenewable resources.
Regional energy use (kWh/capita & TWh) and growth 1990–2008 (%)
kWh/capita
Population (million)
Energy use (1,000 TWh)
7


1990
2008
Growth
1990
2008
Growth
1990
2008
Growth
USA
89,021
87,216
– 2%
250
305
22%
22.3
26.6
20%
EU-27
40,240
40,821
1%
473
499
5%
19.0
20.4
7%
Middle East
19,422
34,774
79%
132
199
51%
2.6
6.9
170%
China
8,839
18,608
111%
1,141
1,333
17%
10.1
24.8
146%
Latin
America
11,281
14,421
28%
355
462
30%
4.0
6.7
66%
Africa
7,094
7,792
10%
634
984
55%
4.5
7.7
70%
India
4,419
6,280
42%
850
1,140
34%
3.8
7.2
91%
Others*
25,217
23,871
nd
1,430
1,766
23%
36.1
42.2
17%
The World
19,422
21,283
10%
5,265
6,688
27%
102.3
142.3
39%
Source: IEA/OECD, Population OECD/World Bank
Energy use = kWh/capita* Mrd. capita (population) = 1000 TWh
Others: Mathematically calculated, includes e.g. countries in Asia and Australia. The use of
energy varies between the "other countries": E.g. in Australia, Japan or Canada energy is used more
per capita than in Bangladesh or Burma.
Energy Supply vs. End Use
Total world energy supply is distinct from actual world energy usage due to energy loss. For example, in
2008, total world energy supply was 143,851 TWh, while end use was 98,022 TWh. Energy loss depends
on the energy source itself, as well as the technology used. For example, Nuclear Power (as of 2008) loses
67% of its energy to water cooling systems.
In 2008, world nuclear energy was 8,283 TWh (constituting 5.8% of total world energy), while nuclear
energy end-use was 2,731 TWh (2.8%). Some renewable energy sources have small energy losses,
although hydropower has essentially non-existent energy loss.
Given significant energy supply-to-usage ratios, It is important to note these differences across various
energy sources.
Emissions
Global warming emissions resulting from energy production are a serious environmental problem. Efforts
to resolve this include the Kyoto Protocol, which is a UN agreement aiming to reduce harmful climate
impacts, which a number of nations have signed. Dangerous concentration remains a subject of debate. A
global temperature rise of 2 degrees Celsius is considered high risk by the SEI. Even to limit global
temperature rise to 2 degrees Celsius demands a 75% decline in carbon emissions in industrial countries
by 2050, if the population is 10 mrd in 2050.Across 40 years, this averages to a 2% decrease every year. In
2011, the warming emissions of energy production continued rising regardless of the consensus of the
basic problem. According to Robert Engelman (World watch institute), in order to prevent collapse,
human civilization must stop increasing emissions within a decade regardless of the economy or
population (2009).
Primary Energy
The United States Energy Information Administration regularly World energy and power supply (TWh)
publishes a report on world consumption for most types of
Energy
Power
primary energy resources. According to IEA total world energy
1990
102 569
11 821
supply was 102,569 TWh (1990); 117,687 TWh (2000); 133,602
TWh (2005) and 143,851 TWh (2008). World power generation
2000
117 687
15 395
was 11,821 TWh (1990); 15,395 TWh (2000); 18,258 TWh
2005
133 602
18 258
(2005) and 20,181 TWh (2008). Compared to power supply
20,181 TWh the power end use was only 16,819 TWh in 2008
2008
143 851
20 181
including EU27: 2 857 TWh, China 2 883 TWh and USA 4 533
Source: IEA/OECD
TWh. In 2008 energy use per person was in the USA 4.1 fold, EU
1.9 fold and Middle East 1.6 fold the world average and in China 87% and India 30% of the world average.
8
In 2008 energy supply by power source was oil 33.5%, coal 26.8%, gas 20.8% (fossil 81%), 'other'
(hydro, peat, solar, wind, geothermal power, biofuels etc.) 12.9%, and nuclear 5.8%. Oil was the most
popular energy fuel. Oil and coal combined represented over 60% of the world energy supply in 2008.
Since the annual energy supply increase has been high, e.g. 2007–2008 4,461 TWh, compared to the total
nuclear power end use 2,731 TWh environmental activists, like Greenpeace, support increase of energy
efficiency and renewable energy capacity. These are also more and more addressed in the international
agreements and national Energy Action Plans, like the EU 2009 Renewable Energy Directive and
corresponding national plans. The global renewable energy supply increased from 2000 to 2008 in total
3,155 TWh, also more than the nuclear power use 2,731 TWh in 2008. The energy resources below show
the extensive reserves of renewable energy.
Energy by power source 2008
TWh
%
Regional energy use (kWh/cap.)
kWh/capita Population (mil)
Fossil
Oil
48 204
33.5% fuels
1990 2008
1990
2008
The
Coal
38 497
26.8% twenti
USA 89 021 87 216
305
eth
Gas
30 134
20.9%
EU-27 40 240 40 821
centur
Nuclear
8 283
5.8%
Middle East 19 422 34 774
199
y saw
Hydro
3 208
2.2% a rapid
China 8 839 18 608
1 333
twenty
Other RE*
15 284
10.6%
Latin America 11 281 14 421
462
fold
Others
241
0.2% increa
Africa 7 094 7 792
984
se
in
Total
143 851
100%
India 4 419 6 280
1 140
the
Source: IEA *`=solar, wind, geothermal use of
The World 19 421 21 283
6 688
and biofuels fossil
Source: IEA/OECD, Population OECD/World Bank
fuels. Between 1980 and 2006, the worldwide
Average power in TW
annual growth rate was 2%. According to the
Fuel type
US Energy Information Administration's 2006
1980
2004
2006
estimate, the estimated 471.8 EJ total
Oil
4.38
5.58
5.74
consumption in 2004 was divided as given in the
Gas
1.80
3.45
3.61
table above, with fossil fuels supplying 86% of the
world's energy:
Coal
2.34
3.87
4.27
Coal fueled the industrial revolution in the 18th
Hydroelectric
0.60
0.93
1.00
and 19th century. With the advent of the
automobile, airplanes and the spreading use of
Nuclear power
0.25
0.91
0.93
electricity, oil became the dominant fuel during the
wind,
twentieth century. The growth of oil as the largest Geothermal,
0.02
0.13
0.16
solar
energy,
wood
fossil fuel was further enabled by steadily dropping
prices from 1920 until 1973. After the oil shocks
Total
9.48
15.0
15.8
of 1973 and 1979, during which the price of oil
Source: The USA Energy Information Administration
increased from 5 to 45 US dollars per barrel, there
was a shift away from oil. Coal, natural gas, and nuclear became the fuels of choice for electricity
generation and conservation measures increased energy efficiency. In the U.S. the average car more than
doubled the number of miles per gallon. Japan, which bore the brunt of the oil shocks, made spectacular
improvements and now has the highest energy efficiency in the world. From 1965 to 2008, the use of
fossil fuels has continued to grow and their share of the energy supply has increased. From 2003 to 2008,
coal was the fastest growing fossil fuel.
If production and consumption of coal continue at the rate as in 2008, proven and economically
recoverable world reserves of coal would last for about 150 years. This is much more than needed for a
irreversible climate catastrophe. Coal is the largest source of carbon dioxide emissions in the world.
According to IEA Coal Information (2007) world production and use of coal have increased considerably in
9
recent years. According to James Hansen the single most important action needed to tackle the climate
crisis is to reduce CO2 emissions from coal.
Coal
Regional coal supply (TWh), share 2010 (%) and share of change 2000–2010
2000
2008
2009*
2010*
%*
Change
2000–2009*
North America
6,654
6,740
6,375
6,470
16%
-1.2%
Asia excl. China
5,013
7,485
7,370
7,806
19%
18.9%
China
7,318
16,437
18,449
19,928
48%
85.5%
EU
3,700
3,499
3,135
3,137
8%
-3.8%
Africa
1,049
1,213
1,288
1,109
3%
0.4%
Russia
1,387
1,359
994
1,091
3%
-2.0%
Others
1,485
1,763
1,727
1,812
4%
2.2%
Total
26,607
38,497
39,340
41,354
100%
100%
Source:
IEA,
*in
2009,
2010
BP*
Change 2000–2009: Region's share of the world change +12,733 TWh from 2000 to 2009
In 2000 coal was used in China 28%, other Asia 19%, North America 25% and the EU 14%. In 2009 the
share of China was 47%.
Single most coal using country is China.
It's share of the world coal production was 28% in 2000 and
Top 10 coal exporters (Mt)
48% in 2009. Coal use in the world increased 48% from 2000 to
Share 2009. In practice majority of this growth occurred in China and
2010 2011
2011 % the rest in other Asia.
1 Indonesia 162 309 29.7% World annual coal production increased 1,905 Mt or 32% in 6
year in 2011 compared to 2005, of which over 70% was
2
Australia 298 285 27.4% in China and 8% on India. Coal production was in 2011 7,783 Mt,
3
Russia
89
99 9.5% and 2009 6,903 Mt, equal to 12.7% production increase in two
years.
4
US
57
85 8.2% Indonesia and Australia exported together 57.1% of the world
5
Colombia
68
76 7.3% coal export in 2011. China, Japan, South Korea, India and Taiwan
had 65% share of all the world coal import in 2011.
6 South Africa
68
70 6.7%
Gas
7 Kazakhstan
33
34 3.3%
In
Regional gas supply (TWh) and share 2010 (%)
2009
8
Canada
24
24 2.3%
2000 2008 2009* 2010*
%
the
9
Vietnam
21
23 2.2%
worl
North America 7,621 7,779 8,839 8,925 27%
d
use
10
Mongolia
17
22 2.1%
Asia excl. China 2,744 4,074 4,348 4,799 14%
of
X
Others
19
14 1.3%
China
270
825 1,015 1,141 3%
gas
was
Total (Mt) 856 1041
EU 4,574 5,107 4,967 5,155 16%
131%
Top ten 97.8% 98.7%
Africa
612
974 1,455 1,099 3% comp
ared to year 2000. 66% of the this
Russia 3,709 4,259 4,209 4,335 13%
growth was outside EU, North America
Latin
Latin America 1,008 1,357
958
nd
nd
America and Russia. Others include
Middle East, Asia and Africa. The gas
Others 3,774 5,745 6,047 7,785 23%
supply increased also in the previous
Total 24,312 30,134 31,837 33,240 100%
regions: 8.6% in the EU and 16% in the
North America 2000–2009.
Source: IEA, in 2009, 2010 BP
10
Nuclear power
As of December 2009, the world had 436 reactors. Since commercial nuclear energy began in the mid
1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two
were connected in 2009.
Annual generation of nuclear power has been on a slight downward trend since 2007, decreasing 1.8% in
2009 to 2558 TWh with nuclear power meeting 13–14% of the world's electricity demand.
Renewable energy
Renewable energy comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat,
which are renewable (naturally replenished). As of 2010, about 16% of global final energy consumption
comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and
3.4% from hydroelectricity. New renewables (small hydro, modern biomass, wind, solar, geothermal, and
biofuels) accounted for another 2.8% and are growing very rapidly. The share of renewables in electricity
generation is around 19%, with 16% of global electricity coming from hydroelectricity and 3% from new
renewables.
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical
power through the use of the gravitational force of falling or flowing water. It is the most widely used
form of renewable energy, accounting for 16 percent of global electricity consumption, and 3,427
terawatt-hours of electricity production in 2010, which continues the rapid rate of increase experienced
between 2003 and 2009.
Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global
hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of
production in 2010, representing around 17 percent of domestic electricity use. There are now three
hydroelectricity plants larger than 10 GW: the Three Gorges Dam in China, Itaipu Dam in Brazil, and Guri
Dam in Venezuela.
Wind power
Wind power: worldwide installed capacity (not actual power generation)
Wind power is growing at the rate of 30% annually, with a worldwide installed capacity of
238,351 megawatts (MW) at the end of 2011, and is widely used in Europe, Asia, and the United
States. Several countries have achieved relatively high levels of wind power penetration, such as 21% of
stationary electricity production in Denmark, 18% in Portugal, 16% in Spain, 14% in Ireland and 9%
in Germany in 2010. As of 2011, 83 countries around the world are using wind power on a commercial
basis.
Solar energy
11
Solar Power Plants
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient
times using a range of ever-evolving technologies. Solar energy technologies include solar heating, solar
photovoltaics, solar thermal electricity and solar architecture, which can make considerable contributions
to solving some of the most urgent problems the world now faces. The International Energy
Agency projected that solar power could provide "a third of the global final energy demand after 2060,
while CO2 emissions would be reduced to very low levels."
Solar technologies are broadly characterized as either passive solar or active solar depending on the way
they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic
panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a
building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and
designing spaces that naturally circulate air.
Geothermal
Geothermal energy is used commercially in over 70
countries. In the year 2004, 200 PJ (57 TWh) of
electricity was generated from geothermal
resources, and an additional 270 PJ of geothermal
energy was used directly, mostly for space heating.
In 2007, the world had a global capacity for 10 GW
of electricity generation and an additional 28 GW
of direct
heating,
including
extraction
by geothermal heat pumps. Heat pumps are small
and widely distributed, so estimates of their total
capacity are uncertain and range up to 100 GW.
Biomass and biofuels
Until the beginning of the nineteenth century biomass was the predominant fuel, today it has only a small
share of the overall energy supply. Electricity produced from biomass sources was estimated at 44 GW for
2005. Biomass electricity generation increased by over 100% in Germany, Hungary, the Netherlands,
Poland, and Spain. A further 220 GW was used for heating (in 2004), bringing the total energy consumed
from biomass to around 264 GW. The use of biomass fires for cooking is excluded.
World production of bioethanol increased by 8% in 2005 to reach 33 billion litres (8.72 billion US gallons),
with most of the increase in the United States, bringing it level to the levels of consumption in
12
Brazil. Biodiesel increased by 85% to 3.9 billion litres (1.03 billion US gallons), making it the fastest
growing renewable energy source in 2005. Over 50% is produced in Germany.
By Country
Energy consumption is loosely correlated with gross national product and climate, but there is a large
difference even between the most highly developed countries, such as Japan and Germany with an
energy consumption rate of 6 kW per person and the United States with an energy consumption rate of
11.4 kW per person. In developing countries, particularly those that are sub-tropical or tropical such as
India, the per person energy use rate is closer to 0.7 kW. Bangladesh has the lowest consumption rate
with 0.2 kW per person.
A map depicting world energy consumption per capita based on 2003 data from the IEA
Energy consumption from 1989 to 1999
The US consumes 25% of the world's energy with a share of global GDP at 22% and a share of the world
population at 4.59%. The most significant growth of energy consumption is currently taking place in
China, which has been growing at 5.5% per year over the last 25 years. Its population of 1.3 billion people
(19.6% of the world population) is consuming energy at a rate of 1.6 kW per person.
One measurement of efficiency is energy intensity. This is a measure of the amount of energy it takes a
country to produce a dollar of gross domestic product.
Oil
Saudi Arabia, Russia and the United States accounted for 34% of oil production in 2011. Saudi Arabia,
Russia and Nigeria accounted for 36% of oil export in 2011.
Top 10 oil producers (Mt)
2005 2008 2009 2010 2011
1 Saudi Arabia
519
509
452
471
Top 10 oil exporters (Mt)
Share
2011
517 12.9%
2011
1 Saudi Arabia
Share
2011 %
333 17.0%
13
2
Russia
470
485
494
502
510 12.7%
2
Russia
3 United States
307
300
320
336
346 8.6%
3
Nigeria
129
6.6%
4
Iran
205
214
206
227
215 5.4%
4
Iran
126
6.4%
5
China
183
190
194
200
203 5.1%
5
UAE
105
5.4%
6
Canada
143
155
152
159
169 4.2%
6
Iraq
94
4.8%
7
UAE
nd
136
120
129
149 3.7%
7
Venezuela
87
4.4%
8
Venezuela
162
137
126
149
148 3.7%
8
Angola
84
4.3%
9
Mexico
188
159
146
144
144 3.6%
9
Norway
78
4.0%
10
Nigeria
133
nd
nd
130
139 3.5% 10
Mexico
71
3.6%
x
Kuwait
nd
145
124
nd
nd
nd
x
Norway
139
nd
nd
nd
nd
nd
x
Others
246 12.5%
609 31.0%
Total (Mt) 1,962
Total 3,923 3,941 3,843 3,973 4,011 100%
Top ten 62% 62% 61 % 62% 63%
Coal
Top 10 coal importers (Mt)
Top 10 coal producers (Mt)
1
2005 2008 2009 2010 2011
Share %
2011
China 2,226 2,761 2,971 3,162 3,576
46%
2
US 1,028 1,076
985
997 1,004
13%
2005 2008 2009 2010 2011
1
China
25
nd
114
157
177
2
Japan
178
186
165
187
175
3
South
Korea
77
100
103
119
129
4
India
37
58
66
88
101
5
Taiwan
61
66
60
63
66
6 Germany
38
46
38
45
41
7
UK
44
43
38
26
32
8
Turkey
nd
19
20
27
24
9
Italy
24
25
19
22
23
10 Malaysia
nd
nd
nd
19
21
3
India
430
521
561
571
586
8%
4
Australia
372
397
399
420
414
5%
5
Indonesia
318
284
301
336
376
5%
6
Russia
222
323
297
324
334
4%
7
South
Africa
315
236
247
255
253
3%
8
Germany
nd
nd
nd
nd
189
2%
9
Poland
160
144
135
134
139
2%
x
Spain
25
19
16
nd
nd
10 Kazakhstan
79
108
101
111
117
2%
x
France
nd
21
nd
nd
nd
11
65
79
73
74
1%
nd
x
US
28
nd
nd
nd
nd
Total 5,878 6,796 6,903 7,229 7,783
100%
Total
778
778
819
Colombia
Top ten
89%
949 1,002
90%
Top ten 69% 75% 78% 79%
79%
* include hard coal and brown coal
Import
of
16% 13% 14% 15%
production
13%
87%
88%
88%
nd
* 2005-2010 hard coal
Natural gas
Top 10 natural gas producers (bcm)
2005 2008 2009 2010 2011
Share
2011
Top 10 natural gas importers (bcm)
2005 2008 2009 2010 2011
Share
2011
14
1
Russia
627
657
589
637
677 20.0%
1
Japan
81
95
93
99
2
US
517
583
594
613
651 19.2%
2
Italy
73
77
69
75
70
8.4%
3
Canada
187
175
159
160
160
4.7%
3
Germany
91
79
83
83
68
8.2%
4
Qatar
nd
79
89
121
151
4.5%
4
US
121
84
76
74
55
6.6%
5
Iran
84
121
144
145
149
4.4%
5 South Korea
29
36
33
43
47
5.6%
6
Norway
90
103
106
107
106
3.1%
6
Ukraine
62
53
38
37
44
5.3%
7
China
nd
76
90
97
103
3.0%
7
Turkey
27
36
35
37
43
5.2%
8 Saudi Arabia
70
nd
nd
82
92
2.7%
8
France
47
44
45
46
41
4.9%
9
Indonesia
77
77
76
88
92
2.7%
9
UK
nd
26
29
37
37
4.4%
10 Netherlands
79
85
79
89
81
2.4%
10
Spain
33
39
34
36
34
4.1%
nd
nd
x
Algeria
93
82
81
nd
nd
nd
x Netherlands
23
nd
nd
nd
x
UK
93
nd
nd
nd
nd
nd
Total
838
783
749
820
Total 2,872 3,149 3,101 3,282 100% 3,388
Top ten
67%
65%
65%
65%
67%
bcm = billion cubic meters
116 13.9%
834 100%
Top ten 70% 73% 71% 69% 67%
Import
of
29% 25% 24% 25% 25%
production
bcm = billion cubic meters
Wind Power
Top
by
nameplate
Country
10
countries
windpower
capacity
(2011 year-end)
Windpower
capacity
ǂ
(MW) provisional
%
Top
by
world
total
windpower
Country
10
electricity
countries
production
(2010 totals)
Windpower
%
production
(TWh)
world
total
ǂ
26.3
United States
95.2
27.6
United States
46,919
19.7
China
55.5
15.9
Germany
29,060
12.2
Spain
43.7
12.7
Spain
21,674
9.1
Germany
36.5
10.6
India
16,084
6.7
India
20.6
6.0
France
ǂ
2.8
Italy
6,747
2.8
United
Kingdom
10.2
3.0
United
Kingdom
6,540
2.7
France
9.7
2.8
Portugal
9.1
2.6
Canada
5,265
2.2
Italy
8.4
2.5
Portugal
4,083
1.7
Canada
8.0
2.3
(rest of world)
32,446
13.8
(rest of world)
48.5
14.1
World total
238,351 MW
100%
World total
344.8 TWh
100%
China
62,733
6,800
15
By Sector
Industrial users (agriculture, mining,
World energy use per sector
manufacturing, and construction) consume
about 37% of the total 15 TW. Personal and
2000
2008 2000 2008
commercial transportation consumes 20%;
TWh
%*
residential heating, lighting, and appliances
Industry 21,733 27,273 26.5 27.8
use 11%; and commercial uses (lighting,
heating and cooling of commercial
Transport 22,563 26,742 27.5 27.3
buildings, and provision of water and sewer
Residential and service 30,555 35,319 37.3 36.0
services) amount to 5% of the total.
The other 27% of the world's energy is lost
Non-energy use 7,119 8,688
8.7
8.9
in energy transmission and generation. In
Total* 81,970 98,022 100 100
2005, global electricity consumption
averaged 2 TW. The energy rate used to Source: IEA 2010, Total is calculated from the given sectors
generate
2 TW
of
electricity
is Numbers
are
the
end
use
of
energy
approximately 5 TW, as the efficiency of a
Total world energy supply (2008) 143,851 TWh
typical existing power plant is around
38%. The new generation of gas-fired plants reaches a substantially higher efficiency of 55%. Coal is the
most common fuel for the world's electricity plants.
Total world energy use per sector was in 2008 industry 28%, transport 27% and residential and service
36%. Division was about the same in the year 2000.
European Union
The European Environmental Agency (EEA) measures final energy consumption (does not include energy
used in production and lost in transportation) and finds that the transport sector is responsible for 31.5%
of final energy consumption, industry 27.6%, households 25.9%, services 11.4% and agriculture 3.7%. The
use of energy is responsible for the majority of greenhouse gas emissions (79%), with the energy sector
representing 31%, transport 19%, industry 13%, households 9% and others 7%.
While efficient energy and resource efficiency are growing as public policy issues, more than 70% of coal
plants in the European Union are more than 20 years old and operate at an efficiency level of between
32–40%. Technological developments in the 1990s have allowed efficiencies in the range of 40–45% at
newer plants. However, according to an impact assessment by the European Commission, this is still
below the best available technological (BAT) efficiency levels of 46–49%. With gas-fired power plants the
average efficiency is 52% compared to 58–59% with best available technology (BAT), and gas and
oil boiler plants operate at average 36% efficiency (BAT delivers 47%). According to that same impact
assessment by the European Commission, raising the efficiency of all new plants and the majority of
existing plants, through the setting of authorisation and permit conditions, to an average generation
efficiency of 51.5% in 2020 would lead to a reduction in annual consumption of 15 billion m3 of natural
gas and 25 Mt of coal.
Alternative energy Paths
16
Wind power in Germany 1990-2011: Capacity (MW) in red and Generated Energy (GW-h) in blue.
Denmark and Germany have started to make investments in solar energy, despite their unfavorable
geographic locations. Germany is now the largest consumer of photovoltaic cells in the world. Denmark
and Germany have installed 3 GW and 17 GW of wind power respectively. In 2005, wind generated 18.5%
of all the electricity in Denmark.
Brazil invests in ethanol production from sugar cane, which is now a significant part of the transportation
fuel in that country. Starting in 1965, France made large investments in nuclear power and to this date
three quarters (75%) of its electricity comes from nuclear reactors. Switzerland is planning to cut its
energy consumption by more than half to become a 2000-watt society by 2050 and the United Kingdom is
working towards a zero energy building standard for all new housing by 2016.
Total Primary energy supply of the world
17
*Other includes geothermal, solar, wind, heat etc.
Total Consumption of the world
18
*Data prior to 1994 for biofuels and waste final consumption have been estimated.
**Others include geothermal, wind, solar, heat etc.
Global supply and consumption
1.3 ENERGY AND BIOMASS CONSUMPTION PATTERNS IN PAKISTAN.
1.5 ENVIRONMENTAL IMPACTS OF BIOMASS ENERGY.
1.5.1 Biomass Energy and the Environment
Unlike any other energy resource, using biomass to produce energy is often a way to dispose of biomass
waste materials that otherwise would create environmental risks. In the following ways, using biomass
for energy can deliver unique environmental dividends as well as useful energy.
1.5.2 Reducing Greenhouse Gases: Carbon Dioxide
Carbon dioxide (CO2), methane, nitrous oxide and certain other gases are called greenhouse gases
because they trap heat in the Earth´s atmosphere. The global concentration of CO2 and other greenhouse
gases is increasing. A natural greenhouse effect of trace gases and water vapor warms the atmosphere
and makes the Earth habitable. However, human-caused greenhouse gas emissions are having an effect
19
on regional climate and weather patterns. The rate and magnitude of climate change effects are not yet
clear.
Trees and plants remove carbon from the atmosphere through photosynthesis, forming new biomass as
they grow. Carbon is stored in biomass. When biomass is burned, carbon returns to the atmosphere in
the form of CO2. This cycle makes it possible for biomass energy to avoid increasing the net amount of
CO2 in the atmosphere.
There is no net increase in atmospheric CO2 if the new growth of plants and trees fully replaces the supply
of biomass consumed for energy. However, if the collection or processing of biomass consumes any fossil
fuel, additional biomass would need to be grown to offset the carbon released from the fossil fuel.
In contrast, the combustion of natural gas, coal and petroleum fuels for energy adds CO2 to the
atmosphere without a balancing cycle to remove it. Using biomass fuels instead of fossil fuels may reduce
the risk of adverse climate change from greenhouse gas emissions.
1.5.3 Reducing Greenhouse Gases: Methane
Compared to CO2, methane has 21 times the global warming potential. Natural decomposition of organic
material, especially in wetlands, releases methane. It has been estimated that 60 to 80 percent of
methane emissions are the result of human activity. For example, solid waste landfills, cattle feedlots and
dairies are sources of human-caused methane emissions. Because human-caused emissions, the global
atmospheric concentration of methane increased 6 percent from 1984 to 1994.
Using biomass-derived methane to produce useful energy consumes methane and reduces the risk to the
environment that would otherwise result from natural decomposition. In addition, generating electricity
with biomass-derived methane fuel can offset power produced from fossil fuels and reduce the net CO2
emissions from electric power generation.
Federal Clean Air Act regulations require collection of methane produced in landfills. The regulations
allow operators to use landfill methane for energy production or burn off the gas to avoid the release of
methane into the atmosphere. Besides the potential effect of methane emissions on climate,
uncontrolled landfill gas emissions cause odor problems and a risk of explosion and fire.
Methane released from decomposition of livestock and poultry manure generates about 9 percent of all
human-caused methane emissions in the United States. Processing manure through anaerobic digesters
can make the methane available for conversion to useful energy and avoid methane emissions to the
atmosphere.
1.5.4 Protecting Clean Water
land on which cattle are fattened for market.
Livestock manure generated at feedlots and dairies poses a risk of surface and ground water
contamination from runoff. Microorganisms such as salmonella, brucella and coliforms in manure can
transmit disease to humans and animals. Anaerobic digestion of manure destroys most of these
microorganisms. The process produces environmentally stable liquid and fiber residue.
The liquid portion of digester residue (called filtrate) contains approximately 75 percent of the nitrogen
present in raw manure but in a more soluble form. In this form, the nitrogen is more available to plants.
However, the filtrate should be applied as close to the ground as possible to avoid volatile ammonia
emissions. Farmers must carefully manage land application of filtrate to avoid overloading the soil with
more nutrients than the plants can use.
1.5.5 Keeping Waste Out of Landfills
Using urban wood waste for fuel reduces the volume of waste that otherwise would be buried in landfills.
The ash residue that remains after combustion of waste wood is less than 1 percent of the volume of the
wood waste consumed. Uncontaminated ash can be used as a soil amendment to add minerals and to
adjust soil acidity.
1.5.6 Reducing Air Pollution
Field burning of agricultural residue emits particulate matter and other air pollutants. Because of air
quality concerns, state regulations have reduced the amount of open field burning of grass seed straw in
Oregon's Willamette Valley. Grass seed straw and other agricultural residues are potential biomass fuels.
These materials are suitable as fuel for appropriately designed combustion boilers to produce heat, steam
or electric power. They are also potential feedstock for conversion to ethanol.
Smoke emissions from forest fires and slash burning adversely affect air quality. Removing biomass from
forested areas where an excess of dead wood has accumulated reduces forest fire risk. Compared to the
smoke emitted from forest fires and slash burning, the emissions from using wood fuel for energy are far
20
less harmful. Industrial combustion boilers with pollution control equipment in place burn more
efficiently and cleanly than open fires.
Residential woodstoves can be a major source of particulate air pollution. Improvements in stove
technology have made woodstoves more efficient and have reduced particulate matter emissions by as
much as 90 percent over older woodstoves and fireplaces. In 1983, Oregon became the first state to
enact regulations restricting woodstove emissions. New woodstoves currently must meet certification
standards of the U.S. Environmental Protection Agency.
1.5.7 Reducing Acid Rain and Smog
Air pollution from burning fossil fuels is the major cause of acid rain. Emissions of sulfur dioxide (SO2) and
nitrogen oxides (NOx) react in the atmosphere with water, oxygen and oxidants to form acidic
compounds (sulfuric acid and nitric acid). Some of these compounds fall to earth in the form of acid rain,
snow or fog. Acid rain increases acidity of lakes and streams and damages trees at high elevations. Acid
rain accelerates the decay of building materials and paints.
Aside from their contribution to acid rain, SO2 and NOx gases and their particulate matter derivatives
(sulfates and nitrates) contribute to smog and endanger public health. Tighter control of these emissions
is desirable in areas with frequent smog problems and in areas protected for their pristine qualities.
Efficient combustion of biomass results in low emissions of SO2 and production of fewer organic
compounds that cause smog compared to emissions from facilities that burn coal or oil. Co-firing biomass
with coal can reduce SO2 and NOx emissions at coal-fired power plants. The level of NOx emissions from
biomass combustion facilities depends on the design of the facility and the nitrogen content of the
feedstock. Pollution control equipment can further reduce NOx and particulate emissions.
1.5.8 Protecting Forests
Dense growth has limited the size and resiliency of trees in some forested areas of the state. In the Blue
Mountains of eastern Oregon, for example, the health of large areas of forestland has deteriorated.
Similar conditions exist in forests throughout the Western United States. In many areas the natural
ecosystem has been significantly altered, creating a high risk of intense wildfire. According to Western
Forest Health and Biomass Energy Potential, a study prepared for the Department of Energy, 39 million
acres (about 30 percent) of National Forest land in the West is threatened by unnatural fuel
accumulations.
The condition of the forest in these overgrown areas is not natural. It is largely the result of fire
suppression and past logging practices. Selective thinning would improve the general health of the
remaining trees and reduce the risk of fire. With less competition for nutrients and water, the remaining
trees would have a better chance of maturing into old growth stands.
The surplus biomass that could be available from thinning unnaturally overgrown forest areas is a large
renewable energy resource. Carefully planned forest thinning activities can preserve wildlife habitat and
minimize soil erosion so that the use of forest biomass can be done in a sustainable manner.
1.5.9 Zero–impact does not exist
Every type of energy utilisation for electricity generation has environmental consequences. The main
consequences of burning fossil fuels and of nuclear power are well-known. Renewable energy sources
(wind, solar, biomass, hydroelectric, geothermal, etc.) are generally thought of as harmless, but this
doesn’t mean they have no environmental consequences at all. Most of them have a significant aesthetic
impact and require large areas of land. Some also have a significant impact on the eco-system (birds,
fishes, etc.).
1.5.10 Avoiding greenhouse gases
The CO2 emissions of fossil fuels are currently the most worrying energy-related environmental problem.
Up to now, nuclear power is still the only solution applicable everywhere on a large scale that has no CO 2
emissions. How to process nuclear waste however is still a problem that largely remains to be solved. And
despite maximum efforts, safety will always remain an issue for nuclear power due to its potential for
large scale contamination.
Renewable energy is still used on too small of a scale to replace all fossil fuels. If one day current
renewable energy systems are applied to replace present fossil fuel output, the resulting aesthetic impact
and land use will be large.
Since every type of energy utilization has some degree of environmental impact, energy conservation
should get top priority in every instance, no matter which mix of primary energy sources is used.
21
1.5.11 Environmental impact
Some forms of forest bioenergy have recently come under fire from a number of environmental
organizations, including Greenpeace and the Natural Resources Defense Council, for the harmful impacts
they can have on forests and the climate. Greenpeace recently released a report entitled Fuelling a
BioMess which outlines their concerns around forest bioenergy. Because any part of the tree can be
burned, the harvesting of trees for energy production encourages Whole-Tree Harvesting, which removes
more nutrients and soil cover than regular harvesting, and can be harmful to the long-term health of the
forest. In some jurisdictions, forest biomass is increasingly consisting of elements essential to functioning
forest ecosystems, including standing trees, naturally disturbed forests and remains of traditional logging
operations that were previously left in the forest. Environmental groups also cite recent scientific
research which has found that it can take many decades for the carbon released by burning biomass to be
recaptured by regrowing trees, and even longer in low productivity areas; furthermore, logging
operations may disturb forest soils and cause them to release stored carbon. In light of the pressing need
to reduce greenhouse gas emissions in the short term in order to mitigate the effects of climate change, a
number of environmental groups are opposing the large-scale use of forest biomass in energy production.
CHAPTER NO.02
BIOMASS ECOLOGY
2.1 BASIC CONCEPTS OF FOREST PRODUCTION ECOLOGY;
Ecologists and ecosystem managers are unlikely to achieve desired management objectives unless they
are familiar with the distribution and movements of energy that are responsible for the character and
productivity of ecosystems under their management(Kimmins2004).
Theoretical production ecology
Theoretical production ecology tries to quantitatively study the growth of crops. The plant is treated as a
kind of biological factory, which processes light, carbon dioxide, water and nutrients into harvestable
parts. Main parameters kept into consideration are temperature, sunlight, standing crop biomass, plant
production distribution, nutrient and water supply.
Modelling
22
Modelling is essential in theoretical production ecology. Unit of modelling usually is the crop, the
assembly of plants per standard surface unit. Analysis results for an individual plant are generalised to the
standard surface, e.g. the Leaf Area Index is the projected surface area of all crop leaves above a unit area
of ground.
Processes
The usual system of describing plant production divides the plant production process into at least five
separate processes, which are influenced by several external parameters.
Two cycles of biochemical reactions constitute the basis of plant production, the light reaction and the
dark reaction.

In the light reaction, sunlight photons are absorbed by chloroplasts which split water into an
electron, proton and oxygen radical which is recombined with another radical and released as
molecular oxygen. The recombination of the electron with the proton yields the energy
carriers NADH and ATP. The rate of this reaction often depends on sunlight intensity, leaf area index,
leaf angle and amount of chloroplasts per leaf surface unit. The maximum theoretical gross
production rate under optimum growth conditions is approximately 250 kg per hectare per day.

The dark reaction or Calvin cycle ties atmospheric carbon dioxide and uses NADH and ATP to
convert it into sucrose. The available NADH and ATP, as well as temperature and carbon
dioxide levels determine the rate of this reaction. Together those two reactions are
termed photosynthesis. The rate of photosynthesis is determined by the interaction of a number of
factors including temperature, light intensity and carbon dioxide.

The produced carbohydrates are transported to other plant parts, such as storage organs and
converted into secondary products, such as amino acids, lipids, cellulose and other chemicals needed
by the plant or used for respiration. Lipids, sugars, cellulose and starch can be produced without
extra elements. The conversion of carbohydrates into amino acids and nucleic acids requires
nitrogen, phosphorus and sulfur. Chlorophyll production requires magnesium, while several enzymes
and coenzymes require trace elements. This means, nutrient supply influences this part of the
production chain. Water supply is essential for transport, hence limits this too.

The production centers, i.e. the leaves, are sources, the storage organs, growth tips or other
destinations for the photosynthetic production are sinks. The lack of sinks can be a limiting factor for
production too, as happens e.g. in apple orchards where insects or night frost have destroyed the
blossoms and the produced assimilates cannot be converted into apples. Biennial and perennial
plants employ the stored starch and fats in their storage organs to produce new leafs and shoots the
next year.

The amount of crop biomass and the relative distribution of biomass over leafs, stems, roots and
storage organs determines the respiration rate. The amount of biomass in leafs determines the leaf
area index, which is important in calculating the gross photosynthetic production.

extensions to this basic model can include insect and pest damage, intercropping, climatical
changes, etc.
Parameters
Important parameters in theoretical production models thus are:
Climate

Temperature - The temperature determines the speed of respiration and the dark reaction. A
high temperature combined with a low intensity of sunlight means a high loss by respiration. A low
temperature combined with a high intensity of sunlight means that NADH and ATP heap up but
cannot be converted into glucose because the dark reaction cannot process them swiftly enough.

Light - Light, also called photosynthetic Active Radiation (PAR) is the energy source for green
plant growth. PAR powers the light reaction, which provides ATP and NADPH for the conversion of
carbon dioxide and water into carbohydrates and molecular oxygen. When temperature, moisture,
carbon dioxide and nutrient levels are optimal, light intensity determines maximum production level.

Carbon dioxide levels - Atmospheric carbon dioxide is the sole carbon source for plants. About
half of all proteins in green leaves have the sole purpose of capturing carbon dioxide.
Although CO2 levels are constant under natural circumstances [on the contrary, CO2 concentration in the
atmosphere has been increasing steadily for 200 years], CO2 fertilization is common in greenhouses and is
23
known to increase yields by on average 24% [a specific value, e.g., 24%, is meaningless without
specification of the "low" and "high" CO2 levels being compared] .
C4 plants like maize and sorghum can achieve a higher yield at high solar radiation intensities, because
they prevent the leaking of captured carbon dioxide due of the spatial separation of carbon dioxide
capture and carbon dioxide use in the dark reaction. This means that their photorespiration is almost
zero. This advantage is sometimes offset by a higher rate of maintenance respiration. In most models for
natural crops, carbon dioxide levels are assumed to be constant.
Crop

Standing crop biomass - Unlimited growth is an exponential process, which means that the
amount of biomass determines the production. Because an increased biomass implies higher
respiration per surface unit and a limited increase in intercepted light, crop growth is a sigmoid
function of crop biomass.

Plant production distribution - Usually only a fraction of the total plant biomass consists of useful
products, e.g. the seeds in pulses and cereals, the tubers in potato and cassava, the leafs in sisal and
spinach etc. The yield of usable plant portions will increase when the plant allocates more nutrients
to this parts, e.g. the high-yielding varieties of wheat and rice allocate 40% of their biomass into
wheat and rice grains, while the traditional varieties achieve only 20%, thus doubling the effective
yield.
Different plant organs have a different respiration rate, e.g. a young leaf has a much higher respiration
rate than roots, storage tissues or stems do. There is a distinction between "growth respiration" and
"maintenance respiration".
Sinks, such as developing fruits, need to be present. They are usually represented by a discrete switch,
which is turned on after a certain condition, e.g. critical day length has been met.
Care

Water supply - Because plants use passive transport to transfer water and nutrients from their
roots to the leafs, water supply is essential to growth, even so that water efficiency rates are known
for different crops, e.g. 5000 for sugar cane, meaning that each kilogram of produced sugar requires
up to 5000 liters of water.

Nutrient supply - Nutrient supply has a twofold effect on plant growth. A limitation in nutrient
supply will limit biomass production as per Liebig's Law of the Minimum. With some crops, several
nutrients influence the distribution of plant products in the plants. A nitrogen gift is known to
stimulate leaf growth and therefore can work adversely on the yield of crops which are accumulating
photosynthesis products in storage organs, such as ripening cereals or fruit-bearing fruit trees.
Phases in crop growth
Theoretical production ecology assumes that the growth of common agricultural crops, such as cereals
and tubers, usually consists of four (or five) phases:
 Germination - Agronomical research has indicated a temperature dependence of germination time
(GT, in days). Each crop has a unique critical temperature (CT, dimension temperature) and
temperature sum (dimensions temperature times time), which are related as follows.
When a crop has a temperature sum of e.g. 150 °C·d and a critical temperature of 10 °C, it will germinate
in 15 days when temperature is 20 °C, but in 10 days when temperature is 25 °C. When the
temperature sum exceeds the threshold value, the germination process is complete.
 Initial spread - In this phase, the crop does not cover the field yet. The growth of the crop is linearly
dependent on leaf area index, which in its turn is linearly dependent on crop biomass. As a result,
crop growth in this phase is exponential.
 Total coverage of field - in this phase, growth is assumed to be linearly dependent on incident light
and respiration rate, as nearly 100% of all incident light is intercepted. Typically, the Leaf Area
Index (LAI) is above two to three in this phase. This phase of vegetative growth ends when the plant
gets a certain environmental or internal signal and starts generative growth (as in cereals and pulses)
or the storage phase (as in tubers).
24
Allocation to storage organs - in this phase, up to 100% of all production is directed to the storage
organs. Generally, the leafs are still intact and as a result, gross primary production stays the same.
Prolonging this phase, e.g. by careful fertilization, water and pest management results directly in a
higher harvest.
 Ripening - in this phase, leafs and other production structures slowly die off. Their carbohydrates and
proteins are transported to the storage organs. As a result, the LAI and, hence, the primary
production decreases.
Existing plant production models
Plant production models exist in varying levels of scope (cell, physiological, individual plant, crop,
geographical region, global) and of generality: the model can be crop-specific or be more generally
applicable. In this section the emphasis will be on crop-level based models as the crop is the main area of
interest from an agronomical point of view.
As of 2005, several crop production models are in use. The crop growth model SUCROS has been
developed during more than 20 years and is based on earlier models. Its latest revision known dates from
1997. The IRRI and Wageningen University more recently developed the rice growth model ORYZA2000.
This model is used for modeling rice growth. Both crop growth models are open source. Other more cropspecific plant growth models exist as well.
SUCROS
SUCROS is programmed in the Fortran computer programming language. The model can and has been
applied to a variety of weather regimes and crops. Because the source code of Sucros is open source, the
model is open to modifications of users with FORTRAN programming experience. The official maintained
version of SUCROS comes into two flavours: SUCROS I, which has non-inhibited unlimited crop growth
(which means that only solar radiation and temperature determine growth) and SUCROS II, in which crop
growth is limited only by water shortage.
ORYZA2000
The ORYZA2000 rice growth model has been developed at the IRRI in cooperation with Wageningen
University. This model, too, is programmed in FORTRAN. The scope of this model is limited to rice, which
is the main food crop for Asia.
Other models
The United States Department of Agriculture has sponsored a number of applicable crop growth models
for various major US crops, such as cotton, soy bean, wheat and rice. Other widely-used models are the
precursor of SUCROS (SWATR), CERES, several incarnations of PLANTGRO, SUBSTOR, the FAOsponsored CROPWAT, AGWATER and the erosion-specific model EPIC.
A less mechanistic growth and competition model, called the Conductance Model, has been developed,
mainly at Warwick-HRI, Wellesbourne, UK. This model simulates light interception and growth of
individual plants based on the lateral expansion of their crown zone areas. Competition between plants is
simulated by a set algorithms related to competition for space and resultant light intercept as the canopy
closes. Some versions of the model assume overtopping of some species by others. Although the model
cannot take account of water or mineral nutrients, it can simulate individual plant growth, variability in
growth within plant communities and inter-species competition. This model was written in Matlab. See
Benjamin and Park (2007) Weed Research 47, 284-298 for a recent review.

2.2 THE BIOMASS PRODUCTION POTENTIAL OF A FOREST ECOSYSTEM;
We can view a forest, a stream, or an ocean as a system that absorbs, transforms, and stores
energy. In this view, physical, chemical, and biological structures and processes are inseparable. When we
look at natural systems in this way we view them as ecosystems. An ecosystem is a biological community
plus all of the abiotic factors influencing that community.
Primary production, the fixation of energy by autotrophs, is one of the most important ecosystem
processes. The rate of primary production is the amount of energy fixed over some interval of time. Gross
primary production is the total amount of energy fixed by all the autotrophs in the ecosystem. Net
primary production is the amount of energy left over after autotrophs have met their own energetic
needs.
Terrestrial primary production is generally limited by temperature and moisture. The variables
most highly correlated with variation in terrestrial primary production are temperature and moisture.
25
Highest rates of terrestrial primary production occur under warm, moist conditions. Temperature and
moisture conditions can be combined in a single measure called annual actual evapotranspiration, or AET,
which is the total amount of water that evaporates and transpires off a landscape during the course of a
year. Annual AET is positively correlated with net primary production in terrestrial ecosystems. However,
significant variation in terrestrial primary production results from differences in soil fertility.
Aquatic primary production is generally limited by nutrient availability. One of the best
documented patterns in the biosphere is the positive relationship between nutrient availability and rate
of primary production in aquatic ecosystems. Phosphorus concentration usually limits rates of primary
production in freshwater ecosystems, while nitrogen concentration usually limits rates of marine primary
production.
Consumers can influence rates of primary production in aquatic and terrestrial
ecosystems. Piscivorous fish can indirectly reduce rates of primary production in lakes by reducing the
density of plankton-feeding fish. Reduced density of planktivorous fish can lead to increased density of
herbivorous zooplankton, which can reduce the densities of phytoplankton and rates of primary
production. Intense grazing by large mammalian herbivores on the Serengeti increases annual net
primary production by inducing compensatory growth in grasses.
Energy losses limit the number of trophic levels in ecosystems. Ecosystem ecologists have simplified
the trophic structure of ecosystems by arranging species into trophic levels based upon the predominant
source of their nutrition. A trophic level is determined by the number of transfers of energy from primary
producers to that level. As energy is transferred from one trophic level to another, energy is lost due to
limited assimilation, respiration by consumers, and heat production. As a result of these losses, the
quantity of energy in an ecosystem decreases with each successive trophic level, forming a pyramidshaped distribution of energy among trophic levels. As losses between trophic levels accumulate,
eventually there is insufficient energy to support a viable population at a higher trophic level.
Stable isotope analysis can be used to trace the flow of energy through ecosystems. The ratios of
different stable isotopes of important elements such as nitrogen and carbon are generally different in
different parts of ecosystems. As a consequence, ecologists can use isotopic ratios to study
the trophic structure and energy flow through ecosystems. Stable isotope analysis has helped quantify
dietary composition of wild populations and the major sources of energy used by prehistoric human
populations.
Primary Production and Energy Flow
Suntight shines down on the canopy of a forest-- some is reflected, some is converted to heat
energy, and some is absorbed by chlorophyll. Infrared radiation is absorbed by the molecules in
organisms, soil, and water, increasing their kinetic state and raising the temperature of the
forest. Forest temperature affects the rate of biochemical reactions and transpiration by forest
vegetation.
Forest plants use photosynthetically active solar radiation, or PAR, to synthesize sugars. The plants
use some of this fixed energy to meet their own energy needs. Some fixed energy goes directly into plant
growth: to produce new leaves, to lengthen the tendrils of vines, to grow new root hairs, and so forth.
Some fixed energy is stored as nonstrucrural carbohydrates, which act as energy stores in roots, seeds, or
fruits. Photosynthesis may increase forest biomass.
A portion of the energy fixed by forest vegetation is consumed by herbivores, some is consumed
by detritivores, and some ends up as soil organic matter. Energy fixed by forest vegetation powers bird
flight through the forest canopy and fuels the muscle contractions of earthworms as they burrow through
the forest soil. The forest vegetation is sunlight transformed, as are all the associated bacteria, fungi, and
animals and all their activities (fig. 18.1).
26
We can view a forest as a system that absorbs,
transforms, and stores energy. In this view, physical,
chemical, and biological structures and processes are
inseparable. When we look at a forest (or stream or coral
reef) in this way we view it as an ecosystem. An
ecosystem is a biological community plus all of
the abiotic factors influencing that community. The term
ecosystem and its definition were first proposed in I935
by the British ecologist Arthur Tansley. Sometime
during his exploration of nature, he realized the
importance of considering organisms and their
environment as an integrated system. Tansley wrote:
"Though the organisms may claim our primary
interest .... we cannot separate them from their special
environment, with which they form one physical system.
It is the [eco]systems so formed which, from the point of
view of the ecologist, are the basic units of nature on the
face of the earth."
FIGURE 18.1 In most ecosystems, sunlight
Ecosystem ecologists study the flows of energy,
water, and nutrients in ecosystems and, as suggested provides the ultimate source of energy to
by Tansley, pay as much attention to physical and power all biological activity, such as the
chemical processes as they do to biological one. Some singing of this treefrog and the growth of
fundamental areas of interest for ecosystem ecologists
the plant on which it sits.
are primary production, energy flow, and nutrient
cycling.
The photosynthetic machinery of plants uses solar energy to synthesize sugars. To considered
photosynthesis from the perspective of the individual grass, tree, or cactus. Here we discuss the
biochemical and physiological details of photosynthesis and even from the individual organism to look at
photosynthesis at the level of the whole ecosystem.
Primary production is the fixation of energy by autotrophs in an ecosystem. The rate of primary
production is the amount of energy fixed over some interval of time. Ecosystem ecologists distinguish
between gross and net primary production. Gross primary production is the total amount of energy fixed
by all the autotrophs in the ecosystem. Net primary production is the amount of energy left over
after autotrophs have met their own energetic needs. Net primary production is gross primary production
minus respiration by primary producers; it is the amount of energy available to the consumers in an
ecosystem. Ecologists have measured primary production in a variety of ways but mainly as the rate of
carbon uptake by primary producers or by the amount of biomass or oxygen produced.
Ecosystem ecologists have simplified the trophic structure of ecosystems by arranging species
into trophic levels based on the predominant source of their nutrition. A trophic level is a position in a
food web and is determined by the number of transfers of energy from primary producers to that level.
Primary producers occupy the first trophic level in ecosystems since they convert inorganic forms of
energy, principally light, into biomass. Herbivores and detritivores are often called primary consumers
and occupy the second trophic level. Carnivores feeding on herbivores and detritivores are called
secondary consumers and occupy the third trophic level. Predators that feed on carnivores occupy a
fourth trophic level. Since each trophic level may contain several species, in some cases hundreds, an
ecosystem perspective simplifies trophic structure.
Primary production, the conversion of inorganic forms of energy into organic forms, is a key
ecosystem process. All consumer organisms, including humans, depend upon primary production for their
existence. Because of its importance and because rates of primary production vary substantially from one
ecosystem to another, ecosystem ecologists study the factors controlling rates of primary production in
ecosystems.
Patterns of natural variation in primary production provide clues to the environmental factors that
control this key ecosystem process. Experiments test the importance of those controls, we discuss the
27
major patterns of variation in primary production in terrestrial and aquatic ecosystems and key
experiments designed to determine the mechanisms producing those patterns.
CASE HISTORIES:
Patterns of terrestrial primary production
Terrestrial primary production is generally limited by temperature and moisture.
The major terrestrial biomes of the geographic variation in rates of primary production. Perhaps you also
developed a feeling for the major environmental correlates with that variation. The variables most highly
correlated with variation in terrestrial primary production are temperature and moisture. Highest rates of
terrestrial primary production occur under warm, moist conditions.
Actual Evapotranspiration and Terrestrial Primary Production
Michael Rosenzweig (1968) estimated the influence of moisture and temperature on rates of
primary production by plotting the relationship between annual net primary production and annual
actual evapotranspiration. Annual actual evapotranspiration (AET) is the total amount of water that
evaporates and transpires off a landscape during the course of a year and is measured in millimeters of
water per year. The AET process is affected by both temperature and precipitation. The ecosystems
showing the highest levels of primary production are those that are warm and receive large amounts of
precipitation. Conversely, ecosystems show low levels of AET either because they receive little
precipitation, are very cold, or both. For instance, both hot deserts and tundra exhibit low levels of AET.
Figure 18.2 shows Rosenzweig's plot of the positive relationship between net primary production
and AET. Tropical forests show the highest levels of net primary production and AET. At the other end of
the spectrum, hot, dry deserts and cold, dry tundra show the lowest levels. Intermediate levels occur in
temperate forests, temperate grasslands, Woodlands, and high-elevation forests. Figure 18.2 shows that
AET accounts for a significant proportion of the variation in annual net primary production among
terrestrial ecosystems.
FIGURE
18.2 Relationship
between
actual evapotranspiration and net aboveground
primary production in a series of terrestrial
28
ecosystems (data from Rosenzweig 1968).
Rosenzweig's analysis
attempts to explain variation in
primary production across the whole spectrum of terrestrial ecosystems. What controls variation in
primary production within similar ecosystems? O. E. Sala and his colleagues (1988)
at Colorado State University explored the factors controlling primary production in the central grassland
region of the United States. Their study was based on data collected by the U.S. Department of
Agriculture Soil Conservation Service at 9,498 sites. To make this large data set more manageable, the
researchers grouped the sites into 100 representative study areas.
The
study
areas
extended
from Mississippi and Arkansas in
the
east
to New
Mexico and Montana in the west and from North Dakota to southern Texas. Primary production was
highest in the eastern grassland study areas and lowest in the western study areas. This east-west
variation corresponds to the westward changes from tall-grass prairie to short-grass prairie that we
reviewed in chapter 2. Sala and his colleagues found that this east-west variation in primary production
among grassland ecosystems correlated significantly with the amount of rainfall (fig. 18.3).
Compare
the
plot
by Sala and his colleagues (fig.
18.3) with the one constructed
by Rosenzweig (fig.18.2). How
are they similar? How are they
different? Both graphs have
primary production plotted on
the vertical axis as a dependent
variable.
However,
while
the Rosenzweig plot includes
ecosystems
ranging
from
tundra to tropical rain forest,
the plot by Sala and his
colleagues includes grasslands
only. In addition, different
variables are plotted on the
horizontal axes of the two
graphs.
While Rosenzweig plotted
actual evapotranspiration,
FIGURE 18.3 Influence of annual precipitation on net aboveground
which
depends
upon
temperature
and primary production in grasslands of central North America (data
from Sala et al. 1988).
precipitation, Sala and
his
colleagues plotted precipitation
only. They found that including temperature in their analysis did not improve their ability to predict net
primary production. Why do you think precipitation alone was sufficient to account for most of the
variation in grassland production? A likely reason is that warm temperatures occur during the growing
season at all of the study areas included by Sala and his colleagues. In contrast, Rosenzweig's study areas
vary widely in growing season temperature.
These researchers found strong correlations between AET or precipitation and rates of terrestrial
primary production. However, their models did not completely explain the variation in primary
production among the study ecosystems. For instance, in figure 18.2 ecosystems with annual AET levels of
500 to 600 mm of water showed annual rates of primary production ranging from 300 to 1,000 g per
square meter. In figure 18.3, grassland ecosystems receiving 400 mm of annual precipitation had annual
rates of primary production ranging from about 100 to 250 g per square meter. These differences in
primary production challenge ecologists for an explanation.
Soil Fertility and Terrestrial Primary Production
Significant variation in terrestrial primary production can be explained by differences in soil fertility.
Farmers have long known that adding fertilizers to soil can increase agricultural production. However, it
was not until the nineteenth century that scientists began to quantify the influence of specific nutrients,
29
such as nitrogen (N) or phosphorus (P), on rates of primary production. Justus Liebig (1840) pointed out
that nutrient supplies often limit plant growth. He also suggested that nutrient limitation to plant growth
could be traced to a single limiting nutrient. This hypothetical control of primary production by a single
nutrient was later called "Liebig's Law of the Minimum." We now know that Liebig's perspective was too
simplistic. Usually several factors, including a number of nutrients, simultaneously affect levels of
terrestrial primary production. However, his work led the way to a concept that remains true today;
variation in soil fertility can significantly affect rates of terrestrial primary production.
Liebig's work, and most practical experience prior to Liebig, concerned the productivity of
agricultural ecosystems. Do nutrients influence rates of primary production in other ecosystems, such as
the tundra or deserts, where human manipulation has been less prominent? Ecologists have
demonstrated the significant influence of nutrients on terrestrial primary production through numerous
experiments involving addition of nutrients to natural ecosystems.
Ecologists have increased primary production by adding nutrients to a wide variety of terrestrial
ecosystems, including arctic tundra, alpine tundra, grasslands, deserts, and forests. For
instance, Gaius Shaver and Stuart Chapin (1988) studied the potential for nutrient limitation in arctic
tundra. They added commercial fertilizer containing nitrogen, phosphorus, and potassium to several
tundra ecosystems in Alaska. They made a single application of fertilizer to half of their experimental
plots and two applications to the remaining experimental plots.
Shaver and Chapin measured net primary production at their control and experimental sites 2 to 4
years after the first nutrient additions. Nutrient additions increased net primary production (by 23%300%) at all of the study sites. The response to fertilization was substantial and clear at most study sites.
Four years after the initial application of fertilizer, net primary production on Kuparuk Ridge was twice as
high on the fertilized plots compared to the unfertilized control plots (fig. 18.4).
Nutrient additions to
alpine tundra indicate that
the
response
of
ecosystems to nutrient
addition is affected by
prior nutrient availability.
William Bowman and his
colleagues (1993) added
nutrients to the alpine
tundra
on Niwot Ridge, Colorado.
They conducted their
experiment in adjacent dry
alpine and wet alpine
meadows at an elevation
of 3,510 m. One of four
treatments was applied in
both the dry and wet
alpine
meadows:
(l)
control
(no
nutrient
additions), (2) nitrogen
added,
(3) phosphors added, and FIGURE 18.4 Effect of addition of nitrogen,
(4)
nitrogen phosphorus, and potassium on net aboveground
and phosphorus added.
primary production in Arctic tundra (data from
The researchers then
Shaver and Chapin 1986).
measured soil nitrogen
and
phosphorus
concentrations and annual net primary production in each study plot.
30
Initial concentration of both nitrogen and phosphorus were higher in the wet meadow
ecosystem~ And while fertilizing raised the concentrations of both nitrogen and phosphorus in the dry
meadow, fertilizing the wet meadow raised the concentration of nitrogen but not phosphorus.
Fertilizing produced greater increases in primary production in the dry meadow than in the wet
meadow. Adding nitrogen to the dry meadow increased primary production by 63%. Adding nitrogen and
phosphorus increased primary production by 178%. In contrast, the wet meadow
only showed relatively small but statistically significant responses to the additions of both nitrogen and
phosphorus (fig. 18.5).
Bowman and his colleagues
suggest that these results
show that nitrogen is the
main nutrient limiting net
primary production in the
dry meadow and that
nitrogen and phosphorus
jointly limit net primary
production in the wet
meadow. They also suggest
that light, not nutrients,
may limit net primary
production in the wet
meadow. In other words,
the higher biomass in the
wet meadow may have
produced enough shading
to inhibit the growth
response of some species
to nutrient additions.
Experiments such as
these have shown that
despite the major influence FIGURE 18.5 Effect of adding phosphorus (P) and/or nitrogen (N) on
of
temperature
and aboveground primary production in two environments in alpine tundra
moisture on rates of
(clara from Bowman et al. 1993).
primary production in
terrestrial ecosystems, variation in nutrient availability can also have measurable influence. As we shall
see in the next Case Histories section, nutrient availability is the main factor limiting primary production
in aquatic ecosystems.
CASE HISTORIES:
patterns of aquatic primary production
Aquatic primary production is generally limited by nutrient availability.
Limnologists and oceanographers have measured rates of primary production and nutrient
concentrations in many lakes and at many coastal and oceanic study sites. These studies have produced
one of the best documented patterns in the biosphere: the positive relationship between nutrient
availability and rate of primary production in aquatic ecosystems.
Patterns and Models
A quantitative relationship between phosphorus, an essential plant nutrient, and phytoplankton
biomass was first described for a series of lakes in Japan (Hogetsu and Ichimura 1954, Ichimura 1956,
Sakamoto 1966). The ecologists studying this relationship found a remarkably good correspondence
between total phosphorus and phytoplankton biomass.
Later, Dillon and Rigler (1974) described a similar positive relationship between phosphorus and
phytoplankton biomass for lake ecosystems throughout the Northern Hemisphere. Remarkably, the
slopes of the lines describing the relationship between phosphorus and phytoplankton biomass for the
Japanese and Canadian lakes were nearly identical (fig. 18.6).
31
The
data
from Japan and North
America strongly support the hypothesis
that nutrients, particularly phosphorus,
control phytoplankton biomass in lake
ecosystems. However, what is the
relationship between phytoplankton
biomass and the rate of primary
production? This relationship was
explored by Val Smith (1979) for 49 lakes
of the north temperate zone. The data
from these lakes showed a strong positive
correlation
between
chlorophyll
concentrations and photosynthetic rates
(fig. 18.7).
Smith also examined the relationship
between total phosphorus concentration
and photosynthetic rate directly. Aquatic
ecologists
have
extended
these
correlational studies of the relationship
between nutrient availability and primary
production by manipulating nutrient
availability in entire lake ecosystems.
Whole Lake Experiments on
Primary
Production
FIGURE
18.6 Relationship
between
phosphorus
concentration and algal biomass in north temperate lakes
(data from Dillon and Rigler 1974).
The Experimental Lakes
Area
was
founded
in
northwestern Ontario, Canada,
in 1968 as a place in which
aquatic
ecologists
could
manipulate
whole
lake
ecosystems
(Mills
and Schindler 1987,
Findlay
and Kasian1987).
For
instance, ecologists manipulated
nutrient availability in a lake
called Lake 226. They used a
vinyl curtain to divide Lake 226
into two 8 ha basins each
containing about 500,000 m3 of
water. Think about these
numbers for a second. This was
a huge experiment! Each subbasin of Lake 226 was fertilized
FIGURE 18.7 Relationship between algal biomass and rate of
from 1973 to 1980. The
primary
production in temperate zone lakes (data from Smith 1979).
researchers added a mixture of
carbon in the form of sucrose
and nitrate to one basin and carbon, nitrate, and phosphate to the other basin. They stopped fertilizing
the lakes after 1980 and then studied the recovery of the Lake 226 ecosystem from 1981 to 1983.
Both sides of Lake 226 responded significantly to nutrient additions. Prior to the
manipulation, Lake 226 supported about the same biomass of phytoplankton as two reference lakes (fig.
18.8). However, when experimenters began adding nutrients, the phytoplankton biomass in Lake 226
32
quickly surpassed that in the reference lakes. Phytoplankton biomass remained elevated in Lake 226 until
the experimenters stopped adding fertilizer at the end of 1980. Then, from 1981 to 1983 the
phytoplankton biomass in Lake 226 declined significantly.
In conclusion, both correlations-between
phosphorus
concentration and rate of
primary production, and whole
lake experiments, involving
nutrient additions---support the
generalization that nutrient
availability controls rates of
primary
production
in
freshwater ecosystems. Now,
let's examine the evidence for
this relationship in marine
ecosystems.
Global Patterns of Marine
Primary Production
The
geographic
distribution of net primary
production in the sea indicates a
positive
influence
of nuUient availability on rates
of
primary
production.
Oceanographers have observed FIGURE 18.8 A whole lake experiment shows the effect of nutrient
on
average
phytoplankton
biomass
(data
that the highest rates of primary additions
from Findlay and Kasian 1987).
production
by
marine
phytoplankton are generally
concentrated in areas with higher levels of nutrient availability (fig. 18.9). The highest rates of primary
production are concentrated along the margins of continents over continental shelves and in areas of
upwelling. Along continental margins nutrients are renewed by runoff from the land and by biological or
physical disturbance of bottom sediments. As we saw in chapter 3, the upwelling that brings nutrientladen water from the depths to the surface is concentrated along the west coasts of continents and
around the continent of Antarctica, areas that appear dark red on figure 18.9, indicating high to very high
rates of primary production.
FIGURE 18.9 Geographic variation in marine primary production (data from F.A.O. 1972).
Meanwhile, the central portions of the major oceans show low levels of nutrient availability and
low rates of primary production. The main source of nutrient renewal in the surface waters of the open
33
ocean is vertical mixing. Vertical mixing is generally blocked in open tropical oceans by a
permanent thermocline. Consequently, the surface waters of open tropical oceans contain very low
concentrations of nutrients and show some of the lowest rates of marine primary production.
What is the experimental evidence for nutrient limitation of marine primary production? Some of
the most thorough studies have been conducted in the Baltic Sea. For instance, Edna Graneli and her
colleagues (1990) have used nutrient enrichment to test whether nutrient availability limits primary
production in the Baltic Sea.
In a test using a single algal species, Graneli added nutrients to filtered seawater from a series of
study sites. She added nitrate to one experimental group, phosphates to another, and nothing to a third
group of flasks (fig. 18.10). Notice that the flasks with additional nitrate showed increased chlorophyll a
concentrations at all sites, while the flasks with additional phosphate had chlorophyll a concentrations
very similar to the control flasks. What do these results indicate? They suggest that the rate of primary
production in the Baltic Sea is limited by nutrients. However, in contrast to most freshwater lakes, the
limiting nutrient appears to be nitrogen, not phosphorus.
34
Graneli did similar enrichment
studies along a series of
stations
in
the Kattegat,
the Belt Sea,
and
the Skagerrak, where the
salinity approaches that of the
open ocean. However, in this
second series of experiments,
she
used
indigenous
phytoplankton rather than a
single
standardized
test
species. Once again the
concentrations of chlorophyll a
were higher in the flasks to
which nitrate had been added
while
the
control
and
phosphate treatment groups
were
virtually
indistinguishable. Again, the
results
indicate
nitrogen
limitation along virtually the
entire study area.
There have been no
experiments done in the
marine environment that are
equivalent to the whole lake
manipulations
at
the
Experimental Lakes Area (e.g.,
Schindler 1990). However, in
one experiment, researchers
were able to alter the nutrient
inputs and concentrations
in Himmer fjard, Sweden, a
brackish water coastal inlet of
the Baltic Sea with a surface
area of 195 km2 (see fig.
18.10). (For comparison, the
lake sub basins manipulated in
the whole lake experiments
were < 0.1 km2.) The results of
this manipulative experiment
indicate
that
nitrogen
FIGURE 18.10 Nitrate control of primary production in the Baltic
limitation
of
primary
Sea (data frorn Graneli etal. 1990).
production can shift to
phosphorus limitation by altering nitrogen: phosphorus ratios. Increasing additions of phosphorus
to Himmer fjord reinforced nitrogen limitation, while decreasing phosphorus additions and increasing
nitrogen additions led to increased phosphorus limitation.
Dillon and Rigler suggested that limnologists pay attention to the scatter of points around lines
showing a relationship between nutrient concentrations and phytoplankton biomass (F.A.O. 1972). We
call that scatter of points residual variation. Residual variation is that proportion of variation not
explained by the independent variable, in this case, by nutrient concentration. Dillon and Rigler suggested
that environmental factors besides nutrient availability significantly influence phytoplankton biomass.
One of those factors is the intensity of predation on the zooplankton that feed on phytoplankton. As we
35
shall see in the next Case Histories section, consumers can influence rates of primary production in both
terrestrial and aquatic ecosystems.
CASE HISTORIES:
consumer influences
Consumers can influence rates of primary production in aquatic and terrestrial ecosystems.
In the first section of this chapter, we emphasized the effects of physical and chemical factors on
rates of primary production. More recently, ecologists have discovered that primary production is also
affected by consumers. Ecologists refer to the influences of physical and chemical factors, such as
temperature and nutrients, on ecosystems as bottom-up controls. The influences of consumers on
ecosystems are known as top-down controls. In the previous two sections we discussed bottom-up
controls on rates of primary production. Here we discuss top-down control.
Piscivores, Planktivores, and Lake Primary Production
Stephen Carpenter, James Kitchell, and James Hodgson (1985) proposed that while nutrient inputs
determine the potential rate of primary production in a lake, piscivorous and planktivorous fish can cause
significant deviations from potential primary production. In support of their hypothesis, Carpenter and his
colleagues (1991) cited a negative correlation between zooplankton size, an indication of grazing
intensity, and primary production.
Carpenter and Kitchell (1988) proposed that the influences of consumers on lake primary
production propagate through food webs. Since they visualized the effects of consumers coming from the
top of food webs to the base, they called these effects on ecosystem properties "trophic cascades.''
The trophic cascade hypothesis (fig. 18.11) is very similar to the keystone species hypothesis (see chapter
17). However, notice that thetrophic cascade model is focused on the effects of consumers on ecosystem
processes, such as primary production, and not on their effects on species diversity.
36
Carpenter
and Kitchell (1993)
interpreted
the trophic cascade in their
study
lakes
as
follows: Piscivores, such as
largemouth bass, feed
on planktivorous fish and
invertebrates. Because of
their
influence
onplanktivorous fish, largemouth bass indirectly affect
populations of zooplankton.
By reducing populations
of planktivorous fish,
largemouth bass reduce
feeding
pressure
on
zooplankton
and
zooplankton populations.
Large-bodied zooplankton,
the preferred prey of sizeselective planktivorous fish
(see chapter 6), soon
dominate the zooplankton
community.
A
dense
population
of
large
zooplankton
reduces
phytoplankton biomass and
the rate of primary
production.
This
interpretation
of
the trophic cascade
is
consistent
with
the
negative
correlation
between zooplankton body
size and primary production
reported by Carpenter and
his research team. This
FIGURE 18.11 The trophic cascade hypothesis.
hypothesis is summarized in figure 18.12.
37
FIGURE 18.12 Predicted effects of piscivores on planktivore, herbivore, and phytoplankton biomass
and production (data from Carpenter: Kitchell, and Hodgson 1985).
Carpenter and Kitchell tested their trophic cascade model by manipulating the fish communities in
two lakes and using a third lake as a control. Figure 18.13 shows the overall design of their experiment.
Two of the lakes contained substantial populations of largemouth bass. A third lake had no bass, due to
occasional winterkill, but contained an abundance of planktivorous minnows. The researchers removed
90% of the large-mouth bass from one experimental lake and put them into the other. They
simultaneously removed 90% of the planktivorous minnows from the second lake and introduced them to
the first. They left a reference lake unmanipulated as a control.
The responses of the study lakes to the experimental manipulations support the trophic cascade
hypothesis (fig. 18.13). Reducing the planktivorous fish population led to reduced rates of primary
production. In the absence of planktivorous minnows, the predaceous invertebrate Chaoborus became
more numerous. Chaoborus fed heavily upon the smaller herbivorous zooplankton, and the herbivorous
zooplankton assemblage shifted in dominance from small to large species. In the presence of abundant,
large herbivorous zooplankton, phytoplankton biomass and rate of primary production declined.
38
FIGURE 18.13 Experimental manipulations of ponds and responses.
Adding planktivorous minnows produced a complex ecological response. Increasing
the planktivorous fish population led to increased rates of primary production. However, though the
researchers increased the population of planktivorous fish in this experimental lake, they did so in an
unintended way. Despite the best efforts of the researchers, a few bass remained. So, by introducing a
large number of minnows they basically fed the remaining bass. An increased food supply combined with
reduced population density induced a strong numerical response by the bass population (see chapter 10).
The manipulation increased the reproductive rate of the remaining largemouth bass 50-fold, producing
an abundance of young largemouth bass that feed voraciously on zooplankton.
The lake ecosystem responded to the increased biomass of planktivorous fish (young largemouth
bass) as predicted at the outset of the experiment. The biomass of zooplankton decreased sharply, the
average size of herbivorous zooplankton decreased, and phytoplankton biomass and primary production
increased.
The results of these whole lake experiments show that the trophic activities of a few species can
have large effects on ecosystem processes. However, the majority of trophic cascades described by
ecologists have been in aquatic ecosystems with algae as primary producers. This pattern prompted
Donald Strong (1992) to ask, "Are trophic cascades all wet?'' Strong suggested that trophic cascades most
likely occur in ecosystems of lower species diversity and reduced spatial and temporal complexity. These
are characteristics of many aquatic ecosystems. Despite these restrictions, consumers have significant
effects on rates of primary production in some terrestrial ecosystems; one of those is the Serengeti
grassland ecosystem.
Grazing by Large Mammals and Primary Production on the Serengeti
The Serengeti-Mara a 25,000 km2 grassland ecosystem that straddles the border
between Tanzania and Kenya, is one of the last ecosystems on earth where great numbers of large
mammals still roam freely. SamMcNanghton (1985) reported estimated densities of the major grazers in
the Serengeti that included 1.4 million wildebeest, Connochaetes taurinus albujubatus, 600,000
Thomson's gazelle, GazeUa thomsonii, 200,000 zebra, Equus burchelli, 52,000 buffalo, Syncerus eaffer,
60,000 topi, Damaliscus korrigum,
and
large
numbers
of
20
additional
grazing
mammals. McNaughton estimated that these grazers consume an average of 66% of the annual primary
39
production on the Serengeti. In light of this estimate, the potential for consumer influences on primary
production seems very high.
Over two decades of research on the Serengeti ecosystem in Tanzania led McNaughton to
appreciate the complex interrelations of abiotic and biotic factors there. For instance, both soil fertility
and rainfall stimulate plant production and the distributions of grazing mammals. However, grazing
mammals also affect water balance, soil fertility, and plant production.
As you might predict, the rate of primary production on the Serengeti is positively correlated with
the quantity of rainfall. However, McNaughton (1976) also found that grazing can increase primary
production. He fenced in some areas in the western Serengeti to explore the influence of herbivores on
production. The migrating wildebeest that flooded into the study site grazed intensively for 4 days,
consuming approximately 85% of plant biomass.
During the month after the wildebeest left the study area, biomass within the enclosures
decreased, while the biomass of vegetation outside the enclosures increased (fig. 18.14). Grazing
increases the growth rate of many grass species, a response to grazing called compensatory growth. The
mechanisms underlying compensatory growth include lower rates of respiration due to lower plant
biomass reduced self-shading. and improved water balance due to reduce leaf area.
FIGURE 18.14 Growth response by grasses grazed by wildebeest (data from McNaughton 1976).
The compensatory growth observed by McNanghton was highest at intermediate grazing intensities
(fig. 18.15). Apparently, light grazing is insufficient to produce compensatory growth and very heavy
grazing reduces the capacity of the plant to recover. The large grazing mammals of the Serengeti have
substantial influences on its rate of primary production. As McNanghton put it, "African ecosystems
cannot be understood without close consideration of the large mammals. These animals interact with
their habitats in complex and powerful patterns influencing ecosystems for long periods."
40
What McNaughton and
his
colleagues
described
is
essentially atrophic cascade in a
terrestrial environment where
the feeding activities of
consumers have a major
influence
on
ecosystem
properties. The Serengeti is
now an exceptional terrestrial
ecosystem but it was not
always so. As we saw in chapter
2, the extensive grasslands of
North
America
and Eurasia were also once
populated by vast herds of
mammalian grazers. Historians
estimate that the population of
North American bison in the
middle of the nineteenth
century numbered up to 60
million.
Such
a
dense
concentration of grazers must
have had significant influences
upon the grassland ecosystems
of which they were part. It
appears
that
terrestrial
FIGURE 18.15 Grazing intensity and primary production of Serengeti
consumers, as well as the
grassland (data from McNaughton 1985).
aquatic ones studied by
Carpenter and Kitchell, can have important influences on primary production.
In the Serengeti, lions are the top predators. Though they are occasionally killed by hyenas, there
are no predators that depend principally upon hunting lions as a source of energy. In the ponds studied
by Carpenter and Kitchell, largemouth bass were the top carnivores. The number of trophic levels in
ecosystems ranges from two to five or six, perhaps seven or eight in exceptional ecosystems. In any case,
ecosystems have a limited number of trophic levels. What limits the number of trophic levels? We will
consider the factors that limit the number of trophic levels in ecosystems in the next section.
CASE HISTORIES: trophic levels
Energy losses limit the number of trophic levels in ecosystems.
We began this chapter with a partial and highly qualitative energy budget for a forest: Sunlight
shines down on the canopy of a forest--some is reflected, some is converted to heat energy, and some is
absorbed by chlorophyll. The energy budgets of ecosystems reveal that with each transfer or conversion
of energy, some energy is lost. To verify that these losses have the potential to limit the number
of tropbic levels in ecosystems, we need to quantify the flow of energy through ecosystems. One of the
very first ecologists to quantify the flux of energy through ecosystems was Raymond Lindeman.
A Trophic Dynamic View of Ecosystems
Raymond Lindeman (1942) received his Ph.D. from the University of Minnesota in 1941, where his
studies of the ecology of Cedar Bog Lake led him to a view of ecosystems far ahead of its
time. Lindeman went from Minnesota to Yale University, where his association with G. E. Hutchinson
from 1941 to 1942 led to the publication of a revolutionary paper with the provocative title, "The TrophicDynamic Aspect of Ecology." In this paper, Lindeman articulated a view of ecosystems centered on energy
fixation, storage, and flows that remains influential to this day. Like Tansley before
him, Lindeman pointed out the difficulty and artificiality of separating organisms from their environment
and promoted an ecosystem view of nature. Lindeman concluded that the ecosystem concept is
fundamental to the study of trophic dynamics, which he defined as the transfer of energy from one part
of an ecosystem to another
41
Lindeman suggested grouping organisms within an ecosystem into trophic levels: primary
producers, primary consumers, secondary consumers, tertiary consumers, and so forth. In this scheme,
each trophic level feeds on the one immediately below it. Energy enters the ecosystem as primary
producers engage in photosynthesis and convert solar energy into biomass. As energy is transferred from
one trophic level to another, energy is lost due to limited assimilation, respiration by consumers, and heat
production. As a result of these losses, the quantity of energy in an ecosystem decreases with each
successive trophic level,
forming
a
pyramid-shaped
distribution
of
energy
among trophic levels. Lindeman called these trophic pyramids "Eltonian pyramids," since Charles Elton
(1927) was the first to propose that the distribution of energy among trophic levels is shaped like a
pyramid.
Figure 18.16 shows the distribution of annual primary production among trophic levels
in Cedar Bog Lake and in Lake Mendota, Wisconsin. Energy losses at each trophic level determine
the trophic structure of these two ecosystems. As predicted by Elton, the distribution of energy
across trophic levels in both lakes is shaped like a pyramid. As suggested at the beginning of this section,
the number of trophic levels is limited in both lakes. Lake Mendota includes four trophic levels,
while Cedar Bog Lake includes just three.
FIGURE 18.16 Annual production by trophic level in two lakes (data from Lindeman 1942).
Following Lindeman's pioneering work, many other ecologists studied energy flow within
ecosystems. One of the most comprehensive of these later studies focused on
the Hubbard Brook Experimental Forest in New Hampshire.
Energy Flow in a Temperate Deciduous Forest
James Gosz and
his
colleagues
(1978)
studied
energy
flow
in
the Hubbard Brook Experimental Forest, which is managed for research by the U.S. Forest Service. They
concentrated their efforts on a stream catchment called watershed 6, which was left undisturbed so it
could serve as a control for experimental studies on other stream catchments. The energy flow in
the Hubbard Brook Experimental Forest was quantified as kilocalories (kcal) per square meter per year.
The results of the analysis are shown in figure 18.17.
42
FIGURE 18.17 Energy budget for a temperate deciduous forest (data from Gosz et al. 1978).
First let's examine the distribution of organic matter among the major components of the Hubbard
Brook ecosystem. The largest single pool of energy in the forest, 122,442 kcal/m2, occurred as dead
organic matter. Most of the dead organic matter, 88,120 kcal/m2, was organic matter in the upper 36
cm of soil. The remainder, 34,322 kcal/m2, occurred as plant litter on the forest floor. Total living-plant
biomass amounted to 71,420 kcal/m2, of which 59,696 kcal/m2 was stored in above ground biomass and
11,724 kcal/m2 as belowground biomass.
The total standing stock of energy occurring as dead organic matter and living plant biomass
was 193,862 kcal/m2. This estimate by Gosz and his colleagues dwarfs the energy stored in all other
portions of the ecosystem. For instance, the energetic content of a caterpillar population during a severe
population outbreak amounted to only 160 kcal/m2. However, even this amount far exceeds the total
energetic content of all vertebrate biomass. The researchers estimated that the total energetic content of
the most numerous vertebrates, including chipmunks, mice, shrews, salamanders, and birds, amounted
to less than 1 kcal/m2. Now that we have inventoried the major standing stocks of energy, let's look at
energy flow through the Hubbard Brook Forest.
The main source of energy for the ecosystem is solar radiation. The total input of solar energy to
the study area during the growing season was estimated to be 480,000 kcal/m2 (expressed as 100% in fig.
18.17). Of this total energy input, 15% was reflected, 41% was converted to heat, and 42% was absorbed
during evapotranspiration. About 2.2% of the solar input was fixed by plants as gross primary production.
Plant respiration accounted for 1.2%, leaving about 1% as net primary production. In other words, only
about 1% of the solar input to the Hubbard Brook ecosystem was available to the herbivores
and detritivores that made up the second trophic level.
2
About 1,199 kcal/m of net primary production in the Hubbard Brook Forest went into plant
growth. Herbivores consumed only about 41 kcal/m2, approximately 1% of net primary production. Most
of the energy available to consumers, approximately 3,037 kcal/m2, occurred as surface litter fall. About
150 kcal/m2 of the litter fall was stored as organic matter on the forest floor. The remainder was used by
43
consumers. An additional source of detritus, amounting to 437 kcal/m2, occurred belowground as
root exudates and litter. Most of the energy consumed by grazers and detritivores, approximately 3,353
kcal/m2, was lost as consumer respiration.
Now let's go back to the concept that started this section: Energy losses limit the number
of trophic levels in ecosystems. The energy budget carefully constructed by Gosz and his colleagues gives
us a basis for understanding this concept. Net primary production in the Hubbard Brook Forest ecosystem
was less than 1% of the input of solar energy. In other words, over 99% of the solar energy available to
the Hubbard Brook was unavailable for use by a second trophic level. Of the net primary production
available to consumers, approximately 96% is lost as consumer respiration. This leaves very little for a
third trophic level. It is such losses with each transfer of energy in a food chain that limit the number
of trophic levels. As these losses between trophic levels accumulate, eventually there is insufficient
energy left over to support a viable population at a higher trophic level.
The top predator on the African savanna is the lion. We might imagine predators fierce enough to
prey on lions, but the energetics of energy conversion and transfer within ecosystems would preclude
such a predator.
We can see from the studies of Gosz and his colleagues and others that ecosystems depend upon
an outside input of energy. Ecosystems store some energy in the form of dead organic matter and
biomass, but most energy flows through. As we shall see in chapter 19, however, ecosystems recycle
elements such as nitrogen and sulfur. In the next Applications and Tools section we review how forms of
these and other elements can be used as a tool to determine the trophic structure of ecosystems.
2.3 PRODUCTION OF ENERGY WOOD AT SPECIAL SHORT-ROTATION PLANTATIONS;
The Production of Short-rotation Woody Crops
Eucalyptus species constitute about 38% of all short-rotation plantations worldwide and hardwoods in
general make up about 63% of all plantations. In temperate regions, poplar, willow, and black locust
predominate. Ranney estimates that about 10 million ha could be classified as short-rotation
plantations. 23 However, he notes that less than half of this planted area could be termed as successful or
commercially viable. Ranney's technical criteria for successful plantations for energy use are described as
follows (with slight modification):
 more than 80% survival of planted materials;
 annual productivity greater than 10-12 dry tonnes/ha of harvested wood and bark;
 uniformity in diameter, height and straightness;
 less than $50/dry tonne in delivered cost;
 and less than 2 tonnes/ha in erosion each year.
This chapter discusses the factors to consider in site and species selection, plantation establishment,
maintenance and protection as well as yield expectations to achieve the above measures of success. In
addition, some of the distinctive aspects of producing trees on short-rotations versus practices used for
producing timber in longer rotations will be addressed. More detailed technical information suitable for
landowners or companies considering woody crop establishment may be located in some of the
references provided in the notes to this chapter.
Site Selection
It is often assumed that tropical countries have a major advantage over temperate regions with regard to
biomass production, but this is not necessarily true. While total annual biomass production does increase
from higher latitudes towards the equator, the increase is primarily in leaf production rather than wood
production
44
Fig. 2.1. Annual production of wood
and leaf biomass of natural forests
across a latitudinal gradient from the
Boreal Zone to the Tropics.25
In general, the annual wood
production of native tropical forests is
slightly less than that of high latitude
native forests. Reasons for the lower
production rates of lowland tropical
forests include acidic, highly leached
soils and warm temperatures that
increase respiration rates and burn off
carbon that would otherwise be used
to produce wood. Fortunately, wellmanaged plantations on good sites in
tropical and temperate zones can
achieve yields 2 to 10 times higher
than natural forests. Examples of plantation yield levels currently being achieved around the world are
summarized in Table 1.
Table 2.1. Plantation biomass annual production rates from around the world
Species
High Yield Average Yield
dry tonnes/ha
Production Region
References26
Poplar
43
9-20
Eastern US & Pacific Northwest
Wright, 1994
Eucalyptus
30
21
13-15
5-8
12.5
NW Spain
SW Spain
Spain
San Miguel, 1988
9-26a
Mid Brazil
Hall et al, 1993
Eucalyptus
Eucalyptus
27
13-27
Hawaii
Whitesell et al, 1992
Willow
24
13-24b
Northeast US
White, 1995
Willow
14
8-14
Sweden
Willebrand et.al 1993
Willow
23
13-23
Sweden
Christinson, 1987
Eucalyptus
28
3-21
NE Brazil
Carpentieri et al 1993
At a global scale, soil fertility generally decreases toward the equator. At a regional scale there is variation
in soil properties relevant to tree growth at scales ranging from 10's of meters to entire continents. Any
farmer or forester is familiar with variations in soil fertility that produce great differences in crop
production across areas as small as a hectare. Factors such as soil depth, water availability, pH, texture
and slope are all extremely important to crop production potential. While naturally fertile soils are most
desirable, there are instances where poorer soils can be managed.24 Soils with moderate limitations can
be used, if technologies are available to manage the soils effectively. These lands with moderate
limitations require careful planning and management to avoid problems related to erosion and water
quality, and soil nutrient deficiencies.
One of the first challenges for any commercial activity requiring short-rotation plantations is to determine
where suitable and available lands are located. A favorable site may allow a project to survive initial
mistakes or miscalculations, while an unfavorable site requires great technical expertise, and even simple
errors can result in major setbacks or failure. In site selection, there is no substitute for test plots of the
potential tree species on the range of soils present on the prospective sites. A potentially disastrous
consequence of over-estimation of yield is the under-estimation of planted area needed to support a
power plant. With the increased plantation area needed on unfavorable, low productivity sites comes
increasing expenses for road and harvesting infrastructure, increasing haul distances, less efficient
harvesting, and greater potential impacts on the environment, society, and biodiversity.
45
Site selection must consider and balance a wide range of biological, economic, and societal factors. The
biomass decision tree shown in Fig. 2.2 summarizes the information required and decisions that need to
be made to determine whether a biomass plantation may be feasible. Site selection and planning at the
national, regional, and local level requires geographically located information on soils and geology,
natural vegetation, current land uses, topography, watershed boundaries, stream/river systems, roads,
local political jurisdictions, land ownership and tenure information, location of cultural and historical
resources, location of nature preserves and rare habitats and species. It is also very valuable to have sitespecific research data on the yields that can be expected from the preferred species. The information is
particularly helpful if it can be conveniently summarized, compared, and presented on maps using
computer-based geographical information systems (GIS). The HNRIS database developed for the state of
Hawaii is an excellent example of the type of data and GIS systems that is very valuable for making
decisions regarding the best locations for biomass plantations.
Fig. 2.2. Biomass project decision tree.
Species Selection
Once a site is chosen, the next key to the success of the plantation is the selection of genetically superior
tree species, varieties or clones suitable for the climate, soils, and desired products of the plantation.
Most species achieve their best growth under a fairly narrow range of climate and soil conditions, and
failure to match species to site has been the cause of the failure of many plantation projects. Even within
a species that is suited to a particular site, there can be great variation in the growth and wood
characteristics from different seed sources or regions within the species range." The largest, cheapest,
and fastest gains in most tree improvement programs can be made by assuring the use of the proper
species and seed sources within species."29 Many of the problems of plantation health, productivity, tree
quality, and the economic viability of early plantation programs were the result of use of inappropriate
species or clones and suboptimal plant materials. For example, Jari Cellulose S/A of Brazil is currently
replacing all of the pines and gmelina planted on over 90,000 ha due to the poor growth.
Although indigenous species would be preferable from an environmental perspective, a large number of
the plantations being successfully established in tropical regions are using exotics such as E.
grandis and P. caribaea. Several acacia species, which are native to many tropical areas are showing good
performance. In the U.S. and Europe, hybrid poplars and willows are, in most cases, outperforming native
poplar species, although fast-growing native poplar clones have also been identified. The best hardwood
species and clones for lumber and veneer are likely to be different than those that are best for energy or
hardwood pulp.
In some temperate agricultural regions, herbaceous energy crops are being investigated. One advantage
of such crops is that they can be planted and harvested using standard agricultural equipment rather than
specialized forestry machinery. Perennial herbaceous crops, such as certain native prairie grasses, have
the advantages of providing quick erosion control and wildlife habitat, quickly reaching full production,
and providing continuous harvests without replanting. The best tropical analogy is sugar cane, although
other tropical grasses or canes might have potential as well.
Normal variation in topography, soils, and moisture conditions dictates that more than one species may
be desirable to optimize sustainable production. While it may be desirable to use both grasses and trees
as feedstock options from an environmental standpoint. Use of mixed tree species plantings would also
provide more desirable habitat for wildlife than single species plantings. Where the conversion
technology or product depends on feedstock uniformity, site differences can be partially compensated for
by using many clones of the preferred species. Pulp companies such as Aracruz Celulose S/A in Brazil have
developed a working set of 40 to 80 clones for taking advantage of small site differences, and attaining
functional diversity for pest management and risk spreading
Nitrogen-fixing species, or fast-growing nurse species could be beneficial components of the overall
species mix. Such species are likely to be particularly important where plantations are being established
on degraded or abandoned agricultural lands though plantings would likely need to be subsidized since
returns to the land owner may be limited due to low yields. In such cases, the initial species mix used to
reclaim the site is likely to be different than the preferred species mix once the site has been improved by
the initial rotations. Conversion technologies which can adjust to changing species composition over time
will offer the greatest opportunity for producing environmentally sound, low-cost feedstocks.
46
Species and clonal selections cannot be made exclusively from a study of literature. Unless a research
program exists in the vicinity of a desired project, some trials of promising species will have to be part of
the project development process. As described by Evans, these trials will normally be of four different
types:31
 Step 1. Species screening and elimination trials to identify the most promising species.
 Step 2. Species refinement trials to examine genetic variation among provenances, families, and
clones.
 Step 3. Larger production trials to provide stand growth data, test cultivation methods.
 Step 4. Tree improvement activities including breeding and clonal propagation.
This sequence takes time and often decisions are made after only step 1. Steps 2 and 3 may be carried
out while a project is being established and result in changes along the way. Step 4 is an ongoing
commitment that is required once significant investment in a project has been made.
Plantation Establishment, Tending, and Protection
Plantation establishment is a critical phase of a large-scale biomass energy project, since the timing of
wood supply must be coordinated with the construction of a complex and expensive power plant.
Mistakes or miscalculations at any one of many stages can result in expensive delays in power generation.
Issues that must be addressed include: site preparation, seedling or cutting supply and quality, availability
of required soil microorganisms, nursery operation, spacing of plantings, fertilization, watering, weed
control, road construction, protection of nursery stock and plantings from insect pests, disease, animals,
humans, fire, and other threats.
The particular properties of each plantation site and the species selected will affect how each of the
above issues should be addressed.
Site Preparation
Site preparation is the key phase of establishing a short-rotation woody crop plantation. Site preparation
on land not already used for cropping includes demarcation of boundaries, planning and construction of
access roads, and installation of erosion control measures. While alteration of drainage to improve
conditions for tree growth and minimize negative effects on the quality of water leaving the plantation
may be needed, care should be taken that wetlands and or water quality regulations are properly
addressed. The primary goal of site preparation is to create the best possible conditions for the growth of
the tree species that will be planted. Site preparation requirements vary greatly among tree species and
with variation in climate and soils. Most current recommendations suggest using land already cleared or
planted in tree crops both for economic and environemental reasons. The most suitable sites for biomass
plantations and the least expensive to prepare are lands recently or currently being used for agriculture.
On many agricultural sites, ripping may be necessary to break-up hard pans that have devoloped over
many years.
On recently abandoned agricultural lands, the main problem is often competition between planted
seedlings or cuttings and pre-existing vegetation. Consequently, the goal of site preparation is to kill or
remove as much as possible of the vegetation without degrading the site and creating erosion. For
species that are extremely sensitive to competition from grasses, including most fast-growing eucalypts,
poplars and willows, complete kill of the competing vegetation is essential. Figure 2.3 indicates the
strategies that may be required depending on existing vegetation.
Fig. 2.3. Steps in a recommended site preparation strategy.32
Both herbicides and cultivation may be required if mowing is not sufficiant. This is particularly important
in areas that have been invaded by aggressive grasses, such as Imperata cylindrica. Other species,
including Acacia mangium, alder, and many pines, are tolerant of some competition from grass, and do
not require such intensive site preparation, but also usually fail to produce high yields at a young age.
Experience in the U.S. suggests that site preparation should begin at least one full year in advance of
planting short-rotation crops, if cultivation is required. Soil cultivation aids in reducing weeds, but also can
be used to improve soil structure for root penetration in areas with compacted soil, impervious clay
layers, or poor drainage. No-till site preparation may be appropriate if herbicides can be effectively used
to achieve total grass and weed kill in strips where trees are to be planted. In some situations, clearing
and burning may be appropriate, although this is usually ineffective for grasses because they have
adapted to fire. Inadequate site preparation is the most common mistake made by companies and
researchers initiating a new short-rotation woody crop project.
47
On severely degraded sites, competition with grass and weeds is less an issue than is the nutrient content
and available moisture in the soil. Appropriate establishment methods may include leaving weeds,
planting grasses in strips, applying organic matter, establishing a cover crop, and/or building berms or
other structures to concentrate water.
Seeds, Cuttings, and Nursery Operation
Many first time plantings fail because high quality plant materials are scarce and poor quality planting
materials are used. The materials may be too small, too big, diseased or too weak. Guidelines for optimal
seedling and cutting size and handling requirements are available for the most commonly planted
species. A common problem is that insufficient quantity of select material is available so the tendency is
to use the poor quality material just to meet planting goals. Obtaining rapid growth early is so important
for short-rotation systems that time and money should not be wasted on planting poor quality or
unhealthy material.
Large centralized plant propagation and nursery operations that are owned by the power companies (or
their subsidiaries) may be required for large-scale biomass power projects. Nursery operations are a
standard component of most pulp and paper operations which depend on plantation grown wood. For
smaller power project operations, it may be easier and more cost-effective to purchase seedlings or
cuttings from commercial nurseries.
If plants are to be established from seed, the issues of seed availability, seed quality, seed storage, and
germination requirements must be fully resolved in the project planning stage. The quality of seeds is
particularly important, and success may depend on having a good supply not just of the desired species,
but of the specific variety or provenance of that species that is best suited for the plantation site. To
assure continuing supplies of improved high quality seeds, some investment in seed orchards and longterm breeding programs is necessary.
Most hardwood species receiving serious consideration as biomass plantations species can be propagated
without seeds, from cuttings of twigs and branches that can be induced to grow roots, from root sections
or branches that can be placed directly into the ground, or from tissue culture and micropropagation
methods. A major advantage of vegetative propagation is that the individual trees that have the most
desirable properties, disease resistance or rapid growth under specific local site conditions, can be rapidly
multiplied as part of a tree improvement or clonal expansion program. Species vary greatly in their
suitability for vegetative propagation, with some easily sprouting roots and leaves, and others only
surviving under the most favorable conditions. Species that sprout and grow readily include:
many Eucalyptus and Populus species, Acacia cyanophylla, Azadiracta indica, Cassia siamea, Chlorophora
excelsa, Cordia alliodora, Dalbergia sissoo, Gmelina arborea, Leucaena leucocephala, Nauclea diderichii,
Paraserianthes falcataria, Pterocarpus spp., Triplochiton scleroxylon, and Tectona grandis.
Depending on whether the species being planted are most effectively established as bareroot seedlings,
containerized stock, or hardwood cuttings, propagation and nursery procedures will be quite different.
Larger-seeded species can be sown in large beds and root- pruned to produce bare-root stock for
planting. Trees being clonally propagated require stool beds of clearly identified clones for generating
cuttings. Sprouts species such as poplars and willows are then harvested from the stool beds, sectioned,
graded for size, packed, and kept in cool temperatures until planting season. Eucalypts which are
produced from small seeds or small cuttings and species produced through micro-propagation, require
well-run seed or propagule handling, containerization, and hardening operations to produce adequate
sized planting stock. In general, container grown plants have a higher survival rate, than bareroot
seedlings or cuttings, particularly in drier areas. However, container grown plants may cost from 25% to
250% more to produce than bare-root seedlings or hardwood cuttings. In all nursery operations,
particular attention must be paid to fertilization and the prevention and control of fungal diseases and
insect pests, as well as plant size and root quality/quantity.
Many species may have unique properties and problems at the nursery stage. Consequently, the
experience that has been gained around the world with particular species under specific climate
conditions should be utilized in nursery design. Local practices that work perfectly well for some species
may result in total failure with different species. When Shell International chose to establish a eucalyptus
plantations in Chile, local builders failed to follow exact specifications from Shell staff with previous
experience in South Africa. This resulted in major problems and loss of much of the planting stock in the
48
first year of operation. Once the buildings were reconstructed according to specifications, propagation
was successful.33
Spacing
A primary question during the planning phase is the spacing (or density). Planting density affects the total
cost of planting stock, the rate at which the tree canopy closes, the growth form of the trees, the optimal
rotation age and the size at optimal rotation or harvest age. While production of large saw logs is most
effective at large spacings or in thinned stands, plantations for biomass or pulp generally use narrower
spacings ranging from about 4 x 4 m down to about 1 x 0.5 m.34 The tightest spacings are characteristic
of willow plantings, which are cut after 1 year to generate many sprouts, thereafter being harvested on a
2 to 3 year schedule. The widest spacings are more characteristic of plantings where the trees are
expected to reach a 15 to 20 cm diameter (d.b.h.) by harvest age.
Within a certain range, maximum short-rotation plantation yields are not particularly sensitive to spacing,
if weeds are effectively controlled and the stand is allowed to grow. The spacing does, however, affect
weed competition. Tight spacings minimize weed problems by closing canopy within the first year. Wider
spacings require weed control for 2 to 3 years, however, weeds can be effectively controlled by
cultivation, and herbicides.
Planting
Planting techniques will vary depending on the type of material being planted and the terrain. Hand
planting is probably the most common approach even in industrialized countries. Hand planting by an
experienced crew can be nearly as fast as mechanized planting with fewer mistakes. Unrooted cuttings
offer the greatest flexibility in choosing hand or machine planting methods. However, it is suggested that
painting or marking tops of unrooted cuttings will ease planting efforts and ensure that the right side is
planted up.
Weed and Pest Control
Weed competition can be severe in the establishment phase of plantations and most establishment
methods involve some use of cultivation and herbicides.35 It is most important to eliminate weeds close
to the trees. Cultivation is most effective if the spacing is square and wide enough to allow cultivation.
Application of herbicides over the trees, prior to leaf out, may accomplish the control needed close to the
trees. Mulching is another alternative. In countries where labor costs are low and chemical costs may be
high, manual labor is likely to be used to reduce weed growth immediately around trees. Depending on
the relative costs of labor, machinery, and chemicals, the most cost-effective weed control practices can
differ greatly from one area to another.
Another weed control alternative is agroforestry in which manual labor is used to tend food crops grown
between rows of trees for one to two years.36 This practice can provide both subsistence and cash crops
to the local community, while accomplishing weed control without harmful chemicals.37 Because of the
economic and environmental advantages shown by agroforestry experiments in Brazil, some forest
companies are beginning to recommend agroforestry in their tree farmer programs.38
Insect and fungal pests tend to be most serious when plants are stressed by poor soils, crowding, or other
unfavorable environmental conditions. Pests can spread rapidly and cause extensive damage in single
species plantations. The incidence of pest problems and thus the need for toxic chemicals could be
reduced by use of multispecies plantings, either intermixed or blocked, by selection of resistant species
and clones, and by carefully matching species and clones to site conditions to minimize stress. A
combination of biological and chemical controls of pests using the principles of Integrated Pest
Management (IPM) is usually much more effective and much less costly than large-scale pesticide
application.
Protection from Fires and Animals
Fires are a major risk factor that must be considered in planning the layout of short-rotation woody crops.
Separation of planting blocks with strips of natural vegetation may assist in reducing fire hazard as well as
increase local biodiversity. The roads needed for harvest access and wood removal should be made wide
enough to serve as fire breaks.
Large animals, such as deer and moose, can create problems by browsing the tender shoots of young
plants. While solar-powered electric fences could be used for keeping out large animals, this would
normally be too expensive for large-scale operations. It may simply be necessary to accept some level of
49
damage and claim credit for game populations in the region. Hunting is considered to be the most
effective means of protecting plantations from excessively large populations of browsing animals.39
Rabbits and rodents can damage or kill trees by gnawing the bark and girdling the base of the trees. There
is little protection for such animals in well managed plantations with low weed cover, thus providing
another rationale for good weed control. There are no other suitable methods for protecting plantations
against small rodents.40
Stand Renewal
The initial planting strategy should include a plan for stand renewal after harvest. Most short-rotation
species being planted or under evaluation offer the option of stand renewal through resprouting or
coppice growth. Although it was originally conceived that plantations would use the natural coppicing
ability of hardwood trees, researchers growing poplar in the U.S. and eucalypts in Brazil are now
suggesting that planting new and higher-yielding clones after each harvest will increase production and
more than offset the increased costs associated with stump removal and site reestablishment.
Continuous introduction of new clones also reduces risks associated with the buildup of pests and
diseases.
2.4 USE OF RESIDUAL BIOMASS FROM TRADITIONAL FORESTRY OPERATIONS FOR ENERGY;
HARVESTING AND TRANSPORTATION LOGISTICS OF ENERGY WOOD PRODUCTION.
Use of Plantation-grown Biomass for Power Generation
The conversion of wood energy feedstocks to energy beginning with harvesting and ending with export of
power to the electric grid is depicted in Fig. 3.1, Process diagram: plantation-grown biomass to power
generation. Post-harvest fuel preparation, transport, storage, and fuel preparation and handling are key
steps linking fuel production with conversion. These process steps influence the efficiency of the
conversion facility through feedstock quality (moisture content, size, uniformity) as well as overall system
cost. Figure 3.1 also shows feedstock handling and long-term storage losses. These losses can be
significant and must be accounted for in determining total feedstock requirements for the conversion
facility. Harvest, transport, storage, and fuel preparation techniques and requirements are discussed in
the following section. A second section provides a brief overview of conversion processes.
Harvesting, Transport, Storage, Handling and Fuel Preparation
Harvesting is a significant cost and a technical barrier to commercialization and use of plantation-grown
biomass for power generation. In the industrialized countries, considerable efforts have been expended
to develop equipment for harvesting plantation-grown trees. Results of studies conducted during the
mid-1980s conclude that cost-effective harvesting requires equipment be appropriately sized and be able
to cut and handle large numbers of relatively small diameter trees. Conventional forest harvesting
equipment tends to be inappropriate because it is designed for single-stemmed severance of large trees.
Such equipment is also high-powered and expensive relative to the value of plantation-grown trees.
Much of the work on harvesting systems in the industrialized countries has been based on the
development of feller bunchers, often as attachments to standard tractors. These harvesters have three
functions: severing or cutting, accumulating, and offloading.41 For example, the prototype Hyd-Mech FB7 continuous feller-buncher uses two counter-rotating saws for severing. Accumulating arms push
severed trees off into holding areas. Once the holding areas are filled (8 to 10 trees), the trees are
dumped alongside and parallel to the feller buncher. Other equipment (forwarder, grapple skidder, or
tractor with grapple) is then used to move the piled trees to a landing area. Here the trees can be chipped
and blown directly into a trailer or van for transport or simply loaded in whole form and hauled to a
conversion facility. In the latter situation, chipping or size reduction is done at the conversion facility.
Stokes and Hartsough analyzed the productivity and cost of three systems for harvesting a small diameter
and large diameter plantation stand. 42Their analysis was based on studies conducted on 7.6 cm
sycamore stand in south Alabama and a 10.2 to 15.2 cm eucalyptus stand in central California. The
systems included a continuous feller-buncher, a three-wheel feller-buncher, and chainsaw harvesting. A
grapple skidder or tractor with winch and a whole-tree chipper were also configured into a balanced
harvesting system. Their results are displayed in Fig. 3.2a and Fig. 3.2b.43
Fig. 3.2. A comparison of productivity and cost of harvesting
systems for a large diameter (15.2 cm) and small diameter (7.6
50
cm) plantation stand.
The first panel shows how tree diameter influences harvest system productivity. For the continuous
feller-buncher system, productivity was significantly higher when harvesting the larger diameter stands.
In contrast, a chainsaw harvesting system was more efficient for the small diameter stand. The second
panel shows a similar relationship -- the continuous feller-buncher is more cost-effective for the larger
diameter stands with chainsaw harvesting more cost-effective for small diameter stands. Although not
specifically shown in Fig. 3.2, the Stokes and Hartsough data indicate that chainsaw felling is about 2.5
times more productive than the continuous feller-buncher for the small-diameter trees. However,
bunching and skidding the cut trees to a landing greatly diminishes the productivity of the chainsaw
system. A comparison of the production rates achieved on other felling machines is shown in Table 3.1.
These data also show a fundamental relationship between tree size (spacing or planting density) and
productivity. A research team at the University of Hawaii (Manoa) has modeled this relationship and used
it to identify optimum spacing and rotation age for short-rotation eucalyptus.44
Table 3.1. Productivity Summary of Machine and Manual Felling in Short Rotation, Biomass
Plantations53
Type of Machine
Species
Average diameter
(cm)
Spacing (m)
(Trees/ha)
Productivitya
(Dry tonnes/hr)
Hyd-Mech FB-7a
Sycamore
6.3
1.5 x 3
8.7
51
(1824)
Hydro-Ax 411
"
4.3
"
2.2
Hydro-Ax 411
"
7.6
1.8 x 2.7
(2017)
13.0
Sycamore
7.6
"
5.3
Chainsaw w/felling frame
"
7.6
"
5.1
Chainsaw
"
4.3
"
1.3
Poplar
8.0
0.5 x 0.9
(21,607)
10.9
Cottonwood
19.8
3.9 x 3.9
(670)
26.2
"
19.8
"
45.4
Eucalyptus
7.0
1x1
(10,116)
9.0
Poplar
11.4
2.4 x 2.4
(1700)
5.8
Morbark Mark V
VPI/DOE Harvester
John Deere 493D
Barko 775
UH Harvester
USFS Harvester
aProductivity converted from green tonnes to dry tonnes assuming 50% moisture content.
The productivity and cost of plantation harvesting systems are quite variable. In industrialized or highlabor cost countries, estimated harvesting costs generally range from about $18 to $35/dry tonne for
felling, skidding, and chipping.45 The low-end costs tend to presume the availability of prototype
plantation harvesters while the high-end costs tend to be based on the use or modification of
conventional forestry equipment.46 A large component of total harvesting system cost (about 30 to 40%)
is tree handling or skidding of bunched trees to a landing for chipping or loading.
In an effort to minimize handling operations, whole-tree energytm (WTEtm) technology is under
development.47 In the WTEtm system, trees are severed, accumulated, and loaded directly onto specially
designed trailers for transport. This concept differs from conventional approaches in following respects.
First, whole-tree harvesting eliminates tree skidding or forwarding, a major cost of plantation harvesting
systems. Second, trees are not chipped or processed in the field. Instead, feedstock size reduction is done
at the conversion plant. Third, the minimization of tree handling steps reduces significantly, if not
eliminates, feedstock handling losses. Fourth, whole-tree harvesting equipment is optimized for singlestem severance (not coppice growth) and is utilized year-round. These factors have potential to reduce
greatly harvesting costs.48 However, a WTE system as now envisioned is likely to be limited to sites that
are relatively flat and accessible. Soil compaction is also a potential concern.
In contrast to the industrialized countries, where harvesting and handling operations have been focused
on the development of dedicated plantation harvesting machinery, developing countries are basing their
harvesting systems on the availability of low-cost and underutilized labor. In Brazil, most felling is done
with chainsaws. A typical harvesting operation has chainsaw operators cutting three rows of trees at a
time, directionally felling the trees so that they line-up.49 The trees are then crowned and cut to length
or left whole for moving to a landing area. Production rates for an experienced chain saw operator can
reach 120 trees/day. This is about 60 m3 or 28 dry tonne (0.47 dry tonne per m3) per day (3.5 dry
tonnes/hour). After felling and cutting to length, grapple loaders are used to forward the logs to a landing
for loading onto trucks (tractor-trailers) for transport to the conversion facility.
For some applications, the availability of excess labor in rural areas, low wage rates, and scarcity of capital
for equipment, maintenance and repairs, and fuel dictates that all harvesting operations (felling and
forwarding) be done manually. For example, in Southwest China, Perlack et al. estimate that 75 workdays
per hectare are required to fell, trim, carry, and stack logs at a roadside.50 Each hectare is assumed to
52
yield 30 dry tonnes of wood energy at harvest excluding the smaller limbs and branches, which are left for
nutrient recycling and fuelwood purposes. This production scenario implies a harvest rate of 0.4 dry
tonnes/day. In the Philippines, Durst estimated that over 130 days would be required to cut, top, and
stack one hectare using handtools.51 This translates into a production rate of about 0.6 dry tonnes/day. A
similar rate is provided by Denton, (100 kg/hour or 0.5 dry tonnes/day assuming a 10 hour workday).52 In
general, it is difficult to summarize production rates for manual harvesting operations because estimates
are highly dependent upon local site conditions (topography, plantation density, tree size, forwarding
distances, climate, season, etc.). However, relative to capital intensive harvesting systems, costs are
generally a smaller percentage of total delivered feedstock costs.
Harvest and handling operations will result in losses in product yield (Fig. 3.1). The significance of these
losses depend on local factors including the degree of mechanization used in harvest operations. Some
studies have conservatively assumed that felling, forwarding, and chipping operations can result in a 5%
loss in the total standing dry weight yield. In manual harvesting operations, losses can be higher
depending on how tree crowns and smaller limbs are treated. It is more likely that these smaller pieces
are left on-site for use as fuelwood (plantation by-product) and for nutrient recycling purposes.
When wood is harvested it normally contains about 50% moisture (wet basis). Moisture and other
physical properties of wood should be taken into account when designing and operating wood-fired
power systems. The presence of moisture in wood can affect combustion by absorbing heat during
evaporation; increasing the time it takes for wood to burn, and reducing the temperature of the
combustion gases. Operational experience suggests that there can be significant decreases in boiler
efficiency when moisture content begins to exceed 50%. If feedstocks are allowed to air-dry to 30%
moisture, there can be usable net heat gains. However, if the feedstock is allowed to absorb moisture
during storage, a point can be reached where combustion can no longer be sustained. In this instance
boiler blackouts can occur and auxiliary fuel will be needed to sustain combustion. Boilers specifically
designed to handle high moisture content fuels do not have these problems, but they tend to be higher in
cost.54 Moisture in wood feedstocks also creates problems in storing fuels for later use. These other
problems include decomposition, self-heating, spontaneous combustion, and buildup of spores and
moulds.55
Research on plantation-grown wood feedstocks in temperate climates has shown that harvest during the
dormant growing season will be required to obtain good coppice regrowth. An added benefit is that
leaves will be left on site to enhance nutrient recycling.56 Under such a scenario several months of
storage is required to ensure a continuous supply of feedstock to the conversion facility.57 When
feedstocks are stored for long periods decomposition losses can be high. Decomposition can be especially
high under conditions of high humidity, rainfall, and evapotranspiration. How the feedstocks are stored
(covered or uncovered) and in what physical form (chips or as bundles of whole-tree) also affects
decomposition and the moisture content of the feedstock. Under less than ideal conditions,
decomposition losses can easily reach 2% per month of storage. One option to avoid storage problems
and decomposition losses is to harvest year-round. With year-round harvesting crop decomposition
losses do not occur as trees are in effect stored on the stump. This practice may not promote good
regrowth and new stands may have to be established. Moreover, there may be periods during year,
especially in tropical climates, where the plantation may not be accessible or roads not passable (e.g.,
during moonsoon periods).
There are numerous factors that must be considered in designing fuel storage facilities. These include:
 the available storage area and its proximity to the boiler;
 the physical properties of the fuel (chips, chunks, whole-trees, etc.);
 additional fuel preparation requirements;
 back-up storage capacity and reliability of the fuel supply;
 seasonal weather conditions; and
 operational requirements of the boiler.
Fuel storage systems that are in use include both open and covered systems. For the open systems, the
fuel is stored either directly on the ground or on a concrete pad. The covered systems can include plastic
on slab (or on ground), open sheds, closed sheds, silos, and air bags. A typical operation is likely to include
two types of storage facilities. An inactive area (open or covered on slab) where fuel is received and an
active area (usually covered) that can store about 3 days supply. Front-end loaders and manual labor are
53
most often used to move chipped wood feedstocks between inactive and active storage areas. The
WTEtm technology uses a very large shed (air supported) to store and dry a 30-day supply of whole-trees
using waste heat from the power plant.
Fuel-feed systems are used to transfer wood from the active storage area to the fuel hopper for metering
and feeding into the boiler. This handling equipment can include various types of conveyors (belt, drag,
screw, pneumatic) and elevators. Fuel hoppers are usually designed to avoid bridging and clogging (e.g.,
sloped walls), and they are covered to prevent sparks and smoke from escaping to the storage area.
Screens and knife hogs or hammermills may also be used to remove unwanted material (e.g., rocks and
debris) and to ensure appropriate particle sizes and uniformity. Uniform feedstock size helps to ensure
more efficient fuel handling and combustion.
The characteristics and quality of biomass feedstocks greatly influences the design, choice, and
performance of conversion technologies as well as the requirements for feedstock storage, fuel handling,
and ash disposal. Biomass feedstocks that are variably sized and high in moisture or ash content can
reduce boiler efficiencies, increase O&M costs, and lower capacity factors.
There is a variety of equipment on the market that can be used for sizing. This equipment ranges from
small-scale chippers that are towed or trailered to a site to large-scale equipment. The large-scale
equipment can be mobile (trailered or self-propelled) or stationary. This equipment is usually configured
with grapples for fuel feeding. Whether small- or large-scale, chips can be blown directly into a van or
trailer for transport or piled at the conversion facility for storage.
There also exists a number of options regarding fuel preparation and handling systems. The wood
feedstocks can be chipped "green" immediately after harvesting. Because many conversion systems are
designed to burn green or high moisture materials (<50%) and a variety of fuels, storing fuels to reduce
the moisture content may not be necessary. Some conversion systems require that the feedstocks be
dried significantly below 50% moisture. In this case, green chips would then have to be stored.
Alternatively, felled trees can be stored in whole form (or chunks) for storage and drying. This practice
would reduce decomposition losses. However, drier wood is more difficult to chip and to ensure uniform
size.
Power Generation Options
The use of plantation-grown biomass can be used for power generation in three general applications,
these include:
 stand-alone, grid-connected biomass-based power plants using plantation grown feedstocks or
mixed with agricultural residues;
 cogeneration at agricultural (e.g., sugar mills and rice mills) and forestry processing facilities for
on-site heat and power needs with export of excess power to the local distribution grid using a
combination of mill wastes (bagasse, rice hull, wood waste) and plantation-grown biomass;
 and co-firing at fossil-fired electric generation facilities.
For each of these applications, the current conversion technology of choice is the steam-turbine cycle
(Rankine cycle). The technology is relatively simple to operate and it can accept a wide variety of biomass
fuels. However, at the scale appropriate for biomass, the technology is expensive and relatively inefficient
when compared with fossil fuel power plants.58 As such, the technology is relegated to applications
where there is a readily available supply of low-, zero-, or negative-cost feedstocks.
The low efficiency of biomass-fired power plants, relative to fossil-fuel plants, is due in part to the use of
more moderate steam conditions. Biomass steam-turbine plants use lower pressures and temperatures
because of the strong scale dependence of the unit capital cost ($/kW).59 Biomass plants can not be built
at sufficiently large sizes to take advantage of scale economies (>300 MWe) because the cost of supplying
fuel to the plant would be excessive. Woody biomass has an energy density of slightly less than 20 GJ/dry
tonne. When freshly cut, wood contains about 50% moisture. The high moisture effectively reduces the
energy content of the wood by half. Relative to coal, a tonne of dry wood has about one-third less heat
value than a tonne of coal. The high costs associated with handling, transporting, and storing large
quantities of biomass effectively will this negate any scale economies associated with building large
conversion facilities.
The remainder of this section examines several combustion technologies for biomass power
generation.60 The technologies can be classified into currently available technologies that are in
operation at the present time or capable of being in operation with minimal developmental barriers, and
54
emerging technologies that are expected to require overcoming some technical barriers, before
commercialization can be considered.
Currently Available Technologies
Conventional steam turbine systems. Except for differences in fuel handling and preparation and
emissions control, wood-fired steam turbine power systems use essentially the same technology as that
found in coal-fired plants. However, the lower density and heating value of wood relative to coal means
that biomass systems require more combustion and heat transfer surface area. The tradeoff between
additional costs of fuel handling and extra boiler combustion area for wood, and simpler emissions
controls relative to coal translates into approximately the same installed costs ($/kWe) for biomass
systems.
In a conventional biomass-fired combustion steam turbine, wood is first prepared (sized and possibly
dried) then burned in a boiler to produce pressurized steam. The steam is expanded in a turbine to
generate electricity. For power production, a fully condensing turbine is used. If process heat is to be
produced in addition to electricity, a condensing-extraction (or back-pressure) turbine is used instead. In
this cogeneration mode, some steam after producing electricity is taken from the turbine for process
heat.
Specific boiler types used to generate steam include pile burners (dutch oven), grate burners (stationary
or traveling grate), suspension burners, and atmospheric fluidized-bed combustors (bubbling-bed or
circulating-bed). These combustion methods will produce boiler efficiencies ranging from 65 to 75% with
net plant efficiencies from 20 to 25%.
The most commonly used boilers for wood-fired systems are grate burners. The grates can be either
stationary or traveling. Stollers are used to fuel wood into the boiler. For wood-fired systems, the
spreader-stokes is most often used decause it can easily handle a wide variety of fuels. A second
combustion design available for biomass are fluidized beds. In these designs wood (biomass) is injected
into the combustion chamber through ports and burned in suspension. Air entering the boiler fluidizes a
bed of hot, granular, inert material. The inert material heats the biomass quickly to ignition temperature,
stores the thermal energy, and provides the appropriate residence time for full combustion.
Co-firing biomass feedstocks with coal. Co-firing plantation-grown biomass feedstocks with coal in
existing utility steam boilers is a potentially useful process to reduce SO2 emissions. The addition of
scrubbers to a coal-fired plant would sharply reduce SO2 emissions, but at a high cost. If only a moderate
amount of SO2 emissions reduction is required, co-firing wood and coal can be a very cost effective
alternative. Additions of new fuel handling equipment, modifications and improvements to boilers and
electrostatic precipitators are required to co-fire with coal, but these changes would likely be less costly
than installing scrubbers, switching to low sulfur coal, or purchasing emission allowances. Because of the
moisture present in wood, some derating of the boiler may occur.
Emerging Technologies
The currently available biomass conversion technologies are relatively robust with minimal operating
problems.61 However, a significant limitation of these technologies are low operating efficiencies that are
due in part to the high moisture inherent in biomass feedstocks. One technology under development and
testing that offers higher conversion efficiency is Whole Tree Energy (WTEtm) technology. WTEtm is an
innovative steam turbine technology that uses an integral fuel drying process.62 Waste heat, preheated
by the flue gas at 54C is used to dry the wood stacked in a large, air-inflated building for 30 days before it
is conveyed to a boiler and burned. Allowing the waste heat to dry the wet whole tree fuel can result in
furnace efficiency approaching 87% with a net plant efficiency comparable to that of a modern coal-fired
plant (35%). WTEtm also reduces wood harvesting and handling costs as well as the need for equipment
such as hammer mills, screens, and chippers that are used for reducing the size of the wood feedstock. In
the Lake States region of the U.S., busbar electricity costs from WTEtm are projected to be about
$0.043/kWh or about $0.015/kWh less than that of a coal-fired plant.63 WTEtm can be built in sizes as
small as 25 MWe; however, it is more likely that the market for this technology will be utility-scaled
systems. Although there exists technical potential to increase the conversion efficiency of WTEtm
technology and other steam-turbine cycle systems, these developments are unlikely to be costeffective.64
According to some experts the most promising technologies for wood-fired power generation lie in the
development of gas turbine cycles.65 Gas turbines (or Brayton cycles) have already been developed for
55
natural gas and clean liquid fuels. A key advantage of gas turbine technology is the potential for
substantially reduced capital costs, which are relatively insensitive to scale, higher conversion efficiencies
(upwards of 45%), and greater modularity. Adapting the technology for biomass (i.e., Biomassgasifier/gas turbine -- BIG/GT) would require the use of a gasifier to thermochemically convert wood to a
gas. The resultant gas would then be cooled and cleaned before being burned in a gas turbine. There are
a number of technology choices for both the gasification and power generation portions of the BIG/GT
cycle.
BIG/GT gasification. There are two principal gasification options for use with biomass or plantationgrown wood. These are the fixed-bed and fluidized-bed gasifiers. The most promising of the fixed-bed
gasifierdesigns for biomass are updraft designs. In these gasifiers, wood is fed from the top of the gasifier
undergoing drying, pyrolysis, and char gasification and combustion as it moves to the bottom of the
gasifier. The gas is removed from the top side of the gasifier with air and steam injected into the bottom
sides of the gasifier. Fixed-bed gasifiers are simple to operate and efficient when used with uniform and
appropriately sized, high bulk density (e.g., wood chips) feedstocks. The most important technical issue
associated with these gasifiers is hot-gas cleanup, primarily the removal of alkali compounds and
particulates. Controlling the temperature of the gas and using cyclones for particulate removal can be
used to provide a gas suitable for the turbines.
Relative to fixed-bed gasifiers, fluidized-bed gasifiers have greater throughput and can handle a greater
variety of fuels including low-density materials such as agricultural wastes. This fuel flexibility
characteristic may make fluidized-bed gasifiers the more appropriate choice for biomass
applications.66 However, the resultant gas from fluidized beds is more problematic for gas cleaning. The
exit gas has a temperature about 300oC higher than that for fixed-beds (500 to 600oC). The higher gas
temperature requires gas cooling to condense the alkali compounds. Particulate control is also likely to be
more problematic and require the use of advanced filtering techniques.
BIG/GT turbine cycles. There are a number of alternative turbine cycles available and under development
that can use clean fuel gas. In a simple-cycle configuration, fuel gas is burned in air pressurized by a
compressor. The hot combustion gases are then used to drive a turbine. The exhaust gases from the
turbine can be discharged (open cycle) or used in a heat recovery steam generator to raise steam for
industrial or agricultural processing needs (cogeneration cycle). Because waste heat is used, the overall
efficiency of the cogeneration cycle is higher than that of the simple cycle.
Both the open cycle and cogeneration cycle can generate electricity with an efficiency of about 32% (less
than that from a modern, large-scale steam-turbine cycle). There are a number of cycles under
development and/or demonstration that have the potential to increase significantly the efficiency of the
power generation side of the cycle. One of these is the BIG/GT combined cycle (BIG/GTCC). This cycle is
similar to the simple cycle except that steam from the heat recovery steam generator is used to generate
additional power in a conventional steam turbine.67 About one-third of the total power output of a
BIG/GTCC would come from the steam-turbine side of the combined cycle.
Steam injected gas turbine systems (BIG/STIG) are another option under development. In the BIG/STIG
system waste steam from the heat recovery steam generator that is not needed for process uses is
injected back into the gas turbine combustor, and at additional points along the flow path the gas is
reheated to turbine inlet temperature, and then passed through the turbine. The additional steam mass
injected into the turbine increases the total power output of the system and does not consume power at
the turbine's compressor. Full steam injection allows the total system efficiency to approach 40%. An
advanced form of the STIG is the intercooled steam-injected gas turbine (ISTIG). This variation of the STIG
can raise both thermal efficiency (from 47% to 50%) and shaft power output.
Environmental and Social Benefits/Costs of Biomass Plantations
Tree biomass plantations potentially offer many direct and indirect environmental benefits, but they may
have negative environmental impacts as well. As recently discussed by Graham, ascertaining the
environmental impacts are complex because the impacts of using biomass for energy must be considered
in the context of alternative energy options while the impacts of producing energy crops must be
considered in the context of alternative land uses.70
Globally significant environmental benefits may result from using wood for energy rather than fossil
fuels. The greatest benefit is derived from substituting biomass energy for coal.71 The degree of benefit
depends greatly on the efficiency with which the wood is converted to electricity. If the efficiency of
56
conversion of wood to electricity is similar to coal conversion to electricity then the benefits are several.
Airborne pollutants such as toxic heavy metals, ozone-forming chemicals, and releases of sulfur that
contribute to acid rain will be reduced. The ash and waste products from burning will, in most cases, be
sufficiently benign to return to the soil. There will be a considerable reduction in net carbon dioxide
emissions that contribute to the greenhouse effect. For example, one dry tonne of wood will displace 15
GJ of coal. The 15 GJ of coal will have the equivalent of 0.37 tonnes of carbon assuming the wood is
converted at an efficiency of 25%.
Table 4.1. Example carbon offsets from short-rotation plantation energy used for power production and
displacing coal
Factor
Wood
Coal
Energy density (GJ/Dry tonne)
19.8
29.3
Heat rates (kJ/kWh)
7,200-18,000
10,900
Feedstock carbon (kg C/GJ)
50
70
% Carbon
25.3
24.1
Input carbon (kg C/GJ)
1.34
0.53
Total carbon (kg C/GJ)
26.62
24.65
1 dry tonne of wood displaces 370 kg of coal carbon (19.8GJ/tonne*10.9/14.4 MJ/kWh)*24.65 kg
C/tonne)
Note: Feedstock carbon is the carbon embodied in the biomass or the carbon sequestered by plant
growth. Input carbon is the carbon embodied in the factor inputs (e.g., diesel fuel) used to grow, harvest,
and transport the biomass.
Locally significant environmental benefits can be maximized when tree biomass plantations replace
annual crops, heavily grazed pastures, or degraded lands.72 Benefits can include:
1. protection of water quality,
2. reduction of floods during wet seasons and maintenance of water supplies during dry seasons,
3. erosion prevention,
4. improvement of local microclimate through evaporative cooling and humidification,
5. wind breaks and shelters that reduce erosion and conserve water, particularly in dry regions,
6. reduction of fire danger,
7. reduction in use of fertilizer and agricultural chemicals,
8. improvement of soil properties, and
9. protection of wildlife and other components of biodiversity.
Negative environmental effects of plantations may occur locally if unmanaged natural forests or forests
managed for low intensity uses are removed and replaced with short-rotation biomass plantations.
Negative impacts can include:
1. increased erosion and reduction of water quality as a result of forest harvesting;
2. increased rates of runoff and decreased water-holding capacity;
3. increased chemical pollution from fertilizers and pesticides;
4. degradation of soil quality and productivity; and
5. reduction of biodiversity through alteration of forest structure, creation of tree monocultures,
and use of non-native tree species which local wildlife are unable to use.73
Concern over possible negative impacts has led environmental groups at both national and international
levels to attempt to establish environmental guidelines prior to the commercialization of biomass energy
technologies.74 In Brazil, early mistakes in establishment of Eucalyptus plantations, along with increasing
environmental sensitivity, have led to substantial regulation of the forest industry.75
To minimize or avoid negative impacts from energy crop production, most proponents of biomass energy
are recommending that biomass plantations be established on existing agricultural lands or degraded
lands.76 Forestry codes and plantation management procedures currently being developed and
57
implemented around the world generally prohibit the conversion of natural forest to forestry plantations.
Many of the natural forests occur on relatively poor soils, and destruction of natural forests is now
recognized to have environmental costs in terms of biodiversity, environmental quality, and economic
sustainability that far outweigh short-term economic gains from forest clearing. Principles recently
formulated in the U.S. for the wise development of biomass resources include the following:77
 Biomass energy system development must be guided by consistent decision criteria and should
foster the multiple goals of environmental protection, economic revitalization, and energy
security.
 Energy crop production practices and energy conversion technologies must be selected to ensure
that the use of biofuels substantially reduces anthropogenic emissions that may contribute to
global climate change. The use of biofuels should not exacerbate greenhouse gas emissions when
compared with conventional fuels on a full-fuel cycle basis.
 The development and management of biomass resources should protect and, wherever possible,
enhance ecological integrity and biological diversity, while minimizing adverse impacts to land,
air, and water.
 The development and management of biomass resources should contribute to the economic well
being of producers, local communities, and the nation as a whole.
 The use of biomass resources for energy purposes must rationalize trade-offs in terms of
competing uses for the land and plants (whether for food, fiber, recreation, wildlife habitat, or
other uses), while also recognizing the impacts and trade-offs implicit in the use of other energy
resources.
The remainder of this chapter provides more discussion of the effects of tree plantation on soils and
water, biodiversity, chemical pollution, and social economics.
Tree Plantations and Soil/water Issues
The beneficial effects of forests on water quality, soil erosion prevention, and the reliability of water
supply have long been recognized. The oldest forest reserve in the Western Hemisphere was established
in Trinidad and Tobago in 1765 with the designation "Reserved in Forest for the Rains," followed by
further assessments in the 1880s into "Forest Conservation and the Maintenance of Water Supplies."
Many natural forest reserves have been established around the world in mountainous areas for the
protection of municipal water supplies. Biomass plantations can also serve this purpose, particularly if the
negative effects of harvest on soils and water supply can be minimized. Plantations are particularly
valuable in improving the water supply on land that has been degraded by deforestation or
desertification.78
Fig. 4.1a. Effects of land-cover type,
precipitation, and slope on surface
runoff at four tropical sites. The
positive effects of plantations on soil
and water conservation results
primarily from protection of the soil
surface from the direct impact of rain
and from the improvement of soil
structure through root penetration
and the addition of organic matter
from decomposing leaves, roots, and
wood. In comparison to either crops
or bare soil, forest greatly reduces the
proportion of rainfall that is lost as
runoff, thus leaving much more water
available to feed springs and streams
during dry periods (Fig. 4.a). The
positive effects of trees on water retention tend to increase over time, so long rotations and practices
that enhance organic matter input into the soil are particularly favorable.
Tree species vary greatly in their effect on soil properties and on water cycling. Some tree species, such
as E. globulus and E. tereticormis, tend to use water very rapidly, leading to reduced water yield from
58
watersheds, stress during dry seasons, and creation of unfavorable conditions for interplanting with food
crops.79 On the other hand, studies on Eucalyptus grandis in Brazil have found the annual variation in soil
water to be similar to that for Pinus caribea and savanna-like native forests.80 Tree plantations have also
been shown to reduce wind erosion, reduce evaporative losses of water, and improve soil moisture
conditions sufficiently to allow cropping on degraded lands.81 Nitrogen-fixing species, such as acacias and
leaucena, can improve the soil, reduce the need for expensive nitrogen fertilizer, and produce fodder for
farm animals.
A primary difference between short rotation plantations, and forests harvested for timber with regard to
erosion and water issues is the frequency of harvesting and replanting. Because 40% of tropical rainfall
falls at erosive rates (greater than 25 mm/hr), soils exposed during and after harvesting are susceptible to
serious erosion. 82
Harvesting and reestablishment practices thus become a very important determinant of the potential for
environmental damage. When reestablishment occurs through coppice resprouting, risk of soil loss is
minimized by rapid regrowth. The use of cover crops or grass strips between the rows can reduce erosion
when replanting is required.
Fig. 4.1b. Effects of land-cover type,
precipitation, and slope on erosion at
four tropical sites.84 The potential for
soil loss increases greatly with
increasing precipitation and on hilly or
mountainous land (Fig. 4.1b).
Harvesting with heavy equipment
during rainy seasons is especially likely
to cause serious soil erosion and soil
compaction and may destroy the longterm productivity of a plantation. Due
to both equipment constraints and
erosion hazards, biomass plantations
that are likely to be harvested every 510 years should not be located on
steep, erodible soils. In general,
tropical soils are much more subject to
degradation from harvesting than forests on younger soils, such as those found in much of the temperate
zone.83
Tree Plantations and Biodiversity
Biodiversity refers to the number of different kinds of plants and animals that are found in a particular
area such as a hectare of forest, and entire country, or the earth. Concern about the loss of biodiversity is
based on the idea that each organism, even those that are unknown and unnamed, has some value. Many
plants and animals are valued for the medicinal chemicals they produce or for their importance to
forestry or agriculture. Other species are valued for their beauty or other special properties. Many
species, even obscure organisms in the soil, may play important but poorly understood roles in improving
soil fertility, in preventing diseases and pests from affecting crops, or otherwise maintaining a balance of
nature that is favorable to human existence. For these and many other reasons, there is a broad
consensus among scientists, citizens, and politicians that biodiversity should be preserved by preventing
the extinction of species wherever possible.
Because many birds, mammals, insects, and other animals depend on one to several particular tree
species, extensive biomass plantations of a single tree species can be extremely destructive to
biodiversity when displacing natural habitats. Clearing natural forests to establish plantations usually
destroys biodiversity and should be avoided. Many of the forests with high biodiversity occur on soils that
are too poor to support productive plantations, so there is usually no economically or biologically sound
reason to replace them with plantations. Establishment of plantations on degraded lands that were
previously deforested will usually have a positive effect on local biodiversity by improving the habitat for
plants and animals that cannot survive deforested areas and may have other benefits such as
improvement of water quality and quantity and soil improvement.
59
Tree plantations can be beneficial to biodiversity if properly designed or can be destructive of biodiversity
when designed inappropriately.85 The effect of biomass plantations on biodiversity may depend as much
on how they fit into the landscape as the particular species and management systems selected. Studies in
the United States on hybrid poplar plantings have shown varied use by wildlife, depending on the
surrounding landscape. For example, plantations adjacent to natural forest seem to reduce "edge effects"
and expand the usable areas for forest interior bird species in predominately agricultural areas.
There is considerable controversy on the use of non-native species on the scale that might be required for
biomass energy. Plantations based on non-native species, such as eucalyptus outside of Australia and teak
outside of Asia, are generally believed to provide little suitable habitat for native animals,86 although
research on this issue is continuing. Depending on the planned energy conversion technology, plantations
for biomass may be able to utilize a wider variety of tree species and thus may support a higher
biodiversity of plants and animals than single-species hardwood or pulp plantations that must produce a
crop that is extremely uniform in form and other properties.
Biomass plantations can have a positive effect on biodiversity if their design includes preserving areas of
natural forest of different types within the overall plantation area. Research has shown that areas of
natural forest included within plantations is favorable for many native species of plants and
animals.87 Properly designed plantations should include areas of natural vegetation, appropriate wooded
buffers for waterways and corridors for wildlife movement, as well as protection of historical
areas.88 Since the 1960s Brazil has required forest companies to either leave 10% of the managed area in
natural vegetation or ensure that 1% of the trees planted are native species. The 10% option has normally
been preferred and has resulted in positive benefits for both bird diversity and insect pest control. 89
Specific guidelines developed by the National Biofuels Roundtable in the United States for improving
habitat are:
 Match native ecosystem cover types as much as possible (e.g., perennial grasses in prairie regions
and trees in woodland regions). In addition, emulate natural vegetation patterns and functions
when establishing energy crops on agricultural lands.
 Locate, plant, and harvest tracts of energy crops in ways that help improve pathways for animals
to move between habitats and across landscapes in any particular year.
 Employ energy crops in ways that minimize the fragmentation of desirable habitats and improve
overall habitat quality of the landscape for native species.
Tree Plantations and Chemical Pollution
The previous use of the land will determine the extent to which chemical pollution is an issue. Plantations
generally require fewer inputs of fertilizers, herbicides, and pesticides than more intensive forms of
agriculture.90 In regions of extensive agricultural activity where non-point pollution of streams is a
problem, tree plantations may improve water quality by serving as a filter of agricultural chemicals.
Establishment of plantations on pasture land, as may occur in many parts of the developing world, would
result in additional use of some chemicals unless hand labor is used to control weeds. As described in
Chapter 2, methods are available to minimize chemical use such as mulching and applying chemical only
in strips around the trees though the relative costs of these measures have not been well established.
Pest control can occur with minimal chemical use if frequent monitoring and biological control methods
are used. The most effective method of pest control is to maintain ongoing breeding and genetic selection
program so that susceptible trees can be eliminated and replaced with resistant varieties. Brazilian pulp
and paper companies have been successful in controlling pest problems though genetic selection
programs.
Tree Plantations and Social Economics
Successful woody crops can provide multiple economic, social, and environmental benefits to a state,
region, country if properly planned and integrated into the multiple landuse opportunities within the
country. In regions where the amount of good quality soil is limited, use of the best soils for biomass crop
production will displace other land uses. The concern expressed most often is that use of land to produce
biomass crops will reduce food availability. Such a concern was expressed in the mid-eighties when
sugarcane establishment was accelerating in the agricultural state of São Paulo, Brazil as a result of
subsidies provided by the National Program for Alcohol production (commonly referred to as ProAlcool).
The article entitled "Brazilian Alcohol: Food versus Fuel" by Rosillo-Calle and Hall describes the complexity
of food production and export policies in Brazil as well as details on the sugar cane expansion.91 The food
60
versus fuel controversy was exaggerated in their view. They conceded that the ProAlcool might be part of
a larger overall problem which would best be described as a "commodity export crop production versus
domestic food production" issue. With 64% of the sugar cane expansion in the state of São Paulo
occurring on pasture land owned by large land-holders, displacement of primary food production was not
the major issue.
Tree plantations always exist in a social and cultural setting based on the inhabitants of the area before
the plantation was created, and the inhabitants who arrived after the plantation was established. To be
economically successful, and to avoid negative effects on society and the natural environment, each
plantation must be designed for its own specific social, cultural, and environmental setting. Factors that
must be considered include
1. preexisting land uses;
2. local agricultural practices;
3. local political systems and hierarchies of authority;
4. local cultural divisions of labor and authority between men and women;
5. local traditions of land tenure and stewardship including private property right; and
6. local cultural values.92
Because plantations must depend on local labor, it is desirable to maintain the structure of the local
community in a way that provides a steady supply of reliable workers. The more the plantation can be
integrated into the daily economic and social life of the community, to the mutual benefit of both the
community and the plantation, the more likely it is to succeed in the long run. For this reason, Brazil and
China are leaders in investigation of agroforestry techniques for large scale use. Tree establishment can
be enhanced, and the need for dangerous chemicals reduced, through the interplanting of agricultural
crops during the first years after planting. This type of agroforestry benefits the plantation as well as the
local community by providing food and/or cash crops.
The use of multipurpose trees that provide energy products, animal fodder, and enrich the soil through
nitrogen fixation are viewed as the ideal energy tree.93 It is likely this is the reason that leucaena was the
species selected for use in the Philippine Dendrothermal program. Research has continued around the
world on leucaena, acacias and other nitrogen fixing trees such as black locust. However, there has been
an unfortunate tendency for these species to be susceptible to insect pests. Leucaena plantings have
largely been destroyed by a psyllid pest and black locust is susceptible to a stem borer. These problems
may be solved through genetic selection, biotechnology or biological control agents ,but at present, the
widespread planting of nitrogen fixing trees for energy or pulp is not occurring. Even so, the multipurpose
tree concept is a good one that deserves continued consideration. One success story is occurring in Brazil
with a company that has a specialized conversion technology to produce pulp, alcohol, cattle feed and
even electricity from a bamboo (Bambusa vulgaris) species.94
In summary, plantations for production of biomass energy have numerous potential environmental
benefits. Conclusions from a roundtable of industry, academic, and government participants in the United
States found that "if energy crops are included in the general mix of agricultural crops in a considered and
informed way, environmental damage can be avoided; in fact, there could be significant environmental
and ecological benefits achieved in tandem with the development of a fully sustainable energy
resource."95
In addition to gas turbines, fuel cells are also under development. Fuel cells convert energy produced by
electrochemical oxidation of a fuel like biomass into electricity. The operation of a fuel cell has gaseous
fuels being fed continuously to the fuel cell's negative electrode (anode), while oxygen or air (oxidant) is
fed continuously to the positive electrode (cathode). A continuous electrochemical reaction occurs which
produces an electrochemical potential or voltage and electric current similar to that of a conventional
lead-acid battery. Several fuel cell types are currently under development. However, the phosphoric acid
fuel cell (PAFC) is closest to commercialization.68 The PAFC fuel cell operates at approximately 390F and
has a cycle efficiency of as high as 45%. Advanced fuel cell designs could reach efficiencies of about 57%
by 2020.69
Biocrude oils can also be produced from wood using a pyrolysis process similar to that used in
gasification. The wood feedstocks are thermochemically converted to a sulfur free mixture of biocrude oil
vapors, non-condensible gases, water vapor, and char particles. The biocrude oil vapors are condensed to
61
form a higher viscosity mixture of organic compounds with a heat value of 8,000 Btu/lb. After the residual
non-condensible gases exit the condenser, the gases are collected and burned as process heat for drying
the feedstock or supplying heat to the reactor. Approximately 60% to 80% of the feedstock can be
converted to biocrude. Biocrude can be used as a substitute for fuel oil for gas turbine cycles. Biocrude
can also be co-fired with other fossil fuels. The pyrolysis process does not have to take place at the power
generation site since the biocrude can be stored and transported.
CHAPTER NO.03
BIOENERGY THECNOLOGY
3.1Introduction
Based on FAO’s Unified Bioenergy Terminology (FAO, 2004), the conceptual view of bio- energy systems
is shown in Figure 2, describing the flow of bio-energy production from biomass as a source of energy.
Biomass
Biofuels
Bio energy
Figure 2. Bio-energy production flow
Bio-energy can be defined as energy obtained from biological and renewable sources (biomass); bioenergy may be derived in the form of heat or transformed into electricity for distribution. Biomass
also can be transformed into biofuels, which are portable feedstock for use in the generation of
bio-energy. Biofuels are defined as feedstock intended for the production of bio-energy, produced
directly or indirectly from biomass. Biofuels can be in solid form (fuelwood, charcoal, wood pellets,
briquettes etc.) or liquid (bioethanol, biodiesel).
With the emerging development on bio-energy today using more modern technology, biomass energy
can be divided into traditional biomass and modern bio-energy. Traditional biomass is the main source
of energy used in developing countries primarily for cooking and space heating at the household level,
mostly using three-stone stoves, or in some areas improved cooking stoves. This source of energy is in
the form of woodfuel (including fuelwood and charcoal), crop residues and animal dung and is often
collected by women and children on a daily basis. In some areas traditional biomass is also traded
within villages and among villages or with nearer townships. Another characteristic of traditional
biomass is using traditional technology with low efficiency due to poor design, uncontrolled and open
burning, which have important health implications. Modern bio-energy, is used mostly for the
generation of electricity or transportation. Liquid biofuels for transportation such as ethanol and
biodiesel are examples of the emerging energy alternatives.
Table 1 describes in detail the key differences between traditional and modern biomass in terms of
input, output and conversion technology. Traditional forms of biomass use are characterized by low
capital, low conversion efficiency, poor utilization of fuel, and poor emission controls whereas modern
forms of biomass use are characterized by higher capital, higher conversion efficiency, better
utilization of fuel, and better emission controls (Rajagopal and Zilberman, 2007). Transformation of
low efficiency fuels to high efficiency convenient fuels involves substantial investments, and often the
transformation process involves loss of energy.
Table 1. Comparison between traditional and modern bio-energy systems
62
(Rajagopal and Zilberman, 2007)
Characteristics of
technology
Traditional
Modern
Fuel
Mostly gathered or collected
and in some cases purchased
Commercially procured
Capital
Low capital cost
High capital cost
Labour
High labour intensity at
household level in collection
of fuel
Conversion
process
Energy uses
Low efficiency and poor
utilization of biomass
Energy for cooking and
heating in poor households in
developing countries
Poor emission controls
Low labour intensity at household
level but overall high labour
intensity compared to other
energy sources
Higher efficiency and higher
utilization of biomass
Commercial heating, electricity
and transportation
Emission
controls
Co-product
No co-products
Controlled emissions
Commercially useful co-products
3.1.1 Wood Bioenergy Basics
What is wood-based biofuel?
Biofuel is one specific form of bioenergy, or
energy derived from biomass. There are many
forms that both biomass and biofuel can take.
However these research projects focus primarily
on woody biomass that will be turned into
cellulosic ethanol and used as a component of
transportation fuel. Some aspects of this
research can also apply to other wood-based
forms of energy, such as heat and electricity.
There are many potential sources of woody
biomass, including shrubs or trees grown on plantations, managed natural forests, and waste products
left behind after forest harvesting or management activities. Different refineries or conversion processes
may require different types of feedstock, or biomass material for their supply.
Using wood as a fuel source has implications for current energy and climate concerns. Carbon dioxide
released by burning fuel can be removed from the atmosphere by the re-growth of plant material.
Replacing fossil fuels with fuel produced from sustainably managed sources of woody biomass can
therefore play a role in mitigating climate change. As a locally available, renewable resource, woody fuels
also have the potential to contribute to energy independence for Michigan.
3.2 A BRIEF INTRODUCTION TO BIO-ENERGY CONVERSION TECHNOLOGIES
3.2.1 Bioenergy Conversion Technologies
 Conversion challenges
 Conversion technologies
There are four types of conversion technologies currently available, each appropriate for specific biomass
types and resulting in specific energy products:
1. Thermal conversion is the use of heat, with or without the presence of oxygen, to convert biomass
materials or feedstocks into other forms of energy. Thermal conversion technolgies include direct
combustion, pyrolysis, and torrefaction.
2. Thermochemical conversion is the application of heat and chemical processes in the production of
energy products from biomass. A key thermochemical conversion process if gasification.
3. Biochemical conversion involves use of enzymes, bacteria or other microorganisms to break down
biomass into liquid fuels, and includes anaerobic digestion, and fermentation.
63
4. Chemical conversion involves use of chemical agents to convert biomass into liquid fuels.
3.2.1.1 Thermal conversion
As the term implies, thermal conversion involves
the use of heat as the primary mechanism for
converting
biomass
into
another
form.
Combustion,
pyrolysis,
torrefaction,
and
gasification are the basic thermal conversion
technologies either in use today or being
developed for the future.
Combustion
Direct combustion is the burning of biomass in the
presence of oxygen. Furnaces and boilers are used
typically to produce steam for use in district
heating/cooling systems or to drive turbines to
produce electricity. In a furnace, biomass burns in a
combustion chamber converting the biomass into
heat. The heat is distributed in the form of hot air
or water. In a boiler, the heat of combustion is
converted into steam. Steam can be used to
produce electricity, mechanical energy, or heating
and cooling. A boiler’s steam contains 60-85% of
the energy in biomass fuel.
Co-firing is a practice which has permitted biomass
feedstocks to be used early on in the renewable
energy transformation. Co-firing is the combustion
of a fossil-fuel (such as coal or natural gas) with a
1 (com.biomasswithplants)
biomass feedstock. Co-firing has a number of
advantages, particularly when electricity is an
output. If the conversion facility is situated near an agro-industrial or forestry product processing plant,
large quantities of low cost biomass residues are available to be burnt with a fossil-fuel feedstock. It is
now widely accepted that fossil-fuel power plants are usually highly polluting in terms of sulfur, CO2 and
other GHGs. Use of existing equipment, with modifications, to co-fire biomass may be a cost-effective
means for meeting more stringent emissions targets. Biomass fuel’s comparatively low sulfur content
allows biomass to potentially offset the higher sulfur content of fossil fuel.
Biomass can also be used in co-generation, also called combined heat and power (CHP) which is the
simultaneous production of heat and electricity. All power plants produce heat as a by-product of
electricity production, and this heat is typically released to the environment through cooling towers
(which release heat to the atmosphere) or discharge into near-by bodies of water. However, in CHP
processes, some of the “waste heat” is recovered for use in district heating. Co-generation coverts about
85% of biomass’ potential energy into useful energy.
Pyrolysis and torrefaction
These processes do not necessarily produce useful energy directly, but under controlled temperature and
oxygen conditions are used to convert biomass feedstocks into gas, oil or forms of charcoal. These energy
products are more energy dense than the original biomass, and therefore reduce transport costs, or have
more predictable and convenient combustion characteristics allowing them to be used in internal
combustion engines and gas turbines.
Pyrolysis is a processes of subjecting a biomass feedstock to high temperatures (greater than 430 °C)
under pressurized environments and at low oxygen levels. In the process, biomass undergoes partial
combustion. Processes of pyrolysis result in liquid fuels and a solid residue called char, or biochar. Biochar
is like charcoal and rich in carbon. Liquid phase products result from temperatures which are too low to
destroy all of the carbon molecules in the biomass so the result is production of tars, oils, methanol,
acetone, etc.
Torrefaction, like pyrolysis, is the conversion of biomass with the application of heat in the absence of
oxygen, but at lower temperatures than those typically used in pyrolysis. In torrefaction temperatures
64
typically range between 200-320 °C. In the torrefaction process water is removed and cellulose,
hemicellulose and lignins are partially decomposed. The final product is an energy dense solid fuel
frequently referred to as “bio-coal”.
Thermochemical conversion
(Corning Museum of
Glass)
Thermochemical
technologies
are
used for converting
biomass into fuel
gases
and
chemicals.
The
thermochemical
process
involves
multiple stages. The
first stage involves
converting
solid
biomass into gases.
In the second stage
the
gases
are
condensed into oils.
In the third and final
stage the oils are
conditioned
and
synthesized to produce syngas. Syngas contains carbon and hydrogen and can be used to produce
ammonia, lubricants, and through the Fischer-Tropsch process can be used to produce biodiesel.
Gasification
Gasification is the use of high temperatures and a controlled environment that leads to nearly all of the
biomass being converted into gas. This takes place in two stages: partial combustion to form producer gas
and charcoal, followed by chemical reduction. These stages are spatially separated in the gasifier, with
gasifier design very much dependant on the feedstock characteristics. Gasification requires temperatures
of about 800°C. Gasification technology has existed since the turn of the century when coal was
extensively gasified in the UK and elsewhere for use in power generation and in houses for cooking and
lighting. A major future role is envisaged for electricity production from biomass plantations and
agricultural residues using large scale gasifiers with direct coupling to gas turbines.
Biochemical conversion
The use of micro-organisms for the production of ethanol is an ancient
art. However, in more recent times such organisms have become
regarded as biochemical "factories" for the treatment and conversion
of biological materials. Fermentation technologies, with the assistance
of biological engineering, are leading to breakthrough processes for
creating fuels and fertilizer, and other products useful in agriculture.
Anaerobic digestion and fermentation are key biochemical conversion
technologies.
Anaerobic digestion
Anaerobic digestion is the use of microorganisms in oxygen-free environments to break down organic
material. Anaerobic digestion is widely used for the production of methane- and carbon-rich biogas from
crop residues, food scraps, and manure (human and animal). Anaerobic digestion is frequently used in the
treatment of wastewater and to reduce emissions from landfills.
Anaerobic digestion involves a multi-stage process. First, bacteria are used in hydrolysis to break down
carbohydrates, for example, into forms digestible by other bacteria. The second set of bacteria convert
the resulting sugars and amino acids into carbon dioxide, hydrogen, ammonia and organic acids. Finally,
still other bacterias convert these products into methane and carbon dioxide. Mixed bacterial cultures are
65
characterized by optimal temperature ranges for growth. These mixed cultures allow digesters to be
operated over a wide temperature range, for example, above 0° C and up to 60° C. When functioning
well, the bacteria convert about 90% of the biomass feedstock into biogas (containing about 55%
methane), which is a readily useable energy source.
Solid remnants of the original biomass input are left over after the digestion process. This by-product, or
digestate, has many potential uses. Potential uses include fertilizer (although it should be chemically
assessed for toxicity and growth-inhibiting factors first), animal bedding and low-grade building products
like fiberboard.
Fermentation
At its most basic, fermentation is the use of yeasts to convert carbohydrates into alcohol – most notably
ethanol, also called bioethanol. The total process involves several stages. In the first stage crop materials
are pulverized or ground and combined with water to form a slurry. Heat and enzymes are then applied
to break down the ground materials into a finer slurry. Other enzymes are added to convert starches into
glucose sugar. The sugary slurry is then pumped into a fermentation chamber to which yeasts are added.
After about 48-50 hours, the fermented liquid is distilled to divide the alcohol from the solid materials left
over.
In the U.S., corn grain is the primary feedstock in ethanol production. About 2.8 gallons of ethanol is
produced from one bushel of corn. A by-product of the corn-to-ethanol process is spent grains. These
spent grains are dried and can be used as feed for livestock – termed Distillers Dried Grains, or DDGs.
Cellulosic ethanol production by fermentation is more complex than conversion of starch or sugar
components of plants. Cellulosic ethanol production involves use of wood, grasses and the stems, leaves
and stalks of non-grass plants. Lignocellulose, the structural material of plants, must first be broken down
into sugars before being fermented into ethanol. Molecules of cellulose, hemicellulose and lignin – the
components of lignocellulose, have strong chemical bonds and are difficult to separate. Mechanical pretreatment and enzymatic are necessary to breakdown lignocellulose. As a result, at present, conversion of
lignocellulosic materials into ethanol is less cost-effective than conversion of starch and sugar crops to
ethanol.
Reducing the cost and improving the efficiency of separating and converting cellulosic materials into
fermentable sugars is one of the keys to a viable industry. Research and development efforts are focusing
on the development of cost-effective biochemical hydrolysis and pretreatment processes to overcome
this barrier. Hydrolysis is a chemical process in which molecules are split into parts with the addition of
water and a salt or weak acid. Another form of hydrolysis involves use of enzymes. Such technological
advances promise substantially lower processing costs.
Chemical conversion
(uiowa.edu)
Chemical conversion of biomass involves use of chemical interactions to transform biomass into other
forms of useable energy. Transesterification is the most common form of chemical-based conversion.
Transesterification is a chemical reaction through which fatty acids from oils, fats and greases are bonded
to alcohol. This process reduces the viscosity of the fatty acids and makes them combustible. Biodiesel is
a common end-product of transesterification, as are glycerin and soaps. Almost any bio-oil (such as
soybean oil), animal fat or tallow, or tree oil can be converted to biodiesel.
3.3 UTILIZATION OF BIO-ENERGY WITH REFERENCE TO THE GLOBAL CARBON CYCLE AND
CLIMATIC CHANGE, ESPECIALLY WITH REGARD TO CO2 EMISSIONS AND CARBON STORAGE;
66
3.3.1 Bio-energy with carbon capture and storage
Bio-energy with carbon capture and storage (BECCS) is a greenhouse gas mitigation technology which
produces negative carbon dioxide emissions by combining biomass use with geologic carbon capture and
storage. The concept of BECCS is drawn from the integration of trees and crops, which extract CO 2 from
the atmosphere as they grow, the use of this biomass in processing industries or power plants, and the
application of carbon capture and storage. BECCS is a form of carbon dioxide removal, along with
technologies such as biochar, carbon dioxide air capture and biomass burial.
According to a recent Biorecro report, there is 550 000 tonnes CO2/year in total BECCS capacity currently
operating, divided between three different facilities (as of January 2012).
It was pointed out in the IPCC Fourth Assessment Report by the Intergovernmental Panel on Climate
Change (IPCC) as a key technology for reaching low carbon dioxide atmospheric concentration targets.
The negative emissions that can be produced by BECCS has been estimated by the Royal Society to be
equivalent to a 50 to 150 ppm decrease in global atmospheric carbon dioxide concentrations and
67
according to the International Energy Agency, the BLUE map climate change mitigation scenario calls for
more than 2 gigatonnes of negative CO2 emissions per year with BECCS in 2050.
The Imperial College London, the UK Met Office Hadley Centre for Climate Prediction and Research, the
Tyndall Centre for Climate Change Research, the Walker Institute for Climate System Research, and the
Grantham Institute for Climate Change issued a joint report on carbon dioxide removal technologies as
part of the AVOID: Avoiding dangerous climate change research program, stating that "Overall, of the
technologies studied in this report, BECCS has the greatest maturity and there are no major practical
barriers to its introduction into today’s energy system. The presence of a primary product will support
early deployment."
According to the OECD, "Achieving lower concentration targets (450 ppm) depends significantly on the
use of BECCS".
Negative emission
The main appeal of BECCS is
in its ability to result in
negative emissions of CO2.
The capture of carbon dioxide
from
bioenergy
sources
effectively removes CO2 from
the atmosphere.
Bio-energy is derived from
biomass which is a renewable
energy source and serves as a
carbon sink during its growth.
During industrial processes,
the biomass combusted or
Carbon flow schematic for different energy systems.
processed re-releases the CO2
into the atmosphere. The process thus results in a net zero emission of CO2, though this may be positively
or negatively altered depending on the carbon emissions associated with biomass growth, transport and
processing, see below under environmental considerations. Carbon capture and storage (CCS) technology
serves to intercept the release of CO2 into the atmosphere and redirect it into geological storage
locations. CO2 with a biomass origin is not only released from biomass fuelled power plants, but also
during the production of pulp used to make paper and in the production of biofuels such as biogas and
bioethanol. The BECCS technology can also be employed on such industrial processes.
It is argued that through the BECCS technology, carbon dioxide is trapped in geologic formations for very
long periods of time, whereas for example a tree only stores its carbon during its lifetime. In its report on
the CCS technology, IPCC projects that more than 99% of carbon dioxide which is stored through geologic
sequestration is likely to stay in place for more than 1000 years. While other types of carbon sinks such as
the ocean, trees and soil may involve the risk of negative feedback loops at increased temperatures,
BECCS technology is likely to provide a better permanence by storing CO2 in geological formations.
The amount of CO2 that has been released to date is believed to be too much to be able to be absorbed
by conventional sinks such as trees and soil in order to reach low emission targets. In addition to the
presently accumulated emissions, there will be significant additional emissions during this century, even
in the most ambitious low-emission scenarios. BECCS has therefore been suggested as a technology to
reverse the emission trend and create a global system of net negative emissions. This implies that the
emissions would not only be zero, but negative, so that not only the emissions, but the absolute amount
of CO2 in the atmosphere would be reduced.
68
Projected cost to reach the respective 350ppm and 450ppm target scenarios by 2100. 265ppm indicates
the pre-industrial atmospheric CO2 level.
Application
Source
CO2 Source
Sector
Electrical power Combustion of biomass or biofuel in steam or gas powered generators
Energy
plants
releases CO2 as a by-product
Heat
plants
power Combustion of biofuel for heat generation releases CO2 as a by-product.
Energy
Usually used for district heating
Pulp and paper
mills
 CO2 produced in recovery boilers
 CO2 produced in lime kilns
 For gasification technologies, CO2 is produced during the gasification of
black liquor and biomass such as the tree bark and woody.
 Huge amounts of CO2 are also released by the combustion of syngas, a
product of gasification, in the combined cycle process.
Industry
Ethanol
production
Fermentation of biomass such as sugarcane, wheat or corn releases CO2 as a
Industry
by-product
Biogas
production
In the biogas upgrading process, CO2 is separated from the methane to
Industry
produce a higher quality gas
Technology
The main technology for CO2 capture from biotic sources generally employs the same technology as
carbon dioxide capture from conventional fossil fuel sources. Broadly, three different types of
technologies exist: post-combustion, pre-combustion, and oxy-fuel combustion.
Cost
The sustainable technical potential for net negative emissions with BECCS has been estimated to 10 Gt of
CO2 equivalent annually, with a economic potential of up to 3.5 Gt of CO2 equivalent annually at a cost of
less than 50 €/tonne, and up to 3.9 Gt of CO2 equivalent annually at a cost of less than 100 €/tonne.
Policy
Based on the current Kyoto Protocol agreement, carbon capture and storage projects are not applicable
as an emission reduction tool to be used for the Clean Development Mechanism (CDM) or for Joint
Implementation (JI) projects. Recognising CCS technologies as an emission reduction tool is vital for the
implementation of such plants as there is no other financial motivation for the implementation of such
systems. There has been growing support to have fossil CCS and BECCS included in the protocol.
Accounting studies on how this can be implemented, including BECCS, have also been done.
Environmental considerations
Some of the environmental considerations and other concerns about the widespread implementation of
BECCS are similar to those of CCS. However, much of the critique towards CCS is that it may strengthen
the dependency on depletable fossil fuels and environmentally invasive coal mining. This is not the case
with BECCS, as it relies on renewable biomass. There are however other considerations which involve
BECCS and these concerns are related to the possible increased use of biofuels.
69
Biomass production is subject to a range of sustainability constraints, such as: scarcity of arable land and
fresh water, loss of biodiversity, competition with food production, deforestation and scarcity of
phosphorus. It is important to make sure that biomass is used in a way that maximizes both energy and
climate benefits. There has been criticism to some suggested BECCS deployment scenarios, where there
would be a very heavy reliance on increased biomass input.
These systems may have other negative side effects. There is however presently no need to expand the
use of biofuels in energy or industry applications to allow for BECCS deployment. There is already today
considerable emissions from point sources of biomass derived CO2, which could be utilized for BECCS.
Though, in possible future bio-energy system upscaling scenarios, this may be an important
consideration.
The BECCS process allows CO2 to be collected and stored directly from the atmosphere, rather than from
a fossil source. This implies that any eventual emissions from storage may be recollected and restored
simply by reiterating the BECCS-process. This is not possible with CCS alone, as CO2 emitted to the
atmosphere cannot be restored by burning more fossil fuel with CCS.
Carbon Cycling and Climate
One of the most daunting challenges facing science in the 21st Century is predicting the response of
Earth’s ecosystems to global climate change. Although the global carbon cycle plays a central role in
regulating atmospheric carbon dioxide (CO₂) levels and thus Earth’s climate, our understanding of the
interlinked biological processes that drive this cycle remains limited. Whether ecosystems will capture,
store, or release carbon is highly dependent on how changing climate conditions affect processes
performed by the organisms that form Earth’s biosphere. Advancing our knowledge of biological
components of the global carbon cycle is crucial to predicting potential climate change impacts, assessing
the viability of climate change adaptation and mitigation strategies, and informing relevant policy
decisions.
Greater insight particularly is needed into the role microbial communities play in many critical carbon
cycle processes. In many cases, these microbially mediated processes are only minimally represented in
carbon cycle models, which may limit their predictive capability and scale of resolution. Elimination of
these so-called “black boxes” will require innovative approaches aimed at linking structural and functional
characterization of microbial communities with quantitative measurement of carbon cycle processes.
70
3.4 AND THE ROLE OF BIO-ENERGY IN PAKISTAN AND OTHER COUNTRIES, ESPECIALLY ITS
POTENTIAL FOR THE DEVELOPMENT OF RURAL AREAS.
3.4.1 A Future Role for Biomass Energy
Biomass could become a central part of future sustainable energy supplies. Both the economic and
practical feasibility of such a developmental approach has been demonstrated by Johansson et al. {1993}
in their Renewables Intensive Global Energy Scenario (RIGES). RIGES demonstrates that it is possible to
provide energy for growth and development at no extra cost compared to conventional fossil-based
systems. A reduction in global CO2 emissions would occur as a result of such an increase in renewablesbased energy supply of which biomass would be a significant energy resource.
Two recent studies have recently emerged which provide independent support for such an important
economic claim. Kulsum Ahmed of the World Bank {1993} has shown that biomass conversion
technologies are capable of providing modern energy carriers at costs comparable with equivalent oilbased carriers if oil is priced at about US$ 20 per barrel. An important conclusion of this report is that
there is a strong downward trend in the costs of biomass based technologies which is likely to continue.
Secondly, a Shell Co. report has shown the promise of biomass based electricity generating units (BIG/GT)
which could be produced at the same or lower capital costs to fossil based units ie. at about US$ 1,500
per MWe, if the anticipated results of an existing Global Environment Funded (GEF) project are achieved.
{Elliott P., 1993}
To put the potential contribution of biomass in context, under RIGES by 2050, biomass would provide
17% of electrical power and 38% of direct fuel use. Altogether, "renewables" could supply 3/5 of electrical
power production and 2/5 of direct fuel use by 2050 at the same or lower cost to future advanced fossil
fuel-based systems. (see section 6)
Such a switch to modern bioenergy systems of the scale outlined above would have significant benefits to
both developing and industrialised countries. In developing countries, the provision of affordable rural
energy supplies will provide important improvements in both food and cash crop yields, mainly by
enabling farmers to provide irrigation and agro-industrial energy at the various levels. Indeed, such rural
biomass-based systems could provide the catalyst for self-sustaining indigenous rural development once
constraints are removed (see below), also providing a sustainable energy source for urban centres. As
such, modern biofuel technologies may actually aid developing country farmers to increase food crop
yields at a faster rate than population growth. In so doing, indigenous biomass energy crops could help
avoid the need to expand food production onto marginal land thus, negating potential food versus fuel
arguments. {Williams, 1994}
A growing number of industrialised countries are beginning to view biomass-based energy systems as an
important policy tool for addressing complex problems such as GHG emissions, rural development and
energy security. Industrialised countries where biomass is providing a fast growing share of the energy
sector include Austria, Denmark, Finland, France, Norway, Sweden and the USA. Sustainably grown
biofuels are CO2-neutral and low acid rain polluters and need large quantities of land. This land use
intensity is regarded as a benefit as it allows policy makers a novel use for the excess cropland areas
which are now emerging due to rationalisation of agricultural policies in Europe and North America.
A major facet of modern bioenergy growth and conversion facilities is their modularity at relatively
modest scales (1 to 100 MW). Modularity is an important concept as it allows energy planners to provide
small incremental additions to the production capacity as opposed to the large-scale (500 to 1,000 MWe)
fossil-based additions usually needed. For example, modern bioenergy conversion facilities are not prone
to the economies of scale of existing fossil-based systems, thus, negating the necessity to add very large
increments (500 to 1,000 MW) to the energy production capacity in order to benefit from those
economies of scale. Thus, inaccurate supply and demand forecasting will not be as important with such
biomass systems. In addition, the relatively large number of small biomass energy generating systems
provides an inherent increase in supply security.
3.4.2 Constraints.
Why then have modern biomass energy technologies not been spontaneously and widely adopted and
thereby obtaining a more significant share of the energy market?
The answer lies partly in the complexity and site specificity of the factors governing biomass growth and
conversion. Whilst in developing countries traditional biomass use may already be highly important,
71
present trends in its use are often unsustainable and of low efficiency. In industrialised countries, biomass
use for energy up until the last few years has been restricted to niche markets where feedstock costs
have been low or zero such as in sawmills, pulp and paper industries, etc.
Despite the site specificity of factors such as feedstock cost, proximity to market and likely market size, a
number of general constraints to increased bioenergy use can be identified:
i.
subsidies to competitors e.g. kerosine, or fossil fuel derived electricity, the so-called "uneven
playing field."
ii.
Scepticism over the reliability and economic feasibility of biomass energy projects due to a
number of high profile biomass energy project failures. Often these failures were due to social
incompatibilities or inflexibility of project aims and not necessarily concerned with the technology
per se, however, the sentiment persists.
iii.
A secure market must exist for biomass-energy products.
iv.
Traditional biomass conversion technologies are dogged by low conversion efficiencies and
viewed more as a means of waste disposal than for energy production.
v.
There is a lack of awareness by senior decision makers, potential users and financiers about the
multiple benefits of bioenergy systems.
vi.
Bioenergy systems require co-operation between sectors which do not normally communicate. At
the national level, the agriculture and forestry sectors must communicate effectively with the
energy and land planning sectors. At the international level there needs to be an integrated
approach between institutions such as the World Bank, the UN (including UNEP, UNDP, FAO) and
multi-national companies which must also involve NGOs.
vii.
At the local/village level there is a need for the strengthening or creation of a transparent
organisational infrastructure so as to ensure technically sound biofuel systems provide effective
and equitable returns to consumers and suppliers alike.
viii.
The initial capital costs of conversion equipment may be higher than comparable fossil fuel
systems, and potential financiers may be difficult to find despite the cheaper full life-cycle costs.
There may also be little or no backup or operation and maintenance facilities due to the novelty
of the technology.
Despite these constraints when full life-cycle costs and potential environmental and wider social benefits
are accounted for biomass-based energy systems will, in many cases be the least-cost long-run option.
3.4.3 Environment & Management.
Besides potential greenhouse abatement benefits of biomass energy, its production can address many
other "secondary" issues. {Ranney, 1992a} Such problematic areas which may benefit from large scale
biomass energy are: soil erosion, raising habitat diversity, control of nitrogen run-off and the protection
of watersheds. (see section 5)
Bioenergy is certainly no panacea for solving the world's energy problems since it is not without its
difficulties. Indeed, the production of the biomass itself can be intensive in planning, management, labour
and land. For sustainable growth, detailed planning will be required from local, to national, to regional
levels. The inappropriate selection and site-matching of species or management strategies can have
deleterious effects and lead to degradation and abandonment of land. However, the correct selection of
plant species can allow the economic production of energy-crops in areas previously only capable of
sustaining low plant productivities; simultaneously multiple benefits may accrue to the environment.
Such selection strategies may allow synergistic increases in food-crop yields and decreased fertiliser
applications whilst providing sustainable local sources of energy and employment.
3.4.4 Biomass Use for Large scale Energy Production.
The perception of biomass energy has changed recently in a number of industrialised countries. This has
led to biomass gaining a growing and significant share of the primary energy sector in USA, Sweden and
Austria (4%, 16% and 10% of primary energy respectively; see section 3). Biomass has previously been
regarded as a low-grade, "poor man's" fuel, but is increasingly viewed as an environmentally and socially
advantageous source of energy. In the newly industrialising countries, for example Brazil, biomass energy
has always been an important traditional energy source, predominantly for the domestic sector.
However, under the initiative of various programmes in a number of countries, such as for ethanol and
electricity production, biomass energy has attained a significantly higher profile. With a better
understanding of the negative aspects of biomass supply and methods for their mitigation, bioenergy is
72
increasingly perceived by energy planners not as a problem, but as an opportunity for the sustainable
provision of energy.
3.4.4 Global Warming
The Intergovernmental Panel on Climate Change's 1992 Supplement (IPCC92) has found no evidence to
markedly change their 1990 global warming predictions. They now state i.e. missions resulting from
human activities are substantially increasing the atmospheric concentrations of greenhouse gases. ii)
modelling studies indicate that the mean surface temperature sensitivity to doubling CO 2 is unlikely to lie
outside the range 1.5°C to 4.5°C, iii) the global mean surface temperature has increased by 0.3°C to 0.6°C
over the past 100 years, and iv) the unequivocal detection of the enhanced greenhouse effect from
observations is not likely for a decade or more. Furthermore, of the 6.0 ±0.5 GtC emitted in 1989/90 from
the two primary atmospheric CO2 sources, mainly, the combustion of fossil-fuels and secondly, land-use
changes, the latter change accounts for 1.6 ± 1.0 GtC. A substantial proportion of the carbon emissions
from land-use changes are derived from the 17 Mha yr.-1 of tropical deforestation estimated to have
occurred between 1981 and 1990, which is expected to continue {IPCC, 1992}.
However, the measured increase in the atmospheric concentration of CO2 is not consistent with the
calculated level of emissions from fossil fuel use and land use changes. These measurements indicate that
either the level of emissions is exaggerated, which seems unlikely, or that more CO 2 is being reabsorbed,
by an unknown mechanism, than estimated, i.e. there exists a "missing sink." The destination of the socalled "missing sink" carbon is still uncertain. It is thought that not all this "missing" CO 2 has been
absorbed into a large oceanic sink but that a terrestrial sink exists possibly resulting from a C0 2
fertilisation effect on vegetation growth. {Wigley 1992.} Even though there is some uncertainty over the
extent of global warming the latest estimates only serve to make the arguments concerning "the
precautionary principle" and the possible benefits from land rehabilitation of greater importance.
3.4.5 A Conflict for Resources
Of greater certainty is that the global population will continue to increase. The IPCC92 revised estimates
of population growth predict rises of between 1.27% and 2.28% per year or the equivalent of a gross
increase of 44% to 80% by the year 2025 from 1990 levels. Population growth makes increasing both food
and energy supplies of paramount importance. Potential conflicts between these resources must be
assessed and planned for.
The perception that all development requires more energy per se, is not necessarily valid. Improvements
in the efficiency with which energy is produced and used, have highlighted the importance of the services
that energy can provide, as opposed to increasing total amounts of energy i.e. less energy can be made to
do more. Future policies for indigenous biomass energy production should ensure that improvements in
income generation, provision of modern energy services and trade benefits are returned in a significant
fraction to the local populations. This implies that the rural incentives and the infrastructure necessary for
the sustainable development and provision of such biomass energy services are developed at the local
level. (see section 3, Hosahalli)
However, the provision of biomass-based energy services should not conflict with land requirements for
food production. Research indicates that the problem is not the size of the land resource, but its efficient
management for biomass production in all its forms- for food, fuel, fodder, etc. (see sections 2 and 3.)
Research on wood energy activities over the last decade (after the 1981 Nairobi Plan of Action), has
shown that contrary to popular belief, "factors other than the use of fuelwood and charcoal are the chief
causes of deforestation; processes such as farming, forest fires and the industrial use of forests are the
chief causes." {FAO, 1993} Small increases in energy inputs (especially where none previously existed) will
provide significant returns in yield improvements, effectively increasing land availability rather than
competing for it, hopefully reducing the pressures causing deforestation and land degradation. Modern,
efficient industrial and domestic energy conversion technologies are also required if full advantage is to
be taken of the potential environmental, economic and health facets of biomass energy. (see chapters 4
& 5).
3.4.6 Energy Balances.
The high yields presently achieved by intensive agriculture require significant energy inputs and
mechanical methods of production. For many crops under intensive management the energy required for
cultivation and processing may exceed the energy content of the food produced. However, the energy
output to input ratio of woody and fibrous energy crops is very favourable (in excess of 10 times and
73
about 6 to 7 times for ethanol from sugarcane); for these crops high energy inputs can be rewarded with
net increases in energy output. {Ledig, 1981; Gladstone & Ledig, 1990} In general, cereal crops give a
positive energy return even under intensive management e.g. maize contains 3.5 times the energy in the
harvested grain alone than it requires to cultivate and process. However, some crops presently require
more energy to produce than they return in the food produced e.g., energy output to input ratios are:
apples 0.9, lettuce 0.2, tomatoes 0.6 and cabbage 0.8 {Pimentel, 1984}. Note that many of these
calculations do not account for the energy content of the associated residues which are significant.
There are considerable opportunities to make farms and forests both net energy exporters and net
carbon sequesterers2. This potential has been highlighted in a recent report by the USA Council for
Agriculture, Science and Technology (CAST, 1992). It states that "a great opportunity for U.S. agriculture
to help mitigate climate change lies (through the) stashing of carbon in soil and trees and displacing fossil
fuel." CAST estimates that US agriculture could plausibly displace 8% of US energy with biomass fuels
which would reduce total US CO2 emissions by 10%.
2
"Sequester" is defined as the net removal of CO2 from the atmosphere and subsequent storage in
organic matter.
However, where fossil fuels are used in the production of biofuels some CO2 is inevitably emitted, even
where this CO2 is effectively re-absorbed through increases in standing carbon or in fossil fuel substitution
benefits. In the future these emissions could be eliminated through the use of biofuels or non-CO2emitting renewables to supply the energy for growth and processing of the biofuels.
3.4.7 The Potential Biomass Energy Resource.
Given appropriate institutional and management policies biomass energy offers the opportunity for the
provision of substantial amounts of energy. At the same time it can provide rural employment and
environmental benefits. The adoption of biomass energy systems globally may, however, require changes
in farming, forestry and energy-use practices. Initially, such energy systems would have to be based
primarily on agricultural residues during the establishment and development of bioenergy plantations.
The potential for sustainable energy supplies from such plantations is considerable. For example, energy
plantations on only 3% of Brazil's land could theoretically provide much more than its current total
primary energy consumption. It is now recognised that biomass presently plays an integral role in the
energy provision of most developing countries. However, the future potential of biomass energy must be
realistically assessed accounting for present (usually very inefficient) production and use, and the
problems of future energy provision.
Prevailing climatic conditions in many developing countries lend themselves to high biomass yields if
growth is not unduly limited by nutrient, water or pest and disease constraints. Many of these countries
e.g. Brazil, Zaire and Thailand are also well endowed with large potential land areas for biomass growth
and could thus become net energy exporters. The development of the rural energy industries required
would provide significant levels of employment and income generation.
It is difficult to over-estimate the range of uses and importance of different traditional and modem forms
of biomass products and residues in both the rural and urban sectors of developing countries. The
industrial sectors of developing countries consume an average of 40 to 60% of commercial fossil fuel
supplies and also use significant amounts of biomass fuels. These biomass fuels are often sold on the
commercial market. Industry also provides roughly 25 to 35% of rural non-farm employment. {OTA, 1991}
Whilst biomass production and supply is almost exclusively rural, its use in the urban sector is highly
diverse, economically important and energetically vital. The consumption of other, more convenient fuels
(especially kerosene) is widespread; however, fuelwood remains the dominant source of energy in many
developing countries.(box 1) Biomass is used mainly in the form of charcoal and fuelwood, but
agricultural residues, including dung and
The uses of biomass include: physical- construction timber, poles (houses and fencing) and thatch;
fibrous-mats and mixed with mud in hut walls; thermal- fuel for cooking, tobacco curing (requiring
approx. 6-60 t of wood per t of cured tobacco produced, i.e. 90 to 900 GJ/t), tea/coffee drying, brick and
tile making (roughly between 1,500 to 19,000 MJ/1000 bricks; 500 to 6,300 MJ/t for 3 kg bricks), paddy
parboiling (4.17 GJ/t), gur making (24.95 GJ/t, brown sugar) rubber making, coconut, bakeries,
tanneries/cloth makers and charcoal in metal production and processing, pulp for paper making, food
preparation in shops and restaurants and shops, (table 8 for various types of industrial biomass use.)
74
There is a large potential for increasing the level of energy services from biomass sources through the
adoption of modernised forms of bioenergy production and the use of energy-efficient equipment,
without proportional increases in the amount of biomass use. Such strategies may make one unit of
biomass work for longer e.g. cook more food from 1 kg of charcoal, or provide more services e.g. light,
water pumping, milling, etc. per unit of biomass consumed, (see Hosahalli village section)
(I) Biomass use in Bangladesh
In Bangladesh in 1988, biomass provided about 70% (519 PJ) of Bangladesh's energy, 20% of which was
used by industry. The remaining 80% of total biomass fuel consumption was for domestic cooking, 45% of
which was used in the urban sector and 65% in rural areas. Commercial fuels (mostly diesel and gas)
provided about 220 PJ.
Whilst most towns have piped gas supplies and many households are connected, consumption is often
overestimated as many households which are connected still use charcoal and agricultural residues due
to the cost of the gas and service facilities. {Ahsan Ul Haye, 1988}
Charcoal.
Charcoal use is wide-spread throughout developing countries, however, its increasing production and use
is causing concern as unsustainable sources of wood are mined, destroying forests and eroding land. It is
preferred by domestic users because of its convenience of use (small size, low weight) and quality of
burning (constant heat, long lasting) compared to other accessible energy sources, such as firewood, crop
residues and dung. It is preferred by industry and charcoal producers because of its energy density (about
30 GJ/t) and relative ease to transport compared to wood (small chunks which pack easily).
The charcoal industry often has a large infrastructure, based on an indigenous, if often unsustainable
supply sources (i.e. forests & woodlands). Charcoal's low price and convenience for transport and use
means that attempts to induce industrial and domestic users to switch from charcoal to other fuel
sources, mainly fossil fuels, are unlikely to succeed in the near to medium term in many developing
countries.
During the 1980's, however, due to increases in the efficiency with which charcoal was produced from
wood, and the switch to plantation derived wood from natural sources, Brazil has been able to
significantly increase its charcoal use. Brazil has been able to achieve this increase without increasing
charcoal production from natural sources. The Brazilian charcoal industry is discussed in detail below.
(II) Brazil
Large amounts of charcoal are consumed in the reduction and heating of iron ore for pig iron production.
In 1990, Brazil consumed over 36 Mm3 of charcoal of which 18.6 Mm3 was for pig-iron production. Before
1975, virtually all the charcoal was supplied from native forests with increasingly detrimental effects to
the environment, mainly resulting from the destruction of natural forests. This essentially free energy
source allowed Brazilian pig iron to become highly competitive in the world markets; it was finally
recognised, however, that the continued exploitation of natural forests at such a rate was unsustainable.
In an effort to establish sustainable wood production for the charcoal and pulp + paper industries the
Government introduced tax incentives for the commercial growth of plantations in its 1965 Forestry Act.
The consequences of this Act have been far reaching as 1t stipulated target percentages of total
production (not quantities) which had to be reached within specified time periods (table 7). Presently all
pulp and paper and 34% of charcoal production is plantation-derived, the wood being provided from an
estimated 4 to 6 Mha of plantations, mostly Eucalyptus. By 1995, the plantation-derived charcoal
percentage is required to rise to 100% according to Brazilian regulations; however, the effective total will
only be around 80% due to a stipulated allowance for charcoal production from forest residues (see table
7).
Estimates of present plantation areas are complicated by the abandonment of young plantations which
had been registered under the Act, or the death of parts of plantations (hence also resulting in lower than
predicted productivities.) It is now believed that between 4 and 6 Mha of commercial plantations are in
operation, with an increase of between 0.2 and 0.45 Mha/yr. since 1970. {de Jesus, 1990; Rosillo-Calle,
1992}.
Pandey {1992} has estimated a net area of plantations in Brazil (1990) of 6.1 Mha. This is dependant on
the success rate for the establishment of plantations having been maintained at the 87% success level
ascertained from the 1981-82 inventory of plantations. {Pandey, 1992} It may be reasonable to expect
this success rate to have increased as the results of continuing R&D are incorporated into plantation
75
management techniques, and hence net plantation areas may actually be higher than suggested. Charcoal
production. The efficiency with which wood is converted to charcoal has also benefited from the Brazilian
regulations since the large iron and steel producing companies have been forced to obtain reliable
supplies of plantation charcoal. This has inevitably led to many of them investing in the development of
large plantation and charcoal production facilities. Such competition has resulted in the need for
increased yields, efficiency and benefits from economies of scale. Most charcoal is still produced using
internally heated beehive kilns (mud or brick, taking 9-50 m3 wood), the technology of which is up to 100
years old and is often inefficient. (Ch.4, carbonisation) There is considerable room for improvement in
efficiency, perhaps to over 30% of the weight of the original wood being converted to charcoal, so also
reducing costs. Present conversion efficiencies are often below 20% by weight.
Larger kiln sizes can allow partial mechanisation of the charcoal making process by using forklift trucks to
load and unload the kilns allowing faster overall production cycle times. For example, the 300 m 3 kilns
now used by CAF in Bahia state can be loaded, carbonized and unloaded in 7 days, resulting in significant
savings in labour and more socially acceptable weekly work patterns. The carbonisation process is also
much more closely controlled increasing the efficiency of conversion. Many of the larger kilns also allow
tar and oil recuperation which is sold as low-grade fueloil; this practice also results in less environmental
damage from the leakage of these oils into surrounding soils.
Costs of wood production for charcoal are highly dependant on the original cost of the land, soil type,
yield and relief. Harvesting costs can increase by up to 75% depending on the steepness of the land. The
four main cost components in charcoal production i.e. wood yields, harvest, carbonisation and transport,
usually result in production costs above 1992 US$ 25 per m 3 charcoal (about US$ 3.5/GJ). Transport costs
are generally above US$ 0.0125 per m3.km, and thus for average transport distances of about 300 km,
total minimum delivered charcoal costs about 1992 US$ 4/GJ. In general, costs for industrially produced
and delivered charcoal are in the range US$ 3.8 to 4.4 per GJ (US$ 27 to 31 per m3). {Rosillo-Calle et al,
1992}
(III) Somalia
Whilst the present political instability of this country makes continued monitoring impossible, detailed
data obtained previously highlights many important aspects of industrial charcoal production in a poor
developing country. It is thus included here.
In many countries, the demand for energy in the cities is having adverse effects on the livelihoods of the
rural inhabitants who reside near the source of biomass to be exploited as a fuel. In Somalia, for example,
the capital city Mogadishu consumed about 42,000 t fuelwood in 1983 or about 0.5 t/capita. Mogadishu's
fuelwood production for domestic consumption was estimated to be about 17,000 t's, institutional
(hospitals, schools, prisons, military) and for the industrial sector (e.g. lime production) more than 29,000
t's. In contrast to Brazil where most of charcoal production is industrial, 95% of Somalian charcoal
produced was consumed for cooking, and was mainly derived from small scale artisanal production,
generally of low efficiency. Households in Mogadishu spent on average about 10% of all household
expenditure on fuel, one third of which was for charcoal.
The concentrated urban purchasing power in Somalia and elsewhere (large centralised market) made it
economically possible to transport fuels over long distances, and therefore spread the influence of the
cities and towns further into the rural sector. Thus, the biomass supply resources were exhausted at ever
increasing distances from the urban centres. The size of the market in Mogadishu resulted in its ability to
absorb rising prices allowing low efficiencies in conversion of fuelwood to charcoal (often less than 15%
by weight); the resulting high costs could be paid for through the gains in energy density of charcoal
thereby facilitating longer transport distances compared to wood. Charcoal contains twice as much
energy per tonne as wood, and is more convenient to package, hence over distances greater than 100 km
the energy lost through conversion to charcoal is compensated for by its lower transportation costs per
GJ. {Robinson, 1989). These factors expand the radius to which forests and woodlands can be exploited
for urban energy provision. This analysis holds true in many other countries where natural vegetation can
be regarded as a free feedstock for charcoal production.
In addition, whilst the exploitation of woodlands around Mogadishu was supposed to be carefully
controlled (only trees above 15 cm dbh of certain species should be cut) monitoring was superficial, if it
existed at all; the wood was therefore regarded as virtually "free". However, the rural populations nearby
the woodland source (of the charcoal) noticed that when the selection criteria for suitable trees to be cut
76
was not being followed, resupply was not ensured and degradation inevitably followed. Improper
harvesting practices render such land areas prone to severe degradation as a result of loss of vegetative
cover leading to soil erosion. Since the costs of restoring the land to its former productivities (if possible)
are not met by the charcoal producers, they can simply afford to move to new sources of wood.
Thus, whilst regulations are an important tool in the control of such industries, they can be rendered
meaningless without proper monitoring and institutional backup. (section 6, policies)
Ethanol.
The need for an economically competitive, indigenous and sustainable supply of liquid fuel for
transportation has resulted in a number of biomass to ethanol projects in developing countries. Most of
these projects have been based on sugarcane as the source of biomass. Sugarcane is the world's most
photosynthetically efficient agronomic crop, utilising about 2-3% of the energy in the incident radiation
for biomass production. Sugarcane is also associated with high levels of by-product formation e.g.
bagasse, molasses, stillage. Much of the by-product is either suitable for processing into higher value
products (such as animal feed) or for use as energy (thermal, electricity).
This multi-product potential, including the ability to upgrade previously unwanted waste products into
useful commodities such as electricity and animal feed, has resulted in renewed interest from
international development funding organisations. For example, the Global Environment Facility is now
funding two major projects involving the utilisation and optimisation of sugarcane for energy. It is
presently providing funds for a Brazilian project (1992 US$ 30 million) for the production of electricity
from both sugarcane and wood residues, and a Mauritian project (1992, US$ 3.3 million) to optimise the
use of bagasse for electricity production (see Electricity section).
The potential of cane to produce products tailored to a changing market has been explored by Smith
{1992}. Based on recent Puerto Rican data he suggests that the concept of a cane mill which produces
ethanol, sugar, animal feed, fiber and recycles refuse would be economically viable. Such a plant would
be theoretically able to provide an internal rate of return of 8.7% and a simple payback of less 7½ years,
based on a plant life of 30 years in Puerto Rico. Instead of using bagasse residues solely for the production
of steam, the majority of the energy required is derived from processed MSW. MSW disposers pay a
significant tipping fee; once sorted, however, it could provide revenue from sales of scrap and energy
from the combustible fraction. Whilst only 26% of sales are projected to be derived from ethanol,
sensitivity analysis suggests that the wide range of products produced (ethanol, feed, fibre and scrap)
make this type of plant relatively immune to inflation. {Smith, 1992}
Brazil
Brazil has been producing ethanol for use as a fuel since 1903. However, after the introduction of
government incentives under the 1975 "Proalcool" programme, ethanol has become a significant energy
source (4% of total energy consumption). Ethanol is produced as a petrol substitute for the transport
sector where it accounted for 18% of fuel consumption by 1987, with annual production now reaching 12
billion litres. It is sold as either a 22% ethanol (0.4% moisture):gasoline blend (Gasohol) for use in
unmodified internal combustion engines, or as neat hydrated ethanol (4.5% moisture) for dedicated
ethanol cars and light vans. In 1989, there were 4.2 million cars running on neat ethanol and about 5
million on gasohol. This programme has been successful at reducing Brazil's foreign exchange burden
from imported liquid fuels. The share of the total energy market occupied by gasoline has dropped from
12% in 1973 to 4% in 1987 and is now equalled by ethanol (substituting for about 250,000 bbl oil/day).
Total savings in oil imports between 1976 and 1987 are estimated at $12.48 billion whilst the total
investment in the programme was only $6.97 billion. Presently ethanol costs about 18.5 US c/1 with a
high value of 23 c/1 and low of 17 c/1 (approx. US $ 7.9 per GJ). At these prices ethanol (as gasohol)
would compete economically with crude oil priced at US$ 24/bbl (1992 US$). {Goldemberg et al., 1992}
Despite such an apparent lack of economic competitiveness, continued gains in productivity and
efficiency have meant that subsidies and price controls are now regarded as detrimental to the viability of
the private ethanol production companies and car manufacturers {Goldemberg, 1992}. Furthermore,
straightforward economic analysis fails to account for the secondary benefits arising from this
programme, such as indigenous employment, wealth generation and reduced atmospheric pollution in
the cities.
77
Zimbabwe
The Zimbabwean Triangle Programme was commissioned in 1980. Construction was carried out entirely
in Zimbabwe using indigenous materials wherever possible. The final cost of 1980 US$ 6.4 million, made it
one of the cheapest plants of its capacity to be constructed. However, this cost effectiveness was not at
the expense of reliability, as it has run with few problems for over a decade. It has a maximum ethanol
production capacity of 40 million litres per year with a target blend of 13% (ethanol; gasoline). Whilst
originally having been conceived with strategic goals in mind, its performance in foreign exchange savings
have been significant and is presently estimated to be reducing foreign exchange spending by over Z$4
million per year {Chadzingwa, 1987}. Furthermore, the alcohol presently costs little more than imported
petrol to produce. {Scurlock et al., 1991}
Heat
The provision of heat in temperate countries is a major source of domestic energy consumption, and
often occurs when power production is most expensive i.e. at night. Even the most efficient thermal
power stations produce large amounts of low quality heat which is no longer useful for power generation.
The use of this "low quality" heat, which is still of sufficient temperature to supply domestic heating
systems, can significantly increase the overall efficiencies of thermal generating systems. In some
countries, the development of district-heating supply infrastructure has allowed this "waste" heat to be
sold as a commodity to the domestic market providing heat in winter. (see below)
Austria.
During the 1980's Austria increased the share of primary energy consumption provided by biomass from
about 2 or 3% to about 10%. This rapid increase in biomass energy use is predominantly due to the
successful promotion of District Heating plants powered by wood chips. The prime political motivation for
this scheme continues to be concern about security of energy supplies, the environment and a wish to
support the rural economy. It has been greatly facilitated by the decentralised form of government which
exits in Austria, and the availability of large quantities of relatively cheap wood residues from forest
industries.
The size of the present forest industry is mainly a function of the large areas of natural forests remaining
in Austria. Presently, approximately 30% of its land area is forest covered, with individual states such as
Steiermark, having an excess of 50%.
There are now over 80 to 90 district heating systems of 1 to 2 MW average capacity (compromising a
total of 11,000 installations), producing 100 PJ (1,200 MW total capacity) which represents about 10% of
total energy consumption in 1991. This is expected to increase to 25% of total primary energy
consumption by the turn of the century. {Howes R., 1992}
The success of this scheme has required both supply and demand side incentives and regulations. Unlike
the UK, for example, there are unlikely to be dedicated wood energy plantations in Austria in the near
future because of the abundance of existing forestry residues. In particular the banning of practices such
as landfill disposal of bark residues by sawmills now means that bark is being sold at 50 to 80 schillings
per m3 (approx. 1991 US$ 19-30/t). Sawdust and offcuts are sold at US$ 28 to $ 38/t. Commercial timber
is sold at above US$ 40/t.
Supply-side incentives are available through the provision of grants for capital equipment. The Federal
government provides 10% of the capital costs and the State government a further 3.3%. In addition, the
Department of Agriculture provides an extra capital grant of 40% of the final cost if a scheme is set up by
a farmer's group. Thus, incentives may be as high as 50% of total capital costs. On the demand side the
government will pay 30% of the heat exchanger costs. Further state grants may be available based on the
connection fee (additional to the cost of the heat exchanger), charged in proportion to the heating
capacity required by each house8. In general this grant is sufficient to cover the connection fee for the
average house (peak demand of 15 KW).
8
Cost of connection is between Schillings 40,000 to 60,000, and thus a 30% grant is equivalent to 1991 US$ 1,100 to 1,700. [Exchange rates are
assumed to 20 schillings = 1991 US$ 1.9]
High capital costs for installed equipment (especially pipes) have rendered these schemes relatively
insensitive to fuel price, with success a function of overall intensity of use (defined as kWh per km of pipe)
and reliability of supply. Subsidies have in effect only reduced payback times from 14 or 15 years to 10 or
11 years. Thus, income received from domestic users covers all the running costs and a slight surplus;
hence the long payback times.
78
The cost of the heat varies, but is in general similar to fossil-fuel (including electrical) heating. It is worth
emphasising, however, that in regions where the cost of wood-fired district heating is greater than its
alternatives, surveys indicate that people are willing to pay slightly more because they perceive that this
money is returned to the local community. It may therefore indirectly benefit the consumer through
increasing local wealth and economic activity. {Howes. 1992}
Combined heat and power (CHP).
Presently thermal conversion efficiencies of well run modern power stations are between 20-35% fuel to
electricity. The maximum efficiencies of thermal conversion facilities (the "Carnot Limit", see chp 4)
means that it is physically impossible for thermal technologies to raise their power generating efficiencies
above 60%. Thus, many countries are now concentrating on methods of using the low-grade "waste heat"
which cannot be turned into a higher value energy carrier. This heat may be ideally suited for space
heating or even for the various heat requirements of an associated factory.
Sweden's Combined Heat and Power programme.
In 1991, biomass provided 25% of the fuel consumed in District Heat and CHP programmes. In total,
biomass (including peat, 1%) provided approximately 15% of Sweden's primary energy consumption.
{NUTEK, 1992} The CHP programme now provides 142 PJ (39.7 TWh) of energy, of which 93% is
consumed as district heat and the rest for electricity.
There is now a considerable infrastructure in place, with over 8,000 km of pipes for heat distribution, and
2.4 GW of installed CHP capacity. Having curtailed the nuclear option for environmental and economic
reasons, Sweden is pursuing methods to increase its energy production from renewable sources. In
particular, it continues to invest large quantities of time and money in woodchip technologies both for
present thermal technology, mainly for district heat supplies, and also gasification for CHP production
from wood powered gas turbines.
While the concept is certainly not new, the technologies being applied and developed are innovative.
Both Sweden and Denmark now run significant programmes for the use of biomass powered CHP. (box 2
Sweden)
Denmark (biogas).
Denmark has a long standing tradition for the use of renewable forms of energy. It is presently best
known for its widespread use of wind-generated electricity for supply to the grid. However, since the
early 1970's it has also provided incentives for the use of cereal straw for heat and the digestion of animal
manure to produce biogas.
The anaerobic digestion of animal manure for the production of biogas has many potential advantages.
These range from the safe disposal of manure (presently a costly procedure for farmers due to stringent
environmental regulations regarding its disposal) and to the production of electricity and heat.
However, during the 1970's all the digesters were of a technically simple design and based on single
farms. This led to problems of maintaining stable conditions in the digester due to their relatively small
capacity and low cost. Forty of such small scale digesters have been built but about 30 of them have since
been abandoned. Nevertheless, animal manure still represents a significant problem and large potential
energy resource.
The first large-scale biogas plant, Vester Hjermitslev, was constructed by the beginning of 1984 and nine
more have since been built. It has a digester capacity of 1,500 m 3 (approx. 50 t manure per day) designed
to produce 3,500 m3/day biogas; it also included a wind turbine for electricity production. The plant was
commissioned and run by a private company consisting entirely of members of the local village, who put
up over 2/3 of the construction cost (DKK 12.4 M; 1992 US$ 2 million). The Danish government provided
DKK 4 M. It was built as part of the North Jutland County Council's "village energy project," designed to
bring a measure of energy self-sufficiency to its villages by providing electricity and heat.
The plant encountered a series of technical problems which never allowed it to meet its specifications,
eventually resulting in its reconstruction in 1989. The costs of the years of development have resulted in
the plant's debts becoming unserviceable, but the county council has arranged a moratorium. During the
reconstruction extra pre-storage was added to enable the plant to use fish processing sludge. Since
reconstruction the plant has increased its gas production substantially and an extra gas-powered
generator has been added.
There are now nine more large-scale biogas plants running in Denmark with the latest plants have
capitalising on the lessons from the previous plants. "Lemvig," the most recent plant to become
79
operational (May 1992) was constructed in only 8 months. It was commissioned by a farmers cooperative who supply the manure; the plant manufacturers entered into a novel service agreement which
makes them responsible for the operation and maintenance of the plant for five years. This contract also
guarantees the co-operative a minimum budgeted profit. The total construction cost was DKK 40 M (1992
US$ 6.5 million) of which the government provided DKK 9.5 M ($ 1.5 million). There have been no serious
problems in operation since its start-up.
Lemvig is the largest plant built to date (7,600 m3) and is based on the continuous one-step design from a
previous plant. It is a thermophilic (55°C) plant, which uses a highly automated wood chip heating process
to maintain the temperature of the digester. The biogas is supplied to CHP gas-engines in the nearby
town via a 4.5 km low pressure pipeline, developed for land-fill gas systems.
In 1986, the Danish government recognised the potential for centralised biogas production and set up an
Action Programme whose task it was to review the potential feasibility of the biogas programme. In June
1991, the Action Programme stated that "it would be possible to establish profitable centralised biogas
plants without subsidies from the public purse." It did, however, qualify this remark by stating that
economic feasibility would continue to depend on the present governments policy of not taxing biogas,
which represents an indirect subsidy.
In 1991, only one plant realised enough income to break-even, whilst five have budgeted sufficient
income to break even in 1992. (table 17) In the Action Programme's report the conditions necessary for
profitability are stated as: 1) 10 to 25% of easily convertible organic material is added to the manure
delivered (the main source is from source-sorted household waste and sewage sludge), 2) there must be
a steady/reliable market, and the biogas must not be taxed, and 3) good management is necessary to
keep down running costs and maintain high gas production levels.
The Danish government has continued its commitment to the biogas programme through the
commissioning of the "follow-up programme," under which six or seven new large-scale plants will be
established. It bases its renewed commitment to several factors:
a) The potential improvements in economic status through continued development, many of which
are already being demonstrated.
b) Presently only 2% (0.5 PJ) of the potential biogas production is being utilised (25-30 PJ).
c) The need for farmers to dispose of their waste products in an environmentally acceptable way.
d) Possible environmental benefits include: displaced CO2 production from fossil fuel use, thus
decreased net CO2 emissions, and decreased methane emissions as this is now burnt in the
collected biogas. Also, correctly timed applications of the digested sludge on farmers land, which
take advantage of the increased availability of nitrogen in digested manure and increased
nutrients from the household waste, results in reduced need for artificial fertilisers. A saving of
both economic and energy inputs.
e) The potential to distribute biogas through the existing natural gas pipeline network, possibly as a
mixture (natural gas and biogas), resulting in considerable savings in transport costs, and siting
problems with the digesters.
f) Helps to dispose of household waste.
g) Stimulus to the rural economy.
Electricity.
United States of America
In 1987, the Public Utility Regulatory Policy Act (PURPA) was introduced requiring US Electricity Utilities to
purchase electricity from other suppliers at the cost they "avoided." The "avoided cost" sets the price the
utilities are obliged to buy electricity from independent suppliers. It is calculated as the marginal cost of
electricity production from a new conventional power station, i.e. equivalent to the cost (c/kWh) of
producing electricity from new coal, gas or oil power stations. PURPA thus forced these utilities to
procure electricity from suppliers who have alternative cheaper fuel supplies. The utilities were obliged to
buy this electricity regardless of internal economic considerations i.e. even if the most economic way of
providing base-load and peak demand was through the use of electricity supplies from other sources,
including their own power stations. {Turnbull, 1993} PURPA resulted in an explosion of co-generators who
use waste materials and by-products as a cheap source of heat. These by-products are obtained from
associated processing plants e.g. saw mills, abattoirs, food processors and paper manufacturers, which
then gain an income from a product which they may previously have had to pay to have removed. The
80
scale of electricity production is generally small scale i.e. < 50 MW. The guaranteed price at which the cogenerators can sell electricity has made long term economic planning possible, thus making it easier to
procure loans and calculate profits.
This Act is largely responsible for the present extent of electricity production from renewable sources;
over 9 GW of installed capacity presently exists. In California, it has stimulated the growth of a market in
biomass residues providing employment and clean energy. It is now being recognised that the use of
these residues can help to reduce the level of US CO2 emissions.
Concern over the present levels of US CO2 emissions have resulted in a number of studies being published
detailing possible mitigation strategies. {Trexler, 1991; CAST, 1992; Ranney, 1992a; Wright et al., 1992}
These studies have highlighted the potential for renewables in providing low cost (or even negative cost)
options for the reduction in net CO2 emissions. One study from the US Environmental Protection Agency
suggests that the "US will probably come close to stabilising its CO 2 emissions at 1990 levels by the year
2000." This, it is hoped, will mainly occur through increases in energy efficiency, the promotion of which
utilities now find more cost effective than the construction of new plants. {Global Climate Change Digest,
1992} The prospects for increasing the production of energy from dedicated renewable sources, in
combination with increased efficiency of production and use, seem auspicious both in the USA and
elsewhere (see below).
In the US, Hall et al {1990} estimated that advanced wood gasifier-based electricity production could be
economically competitive with advanced coal gasifier-powered electricity plants. Much of the wood could
theoretically be supplied from Short Rotation Woody Coppice (SRWC) on the 139 Mha of economically
marginal and environmentally sensitive crop, pasture and under-stocked forest lands held by private
owners other than the forest industry. Furthermore, this would have the effect of offsetting up to 56% of
present US CO2 emissions at negative cost. When compared with estimates for carbon sequestration,
costing between US$ 20 and 40/tC by US forest plantations, or flue-gas CO2 removal from coal-fired
steam electricity plants (estimated for the Netherlands) of about US$ 120/tC, biomass substitution
options look highly competitive. It should be noted that biomass feedstock costs are strongly correlated
with growth rates (estimated by Moulton and Richards {1990} in the US to be 2.7 tC/ha/yr. above ground
productivity or 5.3 tC/ha/yr. if roots and soil carbon production is included); if the productivity is halved
then biomass feedstock costs are roughly doubled.
Brazil
Historically, Brazil has relied on the development of large-scale hydro-electric projects to supply its
increasing demand for energy. Electricity demand has grown at about 5% per year throughout the 1980's.
In 1990, hydro electricity supplied about 96% of total electricity use (226,377 GWh). It thus satisfied the
stated governmental aim of avoiding excessive reliance on imported fossil fuels. However, the most
favourable sites have now been used. Further expansion of the hydro capacity seems limited due to
increasing social and environmental costs and also physical and economic factors. For example,
installation costs have ranged between 1988 US$ 100 and 2,700 per kWh and electricity production costs
1988 0.3 to 3.3 USc/kWh. Future costs are likely to be higher, ranging from US$ 1,000 to 3,200 per kW for
installation, and from 1.8 to 7.8 c/kWh for production costs. {Carpentieri et al., 1992}
There are also problems with the sheer size of the capital costs of such large scale dams. For example, the
Itaipu dam was budgeted at $3.5 billion in 1975, but at final completion it is expected to cost US$ 21
billion, excluding interest payments. {Lenssen, 1992} Such problems have played a significant role in
Brazil's continuing struggle with size of its foreign debt and the associated problems.
When compared to the likely costs of future hydro-electric schemes, the relatively low production costs
and the smaller incremental nature of the installation costs, future biomass energy projects seem highly
competitive and desirable, (see below)
Wood-based electricity. Under the conditions in Northeast Brazil, total life-cycle costs for fuelwood
plantations are estimated to rise particularly sharply at productivities of less than 8 odt ha -1 yr.-1 (17
m3/ha). The average weighted cost (weighted by BCR distribution)10 is US$ 1.36 ±0.20 GJ-1 and falls to US$
1.09 ±0.12 GJ-1 for the highest productivity zone, BCR I. The cost rises to $3.71 ± 0.89 GJ-1 for the worst
zone, BCR V (fig. 5)11. At these costs, plantation-derived electricity could be extremely competitive with oil
at present world traded prices12.
In assessing the potential land areas available for forestry, Carpentieri has analyzed the Northeast region
in detail, breaking it down into Bioclimatic regions (BCR's), using soil and rainfall, annual average
81
temperature, water deficit and altitude parameters. Being sensitive to possible land-use conflicts, only
land which is not at present being utilised for settlements and which is unsuitable for agriculture has been
targeted. This land has been divided into five Bioclimatic regions (analogous to the FAO's Agroecological
zones), each of which is estimated to be capable of supporting average productivities of 44, 33, 28, 15 and
6 m3 ha-1 yr-1 for BCR's I through to V, respectively. The parameter most closely correlating to productivity
was rainfall, and this was used as the dominant BCR allocation criterion.
The weighted average productivity for the NE was 26.6 m 3/ha/yr. All costs are calculated using a 10%
discount rate, wood transported 85 km at 0.39 c/GJ/km and a plantation life time of 30 years.
Most of the cost variation is due to differences in potential land costs.
The price of crude oil is presently (Nov. 1992) about US$ 3.5/GJ @ $20/barrel and 42 GJ/t (LHV).
The costs which are related to a given amount of energy generated can be shown graphically in the form
of "supply curves." Such supply curves show the quantity of wood which can be produced up to a given
cost and are valuable in providing data for a realistic economic comparison with alternative fuel sources
(fig. 5b). For example, the Carpentieri et al. {1992} analysis predicts that over 86% of the potential wood
production would be produced at an average cost of less than $1.35 per GJ, less than half the cost of oil.
The total potential energy production of this scheme, if all the available land were to be planted and
expected productivities achieved, is 12.6 EJ yr.-1. Thus, there is considerable potential to meet future
energy demand when compared to Brazil's total 1990 energy consumption of about 8.1 EJ {AEB91, 1992).
Clearly a very large potential for such a biomass-based industry exists. Even if only a small portion of the
total were to be realised, large amounts of energy could be produced.
One of the main advantages of modern conversion facilities are the relatively small scales at which
electricity production would be possible. The biomass can therefore be converted to electricity obviating
the need for excessive biomass transport costs. 30 MW is envisaged as the largest practical size of a
power generating unit which can be economically supplied by plantations (due to restrictive transport
costs at greater distances). Approximately 12,000 ha of plantation would be required for each 30 MW
unit. For economic reasons, these units will only be commissioned as demand requires, minimising capital
costs (cf. large-scale hydroelectric plants.) Importantly, this modular approach also provides the chance to
rectify technical problems before large capital investments have been made. Plantation biomass-toelectricity programmes would therefore allow energy planners to follow the electricity demand curve
more closely, thus reducing costs resulting from periodic over supply- periods of oversupply are inevitable
after the commissioning of each large-scale hydro plant.
Another benefit resulting from the requirement for large numbers of generating units is an increase in
supply reliability. Increased reliability is due to the relative size differential between the production
capacity of one plant and total production; thus the lack of one or two plants due to failure, will have
relatively little effect on total production.
Sugarcane Electricity. The global energy content of potentially harvestable sugarcane residues is
calculated to be 7.7 EJ {Williams & Larson, 1992}. Production of cash crops can be highly intensive in
many developing countries, resulting in the production of significant amounts of residues. The energy
content of these-residues can equal or even exceed commercial energy consumption e.g. Mauritius,
Belize. Residues therefore represent a large potential energy resource, (table 9)
The energy potential of sugarcane residues was also considered by Carpentieri et al. (1993) for the
Northeast region of Brazil since the sugarcane residue resource is already available and essentially free.
There are, however, sometimes opportunity costs associated with the bagasse resource since a part of it
may already used as animal feed, paper making and fertiliser. Where conflict of use may exist, the relative
benefits of the different types of use must be assessed.
In comparison with the potential for tree plantation biomass the size of the bagasse resource is relatively
small. However, when compared to the present energy consumption of the Northeast Brazil (1.1 EJ), the
bagasse resource could still provide an estimated 174 PJ yr.-1 (16% of present energy consumption). The
main importance of the sugarcane residues is their availability for collection and electricity production.
Energy production from bagasse is well characterised since the quantity, energy content and moisture
content of bagasse produced per tonne of crushed cane varies little from site to site {Alexander, 1985}.
Thus gains in the amount of useful energy produced from bagasse is likely to come from increases in
conversion efficiency and biomass productivity. More recently, more attention has been given to the
energy potential of the tops and leaves, the so called "barbojo." The efficient of use of this barbojo may
82
be able to significantly increase energy production from cane. {Hall et al., 1992; Carpentieri et al., 1992;
Williams and Larson, 1992; Howe and Sreesangkom, 1990; Tugwell et al., 1988.}
Economic analysis shows that the conversion of sugarcane residues into electricity can be very
competitive with alternative fuel sources. When factors such as transport, storage, drying and processing
are accounted for residue-based electricity remains competitive, (table 11) The cost of using stored tops
and leaves as an energy feedstock varies from 0.95-2.21 $/GJ, whilst bagasse is in the range 0.28-1.68
$/GJ. The variation between the costs for bagasse and barbojo arises because the barbojo is assumed to
be collected and transported to the mills off-season, whilst the bagasse is a by-product of the sugar
production. The bagasse is thus effectively transported free when the fresh cane stems are brought to the
mills during harvest, whilst the barbojo requires separate collection and transport costs. The potential
competitiveness of this indigenous source of fuel can be seen when compared to the fossil-fuel
alternatives, i.e. fuel oil, 1985 US$ 2.45-7.50 per GJ and coal, (imported and indigenous) US$ 1985 1.434.22 per GJ.
A similar study for Jamaica concluded that potential (present value) savings of US$ 270 M could be
achieved if sugarcane residue-fired BIG/STIG were to replace state-of-the-art coal-fired CEST technology.
Furthermore, if existing oil-fired plants were replaced, savings of up to US$ 300 million per annum might
be feasible. {Tugwell, 1988}
India
The perceived developmental advantages of widespread access to electricity have been translated from
public demand into the political imperative that every village and farm in India should be connected to
the national grid. To a large extent this has been achieved with over 80% of the 550,000 villages now grid
connected. However, connection has required the construction of many thousands of km's of
transmission lines at a cost of US$ 800 to 1,200 km-1 {Ravindranath, 1993}. Furthermore, during the
1980's, oil imports cost India US$ 36.8 billion, the equivalent to one third of all foreign exchange earnings,
or 87% of its new debt. When the capital cost of the imported electricity generation equipment was
included in this analysis, the total expense for energy amounted to more than 80% of foreign exchange
earnings between 1980 and 1986. {Lenssen, 1992}
In addition, many of the villages connected to the grid only require small amounts of power and can also
be distant from the power station. This combination of low loads and long transmission distances has led
to a number of problems: i) high transmission & distribution losses, with a national average of about
22.4%, ii) low and fluctuating voltages (often below 180 V (estimated 20% of time) despite a nominal
voltage of 220 V), iii) high operation & maintenance costs, iv) erratic supply and poor maintenance
(power cuts are common), and v) the external costs of centralised power production including: CO 2, SO2,
particulate emissions, no provision of local employment or wealth generation. {Ravindranath, 1993}
The production of electricity in India is a significant contributor to Indian greenhouse gas emissions. Coal
combustion accounts for 60% of total CO2 emissions, with 70% of electricity production being coalderived. Presently, the provision of electricity to villages consumes one quarter of total production.
Electricity generation is responsible for a significant fraction of total Indian CO2 emissions even at today's
low levels of per capita electricity consumption (i.e. 61 kWh/yr.). {Ravindranath, 1993}
There are therefore several imperatives for the adoption of widespread decentralised systems for power
generation. In addition to overcoming the above problems, such schemes should reduce the subsidies
burden presently shouldered by the national government. {Reddy and Goldemberg, 1990} However,
electricity production is expected to grow at 10% per year into the next decade. In fact, the constraint on
growth is on the supply-side, with actual demand estimated to be much higher. {Grubb, 1990}
The adoption of decentralised power generation systems which use indigenous energy sources has been
proposed as an environmentally, economically and socially beneficial model for the development of
India's rural villages.{Ravindranath, 1993} Furthermore, all the lighting and power needs of India's rural
villages could be met on only 16 Mha of land; a small area when compared to the estimated 100 Mha of
degraded land potentially available for tree planting. Ravindranath (1993), has further estimated "that
biomass conservation programmes such as biogas and improved cook stoves could provide more than 95
Mt of woody biomass. If gasified, this biomass could provide energy in excess of the total rural energy
requirements." Thus, theoretically, no extra land would be needed.
The whole-hearted adoption of such small-scale systems (5 to 20 kW) by the villagers themselves will only
be achieved if such systems can address their multiple needs at lower overall costs and more
83
conveniently than present traditional methods. Such needs include the provision of water (primarily for
drinking and then for irrigation), light (domestic and street) and shaft power for milling, with cooking
considered a low priority.
According to Rajabapaiah et al. (1992) small scale decentralised systems in India could theoretically be
both more cost effective than present centralised power production and less environmentally damaging.
In fact, such systems could be beneficial to the environment in terms of decreases in the emissions of
pollutants (including greenhouse gases) and in the rehabilitation of degraded lands if they were planted
with energy forests.
The demonstration of three such schemes by the Centre for the Application of Science to Rural Areas
(ASTRA), of the Indian Institute of Science in Bangalore, has shown the feasibility of such an approach.
The projects are based in three villages in Karnataka state South India, namely, Pura, Ungra and Hosahalli
villages.
The Pura village (population of 209) scheme was initially conceived as a biogas-for-cooking project
requiring the collection and use of most of the villages cattle dung production. {Rajabapaiah et al., 1992}
Surplus gas would then be utilised for electricity production, mainly for lighting. However, problems with
inadequate incentives for dung collection resulted is less gas production than planned. Initially insufficient
gas was produced to cook all the villagers' meals and thus the villagers became disinterested in the
project. Thereafter, the implementation of community-based management with a transparent decision
making process altered the project's priorities. The provision of cooking gas was demoted in favour of the
supply of clean water and, at the same time, fair returns for dung provision were allocated. The Pura
village project now recuperates its operation and maintenance costs and is fully accepted and welcomed
by the village as a whole.
This Pura village project demonstrates that local initiatives can be successful if they are adaptable and can
take a longer term view over the provision of social and economic benefits.
Hosahalli, a nearby village, has demonstrated the feasibility of electricity production from the gasification
of fuelwood for lighting, water-pumping, milling and for irrigation (future). Hosahalli is analyzed in more
detail below.
Hosahalli: This is a small, non-electrified village of 42 households and a population of just over 200. As
with Pura village, detailed discussions were undertaken between ASTRA and the villagers before the
initiation of the scheme. The main aim of the project was to demonstrate the feasibility of small-scale
energy plantations for the provision of sufficient wood to sustainably supply a 5 kW wood-gasifier. This
wood-gas is then used in a diesel-engine as a substitute for diesel. The engine is connected to a 5 kWe
alternator which generates 3-phase (nominally 220 V) electricity to supply specified village energy
services. The project funded the hardware, and initially aimed for the operation and maintenance of the
system to be "self funding. This is presently the case, and there are good prospects that developmental
work, both hardware and social, will lead to full economic profitability and a reasonable payback period.
The project is being implemented in 5 phases:
I) Growing 2 ha energy forest to provide a sustainable wood supply. The installation of the wood
gasifier/diesel engine and generating system.
II) Electrification: the provision of lighting to all households (1x40 W fluorescent and 1x25 W
incandescent bulbs) + 9 street lights.
III) Installation of a water pump and tanks for drinking water.
IV) Installation of a flour mill. (5 kW electrical).
V) Provision of water pumping for irrigation. (10 pumps x 3.7 kWe/pump x 300 hr/yr./pump for flood
irrigation).
The engine is modified to run on both diesel and wood-gas, however, starting requires the use of the
diesel-only mode until the gasifier reaches operating temperature. Once the gasifier is operating the
wood-gas produced completely displaces the need for diesel. An overall diesel displacement of 67% has
been achieved when compared to the diesel saved if the engine were running on diesel alone. Presently a
saving of 42 litres of diesel a month is being achieved. A diesel substitution level of over 85% is possible if
the gasifier is run for longer periods which would have significant economic benefits.
Electricity for lighting has been supplied for 3 to 4 hours daily since September 1988, drinking water since
September 1990 and the flour mill (2 hours daily) has been in operation since March 1992. This has been
achieved with a reliability in the supply of power of 95%- a remarkable level of reliability when the
84
consistently high voltage level provided is taken into account, in contrast to the erratic supply and
fluctuating voltage of the central electricity grid. In addition to the provision of these services, two men
have been employed full-time to cut and supply wood from the energy forest and to maintain the gasifier
and engine; more recently a woman has volunteered to be trained in running the equipment.
A proper comparative economic analysis is made difficult because of the high level of subsidies given to
centralised grid electricity. However, according to Ravindranath and Mukunda (1990), at the level of
operation for lighting only (4 hr/day) the wood gasification system would only be economic, in terms of
covering its running costs, if electricity is priced at Rs. 3.5 per kWh (14 USc/kWh). However, if the
gasification system operates beyond 5 hr/day, the unit cost of energy becomes cheaper than the dieselonly system. For comparison, the current subsidised price of grid-based electricity is Rs. 0.65 (equivalent
to about 3 USc/kWh). {Ravindranath, 1993}
An important aspect of this project is that the villagers are prepared to pay over twice as much for their
electricity (approx. Rs. 1.3/kWh (5 USc)) because: i) the supply is reliable, ii) provision of ancillary benefits
(clean drinking water, flour mill, etc.), iii) quality of supply (never below 180 V) and iv) emergence of self
reliance (the formation of village management committee). This emergence of self reliance for the
decentralised and small-scale, provision of energy also plays an important role in the other two projects
being implemented by ASTRA in Pura and Ungra.
At the present rate of diesel-substitution (42 I/month), the monetary savings are equivalent to Rs.
2,520/yr. (US$ 101/yr.). This is the equivalent to a payback period of 9.5 years including the additional
cost of the energy forest, gasification equipment and modification of the diesel engine, (table 15)
However, the other benefits listed above, or the revenue from lighting, paid by each household (Rs.
10/household/month) is not accounted for and would reduce the payback period. A general increase in
energy demand in combination with a demand for more powerful lights is resulting in the gasifier being
run for longer periods of time and therefore should result in decreasing running costs per kWh.
One concern voiced by the villagers was the amount of land which had to be devoted to the growth of
wood for the gasifier. The eventual planting of 2 ha with 6 different species has resulted in an average
annual yield of 6.9 dry t/ha/yr. compared with a total use of only 10.2 t over the 32 month period (3.8
t/ha/yr.). The productivity of this land is therefore considered more than sufficient to meet present and
future demand. The excess wood can be used by the villagers or sold.
Estimates for India as a whole, show that the use of degraded land (or edges of fields) around many
villages would not only provide more than sufficient area to supply present demand, but would also help
to rehabilitate such land. In addition, the potential of this land to becoming a C-sink could be significant,
whilst at the same time helping rural development. {Ravindranath, 1992} (see also Land Use section)
If such decentralised systems are to become widespread then the lessons learnt from these studies must
be built into future policies aimed at their promotion. ASTRA emphasises that it is crucial to listen to and
address the recommendations made by the users, and secondly, the continuing involvement of the
community in the organisation and running of the plant is essential.
Similarly, in Hosahalli, community involvement was only secured when phase II was implemented and
clean drinking water made available. Thus, both Pura and Hosahalli required a long-term commitment
and flexible approach by ASTRA, which have given them the confidence to recommend that decentralised
power production systems, based on the experiences from Pura and Hosahalli, be broadened to
encompass a "cluster" of villages (of about 100 in total). This would allow the system to be realistically
compared with grid electricity. The interconnection of the villages would allow increased reliability and
profitability making decentralised power generation more desirable.
Mauritius
Mauritius is a small island (1,865 km2) off the East coast of Africa with a population of just over 1 million.
About a quarter of the workforce is currently employed in the agricultural sector. Its primary export crop
is sugar, and with the decreasing export value of sugar (and raw commodities in general) the government
has been seeking ways to increase the overall value of its sugarcane crop. There is an emerging view of
sugarcane as a multi-product crop, able to produce both food (sugar and animal feed) and energy
(ethanol, biogas and electricity). Thus sugarcane is increasingly seen as an opportunity for development
and not a hinderance.
Cane production in 1990 totalled over 5.5 Mt (fresh stems) but only one third (29%) of the potential
excess energy from bagasse is presently being utilised. {Comarmond, 1992} However, whilst gross
85
electricity production from bagasse increased from 27 GWh in 1980 to 71 GWh in 1991, total electricity
production doubled from 355 GWh to 737 GWh in the same time period. Consequently, bagasse's share
of electricity rose only slightly from 7.5% to 9.6%.
Prior to 1982, 16 of the 19 cane mills sold electricity during the milling season to the Central Electricity
Board (CEB). All these mills used inefficient low pressure and temperature back pressure technology.
{Comarmond, 1992}. In 1984, 14 of the sugar mills and 1 tea factory supplied 34 GWh of electricity to the
grid. {Purmanund et al., 1992} The main purpose of the technology used is to deliver process steam to
power the mill and secondly, as a means of bagasse disposal. Even so, a total of 31 GWh of bagasse
generated electricity was purchased by the CEB during 1981.
This inefficient technology is only capable of producing 300 kg of steam per tonne of cane (kg/tc), and
thus the opportunities presented by newer technology (able to produce 550 to 600 kg/tc) were evident.
The newer technologies do however, involved higher capital costs. In 1982, the Medine mill started
operating a new 10 MW CEST system to exploit these potential benefits, and during the crushing season
exported an additional 10 GW (2,770 kWh) to the CEB.
In 1985, the largest sugar factory in Mauritius, the Flacq United Estate Limited (FUEL) commissioned a
modern steam boiler capable of burning both bagasse and coal, sufficient to deliver high temperature and
pressure steam to power both the factory and a 24 MW CEST alternator. The dual-fuel ability of the FUEL
boiler enables it to burn bagasse during the harvesting season and coal during the off-season. Total
electricity production is approximately half (40 GWh) from bagasse and half (40 to 45 GWh) from coal.
All year round electricity production is obviously a more valuable commodity for the CEB than seasonal
production. It results in the CEB needing less standby generating equipment to meet demand when
seasonal production is not available. The CEB thus pays a premium for such electricity production; 100
c/KWh for permanent electricity production, 45 c/kWh for seasonal, and only 16 c/kWh for intermittent
(wind, PV, tidal etc,). The tariffs paid by the CEB, are derived from the "avoided costs" that would be
incurred if the demand were to be provided from CEB's own electricity generating plant i.e. specifically
the cost of electricity production from a 24 MW diesel powered generating plant. {GEF, 1992} In fact,
current forecasts for growth in electricity demand have resulted in the commissioning of 106 MW of new
fossil fuel generating capacity; in addition, two future 24 MW bagasse/coal plants have been ordered.
Funding for the two bagasse plants and the enhanced use of the sugar industries by-products is envisaged
to cost about US$ 80 million over an eight year period. The funding will be allocated under the Bagasse
Energy Development Programme (BEDP) which is a central part of the Mauritian Governments Sugar
Energy Development Project (SEDP). Under the SEDP's US$ 55 million financing plan 48% of the funding
(US$ 26.6 million) is from foreign sources, of which only US$ 3.3 million is provided by the Global
Environment Facility (GEF). {GEF, 1992}
The GEF funding is specifically for technical and staff development (US$ 1.9 million) BEDP co-ordination
and for environmental monitoring (US$ 1.4 million). In justifying this funding GEF states that "increased
use of sugarcane biomass as energy in Mauritius will have significant environmental benefits." To this end
it estimates that CO2 emissions will be reduced, in terms of avoided fossil fuel emissions, from 75,000 t/yr.
to between 60,000 and 67,000 t/yr., and at the same time NOx and SOx emissions will be reduced from
4,000 t/yr. to 1,000 t/yr.
The primary aim of the BEDP is to increase cane residue-derived electricity production from the present
level of 70 GWh to about 120 GWh. This will exploit about 56% of the total potential from bagasse, but
due to increased electricity demand bagasse is only expected to provide about 9% of total electricity
production by the year 2000. {Comarmond, 1992}
However, if the full potential of sugarcane residues (bagasse and tops + leaves, and other crop residues)
were to be exploited for electricity production, estimates of the potential resource for electricity
production are much larger. A crude estimate of the theoretical total potential would be about 3,500
GWh (at 40% conversion efficiency, biomass to electricity) or 2,500 GWh at 30% efficiency. When
compared with the CEB forecast of total electricity consumption of 1,678 GWh/yr. {Comarmond, 1992} in
the year 2000, bagasse and barbojo represent a significant energy resource.
Another independent estimate of the total theoretical energy potential from crop, forest and dung
residues, based on 1984 data, is of 4,007.3 GWh (14.4 PJ).13{Purmanund et al., 1992} The energy value of
cane tops & leaves (roughly equivalent to bagasse in weight) was not included in this study as it is
presently either used as animal feed or left on the field to act as a mulch. However, the study did include
86
the potential alcohol production from molasses (8% of the total energy derived from cane). If half the
tops and leaves from the sugarcane were to be used, the total potential energy from residues would rise
to about 5,833 GWh.14 Using the efficiencies assumed (see footnote 13) for conversion to electricity
residue-based energy could produce approximately 1,400 GWh of electricity or virtually the total
Mauritian electricity production forecast for the year 2000. {Comarmond, 1992}
13
If the Purmanund et al. {1992} estimate for conversion efficiencies is used, which assumes a boiler
efficiency of 70% and a thermal conversion efficiency (heat to electricity) of 35%, then an electricity
production potential of 982 GWh is estimated.
14
It is estimated that in Puerto Rico 30 to 50% of the tops and leaves should be left on the field. {GEF,
1992}
Estimates of potential energy production from sugarcane residues, such as those cited above, do not
attempt to estimate the likely effects of optimised strategies for both energy and food production. It is
estimated that large potential gains in both sugar and fibre production could be achieved from sugar cane
if breeding programmes concentrated on total biomass production and not simply increasing the sugar
concentration in the stem. {Alexander, 1985} If likely increases in the efficiencies of conversion of biomass
to useful energy (i.e. electricity) are accounted for i.e. the use of biomass gasification and gas turbine
technologies (BIG/STIG) much larger potentials are estimated. For example, Williams and Larson (1992)
estimate that by 2027, the electricity potential from cane in Mauritius could be 29 times (14,300 GWh)
Mauritius's total 1987 electricity production (490 GWh). This figure is based on the assumption that cane
production grows at 3.1% per year and that BIG/ISTIG technology is used with a conversion efficiency
(biomass to electricity) of 38%.15 {Williams & Larson, 1992} It is interesting to note that the installed cost
in 1989 US$/kWe for BIG/ISTIG is estimated to be between $ 870 and $ 1,380 which is lower than the
present installed cost of CEST at US$ 1,520 per kW.
Biomass Integrated Gasifier/Intercooled Steam Injected Gas Turbine (BIG/ISTIG) technology is a derivative
of BIG/STIG technology (section 4, Energy Conversion) and is used for the co-generation of process steam
and electricity. BIG/ISTIG conversion efficiencies (biomass to electricity) are estimated at about 8% higher
than BIG/STIG (30% efficient); however, commercialisation is expected to take longer.
Employment potential.
If rural communities are to prosper as a country develops then secure and financially beneficial rural
employment must be a central theme. The history of agricultural development is often characterised by
the reduction in man hours per tonne of produce harvested. The fall in manpower required in agriculture
has accentuated, or is a direct cause of urban drift so exacerbating urban unemployment and related
problems.
One trait of agriculture is the seasonably of the employment. In developing countries where the bulk of
the harvest is often carried out manually this requirement for large numbers of temporary jobs during the
harvesting season is regarded as socially damaging. Whilst the quality of the work may be poor it does at
least provide some form of income where there might not otherwise be any. It should therefore not be
the aim of any investment programme to destroy this important opportunity for income. Rather the aim
should be to secure those jobs throughout the year in the most economically efficient way, possibly by
providing alternative employment during the off-season.
The Carpentieri et al. (1992) study of biomass electricity in NE Brazil provided a detailed analysis of the
manpower requirements for both the tree plantation and sugarcane biomass energy sectors. The
sugarcane industry of the Northeast presently employs labour at the rate of 19.8 jobs per km 2 for onseason work and only 2.7 jobs per km for off-season (permanent) employment. If in the future labour was
to be employed to bale and collect the tops & leaves which would be done off-season (an essential
activity if enough energy is to be produced from sugarcane residues), then the on-season requirement for
jobs would hardly change at 19.6 jobs km-2 but the off-season requirement would rise to 23.7 jobs km-2 At
present only about 36,000 people are employed permanently by the sugarcane industry of the Northeast;
however, if the industry became a combined sugar and energy production system the theoretical total
number of permanent jobs is estimated to be more than 326,000. The seasonal requirement (harvesting
period only) would fall from 272,600 to 55,800 people, with all the present seasonal jobs being absorbed
into the extra permanent vacancies.
The tree plantation industry is much less labour intensive with an average requirement of 2.7 jobs km 2.
Approximately 12% of these jobs are needed for research and administration. In analysing the potential
87
plantation requirements to supply the additional electricity demand for the period 2000-2015, 32,454
jobs would be needed. This represents 9 % of the ultimate potential total if all the area identified as "free
for forestry" in the Northeast were eventually to be planted for electricity production.
In the agro-ethanol industry, job quality is also comparable or higher to many of the main large-scale
employers in Brazil. It is estimated that the ethanol industry in Brazil has generated 700,000 jobs with a
relatively low seasonal component compared to other agricultural employment. Job security and wages
are important for workers in this industry; they receive higher wages on average than 80% of the
agricultural sector, 50% of the service sector and 40% of those in industry. {Goldemberg et al., 1992}
One of the most important developmental comparisons is the investment cost per job created. For the
biomass energy industries envisaged above, this lies between $15,000 and $100,000 per job, with costs in
the ethanol agro-industry between $12,000 and $22,000. Such job creation costs compare with the
average employment costs in industrial projects in the Northeast at $40,000 per job created, in the petrochemical industry of about $800,000 per job, and for hydro power over $106 per job. Lower job creation
costs are one of the most significant benefits of biomass energy. {Carpentieri et al., 1992; Goldemberg et
al., 1992}.
CHAPTER NO.04
BIOENERGY PROGREMS
4.1 ASSESSMENT OF BIO-ENERGY PROGRAMS IN PAKISTAN.
88
Energy in useful form is welcomed by the society if the generation process is eco-friendly, renewable and
economical. It is well known that Biomass has been used in all the countries in general and tropical
countries in particular mainly to generate thermal power either for home use or to run industrial boilers.
Biomass is the residues generated out of plants, agricultural crops and trees and hence they are
renewable. The recent advancement in science achieved especially at CGPL, IISc has shown that by
adopting principles of Combustion, Gasification and Pollution control it is possible to generate ‘Clean’ power
which is either in electrical or thermal form. With this technical strength it is found relevant that CGPL
produce a country wide Biomass Atlas to enable assessment of biomass availability to forecast the power
generation potential. Under this context, MNRE [Ministry of New and Renewable Energy] decided to bring
out a Nation wide Biomass Atlas based on the guidelines given by CGPL.
Biomass
Data
Collection
and
Methodology
The Diagram shows the methodology used to integrate the data into Atlas. This software package is
developed at CGPL, IISc, as the National Focal Point (NFP) that provides information on Biomass Residues
form Agro-Crops, as related to Energy generation both in Spatial and Statistical form. The residue
generation based on agricultural output is used to compute the surplus Biomass available for Energy
production after accounting for the societal uses such as Fodder, Domestic Fuel, and Thatching. While all
the use for fodder and thatching is considered unavailable for energy generation, use for domestic fuel is
decided based on the district level surveys conducted with MNRE support. The data on agricultural outputs
are obtained from the published data by Ministry of Agriculture where as the data on residues are obtained
from Taluk and District surveys. The Taluk Study was initiated by MNREand conducted during 1999-2001
for strategically selected taluks (of about 500) across the country. Later, the District Survey instituted by
MNRE was done during 2002-04 for 15 districts country wide.
NFP has integrated these crop related data into a data base to be used for creating the spatial atlasIndian Bio-Residue Map (IBRM). The spatial maps providing the Land use were obtained from RRSSC
(ISRO) through their satellite imagery at a ground resolution of 184x184 m. This was then set into GIS
(Geographical Information System) by NFP (CGPL, IISc, Bangalore) to use the statistical crop data for
spatial distribution at district level. AI based on Fuzzy Logic is adopted for distributing the polygons (with
the appropriate crop names) by combining the information on the areas from the land-use with the
statistical data on the crop area. The Maps were re-processed to also embed the District and taluk level
spatial data extracted from the same crop distributed map.
89
Why Geographical Information System?
The biomass is geographically distributed [spatial] and has to be transported to power generation centers
economically. It is not enough that a simple data base is provided with conventional queries to assess the
biomass. The biomass assessment has to be done geographically based on the location of ‘Use centers’.
Additionally, Biomasses are of different types and exhibit different power generation characteristics. These
features prompt the use of Geographical Information System [GIS] to asses the biomass along with
conventional information data bases. This is done in two ways to make it available to the users. One is a
stand alone digital atlas queriable on the user’s PC and the other is web enabled atlas. Indian Bio-Residue
Map (IBRM) as a stand alone package.
This is redistributable software which can be installed on the client PC which will contain a one time
specific spatial biomass data. The different types of Biomass can be assessed in the circle of interest to
forecast the power generation potential for either budgetary purposes or as an input to a DPR [Detailed
Project Report] to set up an energy generation center. The only problem one may face is to update the
Atlas if the year of assessment required is far away from that of the year of formation of the Atlas.
Web enabled Indian Bio-Residue Map (IBRM)
Unlike the stand alone package this is directly available to any remote client dynamically on his desk top
PC [Personal Computer]. The updates on the biomass information will be seamlessly available to the users
as the data sits on a central information server. The rest of the features are common with a difference that
the circle of interest will be introduced in the next phase. The web Atlas is cautiously designed keeping in
view the internet response to every query of the client. The atlas can be accessed through normal internet
browsers.
Excerpts of Atlas outputs
Sample clippings on a stand alone PC
90
Karnataka Demography Layer
Karnataka Kharif Crop Layer
91
Karnataka Kharif Crop Layer of Dharwad District
Karnataka Rabi Crop Layer
92
Karnataka Rabi Crop Layer of Raichur District
Search option to find Districts
4.2 POWER GENERATION FROM ENERGY PLANTATION
6. The potential use of wood residues for
energy generation
6.1 Introduction
6.2 Sources of available wood residues
6.3 The fuel value of wood residues
6.4 The preparation of wood waste fuel
6.5 Applications for waste-based energy
93
6.6 Combustion
6.7 Cogeneration
6.1 Introduction
Unlike most other industries, the forest industries are fortunate to be able to use their waste to help
meet their energy needs. In mechanical wood processing the greater part of the thermal energy
requirements can be met from the available residues, in fact, the sawmilling industry has the
potential to produce both a surplus of heat and electricity and therefore could support other energy
deficient conversion processes in an integrated complex producing, for example, lumber, plywood
and particleboard or, in the rural areas, to supplying energy for the needs of the surrounding
community.
Over the years many mills have regarded wood waste as a troublesome by-product of the
sawmilling operation, resulting in its being disposed of as landfill or incinerated in Wigwam
burners or the like. However, both have recently become contentious environmental issues and,
combined with the rising costs of energy, mill owners have been forced to seriously consider the
merits of using the residues as an alternative fuel source this has also coincided with the increase
in demand for the residues as furnish for paper-pulp and panel board manufacture, due to the
rising cost and increased competition for solid wood.
Nowadays most wood processing plants being built in developed countries incorporate hog fuel
burners in order to safeguard against certain and costly fossil fuel supply. In instances where the
amount of residues produced are insufficient to meet the plant's thermal needs, purchased hog fuel
and/or fuel oil are used to make-up the balance. However, little use is made of the energy potential
of sawmilling residues in developing countries, this being partly due to the minimal use of kiln
drying and the investment capital involved in the installation of the heat generating plant.
Although the heat produced from wood residues is less than that from oil or gas, its cost compared
to fossil fuels makes it an attractive source of readily available heat or heat and power. In spite of
the growing competition for the residues for other uses, its projected increase in price over the
coming years will undoubtedly be less than that expected for traditional fuels. Although the
handling, processing and combustion of the residues may involve a higher capital outlay,
considerable developments in new and improved technology and plant design are now rendering it
an economically attractive fuel source.
The most effective utilization of wood residues, particularly in the sawmilling and plywood
industry, plays an important role in energy efficient production and it can often prove to be an
important factor in determining whether a sawmill is to operate at a profit or loss, especially if
lumber is manufactured from marginal logs. However, when contemplating the use of wood
residues as an energy source, whether it only be to provide heat for kiln drying or both heat and
power for use in an integrated complex, the following items will need to be examined in detail as
they can influence the economic viability of the venture:
(a) present day and projected future costs of traditional energy sources and their availability;
(b) energy requirements of the plant (heat and electricity);
(c) availability and reliability of residue supplies, their cost, type, size, moisture content and
proportion of contraries;
94
(d) the capital cost of equipment needed to collect, process and combust the wood residues;
(e) disposal cost of residues;
(f) resale value of the residues as a raw material for panel board or pulp manufacture, etc.
It is only by undertaking a professional study of the above, as well as the most appropriate type
and size of plant and the best use of the surplus heat and power, that an efficient waste handling,
treatment and combustion system can be designed in which the return on investment would
warrant capital expenditure. Obviously it would not be logical to invest in a plant in which the
capital and operating costs exceed the gains from using the residues as fuel.
Although residues may represent a free source of readily available fuel, it is a misconception to
believe that it is a free source of energy. The cost of waste handling, treatment and combustion
equipment, together with labour and maintenance can be a costly adjunct to a plant's operating
costs and capital outlay, and may prove to be excessive for some small mills. Also, this
particularly applies to on-site power generation, which, due to the high cost of steam raising and
power generating plant, would not be considered an economically viable investment for most
small- and medium-sized install
6.2 Sources of available wood residues
6.2.1 Forest residues
6.2.2 Mill-site generated wood waste
6.2.3 Integrated production
6.2.4 Alternative uses of residues
The residues generated from the forest products industry may be divided into two parts; that
which results from harvesting and extracting logs from the forest, and generally considered of no
economic use for further processing, and that which is generated by the forest industries
themselves during the process of manufacturing timber, plywood, particleboard and the like (refer
to Figures 1, 2 and 3), namely:
Source
Forest operations
Sawmilling
Plywood production
Particleboard
production
Type of residue
Branches, needles, leaves, stumps, roots, low grade and decayed wood,
slashings and sawdust;
Bark, sawdust, trimmings, split wood, planer shavings, sanderdust;
Bark, core, sawdust, lillypads, veneer clippings and waste, panel trim,
sanderdust;
Bark, screening fines, panel trim, sawdust, sanderdust.
In general it may be said that of a typical tree, less than two-thirds is taken from the forest for
further processing, the remainder being either left, burnt or collected as fuelwood by the local
inhabitants. After processing, only 28 percent of the original tree becomes lumber, the remainder
being residues, as indicated in Table 7.
95
Table 7. Division of a typical tree harvested for sawntimber
Tree part or product
Left in the forest:
Top, branches and foliage
Stump (excluding roots)
Sawdust
Sawmilling:
Slabs, edgings and off-cuts
Sawdust and fines
Various losses
Bark
Sawn timber
Total
Portion
(%)
23.0
10.0
5.0
17.0
7.5
4.0
5.5
28.0
100.0
Sources: (37) (144)
It is only in the last few years that, due to the economics of rapidly rising fuel and wood costs,
industry in the developed countries have invested in ways and means to extract the maximum
quantity of recoverable wood during logging operations. Although this document draws attention
mainly to the energy value of residues produced during the manufacturing operations,
consideration should be given to the potential industrial use of residues left in the forest.
6.2.1 Forest residues
It is not uncommon for some 60 percent of the total harvested tree to be left in the forest and for
non-commercial species to be subjected to slash and burn, or merely felled and left to rot so as to
make access easier for logging. Such practices as sawing and squaring logs in the forest, rather
than at the sawmill, wastes a further eight to ten percent and 30 to 50 percent respectively (29).
Proper training and provision of appropriate tools and logging equipment can do much to improve
the methods of harvesting so as to substantially reduce the excessive wastes, which could
otherwise represent a higher yield of solid wood or a source of fuel.
However, although forest residues may appear to be an attractive fuel source, collection and
handling costs must be taken into consideration, as well as its loss as a valuable soil nutrient. The
viability of its use may be improved if collection be undertaken at the same time as log extraction,
with shared equipment and management, whereby logging slash and marginal timber may be
collected and chipped using portable or semi-portable chippers placed in the immediate logging
areas. By ensuring that leaves, bark and thinnings are left behind, the soil's nutrients would not be
depleted.
Transport costs are also a critical factor in the use of forest residues, due to the low heat values of
such bulky material, for which reason distances are to be kept low so as not to incur unnecessary
expense if the waste is to remain economically attractive as a fuel source. Chipping of the residues
does afford some degree of compaction, also several processes are in operation which further
compress the waste into more manageable forms, such as pellets, thus improving their bulk
handling characteristics. However, due to the high capital and operating costs involved,
96
densification tends to be only financially viable when the waste needs to be transported over long
distances.
Whilst regarding wood as a renewable energy resource, consideration should also be given at
regional or national level to encourage the collection and use of logging residues, be they
branches, tops or whole-tree utilisation, to the establishment of energy plantations using quick
growing species especially selected for their value as a fuel.
6.2.2 Mill-site generated wood waste
If one considers that approximately 45 to 55 percent of the log input to a sawmill or plywood plant
is to become waste, it would be illogical not to maximize its use as a fuel source, if no other
profitable market outlet can be found.
The actual production of residues, or waste, generated from the manufacture of wood products,
differs from plant to plant and depends on several factors, from the properties of the wood to the
type, operation and maintenance of the processing plant. However, mean averages apply to each
type of industry, which, for developing countries have been detailed in Tables 1, 2 and 3 of
Appendix VI, and summarized in Table 8.
Table 8. Proportion of residues generated in selected forest products indu stries 1/
Sawmilling 2/
Finished product
(range)
Finished product
(average)
Residues/Fuel
Losses
Total
%
45-55
Plywood
Manu.
%
40-50
Particleboard
Manu.
%
85-90
Integrated
Operations
%
65-70
50
47
90
68
43
7
100
45
8
100
5
5
100
24
8
100
1/
Excluding bark
2/
Air-dried
All wood waste and bark, which is also commonly referred to as hog fuel due to the process of
reducing the residues in size in a "hogger", has a value as a fuel, although it is produced in a wide
range of sizes with varying moisture contents, as shown in Table 10, and comprises mainly of the
following:
- Bark, which makes up some 10 to 22 percent of the total log volume depending on size and
species, can in itself represent a serious waste disposal problem unless it can be used as a fuel or
removed prior to log preparation;
- Coarse residues, such as slabs, edgings, off-cuts, veneer clippings, sawmill and particleboard
trim, when reduced in size, make ideal fuel, especially when dry. They also have a resale value as
pulp and particleboard furnish;
- Cores, from plywood peeler logs, are generally sold to sawmills or lumber or as pulp chips;
97
- Sawdust, being a product of all mechanical wood processing operations, particularly sawmilling,
is generally not regarded as a prime pulping material due to its small size, although it proves to be
acceptable for the manufacture of particleboard;
- Planer shavings result from dimensioning and smoothing lumber, plywood and particleboard
with planers during the finishing stage. They are considered ideal for particleboard production and
are particularly good for heating kilns and dryers;
- Sanderdust is produced during the abrasive sanding of lumber, plywood and particleboard during
the finishing stage. Due to its size and very low moisture content it is well suited for direct firing;
- Particleboard waste, being in the order of five percent, is negligible compared to that generated
in other mechanical wood-based industries, as it is largely recycled within the production process.
In fact the waste from sawmilling and plywood manufacture make up a large part of particleboard
furnish.
6.2.3 Integrated production
As previously indicated, the sawmilling and plywood industries each produce between 40 to 55
percent of waste from their incoming wood supply, with heat values in the range of 17 to 23
MJ/kg (dry weight), more than sufficient to meet their own energy requirements. Nonetheless, it is
considered uneconomical to generate their own electricity from residues unless they have an
additional sales outlet for the surplus power.
However, particleboard production produces little waste, being in the order of five to ten percent,
and insufficient to cover the needs for heat, yet, would be resolved in the case of an integrated
operation of all three industries - market forces permitting (25).
Sawmilling, veneer, plywood and particleboard production lend themselves quite readily to
integration, with the advantages of shared waste handling processing facilities and services, and
the maximum benefit derived from the use of the residues as a raw material and fuel, whereupon
the surplus energy could be fully and economically used to the best advantage. But, the scale of
such a complex may be beyond the means- of some developing countries.
6.2.4 Alternative uses of residues
Residues derived from the forest industries normally do have alternative outlets, as chips for pulp
manufacture, raw materials for particleboard and fibreboard manufacture and as fuelwood and
building materials to local inhabitants - all dependent on market location and demand. Listed
below are several outlet areas.
Sawmilling
- edgings and slabs
- barked edging chips
Plywood
Manufacture
Particleboard
- peeler log cores
- core chips
- veneer chipping and chips
- uses all the above mentioned residues as raw
material for board manufacture, and the majority of
- low cost building
materials, fuelwood and
pulp manufacture
- pulp manufacture and
fuelwood
- lumber manufacture
- pulp manufacture
- fuelwood
98
its own residues are recycled within the process.
Alternative markets and the sale value of wood residues must, of course, be taken into
consideration when undertaking a feasibility study of a specific manufacturing plant, so as to
assess its availability for fuel and to account for its opportunity value in manufacturing cost
analysis.
Apart from the use of residues as a potential fuel source to meet a plant's own energy
requirements, its direct sale, or as pellets or briquettes, as fuel to other industrial users or
electricity generating companies is becoming an attractive venture for some mills in developed
countries. However, one must take into account its historic use in certain regions, as being a basic
fuel for domestic heating and cooking in the smaller cities, villages and rural areas.
In some countries the use of wood residues as a raw material for the production of say pulp and
paper and particleboard, is deemed to be more beneficial to both the local and national economic
and social well-being, than its use as a fuel. (100) This being due to the value added element in the
form of labour and trade derived during the various stages of processing the residues into a
saleable product, whereas its impact as an alternative fuel is solely to reduce oil imports - a
debatable issue.
6.3 The fuel value of wood residues
6.3.1 Heating value
6.3.2 Effect of moisture content and particle size on heat values
6.3.1 Heating value
When evaluating the properties of a combustible material with respect to its use as a fuel, the
heating value, expressed in this document as gross calorific values or higher heating values, is one
of the most important factors, which indicates the amount of thermal energy which may be
obtained by combusting one mass unit of the material.
The heating value of wood depends very much on the species and the part of the tree being used
and varies between 17 to 23 MJ/kg of bone dry wood; generally softwoods have higher caloric
values than hardwoods, with an average value of 21 MJ/kg BD for resinous woods and 19.8
MJ/kg BD for other woods being used. In fact, there is very little variation in the heating values of
the wood substance itself, being some 19 MJ/kg BD, as it is, in fact, the variation in resin content,
with a calorific value of 40 MJ/kg BD, which accounts for the differences in values between the
species. It is for this reason that bark, with a high gum and resin content, tends to have a higher
value than wood.
However, although the fuel value may be fairly consistent in bone dry wood, the heating value
depends on several factors, namely moisture content, particle size, type and efficiency of
combustion equipment being used and the level of its operation and maintenance. Hence, in order
to put the heating values of various wood residues into perspective one must take into
consideration the heat content per unit of waste according to its moisture content, together with
the efficiency of the energy conversion process which, as indicated in Table 9, provides a
99
comparative analysis to be made with other alternative fuels (refer to Tables 1 and 2 of Appendix
IV).
Table 9. The effect of moisture content on the net heating value of wood compared to that of
other fuels
Fuel
As fired Gross calorific
value
(MJ/kg)
Wood at 0% m.c
19.8
1/
10% m.c
20% m.c.
30% m.c.
40% m.c.
50% m.c.
Anthracite
Lignite
Heavy fuel oil
Light fuel oil
Butane
Propane
17.8
15.9
14.5
12.0
10.0
31.4
26.7
42.6
43.5
49.3
50.0
Typical burner
efficiency
(%)
80
78
76
74
72
67
83
80
82.5
82.5
79.0
78.7
Useable Net heating
value
(MJ/kg)
15.8
13.9
12.1
10.7
8.6
6.7
26.1
21.4
35.1
35.9
38.9
39.4
1/
Wet basis
Sources: (22) (61) (82)
6.3.2 Effect of moisture content and particle size on heat values
Wood at the time of logging generally has a moisture content of approximately 50 to 55 percent,
although the amount varies according to species, age and the portion of the tree from which it
originated, i.e. branches, trunk, etc. Further fluctuations from the mean are influenced according
to the season it is cut and the manner in which it is transported to the mill site and stored; logs that
are floated down stream, wet-debarked or left in conditioning ponds could have moisture contents
as high as 65 to 70 percent, whereas that which is road-hauled and dry-debarked would be in order
of 45 to 50 percent m.c. Spring and summer storage can bring about a moisture loss of 10 to 25
percent.
The moisture content of the manufacturing residues depend very much on at what stage of the
process they are extracted and whether there has been any drying of the product before that stage.
For instance, sanding dust from plywood or particleboard manufacture is taken from the plant
after the driers and hot presses, where its moisture content could be as low as ten percent or less,
as indicated in Table 10.
Table 10. Range of characteristics of typical wood residues
Residues
Sanderdust
Shavings
Size
(mm)
Moisture content 1/ Ash & dirt content 2/
(%)
(%)
-1
2 - 10
0.1 - 0.5
1 - 12
10 - 20
0.1 - 1.0
100
Sawdust
1 - 10
Bark (hogged)
1 - 100
Log-yard clean-up
up to 100
Forest residuals needles to stumps
25 - 40
25 - 75
40 - 60
30 - 60
0.5 - 2.0
1.0 - 2.0
5.0 - 50
3.0 - 20
1/
Wet basis
By weight
Source: (56)
2/
As mentioned previously, moisture content is a major determinant in the heating value of wood
waste, which, from 19.8 MJ/kg at 0 percent m.c. drops to 10 MJ/kg at 50 percent m.c., as can be
seen by refering to Figure 12. Although wood may be burnt at 55 percent m.c., and up to 58
percent m.c. with careful operator attention and boiler tuning, it is always better to aim for a
moisture content of 50 percent or lower in order to achieve satisfactory and substained operation.
When the moisture content rises to 60 percent, burning of the wood residues become difficult as
its heating value drops dramatically, to the extent where, at approximately 68 percent m.c.,
"furnace blackout" occurs, being the point at which combustion can no longer be sustained, unless
a supplementary fuel is used to maintain combustion.
A high moisture content not only lowers the as-fired heat value of wood waste, but seriously
affects the overall combustion efficiency due to the large amount of energy needed to heat
considerable quantities of excess air and to vapourise the moisture in the waste, which, together
with the moisture formed by the combustion process itself is subsequently lost up the stack as
latent heat. Hence, it stands to reason that wood waste at ten percent m.c., with an as-fired heat
value of 17.8 MJ/kg and a combustion efficiency of some 78 percent is preferable to green wood
at 50 percent m.c. with an as-fired heat value of 10 MJ/kg and 67 percent combustion efficiency.
Figure 12. The effect of wood residue moisture content on combustion efficiency (103)
The size and form of the wood particle is also critical in both the handling characteristics and
burning efficiency of residues and plays a major role in their combustibility and the selection and
operation of processing and combustion plant. Whereas fine sanderdust and wood shavings may
be burnt in suspension, larger sized wood-waste, in the form of large chips, coarsely hogged waste
and slabs need a longer dwell time to burn which is generally undertaken on grates.
Hence, all steps taken to reduce the moisture content and size of the residues to a minimum, pays
dividends in energy generation. The provision of prepared storage, suitably protected against the
elements, the use of flue gases to dry the fuel etc., all contribute towards maintaining low residual
moisture and optimum combustion efficiency.
6.4 The preparation of wood waste fuel
6.4.1 Collection and handling
6.4.2 Storage
6.4.3 Size reduction and screening
6.4.4 Fuel drying
6.4.5 Densification
101
The handling, treatment and storage of wood waste fuel is considerably more costly and
troublesome than that required for traditional fossil fuels. Hence, the importance of a well
conceived and equipped woodfuel preparation system cannot be over-emphasized so as to
maximize the fuel potential of a plant's residues and to minimize handling and combustion
problems.
The reduction of particle size and moisture content, together with the most appropriate storage and
handling systems are necessary for an efficiently operated wood waste combustion system.. The
waste preparation process generally involves hogging, dewatering, screening, size reduction, bulk
storage, blending and drying prior to combustion so as to ensure a reliable and consistent supply
of quality fuel to the burners. An equal amount of care and attention needs to be paid to the state
of the wood waste used, as would normally be the case with any other fuel. The use of waste that
is decayed, too wet or containing an excessive amount of contraries is false economy, due to the
difficulty in handling and storing the wet residues, undue wear-and-tear on equipment and the
detrimental effect on the overall combustion efficiency.
6.4.1 Collection and handling
Waste collection and handling does not necessarily need to be either labour intensive or. involve
costly and sophisticated mechanical handling plant, which could otherwise render the use of
residues uneconomical. In small-scale forest industries in developing countries, the collection and
handling of waste is predominantly manual, aided by a tractor or bulldozer to both convey and
push the residues to a belt conveyor: system, thus avoiding the need for an enormous capital
outlay and with maximized use of available labour.
The handling systems should be so designed as to afford the highest degree of flexibility to the
operator and to be able to cater for the full range of sizes and moisture contents of was. e expected
from outside and within the mill. It is the failure to attend to such aspects of design that invariably
give rise to fundamental problems in operation.
Waste brought to the mill-site in the form of forest residues, or as purchased industrial wood
waste, to supplement the plant's own wood-based fuel, may be delivered by road or rail. Methods
of unloading range from the use of manual labour or a knuckle boom loader fitted with a clamshell bucket, to live bottom vans or hydraulically elevated dump trucks, all of which are
determined by economic considerations.
The manner in which mill residues are best removed and handled is again a matter of economics,
availability of labour and the quantity and type of waste produced and is normally undertaken by a
combination of belt. and pneumatic conveyors, front-arid loaders and trucks, with manual
gathering predominating in mills with an input rapacity of 20 000 m3/A and below.
Generally slabs, edgings, peeler cores, veneer waste and trimmings would be transported by
mechanical conveyors or carried manually to a chipper and, after screening, conveyed to storage
piles for use as either furnish for pulp or particleboard manufacture or as fuel. Bark, panel trim
and waste from ply glue spreaders would be hogged and conveyed to the hog-fuel storage area.
Sawdust and sanderdust, depending on the quantities produced, would be pneumatically extracted
and conveyed to a separate storage area (preferably covered). Retrieval is normally achieved by
the use of belt, drag link, flight or pneumatic conveyors, in conjunction with front-end loaders,
which may also be used to build-up the piles.
In order to safeguard against damage to moving parts, stone traps and magnetic separators need to
be incorporated in the handling system, ahead of the reduction plant so as to remove all stones and
102
tramp iron. Depending on the proportion of contraries normally expected in the fuel supply and
the type of burning equipment employed, air classification may need to be employed in order to
remove rocks and sand from the smaller-sized fuel particles, but only if they are comparatively
dry.
6.4.2 Storage
The type of wood waste storage will be largely determined by:
- the form and moisture content of the residues;
- the frequency and reliability of year-round deliveries to the mill and production of residues;
- the availability of land;
- climatic conditions;
- the need for air drying;
- the volume of wood waste fuel involved;
- the system of waste handling and treatment adopted.
Storage systems may be divided into two distinct categories, namely:
Outdoor storage, in piles on prepared concrete or gravel pads to aid drainage and reduce the
entrainment of contraries, is the least expensive means of maintaining stocks. This form of storage
is generally suited for stocks of 20 to 30 day's capacity of green forest residues, bark, moist wood
slabs or chips. However, unless adequate preparations and precautions are taken, deterioration and
fires from overheating and biological action can take place. Hence, residues should be monitored
and those that do not benefit from drying with time should have a fast turnaround and be used on a
first-in-first-out basis (109).
In instances where a large variety of residue sizes are involved, it is always advisable to segregate
according to size, either before or after storage, and, in most cases, it is preferable to reduce the
larger-sized waste in hoggers or chippers at an early stage in order to facilitate handling. Mixing
of wet and dry waste should be avoided, as such a practice will reduce the efficiency of
combustion; it is far better to have dual storage and feed systems in order to segregate the feed to
the burners according to moisture content.
Covered storage systems, to safeguard against loss and damage due to wind and rain, is normally
provided for materials which are readily wind-borne or freely absorb moisture, such as dry
sawdust, planer shavings and sanderdust.
Such storage systems as open-sided buildings, hoppers, bins or silos are usually located in the near
vicinity of the combustion plant, with approximately 48 hours capacity so as to sustain continuous
operation without being hampered by weekends or interruptions in the flow of supply from the
processing plant.
6.4.3 Size reduction and screening
Whereas sawdust, planer shavings and sanderdust may be burnt directly without the need for
further processing, other forms of wood waste have to be reduced in size in order to facilitate
handling, storage and metering to the combustion chamber. By achieving a uniform particle size,
combustion efficiency will be improved due to the uniform and controlled fuel feed rate and the
ability to regulate the air supply. Additionally, in the case of fuels with a high moisture content,
the reduction process exposes a greater surface area of the particle to the heated gases, thus
releasing the moisture more rapidly, thereby enhancing its heating value.
103
Size reduction may be carried out in several stages in a hog or attrition mill, with screening before
and in between.
The hog basically comprises of a set of knives or swing hammers mounted on a rapidly rotating
shaft within a robust casing. The impact of the rotating impellers on the wood waste against the
breaking plate reduces it to a standard size of approximately 20 to 50 mm (100).
Screening, directly before or after the hog, separates the dirt and fines and conserves energy in the
subsequent reduction stages by removing those particles of acceptable size which would otherwise
be reprocessed.
Attrition mills are used to reduce residues still further in size, by passing them between a
stationary and a rotating disc, each fitted with slotted or grooved segments. The particles produced
may, after screening, then be burnt in direct-fired suspension burners to produce hot gases for
drying lumber, plywood and particleboard furnish and other such heating requirements.
6.4.4 Fuel drying
As previously mentioned, combustion efficiency, boiler control and the operator's ability to
provide a quick response to changes in steam demand become seriously impaired by a
combination of high and fluctuating moisture content of incoming fuel. This situation may be
improved by drying the fuel, which will also effectively increase boiler capacity and lead to better
emission control.
The moisture in residues may be reduced either by mechanical pressing, air-drying or the use of
hot air dryers, or a combination of all three. It is common practice for mechanical presses to be
used on bark and wood waste with moisture levels in excess of 70 percent in order to reduce it to
55 to 60 percent m.c., which would then enable the waste to be mixed with dryer incoming
materials to produce a combustible fuel. However, in the event that sufficient supplies of wood
waste are readily available to meet the plant's energy needs and the disposal of bark does not
present a serious problem to the mill, then it is not considered economically justified for it to be
pressed and dried in view of the maintenance, power demand and the high capital intensive plant
involved.
Air-drying of logging residues, assuming the right climatic conditions prevail, can bring about a
moisture loss of some 10 to 15 percent, and the level may even drop further to 25 percent (67)
should the residues be left in clear-felled spaces open to the action of wind and sun. Air-drying of
mill waste, time and space permitting; is preferable under covered well-ventilated areas, especially
for the smaller-sized residues such as sawdust, which is more liable to absorb rainfall and takes
longer to air-dry than say mixed wood waste.
Green whole chips and mixed waste, when stored outside in piles for several months, may lose up
to 10 to 25 percent (105) of their moisture content by way of the drying effect of wind, sun and
spontaneous internal heating due to bacteriological action on the materials in the interior of the
pile (108).
The use of fuel dryers to dry fuel to approximately 30 percent m.c. using plant such as rotary
drum, flash and cascade type dryers employing waste stack gases, direct combustion of residues,
steam or hot water as heating sources, undoubtedly lead to better combustion efficiency and boiler
utilization. Nonetheless, the use of fuel dryers in medium-sized installations is questionable as the
heat energy gained would be off-set by that which would be needed to dry the fuel, added to
which one must take into consideration the high capital and operating costs involved.
104
6.4.5 Densification
A growing awareness has developed in recent years in the use of compacted wood waste, in the
form of briquettes, pellets or "logs", as a domestic or industrial fuel.
Briquettes or logs are generally formed by forcing dry sawdust or shavings through a split
cylindrical die using a hydraulic ram. The exerted pressure, of some 1 200 kg/cm2, and the
resultant heat generated bonds the wood particles into "logs".
The production of pellets involves the reduction of wood waste to the size of sawdust, which is
then dried to approximately 12 percent m.c., before being extruded in specially adapted
agricultural pellet mills to form pellets of some 6 to 18 mm diameter and 15 to 30 mm long, with a
density in the range of 950 to 1 300 kg/m3 1/. Drying of the furnish prior to extrusion is usually
undertaken in rotating drum dryers, fired by approximately 15 to 20 percent of the plant's pellet
production.
1/
Bulk density being 480 to 640 kg/m3 (106)
Although pelleting produces a product with excellent handling and storage characteristics, with
four times the energy concentration of woodfuel, thus greatly reducing transport costs and
improving boiler efficiency, it has been found that high capital investment in the processing plant
and operating costs only prove economically attractive if transportation distances of the fuel
exceed 250 km from the source of the raw material, and is normally not warranted for sitegenerated fuels.
6.5 Applications for waste-based energy
A mill or integrated complex, with a readily available supply of hog-fuel, has several operations
open to it as to the manner in which it may convert its waste into useable energy. However, before
embarking upon a general description of the proven methods of combustion and combustion
plants, a brief outline of several alternative applications for the recovered heat has been listed
below. By examining Figures 5, 7 and 9 in Chapter 2, it becomes apparent which production
centres will gain the most from either onsite heat or power generation or both.
The choice of the most efficient and cost-effective use of waste-based energy, and the selection of
appropriate heating mediums would need to be studied on a case-by-case basis, in view of the
individuality of each mill.
Heating
medium
Hot air
Hot water
and thermic
oil
Broad outline of possible applications
For direct drying of:
(a) lumber;
(b) plywood veneer;
(c) particleboard furnish;
As an indirect means to supply heat for:
(d) log conditioning;
(e) lumber and veneer drying;
(f) glue and resin preparation;
(g) hot pressing of ply and particleboard;
105
Steam
(h) space heating;
May be used as a heating medium in all the above-mentioned applications, as well
as:
(i) to provide transmission power to process plant through the use of a system of
line-shaft and belt drives. (In the past, many sawmills were powered in this way, a
large number of which are still operating successfully);
(j) to directly drive plant, such as boiler feed water pumps, induced draft fans, large
air compressors, etc., by way of small steam turbines;
(k) steam which is surplus to the mill's requirements may be sold to neighbouring
consumers for industrial, commercial and community use;
(l) to produce electricity by way of a turbine-generator to help meet the power
demand of the integrated complex;
(m) in the case of non-integrated sawmills and plywood plants, in which their
residue production far exceeds their actual heat energy needs and market demand,
consideration may be given to on-site power generation to meet their own
requirements, with the sale of the surplus to the public utilities.
6.6 Combustion
6.6.1 Firetube and watertube boilers
6.6.2 Pile burners
6.6.3 Suspension and cyclone burners
6.6.4 Fluidized-bed combustors
The range of combustion systems now available to the forest products industry is quite
considerable, with a large choice of equipment for each category. Apart from the end use of the
heat, particle size plays an important role in influencing the combustion plant. Whereas fine
sanderdust and wood shavings may be burnt in suspension, larger-sized wood waste, in the form
of chips, coarsely hogged residues and slabs need longer to burn which is generally undertaken on
grates. The decision whether to select the combustion plant to suit the available fuel or, process
the fuel to the requirements of the preferred plant, can only be made after a thorough analysis has
been carried out.
Traditional methods of burning hogged fuel for steam or hot water production has been with the
use of firetube and watertube boilers employing the pile burning method of combustion on a grate.
The difference between standard oil or gas fired boilers and those for firing wood waste in that the
slow-burning characteristics of wood, together with its high moisture content, necessitates a larger
combustion chamber capacity with a high furnace so as to create low upward velocities and cater
for the longer residence time needed to burn the wood fuel (16).
The necessity of a larger-sized boiler, together with the need for waste handling plant involves up
to 1.5 to 4 times the investment cost of oil fired package boilers. As indicated in Table 9,
combustion efficiencies of 65 to 75 percent may be expected when burning wood waste,
compared to 80 percent obtained from gas or oil fired units. The difficulty of automatic firing,
slow response to peak demand and the need for ash removal and disposal are other disadvantages
106
which must be carefully weighted up when considering the use of, what may at first appear to be,
a cheap fuel.
The direct firing of sanderdust and pulverized wood waste presents a somewhat simpler way in
which to use the fuel's energy value to heat drying kilns, air heaters and boilers. However, there is
still some hesitation in the industry to adopt the various direct-fire systems and other newer
technologies, such as wood gasifiers, until they have been adequately proven, though they do hold
promising prospects.
A brief description of the basic combustion systems, with the exception of gasification and
pyrolysis, is given, without attempting to make any comparisons as each system has its own
champions and needs to be assessed according to the circumstances of the mills. It must be
pointed out, however, that the capacity ranges, technology and cost of several of the mentioned
plants are inconsistent with medium-sized mills in developing countries.
6.6.1 Firetube and watertube boilers
Boilers fall into two categories, being firetube and watertube. Firetube boilers are principally used
where steam pressures of not more than 20 kg/cm, (12) are required in small to medium-sized
operations, and are well suited for the heat requirements of the mechanical wood-based industry.
They are relatively inexpensive and operate on the principle of hot combustion gases passing
through steel tubes set in a water jacket.
Watertube boilers consist of tubes welded together in such a manner as to form complete walls
enclosing the combustion chamber, through which flows the water to be heated. By virtue of its
construction, the watertube boiler is almost exclusively used where steam pressures above ten
kg/cm2 (12) are employed, especially in providing motive power to turbine-generators.
Both types of boiler may be further sub-divided into those which arrive as a package of fielderected on-site. Package boilers are generally shop assembled units, thus allowing them to be
readily shipped, installed and operated and tend to be less than 22 500 kg/hr steam capacity.
Whereas all the component parts of the field-erected units are entirely assembled and welded onsite.
6.6.2 Pile burners
Pile burners, as the name implies, burn the fuel in piles either on a refractory floor or grate, and
may be divided into two classes, namely:
Heaped pile burning furnaces, such as the tee-pee burners and clutch ovens, which are fed with
fuel from the top of the furnace in batch form via chutes located across the grates or, continuously
by way of variable screw feeders, to be burnt in a pile on a refractory floor or grate. Primary air
for combustion is introduced through ports located on all four sides of each chamber and the heat
transmitted to the boiler surface situated above and behind the combustion chamber.
Such furnaces may be used to burning fuels of up to 65 percent m.c., regardless of size or shape
(98), although they do require a lot of attention and considerable time to build-up and burn down
the pile and have low efficiencies in the order of 50 to 60 percent. In some furnaces, fuel of high
moisture content may be added to the base of the pile by hydraulic rams, thus allowing the waste
to burn more slowly and completely. The provision of more than one chamber permits ash to be
removed in one compartment whilst the other is being fired.
107
Thin pile furnaces burn hogged fuel, up to 55 to 60 percent m.c., as a thin bed spread across the
grate. Sloping grates, pinhole grates, travailing grates are but some of the systems currently in use
enabling the fuel to progressively advance along the grate through the combustion chamber, whilst
being exposed to primary air from below, to be then discharged by an assortment of removal
systems as ash.
Spreader stokers, using pneumatic or mechanical spreaders, are used in the larger-sized furnaces
to evenly meter and distribute hogged wood or particles, of up to 45 to 50 percent m.c., into the
firing zone of the combustion chamber, allowing the finer particles to burn in suspension and for
the larger-sized fuel to fall to the grate where it is burnt.
6.6.3 Suspension and cyclone burners
Suspension and cyclone burners are proven technology, having been successfully used with
pulverized coal for several years and adapted for use with woodfuels.
Suspension burners, as the term suggests, burns fine wood particles in suspension, in either special
combustion chambers or boiler fireboxes, in a highly turbulent environment caused by forced
combustion air. In order to operate efficiently the wood particles need to be no more than 6 mm in
size and a maximum moisture content of 15 percent (98). Such units are particularly well-suited
for use with lumber kilns, veneer and particleboard furnish dryers and boilers.
Apart from combustion efficiencies of approximately 75 percent, they often have a quick response
to swing loads with high turndown ratios, although provision must be made to safeguard against
the risk of explosions due to the nature of the fine fuel particles used.
In the case of cyclone burners, pulverized wood fuel, of a maximum 3.5 mm size and 12 percent
m.c., is mixed in the first stage of the burner and combusted in an external cyclone burner.
6.6.4 Fluidized-bed combustors
Fluidized-bed combustors are capable of burning untreated hog fuel, with moisture levels as high
as 55 to 60 percent (100), in a turbulent mixing zone above a fluidized bed of inert silica sand.
The fuel is maintained in suspension during combustion by a high velocity of air forced through
the bed of sand, which results in the sand adopting free-flowing and fluidized properties.
6.7 Cogeneration
6.7.1 Restrictive regulations and penalties
6.7.2 Economic considerations
The simultaneous production of both electrical power and a useable form of thermal energy, such
as steam, is termed cogeneration. This may be achieved by generating high pressure steam in a
hog-fuel boiler, which would then be passed through a turbine generator for power before being
used as exhaust steam in drying or process heating. Therefore, rather than just generating
electricity from wood waste with a conversion efficiency of 25 to 30 percent, cogeneration raises
the efficiency of energy utilization to some 75 percent (46).
108
The use of a condensing turbine generator with single or double automatic extraction or a backpressure turbine generator are options available to the forest products industry, though the latter is
often favoured. Although the fuel potential of the residues generated from sawmilling and
plywood manufacture exceed the plants' heat and power requirements, energy self-sufficiency in
electricity in an integrated operation, including particleboard production, is more difficult to attain
due to the fact that there is a given ratio between the power output and the output of industrial heat
generated by a back-pressure power plant (approximately 1:1.5) (25). This shortfall may be
overcome by the following alternative solutions: (25) (47)
- to design a power plant in which the ratio between power and heat production meets that of the
integrated complex's consumption ratio. However, this option involves both costly and
sophisticated plant and therefore is not considered suitable for developing countries;
- to supplement the plant's own hog-fuel production with purchases wood and wood residues or
fuel oil. Yet this option either places on increased load on existing waste treatment and
combustion systems or necessitates larger plant capacity, with heat production being surplus to
needs;
- to make-up the balance of the mill's power requirements by either using diesel generating sets or
purchasing power from the national grid.
6.7.1 Restrictive regulations and penalties
In certain countries legislation and regulations discourage the generation of power for sale, and
those mills that meet their own needs for power are often penalized by having to pay higher rates
for their purchased power in the event of a shortfall or shut-down in their on-site power supply
(58).
Although such regulations may well have been established to dissuade mills from investing in
small unviable power plants, they do not take into account the potential for hog-fuelled backpressure power. Hopefully, in the light of the anticipated rise in fuel costs such restrictive tariffs
shall be removed.
6.7.2 Economic considerations
Although it is technically feasible to use wood waste as fuel for power generation, it is the
economics that invariably prove to he the limiting factor in most cases. Whereas there are obvious
benefits to be gained by burning wood residues to reduce a manufacturer's fuel oil and electricity
bill, they may be off-set by the high capital costs involved, low plant efficiencies and increased
manning levels. Of course the economics of wood waste energy generation becomes more
attractive as traditional fuel prices increase, though the real value of the wood waste as a fuel
source must take into account its available heat content, the investment and operating costs of the
plant needed to handle and convert it to useable energy, before any worthwhile comparative
studies can be made.
It must be noted that the capacity of most energy generation plant available to the industry,
especially for cogeneration, exceeds that which can be economically utilized by most mills and
integrated units. Additionally, the limited finance available to the small- and medium-scale mills
tend to be a major deterrent in their contemplating cogeneration as an option worthy of
consideration, regardless of the possible long-term gains.
109
Hence, it is for these reasons that, in spite of their self-sufficiency in self-generated fuel, it is
generally not considered economically justified for the individual sawmill or plywood plant of
less than 150 000 m3/A log input capacity (34) to generate their own power, unless they be part of
an integrated production unit consisting of sawmilling, plywood and particleboard manufacture,
etc., with shared services.
4.3 BIOMASS GASIFICATION-PRODUCER GAS.
Gasification is a process that converts organic or fossil based carbonaceous materials into carbon
monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high
temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam.
The resulting gas mixture is called syngas (from synthesis gas or synthetic gas) or producer gas
and is itself a fuel. The power derived from gasification and combustion of the resultant gas is
considered to be a source of renewable energy if the gasified compounds were obtained from
biomass.[1][2][3][4]
The advantage of gasification is that using the syngas is potentially more efficient than direct
combustion of the original fuel because it can be combusted at higher temperatures or even in fuel
cells, so that the thermodynamic upper limit to the efficiency defined by Carnot's rule is higher or
not applicable. Syngas may be burned directly in gas engines, used to produce methanol and
hydrogen, or converted via the Fischer-Tropsch process into synthetic fuel. Gasification can also
begin with material which would otherwise have been disposed of such as biodegradable waste. In
addition, the high-temperature process refines out corrosive ash elements such as chloride and
potassium, allowing clean gas production from otherwise problematic fuels. Gasification of fossil
fuels is currently widely used on industrial scales to generate electricity[citation needed].
Contents








1 History
2 Chemical Reactions
3 Gasification processes
o 3.1 Counter-current fixed bed ("up draft") gasifier
o 3.2 Co-current fixed bed ("down draft") gasifier
o 3.3 Fluidized bed reactor
o 3.4 Entrained flow gasifier
o 3.5 Plasma gasifier
o 3.6 Free radical gasifier
4 Feedstock
o 4.1 Waste disposal
5 Current applications
o 5.1 Heat
o 5.2 Electricity
o 5.3 Combined heat and power
o 5.4 Transport fuel
o 5.5 Renewable energy and fuels
6 See also
7 References
8 External links
110
History
Adler Diplomat 3 with gas generator (1941)
The process of producing energy using the gasification method has been in use for more than 180
years. During that time coal and peat were used to power these plants. Initially developed to
produce town gas for lighting & cooking in 1800s, this was replaced by electricity and natural gas,
it was also used in blast furnaces but the bigger role was played in the production of synthetic
chemicals where it has been in use since the 1920s.
During both world wars especially the Second World War the need of gasification produced fuel
reemerged due to the shortage of petroleum.[5] Wood gas generators, called Gasogene or
Gazogène, were used to power motor vehicles in Europe. By 1945 there were trucks, buses and
agricultural machines that were powered by gasification. It is estimated that there were close to
9,000,000 vehicles running on producer gas all over the world.
Chemical Reactions
In a gasifier, the carbonaceous material undergoes several different processes:
Pyrolysis of carbonaceous fuels
Gasification of char
1. The dehydration or drying process occurs at around 100°C. Typically the resulting steam
is mixed into the gas flow and may be involved with subsequent chemical reactions,
notably the water-gas reaction if the temperature is sufficiently high enough (see step #5).
2. The pyrolysis (or devolatilization) process occurs at around 200-300°C. Volatiles are
released and char is produced, resulting in up to 70% weight loss for coal. The process is
dependent on the properties of the carbonaceous material and determines the structure and
composition of the char, which will then undergo gasification reactions.
111
3. The combustion process occurs as the volatile products and some of the char reacts with
oxygen to primarily form carbon dioxide and small amounts of carbon monoxide, which
provides heat for the subsequent gasification reactions. Letting C represent a carboncontaining organic compound, the basic reaction here is
4. The gasification process occurs as the char reacts with carbon and steam to produce carbon
monoxide and hydrogen, via the reaction
5. In addition, the reversible gas phase water gas shift reaction reaches equilibrium very fast
at the temperatures in a gasifier. This balances the concentrations of carbon monoxide,
steam, carbon dioxide and hydrogen.
In essence, a limited amount of oxygen or air is introduced into the reactor to allow some of the
organic material to be "burned" to produce carbon monoxide and energy, which drives a second
reaction that converts further organic material to hydrogen and additional carbon dioxide. Further
reactions occur when the formed carbon monoxide and residual water from the organic material
react to form methane and excess carbon dioxide. This third reaction occurs more abundantly in
reactors that increase the residence time of the reactive gases and organic materials, as well as
heat and pressure. Catalysts are used in more sophisticated reactors to improve reaction rates, thus
moving the system closer to the reaction equilibrium for a fixed residence time.
Gasification processes
Several types of gasifiers are currently available for commercial use: counter-current fixed bed,
co-current fixed bed, fluidized bed, entrained flow, plasma, and free radical.[1][6][7][8]
Counter-current fixed bed ("up draft") gasifier
A fixed bed of carbonaceous fuel (e.g. coal or biomass) through which the "gasification agent"
(steam, oxygen and/or air) flows in counter-current configuration.[9] The ash is either removed dry
or as a slag. The slagging gasifiers have a lower ratio of steam to carbon,[10] achieving
temperatures higher than the ash fusion temperature. The nature of the gasifier means that the fuel
must have high mechanical strength and must ideally be non-caking so that it will form a
permeable bed, although recent developments have reduced these restrictions to some extent. The
throughput for this type of gasifier is relatively low. Thermal efficiency is high as the gas exit
temperatures are relatively low. However, this means that tar and methane production is
significant at typical operation temperatures, so product gas must be extensively cleaned before
use. The tar can be recycled to the reactor.
In the gasification of fine, undensified biomass such as rice hulls, it is necessary to force air into
the reactor by means of a fan. This creates very high gasification temperatures, at times as high as
1000 C. Above the gasification zone, a bed of fine, hot char is formed, and as the gas is forced
through this bed, most complex hydrocarbons are broken down into simple components of
hydrogen and carbon monoxide.[citation needed]
Co-current fixed bed ("down draft") gasifier
Similar to the counter-current type, but the gasification agent gas flows in co-current configuration
with the fuel (downwards, hence the name "down draft gasifier"). Heat needs to be added to the
upper part of the bed, either by combusting small amounts of the fuel or from external heat
sources. The produced gas leaves the gasifier at a high temperature, and most of this heat is often
transferred to the gasification agent added in the top of the bed, resulting in an energy efficiency
112
on level with the counter-current type. Since all tars must pass through a hot bed of char in this
configuration, tar levels are much lower than the counter-current type.
Fluidized bed reactor
The fuel is fluidized in oxygen and steam or air. The ash is removed dry or as heavy agglomerates
that defluidize. The temperatures are relatively low in dry ash gasifiers, so the fuel must be highly
reactive; low-grade coals are particularly suitable. The agglomerating gasifiers have slightly
higher temperatures, and are suitable for higher rank coals. Fuel throughput is higher than for the
fixed bed, but not as high as for the entrained flow gasifier. The conversion efficiency can be
rather low due to elutriation of carbonaceous material. Recycle or subsequent combustion of
solids can be used to increase conversion. Fluidized bed gasifiers are most useful for fuels that
form highly corrosive ash that would damage the walls of slagging gasifiers. Biomass fuels
generally contain high levels of corrosive ash.
Entrained flow gasifier
A dry pulverized solid, an atomized liquid fuel or a fuel slurry is gasified with oxygen (much less
frequent: air) in co-current flow. The gasification reactions take place in a dense cloud of very fine
particles. Most coals are suitable for this type of gasifier because of the high operating
temperatures and because the coal particles are well separated from one another.
The high temperatures and pressures also mean that a higher throughput can be achieved, however
thermal efficiency is somewhat lower as the gas must be cooled before it can be cleaned with
existing technology. The high temperatures also mean that tar and methane are not present in the
product gas; however the oxygen requirement is higher than for the other types of gasifiers. All
entrained flow gasifiers remove the major part of the ash as a slag as the operating temperature is
well above the ash fusion temperature.
A smaller fraction of the ash is produced either as a very fine dry fly ash or as a black colored fly
ash slurry. Some fuels, in particular certain types of biomasses, can form slag that is corrosive for
ceramic inner walls that serve to protect the gasifier outer wall. However some entrained flow
type of gasifiers do not possess a ceramic inner wall but have an inner water or steam cooled wall
covered with partially solidified slag. These types of gasifiers do not suffer from corrosive slags.
Some fuels have ashes with very high ash fusion temperatures. In this case mostly limestone is
mixed with the fuel prior to gasification. Addition of a little limestone will usually suffice for the
lowering the fusion temperatures. The fuel particles must be much smaller than for other types of
gasifiers. This means the fuel must be pulverized, which requires somewhat more energy than for
the other types of gasifiers. By far the most energy consumption related to entrained flow
gasification is not the milling of the fuel but the production of oxygen used for the gasification.
Plasma gasifier
In a plasma gasifier a high-voltage current is fed to a torch, creating a high-temperature arc. The
inorganic residue is retrieved as a glass-like substance.
Free radical gasifier
A single stage gasifier that employs a thermolytic (heat energy) and photolytic (light energy)
conversion process in an oxygen starved environment. The free radical gasifier uses electrical
input energy to cause thermal breakdown and ultraviolet light based degradation of material, along
113
with harnessing free radical reactions to further convert carbon-based materials into syngas.[citation
needed]
Feedstock
There are a large number of different feedstock types for use in a gasifier, each with different
characteristics, including size, shape, bulk density, moisture content, energy content, chemical
composition, ash fusion characteristics, and homogeneity of all these properties.
A wide variety of feedstocks can be gasified, with wood pellets and chips, waste wood, plastics
and aluminium, Municipal Solid Waste (MSW), Refuse-derived fuel (RDF), agricultural and
industrial wastes, sewage sludge, switch grass, discarded seed corn, corn stover and other crop
residues all being used.[1]
Chemrec has developed a process for gasification of black liquor.[11]
Waste disposal
HTCW reactor, one of several proposed waste gasification processes. According to the sales and
sales management consultants KBI Group a pilot plant in Arnstadt implementing this process has
completed initial tests.[12]
Waste gasification has several advantages over incineration:




The necessary extensive flue gas cleaning may be performed on the syngas instead of the
much larger volume of flue gas after combustion.
Electric power may be generated in engines and gas turbines, which are much cheaper and
more efficient than the steam cycle used in incineration. Even fuel cells may potentially be
used, but these have rather severe requirements regarding the purity of the gas.
Chemical processing (Gas to liquids) of the syngas may produce other synthetic fuels
instead of electricity.
Some gasification processes treat ash containing heavy metals at very high temperatures so
that it is released in a glassy and chemically stable form.
114
A major challenge for waste gasification technologies is to reach an acceptable (positive) gross
electric efficiency. The high efficiency of converting syngas to electric power is counteracted by
significant power consumption in the waste preprocessing, the consumption of large amounts of
pure oxygen (which is often used as gasification agent), and gas cleaning. Another challenge
becoming apparent when implementing the processes in real life is to obtain long service intervals
in the plants, so that it is not necessary to close down the plant every few months for cleaning the
reactor.
Several waste gasification processes have been proposed, but few have yet been built and tested,
and only a handful have been implemented as plants processing real waste, and most of the time in
combination with fossil fuels.[13]
One plant (in Chiba, Japan using the Thermoselect process[14]) has been processing industrial
waste since year 2000, but has not yet documented positive net energy production from the
process.
In the USA, gasification of waste is expanding across the country. Ze-gen is operating a waste
gasification demonstration facility in New Bedford, Massachusetts. The facility was designed to
demonstrate gasification of specific non-MSW waste streams using liquid metal gasification.[15] In
addition, construction of a biomass gasification plant was approved in DeKalb County, Georgia
on June 14, 2011 and in Green Bay Wisconsin a deal was made with the Oneida Nation and the
city of Green Bay to build a gasification power plant which will supply electricity to over 4,000
homes.[16]
Also in the USA, plasma is being used to gasify municipal solid waste, hazardous waste and
biomedical waste at the Hurlburt Field Florida Special Operations Command Air Force base.
PyroGenesis Canada Inc. is the technology provider.[17]
Current applications
Syngas can be used for heat production and for generation of mechanical and electrical power.
Like other gaseous fuels, producer gas gives greater control over power levels when compared to
solid fuels, leading to more efficient and cleaner operation.
Syngas can also be used for further processing to liquid fuels or chemicals.
Heat
Gasifiers offer a flexible option for thermal applications, as they can be retrofitted into existing
gas fueled devices such as ovens, furnaces, boilers, etc., where syngas may replace fossil fuels.
Heating values of syngas are generally around 4-10 MJ/m3.
Electricity
Industrial-scale gasification is currently mostly used to produce electricity from fossil fuels such
as coal, where the syngas is burned in a gas turbine. Gasification is also used industrially in the
production of electricity, ammonia and liquid fuels (oil) using Integrated Gasification Combined
Cycles (IGCC), with the possibility of producing methane and hydrogen for fuel cells. IGCC is
also a more efficient method of CO2 capture as compared to conventional technologies. IGCC
demonstration plants have been operating since the early 1970s and some of the plants constructed
in the 1990s are now entering commercial service.
115
Combined heat and power
In small business and building applications, where the wood source is sustainable, 250-1000 kWe
and new zero carbon biomass gasification plants have been installed in Europe that produce tar
free syngas from wood and burn it in reciprocating engines connected to a generator with heat
recovery. This type of plant is often referred to as a wood biomass CHP unit but is a plant with
seven different processes: biomass processing, fuel delivery, gasification, gas cleaning, waste
disposal, electricity generation and heat recovery.[18]
Transport fuel
Diesel engines can be operated on dual fuel mode using producer gas. Diesel substitution of over
80% at high loads and 70-80% under normal load variations can easily be achieved.[19] Spark
ignition engines and SOFC fuel cells can operate on 100% gasification gas.[20][21][22] Mechanical
energy from the engines may be used for e.g. driving water pumps for irrigation or for coupling
with an alternator for electrical power generation.
While small scale gasifiers have existed for well over 100 years, there have been few sources to
obtain a ready to use machine. Small scale devices are typically DIY projects. However, currently
in the United States, several companies offer gasifiers to operate small engines. In 2009
21stCenturyMotorworks claimed to have developed gasification technology in a prototype pickup
truck that could use any biomass materials for fuel,[23] the vehicle was displayed at multiple events
including the 2009 Boston Greenfest.
Renewable energy and fuels
Gasification plant Güssing, Austria (2006)
In principle, gasification can proceed from just about any organic material, including biomass and
plastic waste. The resulting syngas can be combusted. Alternatively, if the syngas is clean enough,
it may be used for power production in gas engines, gas turbines or even fuel cells, or converted
efficiently to dimethyl ether (DME) by methanol dehydration, methane via the Sabatier reaction,
or diesel-like synthetic fuel via the Fischer-Tropsch process. In many gasification processes most
of the inorganic components of the input material, such as metals and minerals, are retained in the
ash. In some gasification processes (slagging gasification) this ash has the form of a glassy solid
with low leaching properties, but the net power production in slagging gasification is low
(sometimes negative) and costs are higher.
116
Regardless of the final fuel form, gasification itself and subsequent processing neither directly
emits nor traps greenhouse gases such as carbon dioxide. Power consumption in the gasification
and syngas conversion processes may be significant though, and may indirectly cause CO2
emissions; in slagging and plasma gasification, the electricity consumption may even exceed any
power production from the syngas.
Combustion of syngas or derived fuels emits exactly the same amount of carbon dioxide as would
have been emitted from direct combustion of the initial fuel.[dubious – discuss] Biomass gasification
and combustion could play a significant role in a renewable energy economy, because biomass
production removes the same amount of CO2 from the atmosphere as is emitted from gasification
and combustion.[dubious – discuss] While other biofuel technologies such as biogas and biodiesel are
carbon neutral, gasification in principle may run on a wider variety of input materials and can be
used to produce a wider variety of output fuels.
There are at present a few industrial scale biomass gasification plants. Since 2008 in Svenljunga,
Sweden, a biomass gasification plant generates up to 14 MWth, supplying industries and citizens
of Svenljunga with process steam and district heating, respectively. The gasifier uses biomass
fuels such as CCA or creosote impregnated waste wood and other kinds of recycled wood to
produces syngas that is combusted on site.[24][25] In 2011 a similar gasifier, using the same kinds of
fuels, is being installed at Munkfors Energy's CHP plant. The CHP plant will generate 2 MWe
(electricity) and 8 MWth (district heating).[26][27]
Examples of demonstration projects include:


Those of the Renewable Energy Network Austria,[28] including a plant using dual fluidized
bed gasification that has supplied the town of Güssing with 2 MW of electricity, produced
utilising GE Jenbacher reciprocating gas engines[29][30] and 4 MW of heat,[31] generated
from wood chips, since 2003.
Chemrec's pilot plant in Piteå that has produced 3 MW of clean syngas since 2006,
generated from entrained flow gasification of black liquor.[11]
The US Air Force Transportable Plasma Waste to Energy System (TPWES) facility at Hurlburt
Field, Florida.[17]
Technology of Biomass Gasification
Biomass has been a major energy source, prior to the discovery of fossil fuels like coal and petroleum.
Even though its role is presently diminished in developed countries, it is still widely used in rural
communities of the developing countries for their energy needs in terms of cooking and limited industrial
use. Biomass, besides using in solid form, can be converted into gaseous form through gasification route.
1. Concept and Principle
Gasification is the process of converting solid fuels to gaseous fuel. It is not simply pyrolysis; pyrolysis is
only one of the steps in the conversion process. The other steps are combustion with air and reduction of
the product of combustion, (water vapour and carbon dioxide) into combustible gases, (carbon monoxide,
hydrogen, methane, some higher hydrocarbons) and inerts, (carbon dioxide and nitrogen). The process
leads to a gas with some find dust and condensable compounds termed tar, both of which must be
restricted to less than about 100 ppm each if the gas is to be used in internal combustion engines.
2. Uses of Producer Gas
The producer gas obtained by the process of gasification can have end use for thermal application or for
mechanical/electrical power generation. Like any other gaseous fuel, producer gas has the control for
117
power when compared to that of solid fuel, in this solid biomass. This also paves way for more efficient
and cleaner operation. The producer gas can be conveniently used in number of applications as mentioned
below.
2.1 Thermal
Thermal energy of the order of 5 MJ is released, by flaring 1 m3 of producer gas in the burner. Flame
temperatures as high as 1550 K can be obtained by optimal pre-mixing of air with gas. For applications
which require thermal energy, gasifiers can be a good option as a gas generator, and retrofitted with
existing devices. Few of the devices to which gasifier could be retrofitted are
a) Dryers: Drying is the most essential process in beverage and spices industry like tea and cardamom.
This calls for hot gases in the temperature range of 120 - 130 oC, in the existing designs. Typically the
heat energy required is equivalent to 1 kg of wood for 1 kg made tea. Gasifier is an ideal solution for the
above situation, where hot gas after combustion can be mixed with the right quantity of secondary air, so
as to lower its temperature to the desired level for use in the existing dryers.
b) Kilns: Baking of tiles, potteries require hot environment in the temperature range of 800 - 950 oC. This
is presently being done by combusting large quantities of wood in an inefficient manner. Gasifiers could be
suitable for such applications, which provides a better option of regulating the thermal environment. There
will also be an added advantage of smokeless and sootless operation, whereby enhancing the product
value.
c) Furnaces: In non-ferrous metallurgical and foundry industries high temperatures (~650 - 1000 oC) are
required for melting metals and alloys. This is commonly done by using expensive fuel oils or electrical
heaters. Gasifiers are well suited for such applications.
d) Boilers: Process industries which require steam or hot water, use either biomass or coal as fuel in the
boilers. Biomass is used inefficiently with higher pollutants like NOx and with little control with respect to
power regulation. Therefore these devices are appropriate to be retrofitted with gasifiers for efficient
energy usage.
Apart from these, energy requirements in poultry farms, cold storage devices (vapour compression
refrigerator), rubber industry and so on could be met using wood gasifiers..
2.2 Power Generation
Using wood gas, it possible to operate a diesel engine on dual fuel mode. Diesel substitution of the order
of 80 to 85% can be obtained at nominal loads. The mechanical energy thus derived can be used either
for energising a water pump set for irrigational purpose or for coupling with an alternator for electrical
power generation, either for local consumption or for grid synchronisation.
An appropriate site to realise the above application is an unelectrified village or hamlet. The benefits
derived from this could be many, right from irrigation of fields to the supply of drinking water, and
illuminating the village to supporting village industries. The other suitable sites could be saw mills and
coffee plantations, where waste wood (of course of specified size) could be used as a feed stock in
gasifiers.
3. Wood Gasifier
This system is meant for biomass having density in excess of 250 kg/m3. Theoretically, the ratio of air-tofuel required for the complete combustion of the wood, defined as stoichiometric combustion is 6:1 to
6.5:1, with the end products being CO 2 and H2O. Whereas, in gasification the combustion is carried at substoichiometric conditions with air-to-fuel ratio being 1.5:1 to 1.8:1. The product gas thus generated during
the gasification process is combustible. This process is made possible in a device called gasified, in a
limited supply of air. A gasifier system (Fig. 1) basically comprises of a reactor where the gas is generated,
and is followed by a cooling and cleaning train which cools and cleans the gas. The clean combustible gas
118
is available for power generation in diesel-gen-set. Whereas, for thermal use the gas from the reactor can
be directly fed to the combustor using an ejector.
4. Gasifier Specification
4.4 HIGH DENSITY ENERGY PLANTATIONS (HDEP).
An Assessment of High Density Energy Plantations (HDEP) in Gujarat on Silvicultural,
Ecological, Management and Economic Aspects
Practice of planting forest tree species, particularly eucalypts, more density, which is termed as "High
Density Energy Plantations (HDEP)", is based on the assumption that the factors defining maximum
returns/density of planting are the availability of soil nutrients, sunlight and water. Under tropical
conditions wherein sunlight is ample, with adequate water and soil nutrients, through application of
irrigation and ferlilizers, 5 to 6 times more yield per unit area is expected. Density of planting, however, is
governed by number of other factors viz. availability and economics of inputs like irrigation, fertilisers,
growth hormones, insecticides, managerial skills, industrial base for utilisation of outputs, feasibility of
diverting land and ground water resources which are immensely suitable for agriculture to forestry tree
119
crops etc. Projected Cost/benefits apparently show very attractive net returns and thus practice is gaining
popularity. These projections do not, however stand close scrutiny and thus blind following of the
practice is not advocated. Short and long rang impacts of intensive Euaclyptus tree crop management
under semi-arid conditions are highlighted. A need for evolving appropriate technology packages to
ensure optimum sustained yield under different agro-climatic edaphic conditions and providing basic
nutrient requirements is indicated. In view of its long range impacts on the ecology, there is need for
moderation in providing surh inputs. Approach of dense planting with high inputs is a step in right
direction however, in view of its economic and policy implications the whole issue deed be carefully
examined.
4.5 LAND AND BIOMASS AVAILABILITY FOR SUSTAINABLE BIO ENERGY.
Biomass is a renewable resource, but two specific features distinguish it from all other
renewable energy sources:
The conversion efficiency of solar energy into chemical energy in plants is only 13% which implies significantly more land needed to indirectly harvest solar energy
through terrestrial biomass cultivation than through more concentrated hydro,
direct solar or wind energy systems11.

Biomass is the “stuff of life” on this planet so that changes in biomass production,
e.g. replacing natural vegetation with cultivated plant varieties, collecting forest
residues, or improving crop yields, could have positive or negative impacts on
ecosystem services, carbon balances, and human livelihoods.

Thus, land is a fundamental issue closely related to biomass in general, and to
bioenergy in particular. Therefore, the sustainability of bioenergy depends on the
productivity of the land use12.
As bioenergy can also be derived from biogenic residues and wastes stemming from
various flows of biomass which has previously being grown, harvested and
processed for non-energy purposes, the efficiency of converting such “secondary”
biomass resources into useful energy products is another aspect of sustainable
resource use needed to be addressed.
Indicator: Land Use Efficiency
The productivity of converting cultivated bioenergy feedstocks into useful energy
products such as gaseous, liquid or solid bioenergy carriers, expressed in terms of
available bioenergy carriers per hectare of cultivated area, should be set to a
minimum net energy yield.
As both cultivation and conversion systems evolve over time, these minimum
requirements should be set to different levels for 2020 and 2030 to factor in the
learning curve for yields and conversion efficiencies.
11 See Table 1 in the Annex for data on life-cycle land use figures for non-renewable and renewable electricity
compared to biomass-derived electricity: The overall life-cycle land use intensity of bioelectricity systems (using
2
maize or short-rotation coppices as feedstock) is in the 2030 time horizon around 100-150 m /GJel, while direct
2
solar systems need 2 (CSP in Spain) to 3 m /GJel (PV in Germany), and onshore wind parks require a
120
2
maximum of 0.3 m /GJel. Fossil fuel and nuclear-based powerplants in 2030 will need again less land (0.02-0.1
2
m /GJel). Thus, the land use intensity of bioelectricity from biomass cultivation is approx. 50 times higher than
direct solar, and 300 times higher than from onshore wind.
12 Possible effects of land use changes associated with the incremental production of bioenergy are discussed in
Criterion 3 (see Section 0) with regard to GHG emissions.
121
Furthermore, crop yields depend on cultivation system, input levels, bioclimatic
conditions, and overall land suitability. Thus, a further differentiation is needed to
account for land productivity categories.
In the Annex, results of respective calculations are given for various
“settings” to
produce liquid biofuels, and solid and gaseous bioenergy
carriers13.
From this data, the following minimum net energy yield requirements for
bioenergy carriers were derived:
Setting
2020
2030
unit
smallholder, marginal/degraded land
>25
>35
GJbio/ha
plantation, marginal/degraded land
>50
>75
GJbio/ha
>100
>150
GJbio/ha
plantation, arable land*
Source: compilation by Oeko-Institut; * = mainly for intercropping, agro-forestry
systems, etc.
In calculating the net bioenergy yield (or bioenergy productivity), by- and coproducts along the bioenergy life cycles need to be taken into account14.
Indicator:
Secondary
Resource Use
Efficiency
For bioenergy carriers stemming from the conversion of secondary biomass
resources such as residues and wastes, a minimum efficiency, expressed in
terms of the heating value of the bioenergy output divided by the heating value
of the secondary resource input, should be set to increase the resource-efficient
use of those resources.
Taken into account the results of model calculations15, the minimum conversion
efficiencies for biofuels should be set to 55 % by 2020, and 60% by 2030 for
biodiesel, and 50 % by 2020 and 55 % by 2030 for ethanol, and 65 % for
biomethane (2020 and
2030), again taking into account by- and co-products along the product life
cycles.
For conversion to solid bioenergy carriers (chips, pellets etc.), no minimum
requirement is necessary, as their conversion efficiency is typically > 85%.
Biomass Futures Criteria and Indicators for Sustainable Bioenergy
Table 1:
122
Resource
Criterion
Indicator
Metrics
Sustainable
Use
Land Use Efficiency*
GJbio/ha
Secondary Resource Use Efficiency*
%
Conservation of land with significant
biodiversity values
no-go areas
Land management without negative practices
effects on biodiversity
sustainable
applied
Biodiversity
Climate Protection Life cycle GHG emissions incl. direct
land use changes
75%
Inclusion of GHG effects from indirect
land use changes10
3.5 t CO2/ha/year
Soil Quality
Erosion zero erosion cultivation
systems and practices
Soil Organic Carbon
Soil Nutrient Balance
Water Use and Quality
maintain SOC
identifying
Water Availability and Use Efficiency
Water Quality
maps soil
“go” areas11
TARWR12
+
BOD and P N,
pesticide loadings
SO2 equivalents13
g/GJbioenergy
Particulate Emissions PM10
g/GJbioenergy
Food Security Price and supply of national food
basket
€/t, t/a
Airborne Emissions
Social Use of Land
changes in land tenure and access
evidence14
Healthy Livelihoods and
Labor Conditions
Adherence to ILO Principles
evidence
Source: compiled from OEKO (2012); * = considering by- and co-products of bioenergy life cycles
123
CHAPTER NO.05
BIOFUELS
5.1 BIO-FUELS INTRODUCTION,
A biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include
fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases.
Biofuels are gaining increased public and scientific attention, driven by factors such as oil price hikes
and the need for increased energy security. However, according to the European Environment
Agency, biofuels do not address global warming concerns.
Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or
starch crops such as corn or sugarcane. Cellulosic biomass, derived from non-food sources, such as
trees and grasses, is also being developed as a feedstock for ethanol production. Ethanol can be
used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase
octane and improve vehicle emissions. Bioethanol is widely used in the USA and in Brazil. Current
plant design does not provide for converting the lignin portion of plant raw materials to fuel
components by fermentation.
Biodiesel is made from vegetable oils and animal fats. Biodiesel can be used as a fuel for vehicles in
its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon
monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats
using transesterification and is the most common biofuel in Europe.
In 2010, worldwide biofuel production reached 105 billion liters (28 billion gallons US), up 17% from
2009, and biofuels provided 2.7% of the world's fuels for road transport, a contribution largely made
up of ethanol and biodiesel. Global ethanol fuel production reached 86 billion liters (23 billion
gallons US) in 2010, with the United States and Brazil as the world's top producers, accounting
together for 90% of global production. The world's largest biodiesel producer is the European Union,
accounting for 53% of all biodiesel production in 2010. As of 2011, mandates for blending biofuels
exist in 31 countries at the national level and in 29 states or provinces. According to the
International Energy Agency, biofuels have the potential to meet more than a quarter of world
demand for transportation fuels by 2050.
Liquid fuels for transportation
Most transportation fuels are liquids, because vehicles usually require high energy density, as occurs
in liquids and solids. High power density can be provided most inexpensively by an internal
combustion engine; these engines require clean-burning fuels, to keep the engine clean and
minimize air pollution.
The fuels that are easiest to burn cleanly are typically liquids and gases. Thus, liquids (and gases that
can be stored in liquid form) meet the requirements of being both portable and clean-burning. Also,
liquids and gases can be pumped, which means handling is easily mechanized, and thus less
laborious.
First-generation biofuels
'First-generation' or conventional biofuels are made from sugar, starch, or vegetable oil.
124
Bioalcohols
Biologically produced alcohols, most commonly
ethanol, and less commonly propanol and butanol, are
produced by the action of microorganisms and enzymes
through the fermentation of sugars or starches
(easiest), or cellulose (which is more difficult).
Biobutanol (also called biogasoline) is often claimed to
provide a direct replacement for gasoline, because it
can be used directly in a gasoline engine (in a similar
way to biodiesel in diesel engines).
Neat ethanol on the left (A), gasoline on
Ethanol fuel is the most common biofuel worldwide,
the right (G) at a filling station in Brazil
particularly in Brazil. Alcohol fuels are produced by
fermentation of sugars derived from wheat, corn, sugar beets, sugar cane, molasses and any sugar
or starch from which alcoholic beverages can be made (such as potato and fruit waste, etc.). The
ethanol production methods used are enzyme digestion (to release sugars from stored starches),
fermentation of the sugars, distillation and drying. The distillation process requires significant energy
input for heat (often unsustainable natural gas fossil fuel, but cellulosic biomass such as bagasse, the
waste left after sugar cane is pressed to extract its juice, can also be used more sustainably).
Ethanol can be used in petrol engines as a replacement for gasoline; it can be mixed with gasoline to
any percentage. Most existing car petrol engines can run on blends of up to 15% bioethanol with
petroleum/gasoline. Ethanol has a smaller energy density than that of gasoline; this means it takes
more fuel (volume and mass) to produce the same amount of work. An advantage of ethanol
(CH3CH2OH) is that it has a higher octane rating than ethanol-free gasoline available at roadside gas
stations, which allows an increase of an engine's compression ratio for increased thermal efficiency.
In high-altitude (thin air) locations, some states mandate a mix of gasoline and ethanol as a winter
oxidizer to reduce atmospheric pollution emissions.
Ethanol is also used to fuel bioethanol fireplaces. As they do not require a chimney and are
"flueless", bioethanol fires are extremely useful for newly built homes and apartments without a
flue. The downside to these fireplaces is their heat output is slightly less than electric heat or gas
fires.
In the current corn-to-ethanol production model in the United States, considering the total energy
consumed by farm equipment, cultivation, planting, fertilizers, pesticides, herbicides, and fungicides
made from petroleum, irrigation systems, harvesting, transport of feedstock to processing plants,
fermentation, distillation, drying, transport to fuel terminals and retail pumps, and lower ethanol
fuel energy content, the net energy content value added and delivered to consumers is very small.
And, the net benefit (all things considered) does little to reduce imported oil and fossil fuels required
to produce the ethanol.
Although corn-to-ethanol and other food stocks have implications both in terms of world food prices
and limited, yet positive, energy yield (in terms of energy delivered to customer/fossil fuels used),
the technology has led to the development of cellulosic ethanol. According to a joint research
agenda conducted through the US Department of Energy, the fossil energy ratios (FER) for cellulosic
ethanol, corn ethanol, and gasoline are 10.3, 1.36, and 0.81, respectively.
Even dry ethanol has roughly one-third lower energy content per unit of volume compared to
gasoline, so larger (therefore heavier) fuel tanks are required to travel the same distance, or more
fuel stops are required. With large current unsustainable, unscalable subsidies, ethanol fuel still
costs much more per distance traveled than current high gasoline prices in the United States.
Methanol is currently produced from natural gas, a nonrenewable fossil fuel. It can also be produced
from biomass as biomethanol. The methanol economy is an alternative to the hydrogen economy,
compared to today's hydrogen production from natural gas.
125
Butanol (C4H9OH) is formed by ABE fermentation (acetone, butanol, ethanol) and experimental
modifications of the process show potentially high net energy gains with butanol as the only liquid
product. Butanol will produce more energy and allegedly can be burned "straight" in existing
gasoline engines (without modification to the engine or car), and is less corrosive and less watersoluble than ethanol, and could be distributed via existing infrastructures. DuPont and BP are
working together to help develop butanol. E. coli strains have also been successfully engineered to
produce butanol by hijacking their amino acid metabolism.
Biodiesel
Biodiesel is the most common biofuel in Europe. It is
produced from oils or fats using transesterification and is a
liquid similar in composition to fossil/mineral diesel.
Chemically, it consists mostly of fatty acid methyl (or ethyl)
esters (FAMEs). Feedstocks for biodiesel include animal fats,
vegetable oils, soy, rapeseed, jatropha, mahua, mustard,
flax, sunflower, palm oil, hemp, field pennycress, Pongamia
pinnata and algae. Pure biodiesel (B100) is the lowestemission diesel fuel. Although liquefied petroleum gas and
hydrogen have cleaner combustion, they are used to fuel
much less efficient petrol engines and are not as widely
available.
Biodiesel can be used in any diesel engine when mixed with
mineral diesel. In some countries, manufacturers cover their
diesel engines under warranty for B100 use, although
Volkswagen of Germany, for example, asks drivers to check
by telephone with the VW environmental services
department before switching to B100. B100 may become
more viscous at lower temperatures, depending on the
feedstock used. In most cases, biodiesel is compatible with
In some countries, biodiesel is less
diesel engines from 1994 onwards, which use 'Viton' (by
expensive than conventional diesel.
DuPont) synthetic rubber in their mechanical fuel injection
systems.
Electronically controlled 'common rail' and 'unit injector' type systems from the late 1990s onwards
may only use biodiesel blended with conventional diesel fuel. These engines have finely metered
and atomized multiple-stage injection systems that are very sensitive to the viscosity of the fuel.
Many current-generation diesel engines are made so that they can run on B100 without altering the
engine itself, although this depends on the fuel rail design. Since biodiesel is an effective solvent and
cleans residues deposited by mineral diesel, engine filters may need to be replaced more often, as
the biofuel dissolves old deposits in the fuel tank and pipes. It also effectively cleans the engine
combustion chamber of carbon deposits, helping to maintain efficiency. In many European
countries, a 5% biodiesel blend is widely used and is available at thousands of gas stations. Biodiesel
is also an oxygenated fuel, meaning it contains a reduced amount of carbon and higher hydrogen
and oxygen content than fossil diesel. This improves the combustion of biodiesel and reduces the
particulate emissions from unburnt carbon.
Biodiesel is also safe to handle and transport because it is as biodegradable as sugar, one-tenth as
toxic as table salt, and has a high flash point of about 300°F (148°C) compared to petroleum diesel
fuel, which has a flash point of 125°F (52°C).
In the USA, more than 80% of commercial trucks and city buses run on diesel. The emerging US
biodiesel market is estimated to have grown 200% from 2004 to 2005. "By the end of 2006 biodiesel
production was estimated to increase fourfold [from 2004] to more than" 1 billion US gallons
(3,800,000 m3).
126
Green diesel
Green diesel is produced through hydrocracking biological oil feedstocks, such as vegetable oils and
animal fats. Hydrocracking is a refinery method that uses elevated temperatures and pressure in the
presence of a catalyst to break down larger molecules, such as those found in vegetable oils, into
shorter hydrocarbon chains used in diesel engines. It may also be called renewable diesel,
hydrotreated vegetable oil or hydrogen-derived renewable diesel. Green diesel has the same
chemical properties as petroleum-based diesel. It does not require new engines, pipelines or
infrastructure to distribute and use, but has not been produced at a cost that is competitive with
petroleum. Gasoline versions are also being developed. Green diesel is being developed in Louisiana
and Singapore by ConocoPhillips, Neste Oil, Valero, Dynamic Fuels, and Honeywell UOP.
Vegetable oil
Straight unmodified edible vegetable oil is generally not used as
fuel, but lower-quality oil can and has been used for this purpose.
Used vegetable oil is increasingly being processed into biodiesel, or
(more rarely) cleaned of water and particulates and used as a fuel.
Also here, as with 100% biodiesel (B100), to ensure the fuel
injectors atomize the vegetable oil in the correct pattern for
efficient combustion, vegetable oil fuel must be heated to reduce
its viscosity to that of diesel, either by electric coils or heat
exchangers. This is easier in warm or temperate climates. Big
corporations like MAN B&W Diesel, Wärtsilä, and Deutz AG, as well
as a number of smaller companies, such as Elsbett, offer engines
that are compatible with straight vegetable oil, without the need
for after-market modifications.
Vegetable oil can also be used in many older diesel engines that do
not use common rail or unit injection electronic diesel injection
systems. Due to the design of the combustion chambers in indirect
injection engines, these are the best engines for use with vegetable
oil. This system allows the relatively larger oil molecules more time
to burn. Some older engines, especially Mercedes, are driven
experimentally by enthusiasts without any conversion, a handful of
drivers have experienced limited success with earlier pre-"Pumpe
Duse" VW TDI engines and other similar engines with direct
injection. Several companies, such as Elsbett or Wolf, have
developed professional conversion kits and successfully installed
Filtered waste vegetable oil
hundreds of them over the last decades.
Oils and fats can be hydrogenated to give a diesel substitute. The resulting product is a straight-chain
hydrocarbon with a high cetane number, low in aromatics and sulfur and does not contain oxygen.
Hydrogenated oils can be blended with diesel in all proportions. They have several advantages over
biodiesel, including good performance at low temperatures, no storage stability problems and no
susceptibility to microbial attack.
Bioethers
Bioethers (also referred to as fuel ethers or oxygenated fuels) are cost-effective compounds that act
as octane rating enhancers. They also enhance engine performance, whilst significantly reducing
engine wear and toxic exhaust emissions. Greatly reducing the amount of ground-level ozone, they
contribute to air quality.
127
Biogas
Biogas is methane produced by the process of anaerobic digestion
of organic material by anaerobes. It can be produced either from
biodegradable waste materials or by the use of energy crops fed
into anaerobic digesters to supplement gas yields. The solid
byproduct, digestate, can be used as a biofuel or a fertilizer.
 Biogas can be recovered from mechanical biological
treatment waste processing systems.
Note:Landfill gas, a less clean form of biogas, is produced
in landfills through naturally occurring anaerobic digestion.
If it escapes into the atmosphere, it is a potential
greenhouse gas.
 Farmers can produce biogas from manure from their cattle
Pipes carrying biogas
by using anaerobic digesters.
Syngas
Syngas, a mixture of carbon monoxide, hydrogen and other hydrocarbons, is produced by partial
combustion of biomass, that is, combustion with an amount of oxygen that is not sufficient to
convert the biomass completely to carbon dioxide and water. Before partial combustion, the
biomass is dried, and sometimes pyrolysed. The resulting gas mixture, syngas, is more efficient than
direct combustion of the original biofuel; more of the energy contained in the fuel is extracted.
 Syngas may be burned directly in internal combustion engines, turbines or high-temperature
fuel cells. The wood gas generator, a wood-fueled gasification reactor, can be connected to
an internal combustion engine.
 Syngas can be used to produce methanol, DME and hydrogen, or converted via the FischerTropsch process to produce a diesel substitute, or a mixture of alcohols that can be blended
into gasoline. Gasification normally relies on temperatures greater than 700°C.
 Lower-temperature gasification is desirable when co-producing biochar, but results in syngas
polluted with tar.
Solid biofuels
Examples include wood, sawdust, grass trimmings, domestic refuse, charcoal, agricultural waste,
nonfood energy crops, and dried manure.
When raw biomass is already in a suitable form (such as firewood), it can burn directly in a stove or
furnace to provide heat or raise steam. When raw biomass is in an inconvenient form (such as
sawdust, wood chips, grass, urban waste wood, agricultural residues), the typical process is to
densify the biomass. This process includes grinding the raw biomass to an appropriate particulate
size (known as hogfuel), which, depending on the densification type, can be from 1 to 3 cm (0 to 1
in), which is then concentrated into a fuel product. The current processes produce wood pellets,
cubes, or pucks. The pellet process is most common in Europe, and is typically a pure wood product.
The other types of densification are larger in size compared to a pellet, and are compatible with a
broad range of input feedstocks. The resulting densified fuel is easier to transport and feed into
thermal generation systems, such as boilers.
One of the advantages of solid biomass fuel is that it is often a byproduct, residue or waste-product
of other processes, such as farming, animal husbandry and forestry. In theory, this means fuel and
food production do not compete for resources, although this is not always the case.
A problem with the combustion of raw biomass is that it emits considerable amounts of pollutants,
such as particulates and polycyclic aromatic hydrocarbons. Even modern pellet boilers generate
much more pollutants than oil or natural gas boilers. Pellets made from agricultural residues are
usually worse than wood pellets, producing much larger emissions of dioxins and chlorophenols.
Notwithstanding the above noted study, numerous studies have shown biomass fuels have
significantly less impact on the environment than fossil based fuels. Of note is the US Department of
128
Energy Laboratory, operated by Midwest Research Institute Biomass Power and Conventional Fossil
Systems with and without CO2 Sequestration – Comparing the Energy Balance, Greenhouse Gas
Emissions and Economics Study. Power generation emits significant amounts of greenhouse gases
(GHGs), mainly carbon dioxide (CO2). Sequestering CO2 from the power plant flue gas can
significantly reduce the GHGs from the power plant itself, but this is not the total picture. CO 2
capture and sequestration consumes additional energy, thus lowering the plant's fuel-to-electricity
efficiency. To compensate for this, more fossil fuel must be procured and consumed to make up for
lost capacity.
Taking this into consideration, the global warming potential (GWP), which is a combination of CO 2,
methane (CH4), and nitrous oxide (N2O) emissions, and energy balance of the system need to be
examined using a life cycle assessment. This takes into account the upstream processes which
remain constant after CO2 sequestration, as well as the steps required for additional power
generation. Firing biomass instead of coal led to a 148% reduction in GWP.
A derivative of solid biofuel is biochar, which is produced by biomass pyrolysis. Biochar made from
agricultural waste can substitute for wood charcoal. As wood stock becomes scarce, this alternative
is gaining ground. In eastern Democratic Republic of Congo, for example, biomass briquettes are
being marketed as an alternative to charcoal to protect Virunga National Park from deforestation
associated with charcoal production.
What Is Biodiesel?
Biodiesel is an alternative fuel similar to conventional or ‘fossil’ diesel. Biodiesel can be produced
from straight vegetable oil, animal oil/fats, tallow and waste cooking oil. The process used to convert
these oils to Biodiesel is called transesterification. This process is described in more detail below.
The largest possible source of suitable oil comes from oil crops such as rapeseed, palm or soybean.
In the UK rapeseed represents the greatest potential for biodiesel production. Most biodiesel
produced at present is produced from waste vegetable oil sourced from restaurants, chip shops,
industrial food producers such as Birdseye etc. Though oil straight from the agricultural industry
represents the greatest potential source it is not being produced commercially simply because the
raw oil is too expensive. After the cost of converting it to biodiesel has been added on it is simply too
expensive to compete with fossil diesel. Waste vegetable oil can often be sourced for free or sourced
already treated for a small price. (The waste oil must be treated before conversion to biodiesel to
remove impurities). The result is Biodiesel produced from waste vegetable oil can compete with
fossil diesel. More about the cost of biodiesel and how factors such as duty play an important role
can be found here.
What are the benefits of Biodiesel?
Biodiesel has many environmentally beneficial properties. The main benefit of biodiesel is that it can
be described as ‘carbon neutral’. This means that the fuel produces no net output of carbon in the
form of carbon dioxide (CO2). This effect occurs because when the oil crop grows it absorbs the
same amount of CO2 as is released when the fuel is combusted. In fact this is not completely
accurate as CO2 is released during the production of the fertilizer required to fertilize the fields in
which the oil crops are grown. Fertilizer production is not the only source of pollution associated
with the production of biodiesel, other sources include the esterification process, the solvent
extraction of the oil, refining, drying and transporting. All these processes require an energy input
either in the form of electricity or from a fuel, both of which will generally result in the release of
green house gases. To properly assess the impact of all these sources requires use of a technique
called life cycle analysis. Our section on LCA looks closer at this analysis. Biodiesel is rapidly
biodegradable and completely non-toxic, meaning spillages represent far less of a risk than fossil
diesel spillages. Biodiesel has a higher flash point than fossil diesel and so is safer in the event of a
crash.
Biodiesel Production
129
As mentioned above biodiesel can be produced from straight vegetable oil, animal oil/fats, tallow
and waste oils. There are three basic routes to biodiesel production from oils and fats:
 Base catalyzed transesterification of the oil.
 Direct acid catalyzed transesterification of the oil.
 Conversion of the oil to its fatty acids and then to biodiesel.
Almost all biodiesel is produced using base catalyzed transesterification as it is the most economical
process requiring only low temperatures and pressures and producing a 98% conversion yield. For
this reason only this process will be described in this report.
The Transesterification process is the reaction of a triglyceride (fat/oil) with an alcohol to form esters
and glycerol. A triglyceride has a glycerine molecule as its base with three long chain fatty acids
attached. The characteristics of the fat are determined by the nature of the fatty acids attached to
the glycerine. The nature of the fatty acids can in turn affect the characteristics of the biodiesel.
During the esterification process, the triglyceride is reacted with alcohol in the presence of a
catalyst, usually a strong alkaline like sodium hydroxide. The alcohol reacts with the fatty acids to
form the mono-alkyl ester, or biodiesel and crude glycerol. In most production methanol or ethanol
is the alcohol used (methanol produces methyl esters, ethanol produces ethyl esters) and is base
catalysed by either potassium or sodium hydroxide. Potassium hydroxide has been found to be more
suitable for the ethyl ester biodiesel production, either base can be used for the methyl ester. A
common product of the transesterification process is Rape Methyl Ester (RME) produced from raw
rapeseed oil reacted with methanol.
The figure below shows the chemical process for methyl ester biodiesel. The reaction between the
fat or oil and the alcohol is a reversible reaction and so the alcohol must be added in excess to drive
the reaction towards the right and ensure complete conversion.
The products of the reaction are the biodiesel itself and glycerol.
A successful transesterification reaction is signified by the separation of the ester and glycerol layers
after the reaction time. The heavier, co-product, glycerol settles out and may be sold as it is or it may
be purified for use in other industries, e.g. the pharmaceutical, cosmetics etc.
Straight vegetable oil (SVO) can be used directly as a fossil diesel substitute however using this fuel
can lead to some fairly serious engine problems. Due to its relatively high viscosity SVO leads to poor
atomisation of the fuel, incomplete combustion, coking of the fuel injectors, ring carbonisation, and
accumulation of fuel in the lubricating oil. The best method for solving these problems is the
transesterification of the oil.
The engine combustion benefits of the transesterification of the oil are:
 Lowered viscosity
 Complete removal of the glycerides
 Lowered boiling point
 Lowered flash point
 Lowered pour point
Production Process
130
An example of a simple production flow chart is proved below with a brief explanation of each step.
Mixing of alcohol and catalyst
The catalyst is typically sodium hydroxide (caustic soda) or potassium hydroxide (potash). It is
dissolved in the alcohol using a standard agitator or mixer. Reaction. The alcohol/catalyst mix is then
charged into a closed reaction vessel and the oil or fat is added. The system from here on is totally
closed to the atmosphere to prevent the loss of alcohol. The reaction mix is kept just above the
boiling point of the alcohol (around 160 °F) to speed up the reaction and the reaction takes place.
Recommended reaction time varies from 1 to 8 hours, and some systems recommend the reaction
take place at room temperature. Excess alcohol is normally used to ensure total conversion of the fat
or oil to its esters. Care must be taken to monitor the amount of water and free fatty acids in the
incoming oil or fat. If the free fatty acid level or water level is too high it may cause problems with
soap formation and the separation of the glycerin by-product downstream.
Separation
Once the reaction is complete, two major products exist: glycerin and biodiesel. Each has a
substantial amount of the excess methanol that was used in the reaction. The reacted mixture is
sometimes neutralized at this step if needed. The glycerin phase is much more dense than biodiesel
phase and the two can be gravity separated with glycerin simply drawn off the bottom of the settling
vessel. In some cases, a centrifuge is used to separate the two materials faster.
Alcohol Removal
Once the glycerin and biodiesel phases have been separated, the excess alcohol in each phase is
removed with a flash evaporation process or by distillation. In others systems, the alcohol is
removed and the mixture neutralized before the glycerin and esters have been separated. In either
case, the alcohol is recovered using distillation equipment and is re-used. Care must be taken to
ensure no water accumulates in the recovered alcohol stream.
Glycerin Neutralization
The glycerin by-product contains unused catalyst and soaps that are neutralized with an acid and
sent to storage as crude glycerin. In some cases the salt formed during this phase is recovered for
use as fertilizer. In most cases the salt is left in the glycerin. Water and alcohol are removed to
produce 80-88% pure glycerin that is ready to be sold as crude glycerin. In more sophisticated
operations, the glycerin is distilled to 99% or higher purity and sold into the cosmetic and
pharmaceutical markets.
Methyl Ester Wash
Once separated from the glycerin, the biodiesel is sometimes purified by washing gently with warm
water to remove residual catalyst or soaps, dried, and sent to storage. In some processes this step is
131
unnecessary. This is normally the end of the production process resulting in a clear amber-yellow
liquid with a viscosity similar to petrodiesel. In some systems the biodiesel is distilled in an additional
step to remove small amounts of color bodies to produce a colorless biodiesel.
Product Quality
Prior to use as a commercial fuel, the finished biodiesel must be analyzed using sophisticated
analytical equipment to ensure it meets any required specifications. The most important aspects of
biodiesel production to ensure trouble free operation in diesel engines are:
 Complete Reaction
 Removal of Glycerin
 Removal of Catalyst
 Removal of Alcohol
 Absence of Free Fatty Acids
Rural fuelwood: Significant
relationships
Amulya Kumar N. Reddy
1. Introduction
Solar energy collected by plants and stored, in the form of biomass, particularly as
wood, is a major source of energy in developing countries, as it war in the preindustrial past of developed countries. But wood, is a renewable sources only when
the rate at which it is depleted is less than the rate at which it is regenerated. This is
certainly not the case in most developing countries where wood is a rapidly dwindling
resources due to the multiplicity of its uses and the escalation in the magnitude of its
consumption resulting from the burgeoning populations.
Attention has therefore been focussed on programmes for the regeneration of wood
resources, but very few of those have been successful. The reasons for the failure of
these programmes are many, but one important reason is the fact that wood is
involved in a number of relationships and there is insufficient appreciation of either
the nature or extent of these relationships.
The aim of this paper, therefore, is to develop a scheme which permits the display and
description of (a) the relationships involving the use of wood and (b) the potentialities
of wood as a resources in the economy.
2. The ecosystem approach
One of the most useful ways in which the inter-relationships involving wood can be
portrayed is through the ecosystem approach in which the term ecosystem is used to
designate any area of nature that includes living organism and non-living substances
interacting to produce an exchange of materials between the living and non-living
parts.
The advantage of the ecosystem approach in that it clearly reveals the entities
involved in the functioning of the ecosystem, their interactions, the flows of materials,
nutrients and energy, and above all, the environmental constraints on economic
activities as well au the impact of these activities upon, the environment. If the
depletion and regeneration of wood resources is being considered in a particular
geographical region, then that region becomes the "area of nature" defining the spatial
aspect of the ecosystem. Further, if the society of human beings in that area is
differentiated from other living organisms and assigned special attention, then a
human ecosystem has been defined.









132
There are several types of human ecosystems, but it is the agricultural ecosystem in
developing countries which is particularly relevant to this paper because it involves
wood resources to a significant extent. In additional, there are the two types of forest
ecosystems: one type which involves people living in forests and the other type in
which forests are linked to wood-based industry, but these will not be discussed
further because they are lops relevant to fuelwood projects than agricultural
ecosystems.
3. Agricultural ecosystems
The essential characteristic of an agricultural ecosystem is that it includes a human
settlement engaged in the production of food. One widely prevalent version of such a
settlement is a village. Unfortunately, there have been few investigations of village
agricultural ecosystems, but a recent study of Ungra in South India (Ravindranath et
al 1981, Reddy 1981) provides a useful basis for the present paper which aims at the
development of a methodology rather than a universal analysis.
The study provided quantitative information inter alia on the pattern of land-use
(Table 2-1) and cropping (Table 2-2), the above-ground plant biomass productivities
(Table 2-3), the disaggregation of the above-ground plant biomass into components
such as grain, straw, etc. (Table 2-4), the model of utilization of these components
(Figure 2-1), the fodder consumption by live-stock (Table 2-5) and the sources of fuel
(Table 2-6).1 From this information, it is possible (Ravindranath et al 1981) to
represent the operation of the Ungra village agricultural ecosystem by means of the
usual type of diagram with the symbols used, by Odum (Odum, 1971).
1
The tables and Figure 2-1 appear at the end of the paper.
Such an ecosystem diagram helps to reveal clearly the complex inter-relationships
between human beings, livestock, land, energy and water, and water, and between
food, fuel, fodder and fertilizer. But the inclusion of the Ungra ecosystem diagram in
the present paper would divert attention to a great deal of information directly
relevant to a discussion of wood resources. In addition, it would the detailed
description of a specific village with all its peculiar features, for instance the absence
of fuel exports. Nevertheless, the understanding derived from the Ungra ecosystem is
useful in evolving a simplified generalized diagram which can then be used to discuss
the role of wood in typical village agricultural ecosystems. The procedure will consist
of considering all the ecosystem components and activities land, water, nutrients,
inanimate and animal, energy, fodder, cooking, trees, building, etc.) one by one and
discussing the interactions between fuelwood and each of these components or
activities. This understanding of pair-wise interactions will, then be integrated into an
ecosystem diagram which displays all the complex and varied inter-relationships
involving fuelwood. What follows therefore is the step-by-step development of suck a
diagram and a description of the ecosystem relationships involving wood.
It must be stressed, however, that the ensuing analysis is derived from an
understanding of the Ungra ecosystem. Hence, it refers mainly to India, but it can be
applied after suitable modifications to other parts of the world.
4. Fuelwood projects and development
The goal of fuelwood projects is to advance development, which is viewed as a
process of satisfying the basic needs of human beings, particularly the needs of the
neediest, in a self-reliant, ecologically sound manner. Hence it is vital to consider
wood resources in their relationship to basic needs. Taking the basic needs as food,
clothing and shelter, the following points are obvious.









133
(i) Land must be allocated for food and other crops.
(ii) In addition to land, the growing of crops requires water, nutrients and energy.
(iii) Traditional agriculture is based on human energy, but in India, and much of Asia,
the energy for many critical agricultural operations such as ploughing comes from
draught animals.
(iv) Apart from the grain from crops, human beings also consume milk and meat;
which means that livestock-rearing is an integral part of meeting food requirements.
(v) Draught animals and other livestock require fodder, and this fodder comes from
crop residues and/or grazing in pasture land; hence, pasture lands and fodder
production are crucial.
(vi) Most food is cooked, and the energy required for cooking is obtained primarily
from fuelwood, but agricultural residues and cattle dung are also used.
(vii) Fuelwood comes predominantly from trees which grow in special woodlots
and/or along the sides of fields or roads. Forests may also become a fuelwood sources
if they are close enough to the villages.
(viii) The wood from such trees is used not only as fuel for cooking, but also as fuel in
many industries and as a sources of lumber.
(ix) One of the important categories of industries which depends upon fuelwood is
that involving the production of bricks and tiles for building to satisfy the basic need
for shelter. Another fuelwood-using industry is pottery which provides utensils for
cooking.
(x) Fuelwood, lumber and fuelwood-based products such as bricks are often exported
to or imported from other agricultural ecosystems and towns and cities.
(xi) Apart from providing fuel, trees fulfil many other functions - they give shade,
shelter, edible nuts, oilseeds, medicines, and provide for many other needs.
There are a number of relationships, synergisms and conflicts involved in the situation
which merit elaboration because they have a major influence on the outcome of
fuelwood projects.
Figure 2-2: Land and fuelwood 












134
Figure 2-3: Water and fuelwood


135
5. Land and fuelwood
In an agricultural ecosystem, there are several demands upon the available land it has
to be used for housing and other parts of the human settlement, some in submerged by
natural and artificial water bodies, but the bulk of the land is devoted to crops and
pastures (Figure 2-2).
The traditional land-utilization practice (which embodies a great deal of wisdom) is to
have woodlots only on non-arable land. Since this practice does not lead to any
reduction in the land set apart for crops and pastures, it prevents the development of
any conflict between food and fodder, on the one hand and fuel on the other. In case
non-arable land is unavailable, the growth of trees has to be restricted to the borders
of fields, water-bodies or roads. If however, the fuelwood output of these "border
trees" is inadequate to meet the requirements of the ecosystem, then attempts to
allocate land for separate woodlots will result in a reduction of the area available for
cropland and pastureland, and therefore in a conflict between the need for fuelwood
and the requirement of food and fodder.
Several possible ways of resolving the conflict between woodlots and land, for crops
and pastures can be considered.
(i) The fuelwood requirements can be eliminated by the adoption of alternative fuel(s)
or reduced by improving the efficiency with which fuelwood is used.
(ii) The area set apart for pastureland can be reduced through the cultivation of highproductivity fodder species.







136
(iii) Pastureland can be put to multiple use by combining the growth of fodder species
and fuelwood trees in two-tier forests where the lower tier is devoted to fodder and
the upper tier to fuelwood.
(iv) The land devoted to non-food crops can be reduced and the corresponding land
used for woodlots.
In the absence of such deliberate measures, what generally happens is that land which
is under tree cover is cleared for cultivation. This removal of tree cover leads to soil
erosion - and, in extreme cases, to desertification - and therefore to a deterioration in
the quality of cropland. Thus, as is well known, deforestation to promote food
production may frustrate the very capacity to produce foods The result is the same
when the deforestation is carried out to secure fuelwood, i.e., the satisfaction of the
need for fuelwood can lead to a diminution in the quality of land.
6. Water and fuelwood (figure 2-3)
Crop production is generally water-limited. This water limitation may be due to the
seasonality and insufficiency of rainfall and/or the restricted availability of groundwater and/or the inadequacy of energy to transfer the water from where it in available
to where it is required.
If ground-water resources are limited, then an increase in the supply of water can be
achieved by importing water through irrigation projects or by harvesting rain-water,
i.e. by collecting rain-water from micro-catchments and storing it in tanks and ponds.
The import of water depends upon decisions and actions taken outside the ecosystem,
but water-harvesting within the ecosystem implies an increase in the area occupied by
water-bodies. This increase may take place at the expense of land useful for woodlots
- thus there is a possibility of conflict between water-harvesting and woodlots,
analogous to the conflicts on a large scale between dame and forests. If, however,
ground water is available, then energy must to utilized to lift the water. This energy
must either be imported from sources outside the ecosystem with all the attendant
transmission/transport costs of electricity/oil or be made available from within the
ecosystem through the supply of animate energy (for example, animal power) or
biomass-derived fuels, or the harnessing of wind energy. If these local sources of
energy are used for water-lifting, then there can be conflict between the energy needs
of water-lifting and those of other tasks.
If fuelwood projects are based on irrigation, the above-mentioned conflicts between
water-harvesting and woodlots and between the energy requirements of water-lifting
and other energy needs are aggravated. In such situations, the resolution of these
conflicts can be achieved by ensuring that the irrigation of fuelwood trees satisfies the
following conditions:
Figure 2-5: Inanimate energy and fuelwood 







137
Figure 2-4: Nutrients and fuelwood

(i) The extra volume of harvested rain-water required for woodlot irrigation should be
obtained without increasing the area of water-bodies, i.e., the depth of these waterbodies should be increased, or if the area of these water-bodies increases when the
volume of harvested water is increased to permit woodlot irrigation, the extra water
should be used to obtain, apart from greater fuelwood production, a simultaneous
increase of crop and/or fodder yields so that these increased yields compensate for
any loss of cropland and/or pastureland.



138
(ii) If fuelwood trees are irrigated with ground-water, then the energy for the waterlifting should be derived by energy conservation measures, i.e., by an increased use of
the same draught animals and/or more efficient use of the inanimate energy already
being utilized in the ecosystem so that the delivered energy for other tasks is not
reduced, or by an increased supply of energy in the form of fuelwood.
There can also be the following synergism between water-harvesting and woodlots.
Woodlots tend to reduce water run-off and increase the recharge of stored/ground
water. They generally make the water balance more favourable, particularly with the
use of tree species which draw deep water.
7. Nutrients and fuelwood (figure 2-4)
The supply of nutrients to land use for growing crops and/or fodder and/or trees, or at
least the replenishment of nutrients removed from this land, is essential for,
sustainable agriculture and/or silviculture. In traditional village agricultural
ecosystems, only organic sources are used: (i) farmyard manure obtained by
composting animal waste, (ii) green manure from leguminous crops and/or from
leaves which are the nitrogen - and the phosphorus - rich parts of plants, and (iii)
household wastes. A dependence on farmyard manure implies the existence of
livestock in the ecosystem which in turn creates a demand for fodder and therefore for
land if the fodder comes from pasture land. Thus in an ecoystem depending upon
farmyard manure, there can be a conflict between nutrients and land. If, however, the
dependence is on green manure which can also be consumed by livestock as fodder,
then there is the possibility of a conflict between nutrients and fodder. Under these
circumstances, the introduction of fuelwood projects requiring the use of organic
nutrients is likely to aggravate the situation and lead to a conflict between organic
nutrients and fuelwood trees. The main mechanism for resolving these conflicts is to
import the nutrients which may be required for fuelwood projects. On the other hand,
there is a synergism &rising from the "nutrient pump effect" in which deep-rooted
trees bring up nutrients.
8. Inanimate energy and fuelwood (figure 2-5)
The only sources of inanimate energy available within traditional village agricultural
ecosystems are fuelwood, agricultural wastes and cattle-dung-cakes. All these sources
are used in varying proportions an fuels to provide heat energy.
Since the combustion of dung-cakes leads to the vaporization of nitrogen and
phosphorus, there can be a conflict between fuel and fertilizer, and since the burning
of many agricultural residues deprives cattle of sustenance, there in a possibility of
conflicts between fuel and fodder. The only traditional source of inanimate energy
which does not directly reduce fertilizer and fodder use is fuelwood, a ligneous
material.
But, the problem with the traditional fuelwood technologies used in the agriculture of
developing countries is that they cannot provide mechanical energy for the operation
of stationary and/or mobile equipment.1 Therefore, the requirements of stationary
and/or mobile power must be met with human energy and/or animal energy and/or
electricity/oil generally imported from outside the ecosystem. Dependence on animal
energy increases fodder requirements but at the same time reduces electricity/oil
imports. But, the power output of draught animals in limited to about 0.5 HP, which
means that tasks requiring greater power inputs will necessarily require the
substitution of animal energy with, imported electricity/oil.








139
1
In the early stages of the industrialization of the developed countries, wood-fired
steam/stirling engines were often used.
Figure 2-6 Animal energy and fuelwood 
All this means that if fuelwood trees are going to be irrigated with current
technologies of lifting groundwater, then there will be an increase in the requirements
of animal energy and/or imported electricity/oil leading respectively to increased
fodder requirements and/or decreased self-sufficiency of the ecosystem.
One of the possible ways out of this dilemma is to drive waterpumps with engines
running with wood-based fuels such as producer gas (mainly a mixture of carbon
monoxide and hydrogen) or methanol (obtained by the conversion of producer gas).
Another alternative is to operate diesel-engine-driven pumpsets with biogas (a
mixture of methane and carbon dioxide) obtained by the aerobic fermentation of
animal wastes and/or other non-ligneous cellulosic materials.
9. Animal energy and fuelwood (figure 2-6)
Draught animals are the main source of power for stationary and mobile operations
when the power requirements exceed the output of human beings. In particular,
draught animals supply the power for: (i) agricultural operations such an ploughing,
harrowing, water-lifting, and threshing, (ii) transport with animal-drawn vehicles, and
(iii) many industrial operations such an crushing, grinding, etc. The only way of
replacing animal power is with engines in mobile equipment and with engines and/or
motors in stationary equipment. While this mechanization has permitted an increase in
power beyond the limits of animals, it has created a demand for oil and/or electricity
which invariably have to be imported from outside the ecosystem. In addition,






140
whereas a single draught animal or pair of such animals can accomplish all the
agricultural, transport and industrial functions mentioned above, it is usual to have
separate items of specialized equipment for each -task or class of tasks. Thus, the
replacement of animal power usually requires an array of equipment.
As oil-fuelled and electrical equipment take over the functions of animals, the load
factor on animals goes down. Nevertheless, until all the mechanical functions of
animals are taken over by machines, draught animals must be maintained to carry out
the remaining functions. In these circumstances, the traditional approach is to give the
draught animals just enough fodder to enable them to carry out the residual tasks, bat
despite this, the input cannot go below maintenance levels. At these dietary levels, the
draught animals deliver far less power than what they are capable of with proper
feeding. Thus, the partial, as opposed to complete, substitution of animal power by
machines may increase the productivity of certain operations, but it does not eliminate
the need, for maintenance fodder for draught animals and with such a maintenance
diet their power output and productivity are significantly reduced.
Animal energy, therefore, promotes the self-sufficiency of the ecosystem with respect
to mechanical power but probably achieves this goal at the expense of productivity;
and machines driven with inanimate energy may facilitate greater productivity but
lead to greater dependence on the external environment (of the ecosystem) for oil,
and/or electricity.
This dilemma of animal power vs mechanization can be resolved in several ways. In
situations where the use of animal power is continued, its efficiency can be improved
by better design and/or conditions. For example, the productivity of ploughing with
draught animals can be enhanced by increasing the soil moisture - thin in a synergism
between animal energy and water. Another important approach is to identify those
situations whore the replacement of animal power with machines it; justified and to
drive these machines with wood-based fuels (producer gas and/or methanol) produced
from fuelwood. This would be tantamount to fuelwood replacing animal energy.
Figure 2-7 Fodder and fuelwood 



141
From the transport point of view, however, animal-driven vehicles can provide lowcost transportation for fuelwood. In fact, it appears that, within specific distance
regimes - for example about 0.4 kms. to 3.0 kms. in a particular study made in South
India (Jagadish, 1979) - animal-drawn vehicles are more economical than either
trucks or tractors for fuelwood transport. This implies that animal energy can assist
the distribution aspect of the fuelwood system.
10. Fodder and fuelwood (figure 2-7)
The food requirements of the human beings in the ecosystem include, in addition to
grain, many non-grain components such as milk, meat, vegetables, etc. The grain
components have to be produced by agriculture which requires draught power if it in
based, as it invariably in, on tillage. An already mentioned, the draught power in
traditional agricultural ecosystems comes from draught animals or human beings. The
non-grain components of food include dairy products such as milk, butter, cheese and
eggs as well as meat. This means that agricultural ecosystems must support, in
addition to draught animals, other non-draught categories of livestock such as cows,
buffaloes, goats, sheep, pigs and chickens. In other words livestock are reared to meet
the requirements of both energy and food. Through its ability to provide alternative
fuels for engines, fuelwood production can diminish the energy contribution
demanded of livestock, but the food contribution still remains, necessitating the
rearing of livestock.
Livestock rearing, however, generates a demand for fodder. If arboreal forage is not
considered part of the fodder system, there are two traditional sources of fodder,
agricultural residues and pastureland. The contribution of these two fodder sources to
the total fodder requirement varies very widely from ecosystem to ecosystem ranging





142
from one extreme where all the fodder requirements are met by grazing in pastureland
to the opposite extreme where fodder is supplied to stable-bound livestock.
In situations where agricultural residues contribute significantly to the total fodder
requirements by virtue of their digestibility, it in important that crop varieties are
selected both for their grain and straw output. This seems to have been the case with
the traditional crop varieties, but the modern dwarf varieties of the green revolution
achieve high yields of grain at the expense of the stalk portion which in often used for
livestock. This implies a greater demand for fodder from pastureland, and this demand
way lead to a reduction in the area available for fuelwood production. Thus, highyielding varieties may load to a conflict between food and fodder requirements, which
In turn may result in a conflict between fodder and fuel. (Incidentally, ouch direct
conflicts are avoided in the agricultural systems of the developed countries because
they have virtually eliminated their requirements of draught animal power - and the
associated fodder requirements - through inputs of inanimate energy in the form of
fossil fuel, and because they import significant quantities of livestock feed from the
developing countries.)
Even with traditional crop varieties which produce fodder along with grain, there is
strong demand in village agricultural ecosystems for pastureland. In fact, the netting
apart of land, for livestock grazing was a common feature of these ecosystems in the
not too distant past, but increasingly pastureland has been converted into cropland due
to pressures of population and land distribution and, as a result, the prospects of using
arable land for woodlots have become bleak.
One approach to the resolution of the conflict between food and fodder on the one
hand and fuel on the other is to restrict woodlots only to non-arable land. Even when
this in done, fuelwood trees suffer from very high "infant mortality" because they
become victims of grazing livestock during their seedling and sapling stages of
growth. In other words, the conflict between fodder and fuel can have a destructive
impact on woodlots on non-arable land during the early stages of growth of fuelwood
trees when they are extremely vulnerable to grazing. In this context, the rational
approach is to plan simultaneously for both fodder and fuel requirements through a
two-tier forest and first to ensure fodder production on a renewable basin before
attempting to protect fuelwood seedlings/saplings from grazing.
Figure 2-8 Cooking and fuelwood 



143
11. Cooking and fuelwood (figure 2-8)
Cooking is done almost exclusively with fuelwood (either directly or after conversion
into charcoal), agricultural wastes and dung-cakes. As-already pointed out, the
combustion of agricultural wastes leads to the lose of fodder unless the waste is not
edible by livestock (e.g. sugarcane bagasse) and the burning of dung-cakes results in
the lose of nutrients. In fact, it appears that villagers use dung-cakes as cooking fuel
only when fuelwood is not available or not conveniently accessible. (There are,
however, regions where dung-cakes are used in order to have a very slow-burning
fuel, e.g., to thicken milk). Thus, the general preference for fuelwood has a rational
basis because it does not involve direct conflicts with fodder and fertilizer
requirements.
There are many aspects of the ecological implications of the use of fuelwood for
cooking. If the fuelwood for cooking in the ecosystem is obtained predominantly in
the form of fallen twigs and branches, i.e. without tree felling, - and this is the case in
many regions (Astra 1981) - then the fuelwood resources are being used in a
renewable manner. Thus, cooking in the ecosystem with internally available fuelwood
resources may not be as responsible for deforestation as is sometimes made out. Butt
as soon as the fuelwood has to be transported from or to distances which are far from
the ecosystem (which is what happens in the case of fuelwood imports or exports), the
preference is for a denser form of fuel, in other words for logo or for charcoal made
from such logs. Hence, one of the justifications for planning and establishing
fuelwood projects is to increase the supply of fuelwood and avert the catastrophe of
not being able to cock the food even if food production can keep pace with
population.
At the same time, however, attention is being focussed on the fuelwood utilization
question. Studies of the performance of wood stoves are coming up with efficiency
values of under 10%, and typically 5%, which means that 90-95% of the heat energy
available in fuelwood is being wasted (Geller 1981, De Lepeleire et al., 1981). The
initial hopes that the efficiency of the wood stoves of technologically simple peoples
can be radically improved are diminishing. It now appears that, barring a





144
breakthrough, one cannot expect more than a doubling or trebling of the efficiency of
firewood stoves, and that the ideal stove may well be one in which the wood is
converted in situ into producer gas which then becomes the cooking fuel. None of the
so-called "improved stoves" approach this ideal and many, in fact, lead to enhanced
firewood consumption when subjected to rigorous testing procedures.
All this provides a rational technical basis for villagers to reject the "improved
stoves". In addition, it is a moot point whether the poorer strata will ever consider
wood-burning stoves (even costlier and improved ones!) as an elevation in their
standard of life when they are aware of the fact that the more affluent sections of their
society always prefer cleaner and more convenient cooking fuels to wood. The poor
know that there is a hierarcy of cooking fuels and they view changes from fuelwood
to charcoal to kerosene to electricity/gas as steps in the improvement of the quality of
their life. There is in fact a technical basis for these preferences.
Gaseous cooking fuels offer a tremendous advantage - the rate of gas flow, and
therefore the rate of combustion and the rate of release of heat energy to the cooking
vessel, can be very rapidly altered and easily controlled. This is extremely important
because there are cooking operations such as boiling which require a high power
output from the stove, and others such as simmering which need a low power output
(Dutt 1978). In addition to the control over the gas flow rate, which facilitates easy
and quick variations of the power output, a gaseous cooking fuel permits
manipulation of the air to fuel ratio and therefore ensures the completeness of the
combustion process. The net result of these advantages is that stoves using gaseous
cooking fuels can achieve efficiencies which can be five to ten times the efficiency of
traditional firewood stoves.
In view of this conflict between cooking efficiencies and fuelwood, the option of
conserving fuelwood by using gaseous fuels instead of wood for cooking seems much
more attractive than improving the performance of woodstoves. The two gaseous
fuels which can be generated from the internal resources of agricultural ecosystems
are producer gas obtained by the partial combustion of wood and biogas obtained by
the anaerobic fermentation of livestock wastes.
Figure 2-9 Trees and fuelwood 
Figure 2-10 Other uses of wood





145
Figure 2-11 Wood and buildings


12. Trees and fuelwood (figure 2-9)
Fuelwood is obtained mainly from trees, but Many shrub species also serve as a
source. Since there is a great pressure on land for agriculture, the growth of fuelwood
trees is generally restricted to separate areas, or woodlots. But due to the conflict
between food, fodder and fuel requirements, it is becoming increasingly difficult to
find land, even of the non-arable variety, for woodlots.
Very often, therefore, the only trees are those that can be integrated with agricultural
use of the land with little or no competition with food and fodder; for example, trees
that can be grown on the borders of fields, water-bodies, roads, etc. In a sense, these
"border trees" do not occupy land which is required for food and fodder, particularly
if they are straight and tall and do not deprive the ground crops of too much light. It is
important that they are not profligate with their requirements of water - otherwise, the
conflict between fuel and water will be aggravated. Fuelwood trees must also not be
too demanding with regard to soil nutrients, and should preferably be nitrogen-fixers
so that they enrich the soil. It is an advantage if they also contribute by products of
economic value, such as fodder or fruit. In other words, there can be conflicts between
particular fuelwood species and the requirements of food, water and fertilizer.
Fortunately there are species which satisfy these conditions. Leucaena leucocephala,
for example, casts a light shade, needs little water, is leguminous and if; a source of
fodder.
13. Other uses of wood (figure 2-10)






146
The wood resources of the agricultural ecosystem are used to meet the requirements
of several end uses. Of these, cooking is the most important, but it is essential to
reckon with other end uses. In the household sector, for instance, fuelwood is also
consumed for water heating and space heating. In addition, fuelwood is used in all the
traditional industries which require heat energy. It is only very recently that these
small scale industrial uses of wood fuel in rural areas have started to be investigated
(e.g. Donovan 1980). In particular, attention is being focussed on brick-burning, tilemaking, pottery, processing of tobacco, tea, cardamon, etc., black-smithy, soapmaking, etc. Wood is also used as a structural material in buildings and animal-drawn
vehicles. The scarcity of wood resources implies the possibility of conflicts between
wood as a cooking fuel and wood for other end ages.
14. Wood and buildings (figure 2-11)
Significant quantities of wood are used in the building sector. Wood, is utilized both
directly as a structural material in the form of lumber and indirectly as a fuel for the
production of fired bricks and tiles. In both these applications, twigs and branches are
usually not used, and logo which can only come from felled trees are required. Brickburning in particular generates considerable demand for wood especially when it in
achieved with batch production - in a specific region in South India, approximately
0.4 tonnes of fuelwood is used to burn a 1000 bricks (Jagadish 1979a). It in becoming
clear that, in many parts of the Third World, the depletion of fuelwood resources will
inhibit the success of building programmes based on burnt bricks and tiles. This
implies a conflict between fuelwood and shelter,
There appear to be many ways in which this conflict can be resolved - for instance,
one promising approach is to use unburnt, but machine-compacted and water-proofed,
mud blocks instead of burnt bricks, and alternative roofing materials, preferably based
on agricultural residues, in place of tiles. An interesting synergism between roofing
materials and wooden structural roof supports can be exploited - the lighter the
roofing, the less the volume (and therefore weight) of lumber required to support the
roof.
Figure 2-12: Wood exports and imports 





147
Figure 2-13: Human beings and fuelwood

15. Wood exports and imports (figure 2-12)
The dependence on fuelwood for cooking is not a rural phenomenon only; in most
developing countries, the use of fuelwood and charcoal in urban areas is significant.
In India, for instance, about 20% of the total population lives in towns and cities and
approximately 65% of the urban households use firewood as a cooking fuel - this
corresponds to about 30 million tonnes (Government of India, 1979)
Most towns and cities, however, do not have woodlots as part of their ecosystem,
which means that they import their firewood and/or charcoal from the rural areas.
Further, to facilitate the transport of this firewood, it has to be in the denser form of
logo, which means that tree-felling is almost a necessary part of supplying fuelwood
to urban conglomerations. Thus, both the magnitude of firewood exports to towns and
cities as well as the type of fuelwood exported, logo, constitute a significant drain on
the wood resources of village agricultural ecosystems; they are perhaps far more
responsible for the deforestation in such ecosystems than the internal use of wood as a
cooking fuel. There is a conflict, therefore, between fuelwood exports and the fuel
requirements of agricultural ecosystems. Of course, exports from an ecosystem also
bring income into it, but the point is that an export orientation changes the behaviour
of the ecosystem, sometimes for the worse.
This conflict is aggravated by a common urban preference for charcoal. This
preference arises mainly because charcoal has a higher calorific value per unit
volume, and it neither catches fire nor deteriorates as easily as wood. First, charcoal
produced from twigs and thin branches crumbles and powders easily during storage
and transport. Hence charcoal production requires logs from felled trees. Second,
high-quality charcoal requires wood from the trees with dense wood which are the
best for timber uses Third, in the interest of transport economies, the charcoal
required by towns and cities is produced where wood resources are available and in a
decentralized manner, often on a household scale. Since the conversion efficiency in
such miniscule charcoal-production units is only about 25% (0.25 kgs. charcoal/kg.
wood) and the efficiency of' charcoal stoves is only 1.8 times greater than
woodstoves, the overall consumption of wood resources is greater when fuelwood is
converted into charcoal cooking fuel than when it is used directly. Hence, there is a
conflict between charcoal and fuelwood.
Wood exports from agricultural ecosystems take place not only to supply the cooking
fuel requirements, but also the raw materials needs of lumber mills located in towns
and cities. In this case, too, wood is required in the form of large logs and trunks






148
which can be obtained only by cutting down trees. Thus the export of lumber-wood
from agricultural ecosystems also has a negative impact on their wood resources.
The various unwelcome consequences of wood exports can be diminished by two
important strategies. With regard to urban fuel requirements, programmes can be
initiated (1) to utilize the biogas obtained by the treatment of urban sewage, (2) to
convert town and city garbage into combustible fuels, and (3) to establish green belts
around towns and cities and generate producer gas from the fuelwood obtained from
the trees in these belts. Such programmes can involve piped supply of sewage,
garbage and producer gases.
16. Human beings and fuelwood (figure 2-13)
Of course, human beings are the most important, part of the agricultural ecosystem
and the focus of the development process. Human beings and, wood resources are
related in five obvious ways.
First, there is theoretically a maximum to the population which can be supported by
the food produced from a given area of land, but this so-called "carrying capacity"
depends in part upon the agricultural technologies which are deployed, there being the
possibility of adaptive strategies. Green revolution agricultural technologies have
increased the carrying capacity many-fold, but this increase has been achieved by
increased inputs such as water, fertilizer or inanimate energy. When technologies of
enhancing the carrying capacity are not used (for reasons ouch as the lack of capital,
water, fertilizer, energy or skills), the only way of augmenting food production after
the population approaches the carrying capacity is to increase the area under crop
cultivation, for example by clearing forests. This leads to an indirect conflict between
people and land which is suitable for woodlots.
Figure 2-14 Fuelwood in an agricultural ecosystem 




149
Second, an increasing human population loads, in the absence or non-implementation
of alternative cooking fuels, to an increasing fuelwood demand at the rate of about
600 tonnes per year for every 1000 additional persons. Thus there is a direct conflict
between human beings and fuelwood resources.
Third, a growth in human population loads to increased demand for all the other noncooking-fuel uses of wood - i.e. for other domestic uses and for industrial uses of
fuelwood and lumber.
Fourth, it has been recently argued that domestic chores such as gathering fuelwood,
fetching drinking water and grazing livestock encourage people to have large families
because children contribute a significant fraction of the human energy necessary to
accomplish these tasks which are so vital to a family's survival. As a result, the greater
the distance from which fuelwood has to be gathered, and the more the hardship and
time required for the task of gathering fuel, the more important it is for a family to
have children. Hence there can be a conflict between fuelwood collection and
population control.
Finally, children have to be removed from school in order to perform the tack of
gathering fuelwood, and this creates a conflict between the use of fuelwood and the
education of rural children.
17. Fuelwood in an agricultural ecosystem
The above presentation has focused on a number of pairs of interactions, each pair
consisting of fuelwood and one other ecosystem component or activity. But the pairs
are all inter-related, not only through fuelwood, but because there are separate







150
linkages between the ecosystem components and activities. For example, the landfuelwood and humans-fuelwood pairs are linked through the fact that human energy
plays a major role in utilizing land for growing food. This means that the separate
diagrams (Figures 2-2 - 2-13) portraying each pair interaction must be assembled and
integrated into a single diagram which will display, not only the pair-wise
interactions, but also the inter-relationships between pairs. The result of such a
procedure is shown in Figure 2-14 which reveals the complex, inter-relationships
involving fuelwood. The diagram shows that the planning of a fuelwood project
requires an understanding of all these linkages. What often happens, however, is that
many fuelwood projects ignore crucial interactions and adopt a naive fuelwood-forcooking approach.
There is a further complication. Human beings have been treated thus far as a single
category, as is customary in ecosystem studies. In stratified, societies, however,
several phenomena in human ecosystems become comprehensible only when human
society is disaggregated into the relevant economic categories, particularly those
categories which describe the inequalities in the ownership and control over assets.
Thus, discussions of fuelwood must take into account the fact that in most developing
countries all families do not have the same extent, of dependence on fuelwood or the
same degree and type of access to this fuel.
The rich and powerful sections of rural society own a disproportionately greater
fraction of the land, they derive the greatest benefits from water-bodies and groundwater, they have much better access to trees even when they do not own them, they
can hire labour to obtain fuelwood, they use liquid and gaseous fuels to a greater
extent, and so on. In contrast, the poorest sections, invariably consisting of the
landless groups, have the greatest problems with regard to fuelwood. Almost always,
they have to get their fuel supplies at zero private direct cost by gathering fuelwood
from wherever they are allowed to collect it, and this effort consumes a considerable
amount of time, apart from involving them in a client-patron relationship. Such
groups are usually the least likely to get a proportionate share in the produce of
fuelwood projects, and as a result, they are chary about making contributions of
voluntary or communal labour to fuelwood projects.
Even if the labour for fuelwood projects is paid for, its seasonality must be taken into
account. There can be a conflict between the need for labour on woodlots and the
requirements for labour on the farms. When there is such a conflict, the marginal and
small farmers who are the ones most likely to work on woodlots (i.e., apart from
landless labourers) may prefer to work on their own farms in the hope of much greater
returns from their land.
Families below or around the poverty line usually make illicit use of resources. For
instance, they seek to supplement their incomes by raising livestock - goats, sheep and
cattle - many categories of which have to be taken out for grazing wherever grass and
leaves are available. The saplings of fuelwood trees are usually a prime target in these
grazing expeditions. Thus, the high "infant mortality" of fuelwood species is
predominantly due to the survival value of livestock grazing to the poorest sections of
rural society.
Another important impact of inequalities in land ownership on fuelwood is a result of
a mechanism that is often adopted for satisfying the land hunger of the landless. An
egalitarian approach would consist of redistributing land by imposing ceilings and
distributing the excess land of those with large holdings; instead, the large landowners are often left untouched by the so-called "land reform" and pastureland or land





151
under tree cover is given to the landless. Such measures reduce the fuelwood
availability as well as the land which could be used for woodlots - hence, there can be
a conflict between land distribution and fuelwood.
It appears therefore that whereas the fuelwood situation per se can be remedied if
equity considerations are ignored, it is much more difficult to accomplish fuelwood
projects with equity. The problem is further complicated by three other factors:
(i) Women, rather than men, have a much clearer perception of the fuelwood crisis,
because the burden of gathering firewood falls primarily on women and children;
(ii) fuelwood is often ranked lower than other needs such as food, employment or
water in the villager's perception of priorities;
(iii) fuelwood in many regions is traditionally viewed as a common good and the
persistence of this attitude can interfere with the implementation of projects which
require a different approach.
Table 2-1 Land-use pattern
Cultivated (22)*
Fallow (1)
Grass land (3)
Marsh land (1)
Plantation (coconut, fuel) (2)
Water-bodies (2)
Settlement (houses, road, etc.) (4)
2. Ragi
3. Sorghum
4. Sugarcane
5. Horsegram
6. Coconut
7. Others (20)




Hectares %
243.7
67.7
Crop land
47.0
13.0
290.7
80.7
15.8
4.4
15.4
4.3
0.8
0.3
0.2
37.3
10.3
360.2 100.0
* Number in brackets refers to number of items aggregated.
Table 2-2 Cropping pattern - AY 1979-80
1. (a) Paddy (local)
(b) Paddy (KYV)

Kharif
Summer
June/Jul-Nov./Dec.
Area (ha)
% Area (ha) %
126.7
52.0
33.7
13.8
160.4
65.8
41.1
16.9
10.1
50.8
8.7
3.6
7.1
2.9
7.1
35.7
6.7
2.7
4.6
1.9
228.6
93.8
17.2
86.5
15.1
6.2
2.7
13.5


152
Total
243.7
100.0
19.9
100.0
Table 2-3 Above-ground plant biomass productivity

Entity
Productivity Ratios Production %
(tonnes/ha)
(tonnes)
1. Crops
1(a) Paddy (local)
6.9
1.38
791.5
41.4
1(b) Paddy (HYV)
7.1
1.42
216.5
11.3
1008.0
52.7
1.2 Ragi
3.8
0.76
111.6
5.8
1.3 Sorghum
1.4 Sugarcane
1.5 Horsegram
1.6 Coconut
1.7 Others
6.1
27.3
1.9
9.2
-
1.22
5.46
0.38
1.84
-
2. Grass land
3. Fallow land
4. March
5. Shrub
5.0
5.3
5.0
12.5
1.00
1.06
1.00
2.50
Total average
6.0
50.1
194.0
13.3
97.4
24.2
1498.6
73.7
249.6
76.7
14.4
414.4
1 913.0
2.6
10.1
0.7
5.1
1.3
78.3
3.9
13.1
4.0
0.7
21.7
100.0
Table 2-4 Disaggregation of above-ground plant biomass
Table 2-5 Fodder consumption by livestock


Total Bullocks Cows Calves Buffalo Goat(s) and Sheep
Paddy straw 571
180
207
17
167
Sorghum grain 1
1
Sorghum straw 49
20
23
6
Grass + Fallow 400
78
91
124
107
1021 279
321
17
297
107
Fodder from crops 621 (60.8%)
Fodder from grass = 400 (39.2%)
Land + Fallow land + = 400 (39.2%)
Marsh land = 400 (39.2%)
Table 2-6 Fuel sources
From Ecosystem Tonnes/yr.
Coconut
61

153
Other crops
Trees (Twigs)
Trees (Felled)
Shrubs
2
172
20
5
260
Imports from outside Ecosystem
FW (Bought)
203
Fit (Gathered)
59
262
Total
522
Figure 2-1 Utilization of Paddy Biomass




5.2 TREE BORN OILS (TBO‘S),
5.3 POTENTIALS AND ADVANTAGES,
Benefits of Biomass Energy
As our society experiences high and volatile energy prices as well as issues of national security,
power generated from biomass material is becoming increasingly important.
Biomass power facilities benefit:
 Local communities
 The national economy and
154
 The environment, including significant climate change benefits.
Economic Benefits of Biomass Energy
Biomass energy plants make a substantial, positive impact on local and regional economies by
generating well-paying jobs in:
 Construction and operation of the plant and
 Collection and transportation of biomass material.
Biomass energy plants support local industry and businesses and encourage new investment in rural
communities.
 Biomass energy facilities can help stabilize the local timber and forestry industry by
providing stable demand for biomass material, which allows loggers, harvesters, processors
and transporters to make capital investments.
 Biomass facilities also increase the local tax base without requiring substantial services from
the local community.
Unlike many other energy fuels, the dollars spent on biomass material stay in the local, state and
regional economies since biomass plants primarily use fuel sources that are within 75 miles of the
plant.
During peak construction, a 100-MW biomass power facility will create approximately 400
construction jobs. Once operational, the facility will create approximately 40 direct full-time
positions at the site, and will also generate approximately 700 indirect jobs throughout the region.
Social Benefits of Biomass Energy
As demand for power increases, many regions of the country face potential supply shortfalls. These
shortfalls could result in significantly higher electric prices and potential blackouts. Biomass power
generation can help address this issue by providing a source of electricity that is:
 Reliable,
 Domestically-produced,
 Dispatchable,
 Economically-competitive and
 Environmentally sustainable.
Unlike other forms of renewable energy such as wind and solar energy, biomass energy plants are
able to provide crucial, reliable baseload generation. In addition to providing baseload generation,
biomass plants provide fuel diversity, which protects communities from volatile fossil fuels. Since
biomass energy uses domestically-produced fuels, biomass power greatly reduces our dependence
on foreign energy sources and increases our national security.
Besides these economic development benefits, biomass plants help ensure a sustainable market for
forest products. The jobs created as a result of these facilities help to protect and preserve the
unique culture of many rural communities.
Environmental Benefits of Biomass Energy
Biomass power facilities have numerous attributes, which benefit the environment and world
climate change.
Environmental benefits include:
 Cleaner air and
 Better forestry management.
Biomass plants produce far less particulate matter than the alternative method of open burning
wood wastes.
"In many regions of the United States, the biomass energy industry has become an integral part of
the solid waste disposal infrastructure. If the biomass industry were to fail, finding new disposal
outlets for all the biomass residue material currently being used for fuel would be difficult."
U.S. National Renewable Energy Laboratory
Beyond providing cleaner air, biomass energy plants:
 Encourage better forestry practices which in turn lead to increased protection of critical
wildlife habitats,
155
Produce ash which can be used for soil enhancement in farmland,
Reduce the impact of invasive species,
Reduce wildfire risk,
Improve solid waste management by providing an outlet for land-clearing debris,
diseased/infected trees and other wood wastes rather than open burning or depositing in
already crowded landfills and
 Reduce the impact of natural disasters by providing an outlet for storm debris.
"The record shows that electric generation using biomass that would otherwise be disposed of
under a variety of conventional methods (such as open burning, forest accumulation, landfills,
composting) results in a substantial net reduction in GHG emissions."
California Public Utilities Commission, January 2007, Decision 07-01-039
Climate Change Benefits of Biomass Energy
Unlike energy derived from fossil fuels such as coal, oil and natural gas, biomass energy does not
contribute to climate change. The carbon, which is stored in biomass material as it grows, is already
part of the atmosphere. Biomass energy does not add new carbon to the active carbon cycle,
whereas fossil fuels remove carbon from geologic storage.
Carbon emissions from biomass facilities would have been released back into the atmosphere
through natural decay or disposal through open-burning. The advanced emissions controls on a
biomass energy facility significantly reduce the amount of carbon dioxide emitted into the
atmosphere along with other emissions such as particulate matter.
Biomass energy is considered a "zero-greenhouse-gas-emitting technology" by the Regional
Greenhouse Gas Initiative in the Northeast U.S. and the E.U. Emission Trading Scheme.
In addition to not emitting new carbon into the active carbon cycle, biomass energy has additional
climate change benefits.
 Like all renewable energy technologies, biomass energy displaces the production of an
equivalent amount of energy from fossil fuels. However, biomass energy is not just carbon
neutral but actually carbon negative.
 In the absence of biomass energy, a large portion of biomass material would be left to
decompose naturally, be open-burned or landfilled. Landfilled or naturally decaying biomass
material releases carbon in the form of methane as well as carbon dioxide. Methane is 20 to
25 times more potent as a greenhouse-gas than carbon dioxide.
Biomass energy contributes to forest health and fire resiliency, which increases the amount of
carbon stored on a sustainable basis.




156
5.4 BIO-DIESEL TRANS-ESTERIFICATION,
5.5 IMPORTANT BIO-FUEL SPECIES AND THEIR SILVICULTURAL MANAGEMENT.
CHAPTER NO.06
WOOD BIOMASS PRODUCTION
6.1 Introduction
Energy sources will play an important role in the world’s future. The energy sources have been split
into three categories: fossil fuels, renewable sources and nuclear sources. The fossil fuels are coal,
petroleum and natural gas.
The world’s energy markets rely heavily on the fossil fuels coal, petroleum crude oil, and natural gas
as sources of energy, fuels, and chemicals. Since millions of years are required to form fossil fuels in
the earth, their reserves are finite and subject to depletion as they are consumed.
The only other naturally-occurring, energy-containing carbon resource known that is large enough to
be used as a substitute for fossil fuels is biomass. Biomass is all non-fossil organic materials that have
intrinsic chemical energy content.
They include all water- and land-based vegetation and trees, or virgin biomass, and all waste
biomass such as municipal solid waste, municipal bio-solids (sewage) and wastes. Unlike fossil fuels,
157
biomass is renewable in the sense that only a short period of time is needed to replace what is used
as an energy resource.
Biomass potential includes wood and animal and plant wastes. Biomass is only organic petroleum
substitute that is renewable. The term ‘biomass’ refers to forestry, purposely grown agricultural
crops, trees and plants, organic wastes, agricultural, agroindustrial and domestic wastes (Garg and
Datta, 1998).
Table 1
Biomass and other energy sources: production and consumption in the world
1998 Production quad btu
Percent of total production 1998 consumption
Oil
152.0
40.0%
73.60 million
barrels/day
Natural gas
85.5
22.5%
82.20 tcf/year
Coal
88.6
23.3%
5.01 billion tons/year
Nuclear
24.5
6.5%
2.30 trillion kWh/year
Hydroelectric
26.6
7.0%
2.60 trillion kWh/year
Biomass (other) 2.5
0.7%
196.00 billion
kWh/year
Total
397.7
100.0%
Source: EIA, 1998.
World production of biomass is estimated at 146 billion metric tons a year, mostly wild plant growth
(Cuff and Young, 1980). Biomass fuel is a renewable energy source and its importance will increase
as national energy policy and strategy focuses more heavily on renewable sources and conservation.
Biomass power plants have advantages over fossil-fuel plants because their pollution emissions are
less. Biomass production and consumption in the world is given Table 1.
Biomass Potential
Biomass can be considered as the best option and has the largest potential that meets these
requirements and could insure fuel supply in the future. Mainly in the form of wood, it is the oldest
form of energy used by humans. Biomass has great potential as a renewable energy source, both for
the richer countries and for the developing world (Demirbas, 2001a).
World wide biomass ranks fourth as an energy source, and provides about 14% of the world’s energy
needs. In addition, biomass is a clean renewable energy source. Upon combustion, carbon dioxide is
released into the atmosphere, but carbon dioxide was the source of the carbon to generate the
biomass, so there is no net gain of carbon dioxide (Surmen, 2002).
Biomass is the only renewable source of fixed carbon and therefore, it has attracted considerable
attention as a renewable energy source in recent years (Yorgun et al., 2001). Biomass energy is more
economic to produce and it provides more energy than other energy forms. Biomass production is
eight times greater than the total annual world consumption of all other energy sources.
Biomass mainly now represents only 3% of primary energy consumption in industrialized countries.
However, much of the rural population in developing countries, which represents about 50% of the
world’s population, is reliant on biomass, mainly in the form of wood for fuel. Biomass accounts for
35% of primary energy consumption in developing countries, raising the world total to 14% of
primary energy consumption. Total annual production of biomass is 2,740 quads in the world. The
world primary energy production and consumption by energy sources are given in Table 2 and Table
3.
The United States has only about 5% of the world’s population, but is responsible for about onequarter of the total global primary energy demand. The markets for biomass
Table 2
World primary energy production by energy source (Quadrillion Btu∗)
1990
1992
1994
1996
1998
1999
Oil
136.35
136.50
138.30
144.93
151.89
149.72
158
Natural gas
75.91
Coal
91.87
Hydroelectric power
22.57
Nuclear electric power
20.37
Biomass and others
1.72
British thermal units (Source: EIA, 2001).
76.89
87.87
22.94
21.36
2.00
79.16
86.76
24.48
22.50
2.21
84.06
89.24
26.10
24.13
2.36
85.39
89.36
26.68
24.41
2.63
87.31
84.90
27.10
25.25
2.83
Table 3
World primary energy consumption by energy source (Quadrillion Btu∗)
1990
1992
1994
1996
1998
1999
Oil
134.87
136.61
139.11
145.41
149.84
152.20
Natural gas
74.51
76.12
78.33
84.01
84.50
86.89
Coal
89.96
86.62
87.44
90.41
89.26
84.77
Hydroelectric power
22.66
23.18
24.76
26.42
26.88
27.29
Nuclear electric power
20.37
21.36
22.50
24.13
24.41
25.25
Biomass and others
1.72
2.00
2.21
2.36
2.63
2.83
British thermal units (Source: EIA, 2001).
energy in the United States are therefore already established. They are large, widespread, and
readily available as long as the end-use economics are competitive. The contribution of biomass
energy to U.S. energy consumption in the late 1970s was over 850,000 barrels of oil equivalent
(BOE)/day, or more than 2% of energy consumption at that time. By 1990, it had increased to about
1.4 million BOE/day, or 3.3% of total energy consumption, and is expected to continue to show
significant growth. According to the United Nations, global biomass energy consumption was about
6.7% of the world’s total energy consumption in 1990.
Use of Biomass
Biomass energy is one of humanity’s earliest sources of energy. Biomass is used to meet a variety of
energy needs, including generating electricity, heating homes, fueling vehicles and providing process
heat for industrial facilities (Surmen, 2002).
Energy from biomass fuels is used in electric utility, lumber and wood products, and pulp and paper
industries. Wood fuel is a renewable energy source and its importance will increase in the future.
Three main determinants of the costs of operating and constructing a wood-fired power plant of a
given size exist. They are: the availability of the required fuel, the delivered fuel prices, and the
financing and construction of the desired power plant (Joutz, 1992). Most recent research has
focused on the feasibility of single-source fuel plants. One popular approach has been to examine
the feasibility of short-rotation intensive-cultivation plantations (Jennergren and Thornqvist, 1988).
Source: ISBF (International Slovak
Table 4
Biomass Forum), 2003.
Proportions of carbon, hydrogen and oxygen in fuels
Biomass can be used directly (e.g.,
Ratio of atoms
By weight %
burning wood for heating and cooking) Fuel
C
H
O
C
H
O
or indirectly by converting it into a Coal
1
1
<0.1 85
6
9
liquid or gaseous fuel (e.g., alcohol Oil
1
2
0
85
15
0
from sugar crops or biogas from Methane
1
4
0
75
25
0
animal waste). The net energy Wood
1
1.5
0.7 49
6
45
available from biomass when it is
combusted ranges from about 8 MJ/kg for green wood, to 20 MJ/kg for dry plant matter, to 55
MJ/kg for methane, as compared with about 27 MJ/kg for coal (Demirbas, 2001b).
Plant oils, bio-diesel, bio-gas and ethanol have been successfully introduced and are already in use.
Innovative synthetic fuels are related to aspects and the new developments in conversion
technologies to fuels: Gasification, pyrolysis and upgrading to gasoline, diesel and hydrogen,
methanol, DME as well as the possibilities of their generation from the biomass. Biomass can be
considered as a source for carbon and hydrogen (Table 4). The possible outcome of oil from biomass
159
depends on the productivity of energy plants and up to 9000 oil through modern conversion
technologies from one hectare could be achieved (Table 5).
While a large part of this white paper target is expected to be reached with biomass for heating, it is
expected that biomass will later be used for cogeneration of heat and power as well as for
production of hydrogen for transport.
Industrial and Home Use of Biomass
Wood related industries and homeowners consume the most biomass energy. The lumber, pulp and
paper industries burn their own wood wastes in large furnaces and boilers to supply 60% of the
energy needed to run the factories.
Table 5
Fuel yields from biomass
Biomass yield(t ha−1, y−1, kg−1)
Energy
Conversion
Fuel yield(t Fuel
yield
content(MJ.Kg−1)
efficiency(η) ha−1, y−1)
(1ha−1, y −1)
10
17.5
0.48
1.9
2448 (3000)
20
17.5
0.48
3.8
4895 (6000)
30
17.5
0.48
5.7
7343 (9000)
Source: ISBF, 2003.
Biomass is burned by direct combustion to produce steam, which turns a turbine, and the turbine
drives a generator, producing electricity. Because of potential ash build-up, only certain types of
biomass materials are used for direct combustion.
Gasifiers are used to convert biomass into a combustible gas (biogas). The biogas is then used to
drive a high efficiency, combined cycle gas turbine. Biogas energy conversion devices that are
discussed are reciprocating engines, turbines, micro turbines, fuel cells, and anaerobic digesters.
Simple biogas producing devices create anaerobic digestion by decomposing organic matter like crop
residues or domestic wastes in an oxygen deprived environment. The resulting biogas—a mix of
other gases—can be burnt to provide energy for cooking and space heating, or create electricity to
power other equipment. Since many of the parasites and disease producing organisms in the waste
are killed by the relatively high temperature in the digester tanks, the digested material can also be
used as fertilizer or fish feed.
Heat is used to convert biomass chemically into a pyrolysis oil. The oil, which is easier to store and
transport than solid biomass material, is then burned like petroleum to generate electricity. Pyrolysis
also can convert biomass into phenol oil, a chemical used to make wood adhesives, molded plastics
and foam insulation. Wood adhesives are used to glue together plywood and other composite wood
products.
Electricity Production from Biomass
As older power plants age and need to be replaced, and if the cost of fossil fuels continues to rise,
cogeneration will be an increasingly attractive alternative for generating electricity. The future of
biomass electricity generation lies in biomass integrated gasification/gas turbine technology, which
offers high-energy conversion efficiencies. The electricity is produced by direct combustion of
biomass, advanced gasification and pyrolysis technologies, and is almost ready for commercial scale
use.
A steam power plant is actually a two-fluid system; that is, energy is exchanged between the
combustion gases and water. The feasibility of combining gas and steam expansion in a power cycle
has been extensively explored. Because steam generation involves the flow of large volumes of
combustion gases, gas expansion is most appropriately accomplished in a gas turbine (Sorensen,
1983).
In the short to medium term, biomass waste and residues are expected to dominate biomass supply,
to be substituted by energy crops in the longer term. The future of biomass electricity generation
lies in biomass integrated gasification/gas turbine technology, which offers high-energy conversion
efficiencies. Biomass power plants (BPPs) use technology that is very similar to that used in coal-fired
160
power plants. For example, biomass plants use similar BPP efficiencies of about 25% steam-turbine
generators and fuel delivery systems. Electricity costs are in the −8 c/kWh range. The average BPP is
about 20 MW in size, with a few dedicated wood-fired plants in the 40–50 MW capacity, with gas
turbine/steam combined cycle. Biomass is burned to produce steam, the steam turns a turbine and
drives a generator, producing electricity.
The biomass power industry in the United States has grown from less than 200 MW in 1979 to more
than 6000 MW in 1990. The United States Department of Energy (USDOE) is projecting installed
capacity will grow to about 22 GW by the year 2010 (Bain, 1993). USDOE estimates the present and
future impact of biomass-power production of the US economy (Meridian and Antares, 1992). In the
year 1992, electrical production from biomass, primarily wood, had a net impact of $1.7 billion and
biomass electrical-generating capacity will have grown to approximately 22 GW in 2010. At this
capacity level, the economic benefits are estimated to be $6.2 billion in personal and corporate
income and 238,000 jobs (Demirbas, 2002).
Biomass energy uses, such as electric power generation, also have market entry problems. Tax
incentives have been provided to stimulate and encourage the use of biomassbased power
generation, but several of the incentives have expired or the conditions that permit their use are
difficult to satisfy.
Currently, there are no virgin biomass species that are routinely grown in the United States for use
as power plant fuels. There are many power plants, however, that are fueled throughout the United
States with waste biomass. These plants often take credit for waste disposal, such as the tipping fees
for accepting and disposing of MSW, or the power generated as a by-product and is used on-site, the
plant is located in or near the center of readily available waste biomass whose disposal is a serious
problem, or the power purchase contracts priced at the so-called avoided cost, which is the cost that
the utility would incur by generating the power itself, are sufficiently favorable to justify the
generation of electric power.
Hydrogen from Biomass
Hydrogen is a clean burning fuel. It is not a primary fuel; it must be manufactured from water with
either fossil or non-fossil energy sources. Hydrogen is produced from pyroligneous oils produced
from the pyrolysis of lingocellulosic biomass (Demirbas and Caglar, 1998).
Gasification of solid wastes and sewage is a recent innovation. The synthesis gas formed with air or
oxygen is reformed to hydrogen. The solid waste concept solves two problems: (1) disposal of urban
refuse and sewage, and (2) a source of hydrogen powered vehicles (Veziroglu, 1975). Hydrogen from
biomass has generally been based on the following reactions (Demirbas et al., 1996):
Municipal solid waste + Air = CO + H2
Biomass + H2O + Air = H2 + CO2
Cellulose + H2O + Air = H2 + CO + CH4
Ethanol Production from Biomass
Ethanol costs could be reduced dramatically if efforts to produce ethanol from biomass are
successful. Biomass feed stocks, including forest residue, agricultural residue, and energy crops, are
abundant and relatively inexpensive, and they are expected to lower the cost of producing ethanol
and provide stability to supply and price.
Ethanol is a cleaner-burning, renewable fuel that can be produced from a number of domestic feed
stocks, mostly crops such as corn and grains. Some conventional food crops that are high in starches
and sugars, like sugarcane, corn, sorghum, etc. can be fermented to produce ethanol, a relatively
clean burning, high-energy fuel. The choice of biomass is important as feedstock costs typically make
up 55–80% of the final alcohol selling price (WEC, 1994).
Ethanol is produced by a process known as fermentation. Typically, sugar is extracted from the
biomass crop by crushing, then mixing with water and yeast and warm in large tanks called
fermenters. The yeast breaks down the sugar and converts it to methanol.
161
A distillation process is required to remove the water and other impurities in the diluted alcohol
product (10–15% ethanol). The concentrated ethanol (95% by volume with a single step distillation
process) is drawn off and condensed to a liquid form (Demirbas, 2001b).
Other less expensive biomass feedstock, such as wood or plant wastes, can also be used for ethanol
production, but present conversion techniques in this field are not very efficient, hence, overall cost
of ethanol produced from these sources is relatively greater.
Overall output is forecast to reach 31.4 billion liters compared with 29.9 billion in 2000 and 31.1
billion in 1999. Nevertheless, the world total is still below the all-time high reached in 1997, when a
total of 33.0 billion liters were produced. By the year 2000, 500 million gallons of biomass ethanol
will displace 13 million barrels of oil. By the year 2020, 14 billion gallons of ethanol will displace 348
million barrels of oil.
The Future of Biomass
Biomass provides a number of local environmental gains. Energy forestry crops have a much greater
diversity of wildlife and flora than the alternative land use, which is arable or pasture land. Energy
crops may also offer a corridor for wildlife between woodland habitats. Energy crops that are
carefully sited and designed will enhance local landscapes and provide a new habitat for recreation.
Provision of recreation habitat is important near urban centers.
It is important to underline here that the collection of fuel from European forestry and agriculture
and the use of energy crops is a sustainable activity that does not deplete future resources. By the
year 2050, it is estimated that 90% of the world population will live in developing countries (Ramage
and Scurlock, 1996).
In industrialized countries, the main biomass processes utilized in the future are expected to be
direct combustion of residues and wastes for electricity generation, Bioethanol and bio diesel as
liquid fuels and combined heat and power production from energy crops. The future of biomass
electricity generation lies in biomass integrated gasification/gas turbine technology, which offers
high energy conversion efficiencies.
Biomass will compete favorably with fossil mass for niches in the chemical feedstock industry.
Biomass is a renewable, flexibly and adaptable resource. Crops can be grown to satisfy changing end
use needs (Demirbas, 2001b).
Environmental Impacts
As with all forms of energy production, biomass energy systems raise some environmental issues
that must be addressed. In biomass energy projects, issues such as air pollution, impacts on forest,
and impacts due to crop cultivation must be addressed on a case by case basis. Unlike other nonrenewable forms of energy, biomass energy can be produced and consumed in a sustainable fashion,
and there is no net contribution of carbon dioxide to global warming (Demirbas, 2001b).
The environmental repercussions of using biomass as a source of fuel vary according to the type of
conversion technology. The combustion of biomass produces significantly fewer nitrogen oxides and
sulfur dioxide than the burning of fossil fuels. Liquid biomass fuels like ethanol and methanol
produce less carbon monoxide, hydrocarbons and potentially carcinogenic compounds than gasoline
and diesel. Unlike fossil fuel combustion, the use of biomass fuels in a well managed, sustainable
production programmer will not contribute to carbon dioxide levels that cause global warming. If,
however, a forest region is indiscriminately cleared for fuel, carbon dioxide levels will increase
because carbon dioxide released into the atmosphere is not recycled for new growth.
Biomass fuel is a renewable energy source and its importance will increase as national energy policy
and strategy focuses more heavily on renewable sources and conservation. Biomass power plants
have advantages over fossil-fuel plants, because their pollution emissions are less.
Technologies have advanced to be largely pollution free. There is zero to little production of slag,
ash, SOx, NOx, or CO2 in biomass consumption. However, the use of appropriate, modern technology
is critical, so there is zero to little contribution of pollution to the greenhouse effect. There is also no
162
nuclear waste. Since biomass energy does not contribute anything harmful to the environment, it
lies very consistently with environmental protection policies.
Wood combustion results in lower emissions of SO2 than, for example, coal and would contribute to
amelioration of acid rain. Burning wood produces 90% less sulfur than coal. Research on coutilization of biomass with coal has shown that, through dilution effects, emissions of SO2 are
reduced linearly with increasing percentage of wood used. In some circumstances, reduced NOx
emissions occur because of a reaction between components of the wood and coal particles.
Sulfur can be considered as a part of the ecological balance in nature. No additional sulfur comes
from bio energy. The effects of using wood biomass for energy on the level of emissions of acidifying
compounds are small. Major improvements in heat and power production technology have already
been achieved regarding sulfur emissions. In agricultural land, there may be a certain amount of
sulfur from fertilizer that is recycled in the environment if short rotation forest or grass is used as a
fuel.
The energy dimension of biomass use is importantly related to the possible increased use of this
source as a critical option to tackle the global warming issue. Biomass is generally considered as an
energy source completely CO2-neutral. The underlying assumption is that the CO2 released in the
atmosphere is matched by the amount used in its production. This is true only if biomass energy is
sustainable consumed, i.e., the stock of biomass does not diminish in time. This may not be the case
in many developing countries. The reduction of CO2 emissions applies for electricity production with
biomass as for any other use of biomass source of energy.
Globally significant environmental benefits may result from using wood for energy rather than fossil
fuels. The greatest benefit is derived from substituting biomass energy for coal. The degree of
benefit depends greatly on the efficiency with which the wood is
converted to electricity. If the
Table 6
efficiency of conversion of wood to
Example carbon offsets from short-rotation plantation
electricity is similar to coal
energy used for power production and displacing coal
conversion to electricity, then the Factor
Wood
Coal
benefits are several. The ash and Energy density (GI/dry ton)
19.80
29.30
waste products from burning will, in
Heat rates (kJ/kWh)
7,200–18,000
10.90
most cases, be sufficiently benign to
Feed stock carbon (kgC/GI)
50.00
70.0
return to the soil. There will be a
Carbon %
25.30
24.10
considerable reduction in net carbon
Input carbon (kgC/GI)
1.34
0.53
dioxide emissions that contribute to
Total carbon (kgC/GI)
26.62
24.65
the greenhouse effect. For example,
one dry ton of wood will displace 15 GJ of coal. The 15 GJ of coal will have the equivalent of 0.37 ton
of carbon, assuming the wood is converted at an efficiency of 25%. Example carbon offsets from
short-rotation plantation energy used for power production and displacing coal is given Table 6.
Conclusions
Biomass is the most important renewable energy source in the world. Biomass fuel is a renewable
energy source and its importance will increase as national energy policy and strategy focuses more
heavily on renewable sources and conservation. Biomass power plants have advantages over fossilfuel plants because their pollution emissions are less.
World production of biomass is estimated at 146 billion metric tons a year, through mostly wild
plant growth. Total annual production of biomass is 2,740 quads in the world. In the future, biomass
has the potential to provide a cost-effective and sustainable supply of energy, while at the same
time aiding countries in meeting their greenhouse gas reduction targets.
It is important to underline here that the collection of fuel from European forestry and agriculture
and the use of energy crops is a sustainable activity that does not deplete future resources. By the
year 2050, it is estimated that 90% of the world population will live in developing countries.
163
6.2 OVERVIEW OF THE MARKETS FOR WOOD BIOMASS FOR ENERGY PRODUCTION
GLOBALLY AND WITHIN THE PAKISTAN THIS INCLUDES THE SUPPLY, QUANTITY,
DEMAND, AND CONSUMPTION AS WELL AS CONSUMER MARKET ASPECTS.
6.3 FUNDAMENTALS OF THE POLICIES THAT HAVE IMPACTS ON THE SUPPLY AND
CONSUMPTION OF THE ENERGY WOOD;
In order to build scenarios for future wood supply, forecasts are needed. One main source
for future forest products demand and supply is the European Forest Sector Outlook Study
(2005). In this study, outlooks for industrial roundwood consumption, as well as consumption
of
sawnwood, pulpwood and panels are made. However, no forecasts are made for the
consumption of fuelwood; consumption was assumed to stay level. Since during recent
years
fuelwood consumption for energy generation is becoming increasingly important, the present
study is incorporating this demand by taking policy objectives for renewable energy and
wood
energy in particular to predict the wood demand for 2010 and 2020.
The EFSOS provides three different scenarios on the sectoral growth (of real production
and consumption) of the wood-based industries. The baseline scenario, assuming a
moderate
growth rate, was used in this study since it is considered to reflect best the expected growth
rate of the forest-based industries if energy industries enhance competition for the raw
material.
The others are based on slower economic growth due to environmental considerations and
higher growth taking more globalisation into account.
The reference data (production, net trade, prices, etc) for the EFSOS model is the average
of 1999 - 2001. The annual growth of production, net trade and consumption in the model is
determined by the various input variable to the model. As shown by Schulmeyer (2006) the
EFSOS model predicts the international developments in forest products demand and supply
mostly correctly. However, in some countries, most notably in Germany, the production has
increased substantially more than predicted by EFSOS. Therefore, the reference data for
7
production and consumption of forest products (sawnwood, panels and pulp) was updated
on
the basis of the average data from 2004 - 2006. The annual growth rates (2005 - 2020) for
production and net trade were considered to remain unchanged. These growth rates were
applied to the new reference data, to obtain forecasts for production and consumption of
forest
products for 2010 and 2020.
The assumption that material efficiency of the wood-processing industries (wood input per
unit produced) would remain constant, leads to a slight over-estimation of the wood
consumption in this sector in the future.
3.3 Calculating the consequences of policy objectives
Various paths can be chosen to predicting the future role of wood in energy generation. In
this study, no econometric models were used to forecast the demand for wood energy, since
EFSOS so far does not model the consumption of wood for energy generation, but it was
assumed that the demand would be driven by policies. Prices are not included in the study,
in
order to keep the analysis simple and comprehensible. However, this implies certain
assumptions and restrictions when looking at the results. Thus, no conclusions are made on
the price of reaching the policy targets, but rather on the amounts of wood needed (also in
164
comparison with other wood consumers), and this is leading to the question of possible
impacts
of the policies.
This study has collected national and EU targets for renewable energy, bioenergy and wood
energy (if available) and translated them into wood volumes, by applying number of simple
transparent assumptions:
1. Obtain credible official scenario for total primary energy supply (taking account of
foreseen efficiency savings) if available. Otherwise assume the same energy supply as
in 2005;
2. Apply official policy target for energy production from renewable sources to total energy
supply. If no targets were found the overall EU targets were assumed (2010: 12% and
2020: 20% 4).
3. Apply national target for bioenergy if available. Otherwise, estimate the share of energy
production from biomass as percentage of energy production from renewable sources
(typically by assuming the same share as in 2005)
4. Apply target for wood energy if available. Otherwise, estimate the share of energy
production from wood as percentage of energy production from biomass sources
(typically by assuming the same share as in 2005)
The same methodology was used for 2010 and 2020, bearing in mind that for 2020 much
less
information was found on national targets, or targets for bioenergy or even wood energy.
4 If
the 2010 target was below 12%, and no target was set for 2020, the growth rate of renewable
energy
(as targeted between 2005 and 2010) is assumed to continue. This leads mostly to a lower figure than
20%.
If the target is already above the EU target and no new targets were set, it is assumed to stay.
8
"75 % scenario" for 2020
Wood energy has the highest share of all renewable sources in 2005 in most countries
(wood
energy constitutes over 50% of all renewable energy over the EU as a whole). Therefore, an
increase in renewable energy would affect wood energy the most, if the relative shares of
different energies would remain constant (as suggested in assumptions 3 and 4). However,
in
particular this assumption seems unrealistic in the long term (2020), since other renewable
energies will develop further and faster (form a lower base) and become more competitive.
In
addition, the availability of wood raw material is likely to be decreasing, leading to a wood
price
increase, and in any case the use of wood would probably remain mostly for heating or CHP.
Therefore, the study suggests a scenario, where the relative share of wood compared to all
other renewable energy sources decreases to 75%5 of the percent share in 2005 by 2020.
However, the scenario made the assumption that despite the decrease in relative share of
wood energy compared to other renewable sources, the absolute figures would not be less
then 2010. If targets for wood energy for 2020 were available, the scenario stuck to the
national
targets (as for Finland and Slovakia).
In recent years, wood energy has attracted attention as an environmentally-friendly
alternative to fossil energy, especially in industrial applications for heat and power generation
and co-firing for bioelectricity generation. A key priority is aligning energy policies so that
the production and use of woody biomass for energy is based on what can be sustainably
165
supplied. FAO assists Member States to improve their wood energy situation in terms of
social and economic viability, ecological sustainability, resource efficiency and greenhouse
gas emissions. The Organization supports its Members by:





raising awareness of the importance of wood energy;
collecting, improving and sharing accurate data;
formulating, implementing and monitoring sound wood energy policies;
facilitating cross-sectoral communication and collaboration; and
applying sustainable and resource efficient production and consumption practices.
Read more
Wood energy is most competitive when produced as a by-product of the wood processing
industry. Wood residues from forests provide possibly the greatest immediate opportunity for
bioenergy generation given their availability, relatively low-value and their proximity to
forestry operations. Wood residues from mills represent another, more easily accessible,
source of residues.
FAO regularly conducts wood energy outlook studies for different regions. The latest study
for Europe presents comprehensive scenarios on wood energy development that offers
decision-makers from governments and industries information on the potential impacts of
their decisions and provides guidance on how to prepare for future challenges (e.g. the
intensive mobilization of wood resources).
In many parts of the world, particularly in rural communities in developing countries, wood
from forests remains a very important source of energy for cooking and heating. Wood-based
energy is also widely used in commercial applications such as fish drying, tobacco curing and
brick baking. Total consumption of woodfuel is still increasing in much of Africa, largely due
to population growth. In rural areas of most developing countries, fuelwood is the
predominant form of wood energy. Charcoal remains a significant energy source in many
African, Asian and Latin American households in urban areas.
Paramount to finding viable and sustainable solutions for energy access in rural and urban
settings is a clear understanding of the local impacts of fuelwood collection in forests and
166
from trees outside forests, its role in livelihoods and its impact on forest degradation and
deforestation.
6.4 WOOD BASED FUELS; AND/ OR BIO-ENERGY AND BIO-FUELS‘ MARKETS
World Biofuels Markets: Waste Versus Fuel?
Food versus fuel is the alliterative catchphrase we're all beginning to hear more and more of, as the
global population increases the need for a more sustainable source of fuel rises. Delegates came
together at World Biofuels Markets in Rotterdam earlier this month, to discuss the future of biofuels
and their feedstocks, writes TheBioenergySite Editor, Gemma Hyland.
Speaking at the keynote session was Raffaello Garofalo, Secretary General of the European
Biodiesel Board, Suzanne Hunt, Senior Advisor of the Carbon War Room, Dr Damian
Carrington, Head of Environment for The Guardian and Sander van Bennekom, Policy
Advisor for Oxfam Novib.
"From where I sit, the biofuels industry does have an image problem, which needs to be
addressed," said Dr Carrington.
The Renewable Energy Directive (RED) states that biofuels should account for 10 per cent of
land transport fuel by 2020. However the more the industry tries to reach their ambitious
targets, the more hurdles they come up against.
Initially, in 2006, high oil prices and surplus feedstocks garnered support from governments
to increase research and development into biofuel production.
Fast-forward six years and a slumping economy, expired tax credits, soaring feedstock costs
and a rising population has given way to a new argument on whether biofuel production is
sustainable any longer.
Yes it is, say some, but at what cost?
In November 2011 the global population reached 7 billion and is expected to hit more than 9
billion by 2050.
"Food is an issue in the growing world," said Dr Carrington. "Environment groups should be
the biggest supporters of biofuels. Fossil fuels are driving climate change, which is a problem
for everybody and yet I hear from environment groups every day and they are still not the
greatest supporters of biofuels at the moment and that is mainly down to the link between
biofuels and food prices."
Political Support
"The biofuels industry needs political support. I have spoken to quite a lot of MEP's over the last few
years who are pretty confused at the moment. They say five years ago biofuels were the answer to
everything, yet now they are the villain."
According to the International Energy Agency (IEA) biofuel production dropped for the first time in
167
2011.
"That is not the sign of an industry heading towards 25 per cent of global energy. Ironically I think
the cause of that drop was to do with the rising cost of food prices, the feedstock became more
expensive," concluded Dr Carrington.
In contrast, earlier this month it was reported that ethanol refiners are consuming more of the US
corn crop than livestock producers, for the first time in US history, and this trend is set to continue
until 2014 as government mandates and exports boost fuel demand.
However, respondents to the World Biofuel Markets annual survey declared feedstocks are shifting
to non-food and waste.
When asked which next generation feedstocks they thought would be the most promising in 2012,
the responses were fairly evenly split among municipal solid waste at 26 per cent, non-food energy
crops, such as camelina and jatropha at 24 per cent and algae at 20 per cent. Cellulosic trailed
slightly at around 17 per cent.
"To me, even the title of the debate is sometimes misleading," said Raffaello Garofalo, Secretary
General of the European Biodiesel Board.
"Instead of talking 'food versus fuel' we should talk food and fuel. Are we convinced that we cannot
make it so that the land can sustainably produce both food and fuel? It is a matter of how we can do
it efficiently."
Suzanne Hunt, Senior Advisor of the Carbon War Room stated that she agrees bioenergy has an
important role to play, but there are issues to overcome first.
The one factor mentioned during the debate, which gets increasingly overlooked, is that there can
be no clear winner or loser in this ongoing battle. We need both food and fuel to survive, and better
practise and understanding of how to provide both sustainably.
Surprisingly there was no mention of food waste during the keynote session. In the UK alone 7.2
million tonnes of food is thrown away as each year, even more shockingly the UN Food Agency
reports that 1.3 billion tonnes of food was wasted last year.
"When we talk about making bioenergy sustainable, the thing we should be debating is not whether
it can be done 'right', we all agree that, that's possible, the issue is how to improve it," concluded Ms
Hunt.
March 2012
168
Biofuel trade is expected to expand in the decade to 2021, with cross trade likely to occur.
» Focus: Biofuel mandates in the United States to encourage trade?
Error!
Error!
» See all data for biofuels
Market situation
World ethanol prices increased strongly in 2011 well above the levels of the 2007/08 highs in
a context of strong energy prices, although the commodity prices of ethanol feedstock,
mainly sugar and maize, decreased from their peaks in 2010. The two major factors behind
this increase were the stagnating ethanol supply in the United States and a drop in Brazilian
sugar cane production. Additionally, ethanol production was also significantly below
expectations in developing countries having implemented mandates or ambitious targets for
the use of biofuels.
World biodiesel prices also increased in 2011. Contrary to the global ethanol market,
production did not stagnate in 2011; the four major biodiesel producing regions (the
European Union, the United States, Argentina, and Brazil) increased their supply compared
to 2010. This increase was moderated by a decreasing biodiesel production in Malaysia (from
about 1 Bnl in 2010 to almost nothing in 2011).
Projection highlights


Over the projection period, ethanol and biodiesel prices are expected to remain supported
by high crude oil prices and by the implementation and continuation of policies promoting
biofuel use. Changes in the implementation of biofuel policies can strongly affect biofuel
markets.
Global ethanol and biodiesel production are projected to expand but at a slower pace than
in the past. Ethanol markets are dominated by the United States, Brazil and to a smaller
extent the European Union. Biodiesel markets will likely remain dominated by the European
Union and followed by the United States, Argentina and Brazil.
169

Biofuel trade is anticipated to grow significantly, driven by differential policies among major
producing and consuming countries. The United States, Brazil and the European Union
policies all “score” fuels differently for meeting their respective policies. This differentiation
is likely to lead to additional renewable fuel trade as product is moved to its highest value
market, resulting in potential cross trade of ethanol and biodiesel.
Focus: Biofuel mandates in the United States to encourage trade?
There are many uncertainties concerning the future of biofuel policies. An important one
concerns the policy options faced by the US Environmental Protection Agency (EPA) in the
implementation of the US biofuel policy.
The Outlook report provides a scenario analysis of three alternative policy implementation
options that take into account the fact that the cellulosic mandate as defined in the Energy
Independence and Security Act of 2007 (EISA) will not be met. Those scenarios have been
produced to illustrate the policy space, and not to promote any particular policy option. The
results of the scenario can be summarised as follows:



If the shortfall in the cellulosic mandate in the global US mandate is met by raising the
mandate for advanced biofuels or by allowing more corn-based ethanol, the impacts on
world prices for biofuels (in particular ethanol) as well as for biofuel feedstocks (coarse
grains, sugar cane) are likely to be important. Spill-over effects on other agricultural
commodity prices (including meat and fish) would occur.
Meeting the adjusted US biofuel mandate will require some adjustment in terms of ethanol
production and consumption patterns, as well as in terms of ethanol feedstock use around
the world. Food is likely to cost more as a result of such adjustments.
An important policy driven two-way ethanol trade is likely to emerge between Brazil and the
United States under certain conditions. Brazil is likely to be the sole country able to adapt
and respond to US demand. This is due to the nature of its ethanol production based on
sugar cane, its flexibility to switch between ethanol and sugar production, and to the rising
demand for ethanol used for flex-fuel vehicles in Brazil.
170
CHAPTER NO.07
BIOENERGY RESEARCH AND DEVELOPMENT
7.1 NEED FOR RESEARCH AND DEVELOPMENT ON ENVIRONMENT FRIENDLY AND SOCIO
ECONOMICALLY RELEVANT TECHNOLOGIES.
7.2 ENERGY FROM PLANTS-PROBLEMS AND PROSPECTS.
7.3 PETRO-CROPS.
7.4 CRITERIA FOR EVALUATION OF DIFFERENT SPECIES FOR ENERGY PLANTATION.
171
CHAPTER NO.08
ADVANCED ENERGY TECHNOLOGY
8.1 ADVANCED ENERGY TECHNOLOGIES IN THE PRODUCTION OF BIO-FUELS
Second-generation (advanced) biofuels
Second-generation biofuels are produced from sustainable feedstock. Sustainability of a feedstock is
defined, among others, by availability of the feedstock, impact on GHG emissions, and impact on
biodiversity and land use. Many second-generation biofuels are under development such as
Cellulosic ethanol, Algae fuel., biohydrogen, biomethanol, DMF, BioDME, Fischer-Tropsch diesel,
biohydrogen diesel, mixed alcohols and wood diesel.
Cellulosic ethanol production uses nonfood crops or inedible waste products and does not divert
food away from the animal or human food chain. Lignocellulose is the "woody" structural material of
plants. This feedstock is abundant and diverse, and in some cases (like citrus peels or sawdust) it is in
itself a significant disposal problem.
Producing ethanol from cellulose is a difficult technical problem to solve. In nature, ruminant
livestock (such as cattle) eat grass and then use slow enzymatic digestive processes to break it into
glucose (sugar). In cellulosic ethanol laboratories, various experimental processes are being
developed to do the same thing, and then the sugars released can be fermented to make ethanol
fuel. In 2009, scientists reported developing, using "synthetic biology", "15 new highly stable fungal
enzyme catalysts that efficiently break down cellulose into sugars at high temperatures", adding to
the 10 previously known. The use of high temperatures has been identified as an important factor in
improving the overall economic feasibility of the biofuel industry and the identification of enzymes
that are stable and can operate efficiently at extreme temperatures is an area of active research. In
addition, research conducted at Delft University of Technology by Jack Pronk has shown that
elephant yeast, when slightly modified, can also produce ethanol from inedible ground sources (e.g.
straw).
The recent discovery of the fungus Gliocladium roseum points toward the production of so-called
myco-diesel from cellulose. This organism (recently discovered in rainforests of northern Patagonia)
has the unique capability of converting cellulose into medium-length hydrocarbons typically found in
diesel fuel. Scientists also work on experimental recombinant DNA genetic engineering organisms
that could increase biofuel potential.
Scientists working with the New Zealand company Lanzatech have developed a technology to use
industrial waste gases, such as carbon monoxide from steel mills, as a feedstock for a microbial
172
fermentation process to produce ethanol. In October 2011, Virgin Atlantic announced it was joining
with Lanzatech to commission a demonstration plant in Shanghai that would produce an aviation
fuel from waste gases from steel production.
Scientists working in Minnesota have developed co-cultures of Shewanella and Synechococcus that
produce long-chain hydrocarbons directly from water, carbon dioxide, and sunlight. The technology
has received ARPA-E funding.
Issues with biofuel production and use
There are various social, economic, environmental and technical issues with biofuel production and
use, which have been discussed in the popular media and scientific journals. These include: the
effect of moderating oil prices, the "food vs fuel" debate, poverty reduction potential, carbon
emissions levels, sustainable biofuel production, deforestation and soil erosion, loss of biodiversity,
and impact on water resources, as well as energy balance and efficiency. The International Resource
Panel, which provides independent scientific assessments and expert advice on a variety of
resource-related themes, assessed the issues relating to biofuel use in its first report, Towards
sustainable production and use of resources: Assessing Biofuels. The report outlined the wider and
interrelated factors that need to be considered when deciding on the relative merits of pursuing one
biofuel over another. It concluded not all biofuels perform equally in terms of their impact on
climate, energy security, and ecosystems, and suggested environmental and social impacts need to
be assessed throughout the entire life-cycle.
Although many current issues are noted with biofuel production and use, the development of new
biofuel crops and second-generation biofuels attempts to circumvent these issues. Many scientists
and researchers are working to develop biofuel crops that require less land and use fewer resources,
such as water, than current biofuel crops do. According to the journal Renewable fuels from algae:
An answer to debatable land based fuels, algae are a source for biofuels that could use currently
unprofitable land and wastewater from different industries. Algae are able to grow in wastewater,
which does not affect the land or freshwater needed to produce current food and fuel crops.
Furthermore, algae are not part of the human food chain, so do not take away food resources from
humans.
The effects of the biofuel industry on food are still being debated. According to a recent study,
biofuel production accounted for 3-30% of the increase in food prices in 2008. A recent study for the
International Centre for Trade and Sustainable Development shows market-driven expansion of
ethanol in the US increased corn prices by 21% in 2009, in comparison with what prices would have
been had ethanol production been frozen at 2004 levels. This has prompted researchers to develop
biofuel crops and technologies that will reduce the impact of the growing biofuel industry on food
production and cost.
One step to overcoming these issues is developing biofuel crops best suited to each region of the
world. If each region used a specific biofuel crop, the need to use fossil fuels to transport the fuel to
other places for processing and consumption will be diminished. Furthermore, certain areas of the
globe are unsuitable for producing crops that require large amounts of water and nutrient-rich soil.
Therefore, current biofuel crops, such as corn, are unpractical in different environments and regions
of the globe.
In 2012, the United States House Committee on Armed Services put language into the 2013 National
Defense Authorization Act that would prevent the Pentagon from purchasing biofuels that offered
improved performance for combat aircraft.
Current research
Research is ongoing into finding more suitable biofuel crops and improving the oil yields of these
crops. Using the current yields, vast amounts of land and fresh water would be needed to produce
enough oil to completely replace fossil fuel usage. It would require twice the land area of the US to
be devoted to soybean production, or two-thirds to be devoted to rapeseed production, to meet
current US heating and transportation needs. Specially bred mustard varieties can produce
173
reasonably high oil yields and are very useful in crop rotation with cereals, and have the added
benefit that the meal leftover after the oil has been pressed out can act as an effective and
biodegradable pesticide.
The NFESC, with Santa Barbara-based Biodiesel Industries, is working to develop biofuels
technologies for the US navy and military, one of the largest diesel fuel users in the world. A group of
Spanish developers working for a company called Ecofasa announced a new biofuel made from
trash. The fuel is created from general urban waste which is treated by bacteria to produce fatty
acids, which can be used to make biofuels.
Ethanol biofuels
As the primary source of biofuels in North America, many organizations are conducting research in
the area of ethanol production. The National Corn-to-Ethanol Research Center (NCERC) is a research
division of Southern Illinois University Edwardsville dedicated solely to ethanol-based biofuel
research projects. On the federal level, the USDA conducts a large amount of research regarding
ethanol production in the United States. Much of this research is targeted toward the effect of
ethanol production on domestic food markets. A division of the U.S. Department of Energy, the
National Renewable Energy Laboratory (NREL), has also conducted various ethanol research
projects, mainly in the area of cellulosic ethanol.
Algal biofuels
From 1978 to 1996, the US NREL experimented with using algae as a biofuels source in the "Aquatic
Species Program".A self-published article by Michael Briggs, at the UNH Biofuels Group, offers
estimates for the realistic replacement of all vehicular fuel with biofuels by using algae that have a
natural oil content greater than 50%, which Briggs suggests can be grown on algae ponds at
wastewater treatment plants. This oil-rich algae can then be extracted from the system and
processed into biofuels, with the dried remainder further reprocessed to create ethanol. The
production of algae to harvest oil for biofuels has not yet been undertaken on a commercial scale,
but feasibility studies have been conducted to arrive at the above yield estimate. In addition to its
projected high yield, algaculture — unlike crop-based biofuels — does not entail a decrease in food
production, since it requires neither farmland nor fresh water. Many companies are pursuing algae
bioreactors for various purposes, including scaling up biofuels production to commercial levels. Prof.
Rodrigo E. Teixeira from the University of Alabama in Huntsville demonstrated the extraction of
biofuels lipids from wet algae using a simple and economical reaction in ionic liquids.
Jatropha
Several groups in various sectors are conducting research on Jatropha curcas, a poisonous shrub-like
tree that produces seeds considered by many to be a viable source of biofuels feedstock oil. Much of
this research focuses on improving the overall per acre oil yield of Jatropha through advancements
in genetics, soil science, and horticultural practices.
SG Biofuels, a San Diego-based jatropha developer, has used molecular breeding and biotechnology
to produce elite hybrid seeds that show significant yield improvements over first-generation
varieties. SG Biofuels also claims additional benefits have arisen from such strains, including
improved flowering synchronicity, higher resistance to pests and diseases, and increased coldweather tolerance.
Plant Research International, a department of the Wageningen University and Research Centre in
the Netherlands, maintains an ongoing Jatropha Evaluation Project that examines the feasibility of
large-scale jatropha cultivation through field and laboratory experiments. The Center for Sustainable
Energy Farming (CfSEF) is a Los Angeles-based nonprofit research organization dedicated to jatropha
research in the areas of plant science, agronomy, and horticulture. Successful exploration of these
disciplines is projected to increase jatropha farm production yields by 200-300% in the next 10 years.
Fungi
A group at the Russian Academy of Sciences in Moscow, in a 2008 paper, stated they had isolated
large amounts of lipids from single-celled fungi and turned it into biofuels in an economically
efficient manner. More research on this fungal species, Cunninghamella japonica, and others, is
174
likely to appear in the near future. The recent discovery of a variant of the fungus Gliocladium
roseum points toward the production of so-called myco-diesel from cellulose. This organism was
recently discovered in the rainforests of northern Patagonia, and has the unique capability of
converting cellulose into medium-length hydrocarbons typically found in diesel fuel.
Greenhouse gas emissions
According to Britain's National Non-Food Crops Centre, total net savings from using first-generation
biodiesel as a transport fuel range from 25-82% (depending on the feedstock used), compared to
diesel derived from crude oil. Nobel Laureate Paul Crutzen, however, finds that the emissions of
nitrous oxide due to nitrate fertilisers is seriously underestimated, and tips the balance such that
most biofuels produce more greenhouse gases than the fossil fuels they replace. Producing
lignocellulosic biofuels offers potentially greater greenhouse gas emissions savings than those
obtained by first-generation biofuels. Lignocellulosic biofuels are predicted by oil industry body
CONCAWE to reduce greenhouse gas emissions by around 90% when compared with fossil
petroleum, in contrast first generation biofuels were found to offer savings of 20-70%.
Some scientists have expressed concerns about land-use change in response to greater demand for
crops to use for biofuel and the subsequent carbon emissions. The payback period, that is, the time
it will take biofuels to pay back the carbon debt they acquire due to land-use change, has been
estimated to be between 100 and 1000 years, depending on the specific instance and location of
land-use change. However, no-till practices combined with cover-crop practices can reduce the
payback period to three years for grassland conversion and 14 years for forest conversion. Biofuels
made from waste biomass or from biomass grown on abandoned agricultural lands incur little to no
carbon debt.
Biomass planting mandated by law (as in European Union) is causing concerns over raising food
prices and actual emissions reductions, as large quantities of biomass are being transported to the
EU from Africa, Asia, and the Americas (Canada, USA, Brazil). For example in Poland, as much as 85%
of biomass used is imported from outside of the EU, with a single electric plant in Łódź importing
over 7000 tons of wood biomass from the Republic of Komi (Russia) over distance of 7000 kilometers
on monthly basis.
175
CHAPTER NO.09
Acetic acid: An acid with the structure of
C2H4O2. Acetyl groups are bound through an
ester linkage to hemicellulose chains—
especially xylans—in wood and other plants.
The natural moisture present in plants
hydrolyzes the acetyl groups to acetic acid,
particularly at elevated temperatures.
Acid detergent fiber (ADF): Organic matter,
often cellulose and lignin based, that is not
solubilized after one hour of refluxing in an
acid detergent of cetyltrimethyl ammonium
bromide in 1N sulfuric acid.
Acid hydrolysis: The treatment of cellulosic,
starch, or hemicellulosic materials using acid
solutions (usually mineral acids) to break
down the polysaccharides to simple sugars.
Acid insoluble lignin: Mostly insoluble in
mineral acids so it can be analyzed
gravimetrically after hydrolyzing the cellulose
and hemicellulose fractions of the biomass
with sulfuric acid. ASTM E-1721-95 describes
the standard method for determining acid
insoluble lignin in biomass. See lignin and acid
soluble lignin.
Acid soluble lignin: A small fraction of the
lignin in a biomass sample that is solubilized
during the hydrolysis process of the acid
insoluble lignin method. May be quantified by
ultraviolet spectroscopy.
Acid: A solution that has an excess of
hydrogen ions (H+), with a pH of less than 7.
Acre — An area of land measuring 43,560
square feet.
GLOSSARY
Adaptive Management — A dynamic
approach to forest management in which the
effects of treatments and decisions are
continually monitored and used, along with
research results, to modify management on a
continuing basis to ensure that objectives are
being met.
Adsorption: The adhesion of molecules (as in
gases, solutions, or liquids) in an extremely
thin layer to the surface of solid bodies or
liquids with which they are in contact.
Aerobic
fermentation: Fermentation
processes that require the presence of
oxygen.
Aerobic: Able to live, grow, or take place only
where free oxygen is present.
Agricultural Residue - Agricultural crop
residues are the plant parts, primarily stalks
and leaves, not removed from the fields with
the primary food or fiber product. Examples
include corn stover (stalks, leaves, husks, and
cobs); wheat straw; and rice straw. With
approximately 80 million acres of corn
planted annually, corn stover is expected to
become a major biomass resource for
bioenergy applications.
Air dry - The state of dryness at equilibrium
with the water content in the surrounding
atmosphere. The actual water content will
depend upon the relative humidity and
temperature of the surrounding atmosphere.
Alcohol - The family name of a group of
organic chemical compounds composed of
176
carbon, hydrogen, and oxygen. The molecules
in the series vary in chain length and are
composed of a hydrocarbon plus a hydroxyl
group. Alcohol includes methanol and
ethanol. OR An organic compound with a
carbon bound to a hydroxyl (hydrogen and
oxygen, or –OH) group. Examples are
methanol, CH3OH, and ethanol, CH3CH2OH.
Aldehyde: Any of a class of highly reactive
organic chemical compounds characterized by
the common group CHO and used in the
manufacture of resins, dyes, and organic
acids.
Aldoses: Occurs when the carbonyl group of a
monosaccharide is an aldehyde. (Source:
Voet, D.; Voet, J. G. Biochemistry. New York:
John Wiley, 1990.)
Algae: Simple
photosynthetic
plants
containing chlorophyll, often fast growing and
able to live in freshwater, seawater, or damp
oils. May be unicellular and microscopic or
very large, as in the giant kelps.
Alkali lignin: Lignin obtained by acidification
of an alkaline extract of wood.
Alkali: Soluble
mineral
salts
with
characteristically "basic" properties. A
defining characteristic of alkali metals.
Alkaline hydrolysis: The use of solutions of
sodium hydroxide (or other alkali) in the
treatment of cellulosic material (wood) to
break down cellulose to simple sugars.
Alkaline metals - Potassium and sodium
oxides (K2O + NaO2) that are the main
chemicals in biomass solid fuels that cause
slagging and fouling in combustion chambers
and boilers.
Amylase: Family of enzymes that act together
to hydrolyze starch to individual glucose and
dextran units.
Anaerobic Digestion — Decomposition of
biological wastes by micro-organisms, usually
under wet conditions, in the absence of
oxygen, to produce a gas comprising mostly
methane and carbon dioxide. or Degradation
of organic matter by microbes that produces a
gas comprised mostly of methane and carbon
dioxide, usually under wet conditions, in the
absence of oxygen.
Anaerobic: Living or active in environment
without oxygen.
Anhydrous: A material that does not contain
water, either adsorbed on its surface or as
water of crystallization.
Annual Removals — The net volume of
growing stock trees removed from the
inventory during a specified year by
harvesting, cultural operations such as
timber stand improvement, or land clearing.
Aquatic
plants: The
aquatic
biomass
resources, such as algae, giant kelp, other
seaweed, and water hyacinth. Certain
microalgae can produce hydrogen and oxygen
while others manufacture hydrocarbons and a
host of other products. Microalgae examples
include Chlorella, Dunaliella, and Euglena.
Arabinan: The polymer of arabinose with a
repeating unit of C5H8O4. Can be hydrolyzed
to arabinose. (Source: Voet, D.; Voet, J. G.
Biochemistry. New York: John Wiley, 1990.)
Arabinose: A five-carbon sugar: C5H10O5. A
product of the hydrolysis of arabinan found in
the hemicellulose fraction of biomass.
Archaea (formerly Archaebacteria): A group
of single-celled microorganisms. A single
individual or species from this domain is
called an archaeon (sometimes spelled
"archeon"). They have no cell nucleus or any
other organelles within their cells.
Aromatic: A chemical that has a benzene ring
in its molecular structure (benzene, toluene,
xylene). Aromatic compounds have strong,
characteristic odors.
ASABE Standard X593 - The American Society
of Agricultural and Biological Engineers
(ASABE) in 2005 produced a new standard
(Standard X593) entitled “Terminology and
Definitions
for
Biomass
Production,
Harvesting
and
Collection,
Storage,
Processing, Conversion and Utilization.” The
purpose of the standard is to provide uniform
terminology and definitions in the general
area of biomass production and utilization.
This standard includes many terminologies
that are used in biomass feedstock
production, harvesting, collecting, handling,
storage, pre-processing and conversion,
bioenergy, biopower and bioproducts. The
terminologies were reviewed by many experts
from all of the different fields of biomass and
bioenergy before being accepted as part of
177
the standard. The full-text is included on the
online
Technical
Library
of
ASABE
(http://asae.frymulti.com); members and
institutions holding a site license can access
the online version. Print copies may be
ordered for a fee by calling 269-429-0300, emailing martin@asabe.org, or by mail at:
ASABE, 2950 Niles Rd., St. Joseph, MI 49085.
Asexual
reproduction - The
naturally
occurring ability of some plant species to
reproduce asexually through seeds, meaning
the embryos develop without a male gamete.
This ensures the seeds will produce plants
identical to the mother plant.
Ash — The noncombustible components
of fuel.
Ash content: Residue remaining after ignition
of a sample determined by a definite
prescribed procedure.
Attainment area: A geographic region where
the concentration of a specific air pollutant
does not exceed federal standards.
Auger: A rotating, screw-type device that
moves material through a cylinder. In alcohol
production, it is used to transfer grains from
storage to the grinding site and from the
grinding site to the cooker.
Avoided costs - An investment guideline
describing the value of a conservation or
generation resource investment by the cost of
more expensive resources that a utility would
otherwise
have
to
acquire.
Baghouse - A chamber containing fabric filter
bags that remove particles from furnace stack
exhaust Gases. Used to eliminate particles
greater than 20 microns in diameter.
B20: A mixture of 20% biodiesel and 80%
petroleum diesel based on volume.
Bacteria: A small single-cell organism.
Bacteria do not have an organized nucleus,
but they do have a cell membrane and
protective cell wall. Bacteria can be used to
ferment sugars to ethanol.
Bagasse: Residue remaining after extracting a
sugar-containing juice from plants like sugar
cane.
Bark: The outer protective layer of a tree,
including the inner bark and the outer bark.
The inner bark is a layer of living bark that
separates the outer bark from the cambium.
In a living tree, inner bark is generally soft and
moist while the outer bark is a layer of dead
bark that forms the exterior surface of the
tree stem. The outer bark is frequently dry
and corky.
Barrel of Oil Equivalent (BOE) — The
amount of energy contained in a barrel of
crude oil, i.e. approximately 6.1 GJ (5.8
million Btu), equivalent to 1,700 kWh. A
"petroleum barrel" is a liquid measure equal
to 42 U.S. gallons (35 Imperial gallons or 159
liters); about 7.2 barrels are equivalent to
one metric ton of oil.
Barrel (of oil): A liquid measure equal to 42
U.S. gallons (35 Imperial gallons or 159 liters);
about 7.2 barrels are equivalent to one tonne
of oil (metric), or typically about 306 pounds
of oil. One barrel equals 5.6 ft3; for crude oil,
one barrel contains about 5.8 x 106 Btu of
energy (6.1 GJ, equivalent to 1,700 kWh).
Basal Area — (a) The cross- sectional area (in
square feet) of a tree trunk at 4.5 feet above
the ground (Basal area of a tree is feet per
acre. OR The area of the cross section of a
tree stem, including the bark, measured at
breast height (4.5 feet above the ground).
Base: A solution that has an excess of
hydroxide ions (OH-) in aqueous solution and
has a pH greater than 7.
Batch distillation: A process in which the
liquid feed is placed in a single container and
the entire volume is heated (see batch
fermentation and batch process).
Batch fermentation: Fermentation conducted
from start to finish in a single vessel without
addition to, or removal of, a major substrate
or product stream until the process is
complete (see batch distillation and batch
process).
Batch process: Unit operation where one
cycle of feedstock preparation, cooking,
fermentation, and distillation is completed
before the next cycle is started (see batch
distillation and batch fermentation).
Beer: A fermented broth that consists of
water, ethanol, and small amounts of ether
and assorted alcohols.
Benzene: An aromatic component of gasoline,
which is a known cancer-causing agent. It is a
178
6-sided structure with three alternating
double bonds.
Best Management Practices: maintain and
improve the environmental values of forests
associated with soils, water, and biological
diversity; primarily used for the protection of
water quality.
Biobased product - The term 'biobased
product,' as defined by Farm Security and
Rural Investment Act (FSRIA), means a
product determined by the U.S. Secretary of
Agriculture to be a commercial or industrial
product (other than food or feed) that is
composed, in whole or in significant part, of
biological products or renewable domestic
agricultural materials (including plant, animal,
and marine materials) or forestry materials.
Biochar — A type of charcoal produced from
biomass via pyrolysis. Often used as a soil
amendment.
Biochemical Conversion — The use of
fermentation or anaerobic digestion to
produce fuels and chemicals from organic
sources. OR A general term describing the
use of biological systems to transform one
compound into another. Examples are
digestion of organic wastes or sewage by
microorganisms to produce methane and
the synthesis of organic compounds from
carbon dioxide and water by plants.
Biodiesel — A form of fuel for use in diesel
engines that is produced through a
chemical process called transesterfication
whereby glycerin is separated from
organically derived oils and fats. OR Fuel
derived from vegetable oils or animal fats. It
is produced when a vegetable oil or animal
fat is chemically reacted with an alcohol. OR
A biodegradable transportation fuel for use
in diesel engines that is produced through
the transesterfication of organically derived
oils or fats. It may be used either as a
replacement for or as a component of
diesel fuel.
Biodiversity — The variety of life forms in a
given area. Diversity can be categorized in
terms of the number of species, the variety in
the area’s plant and animal communities, the
genetic variability of the animals, or a
combination of these elements.
Bioenergy — Renewable energy produced
from organic matter through the conversion
of complex carbohydrates. This energy may
either be used directly as fuel, processed into
liquids or gasses, or be a residual of the
processing or conversion mechanisms. OR
Useful, renewable energy produced from
organic matter - the conversion of the
complex carbohydrates in organic matter to
energy. Organic matter may either be used
directly as a fuel, processed into liquids and
gasses, or be a residual of processing and
conversion.
Bioethanol - Ethanol produced from biomass
feedstocks. This includes ethanol produced
from the fermentation of crops, such as corn,
as well as cellulosic ethanol produced from
woody plants or grasses.
Biofuels — Liquid, solid, or gaseous fuels
made from biomass resources, or their
processing and conversion derivatives.
Examples include biodiesel from vegetable
oil, bioethanol from sugar cane or wood
chips,
and
biogas
from
anaerobic
decomposition of wastes.
Biogas - A combustible gas derived from
decomposing
biological
waste
under
anaerobic conditions. Biogas normally consists
of 50 to 60 percent methane. See also landfill
gas. OR A gaseous mixture of carbon dioxide
and methane produced by the anaerobic
digestion of organic matter.
Biogasification or biomethanization - The
process of decomposing biomass with
anaerobic bacteria to produce biogas.
Biological oxygen demand (BOD) - An indirect
measure of the concentration of biologically
degradable material present in organic
wastes. It usually reflects the amount of
oxygen consumed in five days by biological
processes breaking down organic waste.
Biomass energy - See Bioenergy.
Biomass processing residues - Byproducts
from processing all forms of biomass that
have significant energy potential. For
example, making solid wood products and
pulp from logs produces bark, shavings and
sawdust, and spent pulping liquors. Because
these residues are already collected at the
point of processing, they can be convenient
179
and relatively inexpensive sources of biomass
for energy.
Biomass - Any organic matter that is available
on a renewable or recurring basis, including
agricultural crops and trees, wood and wood
residues, plants (including aquatic plants),
grasses, animal manure, municipal residues,
and other residue materials. Biomass is
generally produced in a sustainable manner
from water and carbon dioxide by
photosynthesis. There are three main
categories of biomass - primary, secondary,
and tertiary. OR Biomass is any organic matter
including forest and mill residues, agricultural
crops and wastes, wood and wood wastes,
animal wastes, livestock operation residues,
aquatic plants, and municipal and industrial
wastes. OR An energy resource derived from
organic matter. These include wood,
agricultural waste, and other living-cell
material that can be burned to produce heat
energy. They also include algae, sewage, and
other organic substances that may be used to
make energy through chemical processes.
Biopower - The use of biomass feedstock to
produce electric power or heat through direct
combustion of the feedstock, through
gasification and then combustion of the
resultant gas, or through other thermal
conversion processes. Power is generated
with engines, turbines, fuel cells, or other
equipment.
Bioproduct: Materials that are derived from
renewable feedstocks. Examples include
paper, ethanol, and palm oil.
Biorefinery — A facility that processes and
converts biomass into value-added products.
These products include biomaterials, fuels
(ethanol), or important feedstocks for the
production of chemicals and other materials.
Biorefineries can be based on a number of
processing platforms using mechanical,
thermal,
chemical,
and
biochemical
processes.
Black Liquor — Solution of lignin-residue and
the pulping chemicals used to extract lignin
during the manufacture of paper.
Bone dry - Having zero percent moisture
content. Wood heated in an oven at a
constant temperature of 100°C (212°F) or
above until its weight stabilizes is considered
bone dry or oven dry.
Bone-dry-unit (BDU): 2,400
pounds
of
moisture-free wood, unless otherwise stated.
Bottom Ash — Ash that collects under the
grates of a combustion furnace.
Bottoming cycle - A cogeneration system in
which steam is used first for process heat and
then for electric power production.
Bound nitrogen - Some fuels contain about
0.1-5 % of organic bound nitrogen which
typically is in forms of aromatic rings like
pyridine or pyrrole.
British thermal unit - (Btu) A non-metric unit
of heat, still widely used by engineers. One
Btu is the heat energy needed to raise the
temperature of one pound of water from 60°F
to 61°F at one atmosphere pressure. 1 Btu =
1055 joules (1.055 kJ).
BTL - Biomass-to-Liquids.
Btu = 1055 joules (1.055 kJ).
Btu/hr.
Btu/lb.
Bulk density - Weight per unit of volume,
usually specified in pounds per cubic foot.
Bundlers — A machine that collects,
compresses, and binds forest residues in
to bundles.
Bunker - A storage tank.
Buyback Rate - The price a utility pays to
purchase electricity from an independent
generator.
By-product - Material, other than the
principal
product,
generated
as
a
consequence of an industrial process or as a
breakdown product in a living system.
OR Leftover material, generated as a result
of an industrial process or as a breakdown
product
in
a
living
system.
Capacity factor - The amount of energy that a
power plant actually generates compared to
its maximum rated output, expressed as a
percentage.
Calorific Value — The maximum amount
of energy that is available from burning a
substance. See Higher Heating Value.
Cambium: The layer of reproducing cells
between the inner bark (phloem) and the
wood (xylem) of a tree that repeatedly
subdivides to form new wood and bark cells.
180
Cant — The remaining square section of a log
when rounded edges and bark are removed.
Capacity: The maximum instantaneous output
of an energy conversion device, often
expressed in kilowatts (kW) or megawatts
(MW).
Capital cost: The total investment needed to
complete a project and bring it to an operable
status. The cost of construction of a new
plant. The expenditures for the purchase or
acquisition of existing facilities.
Carbohydrate: A class of organic compounds
including sugars and starches. The name
comes from the fact that many (but not all)
carbohydrates have the basic formula CH2O.
Carbon Cycle — The distribution and
transfer of carbon through the Earth’s
ecosystem that includes such processes as
photosynthesis,
decomposition,
and
respiration. OR The carbon cycle includes
the uptake of carbon dioxide by plants
through photosynthesis, its ingestion by
animals and its release to the atmosphere
through respiration and decay of organic
materials. Human activities like the burning
of fossil fuels contribute to the release of
carbon dioxide in the atmosphere.
Carbon Dioxide (CO2) — A colorless,
odorless, incombustible gas formed during
respiration, combustion of fossil fuels, and
organic decomposition. OR A colorless,
odorless, non-poisonous gas that is a normal
part of the ambient air. Carbon dioxide is a
product of fossil fuel combustion. OR A
colorless, odorless gas produced by the
respiration and combustion of carboncontaining fuels, used by plants as food in the
photosynthesis process. Represented as CO2.
Carbon Displacement — Offsetting of carbon
dioxide emissions from fossil fuel combustion
by substituting fossil fuels with bioenergy.
Carbon monoxide: A colorless, odorless,
poisonous gas produced by incomplete
combustion. Represented as CO.
Carbon Sequestration — The long-term
storage of carbon in the terrestrial
biosphere, underground, or oceans to
reduce the buildup of atmospheric carbon
dioxide concentrations.
Carbonization - The conversion of organic
material into carbon or a carbon-containing
residue through pyrolysis.
Catalyst - A substance that increases the rate
of a chemical reaction, without being
consumed or produced by the reaction.
Enzymes are catalysts for many biochemical
reactions.
Cellulase: A family of enzymes that break
down cellulose into glucose molecules.
Cellulose — A carbohydrate that is the
principal component of the cell secondary
walls of trees and other higher-order plants. It
occurs with other components such as lignin’s,
hemicellulose, waxes, and gums to form long,
hollow fibers. OR The main carbohydrate in
living plants. Cellulose forms the skeletal
structure of the plant cell wall. OR A
carbohydrate that is the principal component
of wood. It is made of linked glucose
molecules (a six-carbon sugar) that strengthen
the cell walls of most plants. Cellulosic/woody
biomass contains cellulose components.
Cetane number: A measurement of the
combustion quality of diesel fuel during
compression ignition. It serves as an
expression of diesel fuel quality among a
number of other measurements that
determine overall diesel fuel quality (often
abbreviated as CN).
Cetane (also called Hexadecane): An alkane
hydrocarbon with the chemical formula
C16H34. Consists of a chain of 16 carbon
atoms, with 3 hydrogen atoms bonded to the
2 end carbon atoms, and 2 hydrogens bonded
to each of the 14 other carbon atoms. Cetane
is often used as a short-hand for cetane
number, a measure of the detonation of
diesel fuel. Cetane ignites very easily under
compression; for this reason, it is assigned a
cetane number of 100, and serves as a
reference for other fuel mixtures.
CFM: Cubic feet per minute (1,000 cfm =
0.472 cubic meters per second, m3/s).
Char: The remains of solid biomass that has
been incompletely combusted (e.g., charcoal,
if wood is incompletely burned). See Biochar.
Chemical oxygen demand (COD) - The
amount of dissolved oxygen required to
combine with chemicals in wastewater. A
181
measure of the oxygen equivalent of that
portion of organic matter that is susceptible
to oxidation by a strong chemical oxidizing
agent.
Chip Van —Enclosed box trailers, generally 8
to 8.5 ft in width, designed to be less than
12.50 ft high when pulled by a road tractor.
The difference between the box trailers seen
on most highways and vans hauling harvesting
products (bulk vans) is that most box trailers
are built for containerized cargo (commodities
in boxes or on pallets).
Chip-n-saw — A cutting method used in
cutting lumber from trees that measure
between 6 and 14 inches diameter at breast
height. The process chips off the rounded
outer layer of a log before sawing the
remaining cant or rectangular inside section
into lumber. Chip-n-saw mills provide a
market for trees larger than pulpwood and
smaller than sawtimber.
Chipper — A large mechanized device that
reduces logs, whole trees, slab wood, or
lumber to chips of more or less uniform size.
Stationary chippers are used in sawmills,
while trailer-mounted whole-tree chippers
are used in the woods.
Chips — Woody material cut into short, thin
wafers. Chips are used as raw material for
production of paper, fiberboard, biomass fuel,
and other products. OR Small fragments of
wood chopped or broken by mechanical
equipment. Total tree chips include wood,
bark, and foliage. Pulp chips or clean chips are
free of bark and foliage.
Clean Chips — Chipped wood free of
bark, needles, leaves, and soil
contamination.
Cleaning — Release treatment made in
forest stand not past the sapling stage
to free the favored trees from less
desirable vegetation that currently or
soon will overtop them.
Clearcutting
—
Regeneration
or
harvesting method that removes
essentially all woody vegetation that
would otherwise compete with future
crop trees in a single harvesting
operation.
Closed-loop biomass - Crops grown, in a
sustainable manner, for the purpose of
optimizing their value for bioenergy and
bioproduct uses. This includes annual crops
such as maize and wheat, and perennial crops
such as trees, shrubs, and grasses such as
switchgrass.
Cloud point - The temperature at which a
fuel, when cooled, begins to congeal and take
on a cloudy appearance due to bonding of
paraffins.
Coarse materials - Wood residues suitable for
chipping, such as slabs, edgings, and
trimmings.
Coarse materials: Wood residues suitable for
chipping, such as slabs, edgings, and
trimmings.
Co-firing — Utilization of bioenergy
feedstocks to supplement energy source
in high efficiency boilers, usually with
coal. OR The use of a mixture of two
fuels within the same combustion
chamber.
Co-generation — The sequential production
of electricity and useful heat energy from a
common fuel source. Heat from this
industrial process can be used to power an
electric generator, used for industrial
processes, or space and water heating
purposes.
Combined cycle: Two or more generation
processes in a series or in parallel, configured
to optimize the energy output of the system.
Combined heat and power: More commonly
referred to as CHP. See co-generation.
Combined-cycle
power
plant: The
combination of a gas turbine and a steam
turbine in an electric generation plant. The
waste heat from the gas turbine provides the
heat energy for the steam turbine.
Combustion — Burning. The transformation
of biomass fuel into heat, chemicals, and
gases through chemical combination of
hydrogen and carbon in the fuel with oxygen
in the air. OR A chemical reaction between a
fuel and oxygen that produces heat (and
usually light).
Combustion air: The air fed to a fire to
provide oxygen for combustion of fuel.
Combustion Efficiency — A measure of the
182
productive capture of chemical energy in
the fuel to heat energy, often expressed as a
percentage or ratio. OR Actual heat
produced by combustion, divided by total
heat potential of the fuel consumed.
Combustion turbine - A type of generating
unit normally fired by oil or natural gas. The
combustion of the fuel produces expanding
gases, which are forced through a turbine,
which produces electricity by spinning a
generator.
Commercial forest land: Forested land which
is capable of producing new growth at a
minimum rate of 20 cubic feet per acre per
year, excluding lands withdrawn from timber
production by statute or administrative
regulation.
Commercial species - Tree species suitable for
industrial wood products.
Comminuted Material — Biomass
material that has been pulverized or
precision reduced into smaller sized
material.
Condensing turbine - A turbine used for
electrical power generation from a minimum
amount of steam. To increase plant efficiency,
these units can have multiple uncontrolled
extraction openings for feed-water heating.
Conifer: A tree, usually evergreen, with cones
and needle-shaped or scalelike leaves,
producing wood known commercially as
softwood.
Conservation
Reserve
Program (CRP): Provides farm owners or
operators with an annual per-acre rental
payment and half the cost of establishing a
permanent land cover in exchange for retiring
environmentally sensitive cropland from
production for 10- to 15-years. In 1996,
Congress
reauthorized
the
program,
commonly referred to as CRP, for an
additional round of contracts, limiting
enrollment to 36.4 million acres at any time.
The 2002 Farm Act increased the enrollment
limit to 39 million acres. Producers can offer
land for competitive bidding based on an
Environmental Benefits Index (EBI) during
periodic signups or can automatically enroll
more limited acreages in practices such as
riparian buffers, field windbreaks, and grass
strips on a continuous basis. CRP is funded
through the Commodity Credit Corporation.
Construction and Demolition (C&D) Debris Building materials and solid waste from
construction, deconstruction, remodeling,
repair, cleanup or demolition operations.
Container Trailer — A trailer designed to hold
bulk material. Built to be sturdy and abused,
they can be left on a site and filled as desired,
and then removed and replaced with an
empty container.
Continuous fermentation: A steady-state
fermentation system in which substrate is
continuously added to a fermenter while
products and residues are removed at a
steady rate.
Coppice regeneration: The ability of certain
hardwood species to regenerate by producing
multiple new shoots from a stump left after
harvest.
Coppicing - A traditional method of woodland
management, by which young tree stems are
cut down to a low level, or sometimes right
down to the ground. In subsequent growth
years, many new shoots will grow up, and
after a number of years the cycle begins again
and the coppiced tree or stool is ready to be
harvested again. Typically a coppice woodland
is harvested in sections, on a rotation. In this
way each year a crop is available.
Co-products: The resulting substances and
materials that accompany the production of a
fuel product.
Cord — A stack of round or split wood
consisting of 128 cubic feet f wood, bark,
and airspace. A standard cord measures 4
feet by 4 feet by 8 feet. One cord weighs
approximately 2.68 tons for pine and 2.90
tons for hardwoods. OR A stack of wood
comprising 128 cubic feet (3.62 m3);
standard dimensions are 4 x 4 x 8 feet,
including air space and bark. One cord
contains approximately 1.2 U.S. tons (ovendry) = 2400 pounds = 1089 kg.
Corn Distillers Dried Grains (DDG) - Obtained
after the removal of ethanol by distillation
from the yeast fermentation of a grain or a
grain mixture by separating the resultant
coarse grain fraction of the whole stillage and
183
drying it by methods employed in the grain
distilling industry.
Corn stover: The refuse of a corn crop after
the grain is harvested.
Course Woody Debris — Any piece(s) of dead
woody material (includes trunks, branches,
and roots) on the ground in forest stands or
streams with the large end diameter often
greater than 5 inches.
Cracking: A reduction of molecular weight by
breaking bonds, which may be done by
thermal, catalytic, or hydrocracking. Heavy
hydrocarbons, such as fuel oils, are broken up
into lighter hydrocarbons such as gasoline.
Crop failure: consists mainly of the acreage
on which crops failed because of weather,
insects, and diseases, but includes some land
not harvested due to lack of labor, low market
prices, or other factors. The acreage planted
to cover and soil improvement crops not
intended for harvest is excluded from crop
failure and is considered idle.
Crop Tree — Any tree selected to grow to final
harvest or to a selected size. Crop trees are
selected for quality, species, size, timber
potential, or wildlife value.
Cropland harvested: includes row crops and
closely sown crops; hay and silage crops; tree
fruits, small fruits, berries, and tree nuts;
vegetables and melons; and miscellaneous
other minor crops. In recent years, farmers
have double-cropped about 4 percent of this
acreage.
Cropland pasture - Land used for long-term
crop rotation. However, some cropland
pasture is marginal for crop uses and may
remain in pasture indefinitely. This category
also includes land that was used for pasture
before crops reached maturity and some land
used for pasture that could have been
cropped without additional improvement.
Cropland pasture: Land used for long-term
crop rotation. However, some cropland
pasture is marginal for crop uses and may
remain in pasture indefinitely. This category
also includes land that was used for pasture
before crops reached maturity and some land
used for pasture that could have been
cropped without additional improvement. OR
Includes cropland harvested, crop failure, and
cultivated summer fallow. Cropland harvested
includes row crops and closely sown crops;
hay and silage crops; tree fruits, small fruits,
berries, and tree nuts; vegetables and melons;
and miscellaneous other minor crops.
Cropland used for crops - Cropland used for
crops includes cropland harvested, crop
failure, and cultivated summer fallow.
Cropland - Total cropland includes five
components: cropland harvested, crop failure,
cultivated summer fallow, cropland used only
for pasture, and idle cropland.
Crown Thinning — Removal of trees from the
upper level in the canopy in order to favor
desired crop trees whose crowns are at a
lower position in the canopy.
Cull — A tree or log of marketable size
that is rejected because it does not meet
certain specifications of usability or grade
because of species type or defects.
Defects can include crookedness, decay,
injuries, or damage from disease or
insects.
Cull tree - A live tree, 5.0 inches in diameter
at breast height (dbh) or larger that is nonmerchantable for saw logs now or
prospectively because of rot, roughness, or
species. (See definitions for rotten and rough
trees.)
Cultivated summer fallow: refers to cropland
in sub-humid regions of the West cultivated
for one or more seasons to control weeds and
accumulate moisture before small grains are
planted. This practice is optional in some
areas, but it is a requirement for crop
production in the drier cropland areas of the
West. Other types of fallow, such as cropland
planted with soil improvement crops but not
harvested and cropland left idle all year, are
not included in cultivated summer fallow but
are included as idle cropland.
Cut-to-Length — A harvest system in
which trees are felled, delimbed, and cut
to various log lengths at the stump.
Deadwood — Dead, standing or fallen,
woody biomass from trees or shrubs.
Deadwood can be the results of old age,
fire, disease, logging, and natural
disasters.
Deck — A pile of logs on a landing. See
184
Landing. OR
(also known as "landing",
"ramp", "set-out") An area designated on a
logging job for the temporary storage,
collection, handling, sorting and/or loading of
trees or logs.
Dehydration: The removal of the water from
any substance.
Dehydrogenation: The removal of hydrogen
from a chemical compound.
Denaturant: A substance that makes ethanol
unfit for consumption.
Denatured - In the context of alcohol, it refers
to making alcohol unfit for drinking without
impairing its usefulness for other purposes.
Deoxygenation - A chemical reaction
involving the removal of molecular oxygen
(O2) from a reaction mixture or solvent.
Dewatering: The separation of free water
from the solids portion of spent mash, sludge,
or whole stillage by screening, centrifuging,
filter pressing, or other means.
Diameter at breast height (dbh): The
diameter measured at approximately breast
height from the ground (often between 1.3
and 1.5 meters depending on the country and
tree type). OR
Digester — An airtight vessel or
enclosure in which bacteria decomposes
biomass in water to produce gas. Also a
chemical process for pulping operations.
OR A biochemical reactor in which
anaerobic bacteria are used to
decompose biomass or organic wastes
into methane and carbon dioxide.
Dimethyl
ether Also
known
as
methoxymethane, methyl ether, wood ether,
and DME, is a colorless, gaseous ether with
with an ethereal smell. Dimethyl ether gas is
water soluble and has the formula CH3OCH3.
Dimethyl ether is used as an aerosol spray
propellant. Dimethyl ether is also a cleanburning alternative to liquified petroleum gas,
liquified natural gas, diesel and gasoline. It
can be made from natural gas, coal, or
biomass.
Dirty Chips — Chipped wood containing
bark, needles, leaves, and soil.
Disaccharides: The class of compound sugars
that yields two monosaccharide units upon
hydrolysis; examples are sucrose, maltose,
and lactose.
Discount rate - A rate used to convert future
costs or benefits to their present value.
Distillate: The portion of a liquid that is
removed as vapor and condensed during a
distillation process.
Distillation: The process by which the
components of a liquid mixture are separated
by boiling and recondensing the resultant
vapors. The main components in the case of
alcohol production are water and ethanol.
Distillers Dried Grains (DDG) - The dried grain
byproduct of the grain fermentation process,
which may be used as a high-protein animal
feed.
Distillers Wet Grains (DWG) - is the product
obtained after the removal of ethyl alcohol by
distillation from the yeast fermentation of
corn.
Distributed generation - The Generation of
electricity from many small on-site energy
sources. It has also been called also called
dispersed generation, embedded generation
or decentralized generation.
Down Woody Debris — Any piece(s) of dead
woody material (includes trunks, branches,
and roots) on the ground in forest stands or
streams.
The woody debris can be
categorized as course woody debris or fine
woody debris based on its large-end
diameter.
Downdraft gasifier - A gasifier in which the
product gases pass through a combustion
zone at the bottom of the gasifier.
Drop-in fuel: A substitute for conventional
fuel that is completely interchangeable and
compatible with conventional fuel. A drop-in
fuel does not require adaptation of the
engine, fuel system, or the fuel distribution
network and can be used "as is" in currently
available engines in pure form and/or blended
in any amount with other fuels.
Dry ton: 2,000 pounds of biomass on a
moisture-free basis.
Drying: Moisture removal from biomass to
improve serviceability and utility.
Dutch oven furnace - One of the earliest
types of furnaces, having a large, rectangular
box lined with firebrick (refractory) on the
185
sides and top. Commonly used for burning
wood. Heat is stored in the refractory and
radiated to a conical fuel pile in the center of
the furnace.
E-10: A mixture of 10% ethanol and 90%
gasoline based on volume. In the United
States, it is the most commonly found mixture
of ethanol and gasoline.
E-85: A mixture of 85% ethanol and 15%
gasoline based on volume.
Ecology — The science or study of the
relationships between organisms and their
environment.
Ecosystem Services — Benefits people obtain
from ecosystems. These include provisioning
services such as food, water, timber, and
fiber; regulating services that affect climate,
floods, disease, wastes, and water quality;
cultural services that provide recreational,
aesthetic, and spiritual benefits; and
supporting services such as soil formation,
photosynthesis, and nutrient cycling.
Effluent — The liquid or gas discharged from
a process or chemical reactor, usually
containing residues from that process. OR
The liquid or gas discharged after processing
activities, usually containing residues from
such use. Also discharge from a chemical
reactor.
Effluent - The liquid or gas discharged from a
process or chemical reactor, usually
containing residues from that process.
Elemental analysis: The determination of
carbon, hydrogen, nitrogen, oxygen, sulfur,
chlorine, and ash in a sample. See ultimate
analysis.
Emissions - Waste substances released into
the air or water. See also Effluent.
Energy crop: A commodity (crop) grown
specifically for its fuel value. These include
food crops such as corn and sugarcane and
nonfood crops such as poplar trees and
switchgrass. OR Crops grown specifically for
their fuel value. These include food crops such
as corn and sugarcane, and nonfood crops
such as poplar trees and switchgrass.
Currently, two types of energy crops are
under development; short-rotation woody
crops, which are fast-growing hardwood trees
harvested in 5 to 8 years, and herbaceous
energy crops, such as perennial grasses, which
are harvested annually after taking 2 to 3
years to reach full productivity.
Energy Ratio — The ratio of the energy output
versus the energy input. The energy ratio of a
bioenergy process can be calculated and
compared to a conventional fuel lifecycle. An
energy ratio below one suggests energy input
is greater than energy yield.
Environment — The interaction of climate,
soil, topography, and other plants and
animals in any given area. An organism’s
environment influences its form, behavior,
and survival.
Enzymatic hydrolysis: Use of an enzyme to
promote the conversion, by reaction with
water, of a complex substance into two or
more smaller molecules.
Enzyme - A protein or protein-based molecule
that speeds up chemical reactions occurring in
living things. Enzymes act as catalysts for a
single reaction, converting a specific set of
reactants into specific products.
Ester: A compound formed from the reaction
between an acid and an alcohol. In esters of
carboxylic acids, the -COOH group of the acid
and the -OH group of the alcohol lose a water
and become a -COO linkage.
Ethanol (CH3CH2OH): A colorless, flammable
liquid produced by fermentation of sugars.
Ethanol is used as a fuel oxygenate; the
alcohol found in alcoholic beverages.
Ethanol (CH5OH) - Otherwise known as ethyl
alcohol, alcohol, or grain-spirit. A clear,
colorless, flammable oxygenated hydrocarbon
with a boiling point of 78.5 degrees Celsius in
the anhydrous state. In transportation,
ethanol is used as a vehicle fuel by itself (E100
– 100% ethanol by volume), blended with
gasoline (E85 – 85% ethanol by volume), or as
a gasoline octane enhancer and oxygenate
(E10 – 10% ethanol by volume).
Even-aged Management — Management
technique for a stand of trees composed of a
single age class.
Examples of petrochemical feedstocks
are ethylene, propylene, butadiene,
benzene,
toluene,
xylene,
and
naphthalene.
186
Exotic species - Introduced species not native
or endemic to the area in question.
Externality - A cost or benefit not accounted
for in the price of goods or services. Often
"externality" refers to the cost of pollution
and other environmental impacts.
Extractives: Any
number
of
different
compounds in biomass that are not an
integral part of the cellular structure. The
compounds can be extracted from wood by
means of polar and non-polar solvents
including hot or cold water, ether, benzene,
methanol, or other solvents that do not
degrade the biomass structure. The types of
extractives found in biomass samples are
entirely dependent upon the sample itself.
(Source: Fengel, D.; Gerd, W. Wood
Chemistry, Ultrastructure, and Reactions.
Berlin-New York: Walter de Gruyter, 1989.)
Farmgate price - A basic feedstock price that
includes cultivation (or acquisition), harvest,
and delivery of biomass to the field edge or
roadside. It excludes on-road transport,
storage, and delivery to an end user. For
grasses and residues this price includes baling.
For forest residues and woody crops this
includes minimal comminution (e.g. chipping).
Fast pyrolysis - Thermal conversion of
biomass by rapid heating to between 450 and
600 degrees Celsius in the absence of oxygen.
OR Pyrolysis in which reaction times are short,
resulting in higher yields of certain fuel
products, ranging from primary oils to olefins
and aromatics, depending on the severity of
conditions.
Fatty acid: A fatty acid is a carboxylic acid (an
acid with a -COOH group) with long
hydrocarbon side chains. OR A group of
chemical compounds characterized by a chain
made up of carbon and hydrogen atoms and
having a carboxylic acid (COOH) group on one
end of the molecule. They differ from each
other in the number of carbon atoms and the
number and location of double bonds in the
chain. When they exist unattached to the
other compounds, they are called free fatty
acids.
Feedstock — Raw material used for the
generation of bioenergy and the creation
of other bioproducts.
Feedstock - A product used as the basis for
manufacture of another product. OR Any
material used directly as a fuel, or converted
to another form of fuel or energy product.
Bioenergy feedstocks are the original sources
of biomass. Examples of bioenergy feedstocks
include corn, crop residue, and woody plants.
Feller-buncher — A self-propelled
machine that cuts trees with saw or
shears near ground level and then stacks
the trees in piles to await transport
(skidding).
Fermentation — Conversion of carboncontaining
compounds
by
microorganisms for production of fuels and
chemicals such as alcohols, acids or
energy-rich gases. OR A biochemical
reaction that breaks down complex
organic
molecules
(such
as
carbohydrates) into simpler materials
(such as ethanol, carbon dioxide, and
water). Bacteria or yeasts can ferment
sugars to ethanol.
Fiber products - Products derived from fibers
of herbaceous and woody plant materials.
Examples include pulp, composition board
products, and wood chips for export.
Fine materials - Wood residues not suitable
for chipping, such as planer shavings and
sawdust.
Fine Woody Debris — Any piece(s) of
dead woody material (includes trunks,
branches, and roots) on the ground in
forest stands or streams with the large
end less than 5 inches in diameter.
Firm power - (firm energy) Power which is
guaranteed by the supplier to be available at
all times during a period covered by a
commitment. That portion of a customer's
energy load for which service is assured by
the utility provider.
Fischer-Tropsch Fuels - Liquid hydrocarbon
fuels produced by a process that combines
carbon monoxide and hydrogen. The process
is used to convert coal, natural gas and lowvalue refinery products into a high-value
diesel substitute fuel.
Fixed bed: A collection of closely spaced
particles through which gases move up or
187
down for purposes of gasification or
combustion.
Fixed carbon: The carbon that remains after
heating in a prescribed manner to decompose
thermally unstable components and distill
volatiles. Part of the proximate analysis group.
Flail Delimber — A machine used for
delimbing tree stems.
Flails are
mounted on spinning drums that
mechanically beat the limbs from the
tree stem.
Flash point: The temperature at which a
combustible liquid will ignite when a flame is
held over the liquid; anhydrous ethanol will
flash at 51°F.
Flash pyrolysis - See fast pyrolysis.
Flash vacuum pyrolysis (FVP) - Thermal
reaction of a molecule by exposing it to a
short thermal shock at high temperature,
usually in the gas phase.
Flow control - A legal or economic means by
which waste is directed to particular
destinations. For example, an ordinance
requiring that certain waste be sent to a
landfill is waste flow control.
Flow rate - The amount of fluid that moves
through an area (usually pipe) in a given
period of time.
Fluidized bed: A gasifier or combustor design
in which feedstock particles are kept in
suspension by a bed of solids kept in motion
by a rising column of gas. The fluidized bed
produces
approximately
isothermal
conditions with high heat transfer between
the particles and gases.
Fluidized-bed boiler - A large, refractory-lined
vessel with an air distribution member or
plate in the bottom, a hot gas outlet in or near
the top, and some provisions for introducing
fuel. The fluidized bed is formed by blowing
air up through a layer of inert particles (such
as sand or limestone) at a rate that causes the
particles to go into suspension and
continuous motion. The super-hot bed
material increased combustion efficiency by
its direct contact with the fuel.
Fly Ash — Ash transported through the
combustion chamber by the exhaust
gases and generally deposited in the
boiler heat exchanger. OR Small ash
particles
carried
in suspension in
combustion products.
FOB — An acronym for free on board,
indicating that the price quoted
includes loading on or in the specified
container.
Foliage — trees and other plant
leaves, considered as a group.
Forest Health — A measure of the vigor of
forest ecosystems. Forest health includes
biological diversity; soil, air, and water
productivity; natural disturbances; and the
capacity of the forest to provide a sustained
flow of goods and services for people. OR A
condition of ecosystem sustainability and
attainment of management objectives for a
given forest area. Usually considered to
include green trees, snags, resilient stands
growing at a moderate rate, and endemic
levels of insects and disease. Natural
processes still function or are duplicated
through management intervention.
Forest land - Land at least 10 percent stocked
by forest trees of any size, including land that
formerly had such tree cover and that will be
naturally or artificially regenerated. Forest
land includes transition zones, such as areas
between heavily forested and nonforested
lands that are at least 10 percent stocked with
forest trees and forest areas adjacent to
urban and built-up lands. Also included are
pinyon-juniper and chaparral areas in the
West and afforested areas. The minimum
area for classification of forest land is 1 acre.
Roadside, streamside, and shelterbelt strips of
trees must have a crown width of at least 120
feet to qualify as forest land. Unimproved
roads and trails, streams, and clearings in
forest areas are classified as forest if less than
120 feet wide.
Forest Residue — Tops, limbs, bark,
foliage, and other woody materials, left
after a harvest.
Forest Type — Groups of tree species
commonly growing in association because of
similar
environmental
requirements.
Examples include pine and mixed hardwood;
cypress, tupelo, and black gum; and oak and
hickory.
188
Forestry residues - Includes tops, limbs, and
other woody material not removed in forest
harvesting
operations
in
commercial
hardwood and softwood stands, as well as
woody material resulting from forest
management
operations
such
as
precommercial thinnings and removal of dead
and dying trees.
Forwarder — A vehicle that carries logs
completely off the ground from stump to
road side landing. OR A self-propelled
vehicle to transport harvested material
from the stump area to the landing. Trees,
logs, or bolts are carried off the ground on a
stake-bunk, or are held by hydraulic jaws of
a clam-bunk. Chips are hauled in a
dumpable or open-top bin or chip-box.
Fossil fuel - Solid, liquid, or gaseous fuels
formed in the ground after millions of years
by chemical and physical changes in plant and
animal residues under high temperature and
pressure. Oil, natural gas, and coal are fossil
fuels. OR A carbon or hydrocarbon fuel
formed in the ground from the remains of
dead plants and animals. It takes millions of
years to form fossil fuels. Oil, natural gas, and
coal are fossil fuels.
Fouling - The coating of heat transfer surfaces
in heat exchangers such as boiler tubes
caused by deposition of ash particles.
Fuel Cell — A device that converts the
energy of a fuel directly to electricity and
heat, without combustion.
Fuel cycle - The series of steps required to
produce electricity. The fuel cycle includes
mining or otherwise acquiring the raw fuel
source, processing and cleaning the fuel,
transport, electricity generation, waste
management and plant decommissioning.
Fuel handling system: A system for unloading
wood fuel from vans or trucks, transporting
the fuel to a storage pile or bin, and conveying
the fuel from storage to the boiler or other
energy conversion equipment.
Fuel Treatment Evaluator (FTE) - A strategic
assessment tool capable of aiding the
identification, evaluation, and prioritization of
fuel treatment opportunities.
Fuel Treatment Thinnings — The process of
harvesting trees and underbrush from the
forest to reduce the risk of wildfires.
Fuelwood - Wood used for conversion to
some form of energy, primarily for residential
use.
Full Cost Method — Cost accounting method
that allocates the total production cost across
biomass and conventional wood products.
Fungi: Plant-like organisms with cells with
distinct nuclei surrounded by nuclear
membranes, incapable of photosynthesis.
Fungi are decomposers of waste organisms
and exist as yeast, mold, or mildew.
Furfural: An aldehyde derivative of certain
biomass conversion processes; used as a
solvent.
Furnace: An enclosed chamber or container
used to burn biomass in a controlled manner
to produce heat for space or process heating.
Galactan: The polymer of galactose with a
repeating unit of C6H10O5. Found in
hemicellulose; it can be hydrolyzed to
galactose.
Galactose: A six-carbon sugar with the
formula C6H12O6. A product of hydrolysis of
galactan found in the hemicellulose fraction
of biomass.
Gas Turbine: Sometimes called a combustion
turbine; a gas turbine converts the energy of
hot compressed gases (produced by burning
fuel in compressed air) into mechanical
power, which can be used to generate
electricity.
Gasification: A chemical or heat process
to convert a solid fuel to a gaseous form.
OR Any chemical or heat process used to
convert a feedstock to a gaseous fuel.
Gasifier: A device for converting solid fuel into
gaseous fuel. In biomass systems, the process
is referred to as pyrolitic distillation. See
Pyrolysis. OR A device that converts solid fuel
to gas. Generally refers to thermochemical
processes.
Gasohol - A mixture of 10% anhydrous
ethanol and 90% gasoline by volume; 7.5%
anhydrous ethanol and 92.5% gasoline by
volume; or 5.5% anhydrous ethanol and
94.5% gasoline by volume. There are other
fuels that contain methanol and gasoline, but
these fuels are not referred to as gasohol.
189
Genetic selection: Application of science to
systematic improvement of a population, e.g.
through selective breeding.
Geographic
Information
Systems (GIS): Technology
used
as
a
framework for gathering and organizing
spatial data and related information so it can
be displayed and analyzed. A GIS is an
integrated collection of computer software
and data used to view and manage
information about geographic places, analyze
spatial relationships, and model spatial
processes. A GIS enables users to quickly
visualize data, extract trends, optimize routes,
and interpret other relationships via maps
and charts. The technology helps solve
problems and answer questions by presenting
complex data in understandable and easily
sharable ways.
Gigawatt (GW): A measure of electrical power
equal to 1 billion watts (1,000,000 kW). A
large coal or nuclear power station typically
has a capacity of about 1 GW.
Global Climate Change - Global climate
change could result in sea level rises, changes
to patterns of precipitation, increased
variability in the weather, and a variety of
other consequences. These changes threaten
our health, agriculture, water resources,
forests, wildlife, and coastal areas.
Global warming: A term used to describe the
increase in average global temperatures due
to the greenhouse effect. Scientists generally
agree that the Earth's surface has warmed by
about 1ºF in the past 140 years.
Glucan: The polymer of glucose with a
repeating unit of C6H10O5. Cellulose is a form
of glucan. Can be hydrolyzed to glucose.
(Source: Voet, D.; Voet, J. G. Biochemistry.
New York: John Wiley, 1990.)
Glucose (C6H12O6): A six-carbon fermentable
sugar.
Glycerin (C3H8O3): A liquid by-product of
biodiesel
production.
Used
in
the
manufacture of dynamite, cosmetics, liquid
soaps, inks, and lubricants.
Grade — Utilization and established
quality or use classification of
lumber, trees, or other forest
products.
Grassland pasture and range: Grassland
pasture and range comprises all open land
used primarily for pasture and grazing,
including shrub and brush land types of
pasture; grazing land with sagebrush and
scattered mesquite; and all tame and native
grasses, legumes, and other forage used for
pasture or grazing. Because of the diversity in
vegetative composition, grassland pasture
and range are not always clearly
distinguishable from other types of pasture
and range. At one extreme, permanent
grassland may merge with cropland pasture,
or grassland may often be found in
transitional areas with forested grazing land.
Green diesel: A diesel fuel substitute made
from renewable feedstocks by using
traditional distillation methods. It is also
known as renewable diesel.
Green gasoline: A liquid identical to
petroleum-based gasoline, but is produced
from biomass such as switchgrass and poplar
trees. In the United States, it is still in the
development stages. It is also known as
renewable gasoline.
Green
Power
Purchasing/Aggregation
Policies - Municipalities, state governments,
businesses, and other non-residential
customers can play a critical role in supporting
renewable energy technologies by buying
electricity from renewable resources. At the
local level, green power purchasing can mean
buying green power for municipal facilities,
streetlights, water pumping stations and
other public infrastructure. Several states
require that a certain percentage of electricity
purchased for state government buildings
come from renewable resources. A few states
allow local governments to aggregate the
electricity loads of the entire community to
purchase green power and even to join with
other communities to form an even larger
green power purchasing block. This is often
referred to as "Community Choice." Green
power purchasing can be achieved via utility
green pricing programs, green power
marketers (in states with retail competition),
special contracts, or community aggregation.
Green Power - Electricity that is generated
from renewable energy sources is often
190
referred to as “green power.” Green power
products can include electricity generated
exclusively from renewable resources or,
more frequently, electricity produced from a
combination of fossil and renewable
resources. Also known as “blended” products,
these products typically have lower prices
than 100 percent renewable products.
Customers who take advantage of these
options usually pay a premium for having
some or all of their electricity produced from
renewable resources.
Green Ton — 2000 lbs of undried
biomass. Moisture content must
be specified if green tons are
used as a measure of fuel energy.
Greenhouse effect: The heat effect due to the
trapping of the sun's radiant energy, so that it
cannot be reradiated. In the earth's
atmosphere, the radiant energy is trapped by
greenhouse gases produced from both
natural and human sources. OR The effect of
certain gases in the Earth's atmosphere in
trapping heat from the sun.
Greenhouse gas: A gas, such as water
vapor, carbon dioxide, tropospheric
ozone, methane, and low level ozone,
which contributes to the greenhouse
effect. OR A gas that absorbs radiant
energy from the earth, re-emitting it as
infrared radiation, contributing to the
warming of the earth. Examples of
greenhouse gases include carbon dioxide
and water vapor. OR Gases that trap the
heat of the sun in the Earth's atmosphere,
producing the greenhouse effect. The two
major greenhouse gases are water vapor
and carbon dioxide. Other greenhouse
gases
include
methane,
ozone,
chlorofluorocarbons, and nitrous oxide.
Grid: An electric utility's system for
distributing power.
Grinder — A machine that reduce particles
in size by repeatedly pounding them into
smaller pieces through a combination of
tensile, shear and compressive forces.
Gross heat of combustion: See higher heating
value.
Group Selection — Is an uneven-aged
regeneration method used for sun loving
tree species in which trees are removed and
new age classes are established in groups.
The width of a group is approximately twice
the height of mature trees.
Growing stock: A classification of timber
inventory that includes live trees of
commercial species meeting specified
standards of quality or vigor. Cull trees are
excluded. When associated with volume,
includes only trees 5.0 inches dbh and larger.
Guaiacyl: A chemical component of lignin. It
has a six-carbon aromatic ring with one
methoxyl group attached. It is the
predominant aromatic structure in softwood
lignins. See syringyl.
Habitat: The area where a plant or
animal lives and grows under natural
conditions. Habitat includes living and
non-living attributes and provides all
requirements for food and shelter. OR
The place or environment where a plant
or animal naturally or normally lives,
grows and reproduces.
Hammermill - A device consisting of a rotating
head with free-swinging hammers which
reduce chips or wood fuel to a predetermined
particle size through a perforated screen.
Hardwood: One of the botanical groups of
dicotyledonous trees that have broad leaves
in contrast to the conifers or softwoods. The
botanical name is angiosperms; hardwood has
no reference to the actual hardness of the
wood. Short-rotation, fast growing hardwood
trees are being developed as future energy
crops. OR Usually broad-leaved and deciduous
trees.
Heat rate: The amount of fuel energy
required by a power plant to produce one
kilowatt-hour of electrical output. A measure
of generating station thermal efficiency,
generally expressed in Btu per net kWh. It is
computed by dividing the total Btu content of
fuel burned for electric generation by the
resulting net kWh generation.
Heat transfer efficiency: Useful heat output
released / actual heat produced in the firebox.
Heating value - The maximum amount of
energy that is available from burning a
substance. See higher heating value and lower
heating value.
191
Hectare: Common metric unit of area, equal
to 2.47 acres. 100 hectares = 1 square
kilometer.
Hemicellulose: Consists of short, highly
branched chains of sugars. In contrast to
cellulose, which is a polymer of only glucose, a
hemicellulose is a polymer of five different
sugars. It contains five-carbon sugars (usually
D-xylose and L-arabinose), six-carbon sugars
(D-galactose, D-glucose, and D-mannose), and
uronic acid. The sugars are highly substituted
with acetic acid. The branched nature of
hemicellulose renders it amorphous and
relatively easy to hydrolyze to its constituent
sugars compared to cellulose. When
hydrolyzed,
the
hemicellulose
from
hardwoods releases products high in xylose (a
five-carbon
sugar).
The
hemicellulose
contained in softwoods, by contrast, yields
more six-carbon sugars. OR A polysaccharide
(complex carbohydrate) found in plant cells
that is easily extracted by dilute alkalies.
Herbaceous energy crops: Perennial nonwoody crops that are harvested annually,
though they may take two to three years to
reach full productivity. Examples include:
Switchgrass (Panicum virgatum), Reed
canarygrass
(Phalaris
arundinacea),
Miscanthus (Miscanthus x giganteus), and
Giant reed (Arundo donax).
Herbaceous plants: Non-woody type of
vegetation, usually lacking permanent strong
stems, such as grasses, cereals and canola
(rape).
Hexose: Any of various simple sugars that
have six carbon atoms per molecule (e.g.,
glucose, mannose, and galactose).
HFCS - High fructose corn syrup.
High Grading — A harvesting technique that
removes only the biggest and most valuable
trees from a stand and provides high returns
at the expense of future growth potential.
Poor quality, shade-loving trees tend to
regenerate and dominate high- graded sites.
Higher heating value (HHV): The heat
produced by combustion of one unit of
substance at constant volume in an oxygen
bomb calorimeter under specified conditions.
The conditions are: initial oxygen pressure of
2.0–4.0 MPa (20–40 atm), final temperature
of 20º–35ºC, products in the form of ash,
liquid water, gaseous CO2and N2, and dilute
aqueous HCl and H2SO4. It is assumed that if
significant quantities of metallic elements are
combusted, they are converted to their
oxides. In the case of materials such as coal,
wood, or refuse, if small or trace amounts of
metallic elements are present, they are
unchanged during combustion and are part of
the ash. Also known as gross heat of
combustion. OR (HHV) The maximum
potential energy in dry fuel. For wood, the
range is from 7,600 to 9,600 Btu/lb and
grasses are typically in the 7,000 to 7,500
Btu/lb range.
Hog Fuel — Wood and wood waste biomass
processed by grinding for use in a combustor.
Hog - A chipper or mill which grinds wood into
an acceptable form to be used for boiler fuel.
Holocellulose: The total carbohydrate fraction
of wood; cellulose plus hemicellulose.
Horsepower (electrical horsepower; hp): A
unit for measuring the rate of mechanical
energy output, usually used to describe the
maximum output of engines or electric
motors. 1 hp = 550 foot-pounds per second =
2,545 Btu per hour = 745.7 watts = 0.746 kW.
Hybrid: The offspring of genetically different
parents; combines the characteristics of the
parents or exhibits completely new traits. The
term is applied as well to the progeny from
matings within species and to those between
species.
Hydrocarbon emissions: In vehicle emissions,
these are usually vapors of hydrogen-carbon
compounds created from incomplete
combustion or from vaporization of liquid
gasoline.
Emissions
of
hydrocarbons
contribute to ground-level ozone.
Hydrocarbon Feedstock — Petroleum
(hydrocarbon) based substance used as a raw
material in an industrial process of
petrochemical feedstocks are ethylene,
propylene, butadiene, benzene, toluene,
xylene, and naphthalene.
Hydrocarbon (HC): An organic compound
molecule that contains only hydrogen and
carbon. OR A compound containing only
hydrogen and carbon. The simplest and
lightest forms of hydrocarbon are gaseous.
192
With greater molecular weights they are
liquid, while the heaviest are solids.
Hydrocracking: A process in which hydrogen
is added to organic molecules at high
pressures and moderate temperatures;
usually used as an adjunct to catalytic
cracking.
Hydrogenation: Treatment of substances with
hydrogen and suitable catalysts at high
temperature and pressure to saturate double
bonds.
Hydrolysis: A chemical reaction that releases
sugars that are normally linked together in
complex chains. In ethanol production,
hydrolysis reactions are used to break down
the cellulose and hemicellulose in the
biomass. OR A chemical reaction that releases
sugars from cellulose and hemicellulose,
which are normally linked together in
complex chains. OR A process of breaking
chemical bonds of a compound by adding
water to the bonds.
Idle cropland: Land in cover and soil
improvement crops; cropland on which no
crops were planted. Some cropland is idle
each year for various physical and economic
reasons. Acreage diverted from crops to soilconserving uses (if not eligible for and used as
cropland pasture) under federal farm
programs is included in this component.
Cropland enrolled in the federal Conservation
Reserve Program (CRP) is included in idle
cropland.
Improvement Cutting — An intermediate,
partial, harvest that removes less
desirable trees of any species to improve
the form, quality, health or wildlife
potential of the remaining trees. Usually
occurs after the sapling stage and before
final harvest.
Incinerator: Any device used to burn solid or
liquid residues or wastes as a method of
disposal. In some incinerators, provisions are
made for recovering the heat produced.
Inclined grate: A type of furnace in which fuel
enters at the top part of a grate in a
continuous ribbon, passes over the upper
drying section where moisture is removed,
and descends into the lower burning section.
Ash is removed at the lower part of the grate.
Incremental energy costs: The cost of
producing and/or transporting the next
available unit of electrical energy above a
previously determined base cost. OR The cost
of producing and transporting the next
available unit of electrical energy. Short run
incremental costs (SRIC) include only
incremental operating costs. Long run
incremental costs (LRIC) include the capital
cost of new resources or capital equipment.
Independent power producer: A power
production facility that is not part of a
regulated utility.
Indirect Impacts — The inter-industry
effects of input-output analysis; the
impacts above and beyond the direct
effects when applied to Type I multipliers.
Indirect liquefaction: Conversion of biomass
to a liquid fuel through a synthesis gas
intermediate step.
individual trees within 1 acre of forest. For
example a wellInduced Impacts — The impacts of
household expenditures in input-output
analysis.
Industrial wood: All commercial roundwood
products, except fuelwood.
Inoculum: Microorganisms produced from a
pure culture; used to start a new culture in a
larger vessel than that in which they were
grown.
Invasive species - A species that has moved
into an area and reproduced so aggressively
that it threatens or has replaced some of the
original species.
Iodine number - A measure of the ability of
activated carbon to adsorb substances with
low molecular weights. It is the milligrams of
iodine that can be adsorbed on one gram of
activated carbon.
Joule - Metric unit of energy, equivalent to
the work done by a force of one Newton
applied over a distance of one meter (= 1 kg
m2/s2). One joule (J) = 0.239 calories (1
calorie = 4.187 J).
Joule: Metric unit of energy, equivalent to the
work done by a force of one Newton applied
over a distance of one meter (= 1 kg m2/s2).
One joule (J) = 0.239 calories (1 calorie =
4.187 J).
193
JP-8 (or JP8 for "Jet Propellant 8"): A
kerosene-based jet fuel, specified in 1990 by
the U.S. government, as a replacement for the
JP-4 fuel; the U.S. Air Force replaced JP-4 with
JP-8 completely by the fall of 1996, to use a
less flammable, less hazardous fuel for better
safety and combat survivability. The U.S. Navy
uses a similar formula, JP-5.
KG and Pile — A site preparation method in
which stumps are pushed up, sheared off, or
split apart by a specially designed blade
mounted on a bulldozer. Debris is then piled
or placed in long rows (windrows) so that an
area can be bedded or flat planted.
KG Blade — A bulldozer-mounted blade used
in forestry and land-clearing operations. A
single spike splits and shears stumps at their
base.
Kilowatt hour (kWh): A measure of energy
equivalent to the expenditure of one kilowatt
for one hour. For example, 1 kWh will light a
100-watt light bulb for 10 hours. 1 kWh =
3,412 Btu.
Kilowatt - (kW) A measure of electrical power
equal to 1,000 watts. 1 kW = 3412 Btu/hr =
1.341 horsepower. See also watt.
Klason lignin: Lignin obtained from wood
after the non-lignin components have been
removed with a prescribed sulfuric acid
treatment. A specific type of acid-insoluble
lignin analysis.
Kraft process: Chemical pulping process in
which lignin is dissolved by a solution of
sodium hydroxide and sodium sulfide.
Landfill gas: Biogas produced from the natural
degradation of organic material in landfills.
OR A type of biogas that is generated by
decomposition of organic material at landfill
disposal sites. Landfill gas is approximately 50
percent methane. See also biogas.
Landing — A cleared working area in the
forest where trees and logs are transported
(skidded) to be sorted, processed, and
loaded on a truck. See Deck.
Legume - Any plant belonging to the
leguminous family. Characterized by pods as
fruits and root nodules enabling the storage
of nitrogen.
Levelized life-cycle cost: The present value of
the cost of a resource, including capital,
financing and operating costs, expressed as a
stream of equal annual payments. This stream
of payments can be converted to a unit cost
of energy by dividing the annual payment
amount by the annual kilowatt-hours
produced or saved. By levelizing costs,
resources with different lifetimes and
generating capabilities can be compared.
Liberation Cutting — Removal of poor
quality or un-merchantable trees to favor
the growth of desirable trees.
Life-cycle assessment (LCA): The investigation
and evaluation of the environmental impacts
of a given product or service caused or
necessitated by its existence. Also known as
life-cycle analysis, ecobalance, and cradle-tograve analysis.
Lignin pseudo-molecule for modeling: The
lignin ratio of methoxy groups to
phenylpropanoid groups (MeO:C9) is used to
calculate an ultimate analysis for the lignin
pseudo-molecule. This ultimate analysis is
used to estimate other properties of the
molecule, such as its higher heating
value and lower heating value.
Lignin methoxy (MeO) to phenlypropanoid
(C9) ratio: Lignin empirical formulae are based
on ratios of methoxy groups to
phenylpropanoid groups (MeO:C9). The
general empirical formula for lignin
monomers is C9H10O2 (OCH3)n, where n is the
ratio of MeO to C9 groups. Where no
experimental ratios have been found, they are
estimated as follows: 0.94 for softwoods; 1.18
for grasses; 1.4 for hardwoods. These are
averages of the lignin ratios found in the
literature. Paper products, which are
produced primarily from softwoods, are
estimated to have an MeO:C9 ratio of 0.94.
Lignin: A complex polymer that serves
as a component of wood and vascular
plants, making them firm and rigid.
Produces energy in the form of
electricity when burned. OR Structural
constituent of wood and (to a lesser
extent) other plant tissues, which
encrusts the cell walls and cements the
cells together.
194
Lignocellulose: Refers to plant materials
made up primarily of lignin, cellulose,
and hemicellulose.
Live cull: A classification that includes live cull
trees. When associated with volume, it is the
net volume in live cull trees that are 5.0
inches dbh and larger.
Log Rule or Log Scale — A table that
estimates volume or product yield
from logs and trees, based on a
diagram or mathematical formula.
Log Trailer — A trailer designed to haul
trees, poles, or shortwood in racks.
They are lightweight and have high
payload capacities.
Logging residues: The unused portions of
growing-stock and non-growing-stock trees
cut or killed by logging and left in the woods.
Low Thinning — Removal of smaller,
weaker, and most deformed trees whose
crowns are in the lower portion of the
stand canopy.
Lower
heating
value (LLV): The
heat
produced by combusting one unit of a
substance, at atmospheric pressure, under
conditions such that all water in the products
remains in the form of vapor. The net heat of
combustion is calculated from the gross heat
of combustion at 20oC by subtracting 572
cal/g (1,030 Btu/lb) of water derived from one
unit mass of sample, including both the water
originally present as moisture and that
formed by combustion. This subtracted
amount is not equal to the latent heat of
vaporization of water because the calculation
also reduces the data from the gross value at
constant volume to the net value at constant
pressure. OR The potential energy in a fuel if
the water vapor from combustion of
hydrogen is not condensed.
Lump Sum Sale — A timber sale in which
the buyer and seller agree on a total price
for the standing timber. The standing
timber is either marked or is in a
delineated area.
Mannan: The polymer of mannose with a
repeating unit of C6H10O5. Can be hydrolyzed
to mannose.
Mannose (C6H12O6): A six-carbon sugar. A
product of hydrolysis of mannan found in the
hemicellulose fraction of biomass.
Marginal Cost Method — Cost
accounting method that counts only
the additional costs from the
conventional logging operation as
the biomass production cost.
Marginal Land — Land that does not
consistently produce a profitable crop
because of infertility, drought, or other
physical limitations such as shallow soils.
Mash: A mixture of grain and other
ingredients with water to prepare wort for
brewing operations.
Mass closure (%): The percent by weight of
the total samples extracted from the biomass
sample, compared to the weight of the
original sample. It is a sum of the weight
percent of moisture, extractives, ash, protein,
total lignin, carboxylic acids, and five and six
carbon sugar monomers and polymers. This is
a good indicator of the accuracy of a complete
biomass compositional analysis.
MBF — Abbreviation denoting 1,000 board
feet. MBF is a typical unit of trade for
dimension
lumber
and
sawtimber
stumpage.
Megawatt (MW): A measure of electrical
power equal to one million watts (1,000 kW).
See also watt.
Merchantable Height — The stem length,
measured from one foot above the ground to
a 10-, 6-, or 4-inch diameter top, above which
no other saleable product can be cut.
Diameter, local markets, limbs, knots, and
other
defects
collectively
influence
merchantable height.
Merchantable - Logs from which at least
some of the volume can be converted into
sound grades of lumber ("standard and
better" framing lumber).
Metabolism: The sum of the physical and
chemical processes involved in the
maintenance of life and by which energy is
made available to the organism.
Methane (CH4): The major component of
natural gas. It can be formed by anaerobic
digestion of biomass or gasification of coal or
biomass.
195
Methanol (wood alcohol) (CH3OH): A Methyl
alcohol having the chemical formula CH30H.
Also known as wood alcohol, methanol is
usually produced by chemical conversion at
high temperatures and pressures. Although
usually produced from natural gas, methanol
can be produced from gasified biomass
(syngas).
Microorganism: Any microscopic organism
such as yeast, bacteria, fungi, etc.
Mill residue: Wood and bark residues
produced in processing logs into lumber,
plywood, and paper. OR Excess material
generated from wood processing mills and
pulp and paper mills.
Mill/kWh: A common method of pricing
electricity in the United States. Tenths of a
U.S. cent per kilowatt hour.
Mixed Stand — A timber stand containing
two or more prominent species in the main
canopy.
MMBtu — One million British thermal
units.
Moisture Content — The weight of the water
contained in wood, usually expressed as a
percentage of weight, either oven-dry or as
received (green).
Moisture content, dry basis - Moisture
content expressed as a percentage of the
weight of oven-dry wood, i.e.: [(weight of wet
sample - weight of dry sample) / weight of dry
sample] x 100
Moisture content, wet basis - Moisture
content expressed as a percentage of the
weight of wood as-received, i.e.: [(weight of
wet sample - weight of dry sample) / weight
of wet sample] x 100
Moisture: The amount of water and other
components present in the biomass sample
that are volatilized at 105ºC.
Moisture-free basis: Biomass composition
and chemical analysis data is typically
reported on a moisture free or dry weight
basis. Moisture (and some volatile matter) is
removed prior to analytical testing by heating
the sample at 105ºC to constant weight. By
definition, samples dried in this manner are
considered moisture free.
Monoculture: The cultivation of a single
species crop.
Monosaccharide: A simple sugar such as a
five-carbon sugar (xylose, arabinose) or sixcarbon sugar (glucose, fructose). Sucrose, on
the other hand is a disaccharide, composed of
a combination of two simple sugar units,
glucose and fructose.
Municipal solid waste (MSW): Any organic
matter, including sewage, industrial, and
commercial wastes, from municipal waste
collection systems. Municipal waste does not
include agricultural and wood wastes or
residues.
National Environmental Policy Act (NEPA) - A
federal law enacted in 1969 that requires all
federal agencies to consider and analyze the
environmental impacts of any proposed
action. NEPA requires an environmental
impact statement for major federal actions
significantly affecting the quality of the
environment. NEPA requires federal agencies
to inform and involve the public in the
agency´s decision making process and to
consider the environmental impacts of the
agency´s decision.
Native lignin: Lignin as it exists in the
lignocellulosic complex before separation.
net heat of combustion: See lower heating
value.
Natural Stand — A stand of trees grown
from natural seed fall or sprouting.
Negotiated Sale — A timber sale in which
the buyer and seller negotiate a price for
the standing timber. The standing timber
is either marked or is in a delineated area.
Net Annual Growth — The average
annual net increase in the volume of
trees during the period between
inventoies.
Net heat of combustion: See lower heating
value.
Net Metering - For those consumers who
have their own electricity generating units,
net metering allows for the flow of electricity
both to and from the customer through a
single, bi-directional meter. With net
metering, during times when the customer's
generation exceeds his or her use, electricity
from the customer to the utility offsets
electricity consumed at another time. In
effect, the customer is using the excess
196
generation to offset electricity that would
have been purchased at the retail rate. Under
most state rules, residential, commercial, and
industrial customers are eligible for net
metering, but some states restrict eligibility to
particular customer classes.
Net present value: The sum of the costs and
benefits of a project or activity. Future
benefits and costs are discounted to account
for interest costs.
Neutral
detergent
fiber (NDF): Organic
matter that is not solubilized after one hour of
refluxing in a neutral detergent consisting of
sodium lauryl sulfate and EDTA at pH 7. NDF
includes hemicellulose, cellulose, and lignin.
Nitrogen fixation: The transformation of
atmospheric
nitrogen
into
nitrogen
compounds that can be used by growing
plants.
Nitrogen
oxides (NOx): A
product
of
photochemical reactions of nitric oxide in
ambient air; the major component of
photochemical smog. OR Gases consisting of
one molecule of nitrogen and varying
numbers of oxygen molecules. Nitrogen
oxides are produced from the burning of fossil
fuels. In the atmosphere, nitrogen oxides can
contribute to the formation of photochemical
ozone (smog), can impair visibility, and have
health consequences; they are thus
considered pollutants.
Nonattainment area - Any area that does not
meet the national primary or secondary
ambient air quality standard established by
the Environmental Protection Agency for
designated pollutants, such as carbon
monoxide and ozone.
Non-condensing,
controlled
extraction
turbine: A turbine that bleeds part of the
main steam flow at one (single extraction) or
two (double extraction) points.
Non-forest land: Land that has never
supported forests and lands formerly forested
where use of timber management is
precluded by development for other uses. OR
Land that has never supported forests and
lands formerly forested where use of timber
management is precluded by development for
other uses. (Note: Includes area used for
crops, improved pasture, residential areas,
city parks, improved roads of any width and
adjoining clearings, powerline clearings of any
width, and 1- to 4.5-acre areas of water
classified by the Bureau of the Census as land.
If intermingled in forest areas, unimproved
roads and nonforest strips must be more than
120 feet wide, and clearings, etc., must be
more than 1 acre in area to qualify as
nonforest land.)
Nonindustrial Private Forest (NIPF) —
Forest land that is privately owned by
individuals or corporations other than
forest industry.
Non-industrial private: An ownership class of
private lands where the owner does not
operate wood-using processing plants.
Non-renewable resource: A resource that
cannot be replaced after use. Although fossil
fuels like coal and oil are in fact fossilized
biomass resources, they form at such a slow
rate, that in practice, they are non-renewable.
Octane rating (octane number): A measure of
a fuel's resistance to self-ignition, hence a
measure of the antiknock properties of the
fuel. Diesel fuel has a low octane rating, while
gasoline and alcohol have high octane ratings,
suitable for spark-ignition engines.
Oilseed crops - Primarily soybeans, sunflower
seed, canola, rapeseed, safflower, flaxseed,
mustard seed, peanuts and cottonseed, used
for the production of cooking oils, protein
meals for livestock, and industrial uses.
Old growth: Timber stands marked by the
following characteristics: large mature and
over-mature trees in the overstory, snags,
dead and decaying logs on the ground, and a
multi-layered canopy with trees of several age
classes.
On the Stump — Standing, uncut timber.
One-pass Method — A harvest
practice
where
biomass
and
conventional roundwood (sawlogs) are
harvested
and
recovered
simultaneously.
Open-loop biomass - Biomass that can be
used to produce energy and bioproducts even
though it was not grown specifically for this
purpose. Examples of open-loop biomass
include agricultural livestock waste and
197
residues from forest harvesting operations
and crop harvesting.
Organic compound: Compound containing
carbon chemically bound to hydrogen. Often
contain other elements (particularly O, N,
halogens, or S).
Organic residuals: Surplus or waste organic
materials derived from biomass, including,
but not necessarily limited to products,
production and processing wastes and
byproducts,
remnants,
bodily
fluids,
excrement or effluents derived from plants,
animals, or microorganisms that have been
previously used, processed, preprocessed, or
remain after their primary production or use
has occurred.
Other forest land: Forest land other than
timberland and reserved forest land. It
includes available forest land, which is
incapable of annually producing 20 cubic feet
per acre of industrial wood under natural
conditions because of adverse site conditions
such as sterile soils, dry climate, poor
drainage, high elevation, steepness, or
rockiness.
Other removals: Unutilized wood volume
from cut or otherwise killed growing stock,
from
cultural
operations
such
as
precommercial thinnings, or from timberland
clearing. Does not include volume removed
from inventory through reclassification of
timberland to productive reserved forest land.
Other sources: Sources of roundwood
products that are not growing stock. These
include salvable dead, rough, and rotten
trees, trees of noncommercial species, trees
less than 5.0 inches dbh, tops, and
roundwood harvested from nonforest land
(for example, fence rows).
Output — The value of production
by industry for a specific time
period.
Oven dry ton: An amount of wood that
weighs 2,000 pounds at 0% moisture content.
Overstory — The portion of the trees
forming the uppermost canopy in a
forest stand.
Oxygenate: A compound which contains
oxygen in its molecular structure. Ethanol and
biodiesel act as oxygenates when they are
blended with conventional fuels. Oxygenated
fuel improves combustion efficiency and
reduces tailpipe emissions of CO. OR A
substance which, when added to gasoline,
increases the amount of oxygen in that
gasoline blend. Includes fuel ethanol,
methanol, and methyl tertiary butyl ether
(MTBE).
Ozone: A compound formed when oxygen
and other compounds react in sunlight. In the
upper atmosphere, ozone protects the earth
from the sun's ultraviolet rays. Though
beneficial in the upper atmosphere, at ground
level, ozone is called photochemical smog,
and is a respiratory irritant and considered a
pollutant. OR A compound that is formed
when oxygen and other compounds react in
sunlight. In the lower atmosphere (groundlevel) it is photochemical smog and is
considered a pollutant.
Particulates: A fine liquid or solid particle
such as dust, smoke, mist, fumes, or smog,
found in air or emissions. OR A small, discrete
mass of solid or liquid matter that remains
individually dispersed in gas or liquid
emissions. Particulates take the form of
aerosol, dust, fume, mist, smoke, or spray.
Each of these forms has different properties.
Per-unit Sale — A timber sale in which the
buyer and seller negotiate a price per unit of
harvested wood, and the buyer pays for the
timber after it is cut and the volume is
determined.
Petrochemical Feedstock — Petroleum
(hydrocarbon) based substance used as a raw
material in an industrial process. Examples
Petroleum: Substance comprising a complex
blend of hydrocarbons derived from crude oil
through the process of separation,
conversion, upgrading, and finishing, including
motor fuel, jet oil, lubricants, petroleum
solvents, and used oil.
Phloem: The principal tissue in a tree
concerned with the transport of sugars and
other nutrients from the leaves. In plants, the
inner bark.
Photoautotroph: An organism, typically a
plant, obtaining energy from sunlight as its
source of energy to convert inorganic
materials into organic materials for use in
198
cellular functions such as biosynthesis and
respiration.
Photoconversion: Conversion of light into
other forms of energy by chemical, biological,
or physical processes.
Photoheterotroph: Heterotrophic organisms
that use light for energy, but cannot use
carbon dioxide as their sole carbon source.
Consequently, they use organic compounds
from the environment to satisfy their carbon
requirements such as carbohydrates, fatty
acids, and alcohols. Examples are purple nonsulfur bacteria, green non-sulfur bacteria, and
heliobacteria.
Photosynthesis: A complex process used by
many plants and bacteria to build
carbohydrates from carbon dioxide and
water, using energy derived from light.
Photosynthesis is the key initial step in the
growth of biomass and is depicted by the
equation: CO2 + H2O + light + chlorophyll =
(CH2O) + O2 OR A complex process that occurs
in the chlorophyll cells of plants to build
carbohydrates from carbon dioxide and
water, using energy derived from light. OR
Process by which chlorophyll-containing cells
in green plants concert incident light to
chemical energy, capturing carbon dioxide in
the form of carbohydrates.
Pilot scale: The size of a system between the
small laboratory model size (bench scale) and
a full-size system.
Plantation — Planted pines or hardwoods,
typically in an ordered configuration such as
equally spaced rows.
Poletimber trees: Live trees at least 5.0 inches
in dbh, but smaller than sawtimber trees. OR
Trees from 5 to 7 inches in diameter at breast
height.
Polymer: A large molecule made by linking
smaller molecules ("monomers") together.
Polysaccharide: A carbohydrate consisting of
a large number of linked simple sugar, or
monosaccharide,
units.
Examples
of
polysaccharides are cellulose and starch.
Pour point - The minimum temperature at
which a liquid, particularly a lubricant, will
flow.
Pre-commercial Thinning — Thinning that
occurs when trees are too young, too small, or
of species undesirable to be used for
traditional timber products.
Prescribed fire - Any fire ignited by
management actions to meet specific
objectives. Prior to ignition, a written,
approved prescribed fire plan must exist, and
National Environmental Protection Act
requirements must be met.
Present value: The worth of future receipts or
costs expressed in current value. To obtain
present value, an interest rate is used to
discount future receipts or costs.
Primary wood-using mill: A mill that converts
roundwood products into other wood
products. Common examples are sawmills
that convert saw logs into lumber and pulp
mills that convert pulpwood roundwood into
wood pulp.
Process development unit: An experimental
facility that establishes proof of concept,
preliminary
process
economics,
and
engineering feasibility for a pilot or
demonstration plant.
Process heat: Energy, usually in the form of
hot air or steam, needed in the manufacturing
operations of an industrial plant. OR Heat
used in an industrial process rather than for
space heating or other housekeeping
purposes.
Producer gas: Fuel gas high in carbon
monoxide (CO) and hydrogen (H2), produced
by burning a solid fuel with insufficient air or
by passing a mixture of air and steam through
a burning bed of solid fuel.
Proof: The ethanol content of a liquid at 60°F,
stated as twice the percent by volume of the
ethyl alcohol.
Protein: A chain of up to several hundred
amino acids, folded into a more or less
compact structure. About 20 different amino
acids are used by living matter in making
proteins, making the variety of protein types
numerous. In their biologically active states,
proteins function as catalysts in metabolism
and to some extent as structural elements of
cells and tissues. Protein content in biomass
(in mass %) can be estimated by multiplying
the mass % nitrogen of the sample by 6.25.
Proximate analysis: The determination, by
prescribed methods, of moisture, volatile
199
matter, fixed carbon (by difference), and ash.
Does not include determinations of chemical
elements or determinations other than those
named. The group of analyses is defined in
ASTM D 3172. OR An analysis which reports
volatile matter, fixed carbon, moisture
content, and ash present in a fuel as a
percentage of dry fuel weight.
Public power - The term used for not-forprofit utilities that are owned and operated
by a municipality, state or the federal
government.
Public utility commissions: State agencies
that regulate investor-owned utilities
operating in the state.
Public
Utility
Regulatory
Policies
Act (PURPA): A federal law requiring a utility
to buy the power produced by a qualifying
facility at a price equal to that which the
utility would otherwise pay if it were to build
its own power plant or buy power from
another source.
Pulp chips - Timber or residues processed into
small pieces of wood of more or less uniform
dimensions with minimal amounts of bark.
Pulpwood: Roundwood, whole-tree chips, or
wood residues that are used for the
production of wood pulp. OR Wood used in
the manufacture of paper, fiberboard, or
other wood fiber products. Pulpwood- sized
trees are usually a minimum of 4 inches in
diameter.
Pyrolysis: The breaking apart of complex
molecules by heating in the absence of
oxygen, producing solid, liquid, and gaseous
fuels. OR The thermal decomposition of
biomass at high temperatures (greater than
400° F, or 200° C) in the absence of air. The
end product of pyrolysis is a mixture of solids
(char), liquids (oxygenated oils), and gases
(methane, carbon monoxide, and carbon
dioxide) with proportions determined by
operating temperature, pressure, oxygen
content, and other conditions.
Quad: One quadrillion Btu (1015 Btu) = 1.055
exajoules (EJ), or approximately 172 million
barrels of oil equivalent.
Reaction: A dissociation, recombination, or
rearrangement of atoms.
Reburning - Reburning entails the injection of
natural gas, biomass fuels, or other fuels into
a coal-fired boiler above the primary
combustion zone—representing 15 to 20
percent of the total fuel mix—can produce
NOx reductions in the 50 to 70 percent range
and SO2reductions in the 20 to 25 percent
range. Reburning is an effective and economic
means of reducing NOx emissions from all
types of industrial and electric utility boilers.
Reburning may be used in coal or oil boilers,
and it is even effective in cyclone and wetbottom boilers, for which other forms of NOx
control are either not available or very
expensive.
Recombinant DNA: DNA that has been
artificially introduced into a cell, resulting in
alteration of the genotype and phenotype of
the cell, and is replicated along with natural
DNA. Used in industrial micro-organisms to
produce more productive strains.
Recovery boiler: A pulp mill boiler in which
lignin and spent cooking liquor (black liquor) is
burned to generate steam.
Reforestation — Reestablishing a forest by
planting or seeding an area from which
forest vegetation has been removed.
Refractory lining: A lining capable of resisting
and maintaining high temperatures. Usually
ceramic.
Refuse-derived fuel (RDF): Fuel prepared
from municipal solid waste. Noncombustible
materials such as rocks, glass, and metals are
removed, and the remaining combustible
portion of the solid waste is chopped or
shredded. RDF facilities process typically
between 100 and 3,000 tons of MSW per day.
Regeneration Cut — A cutting strategy in
which old trees are removed while
favorable environmental conditions are
created for the establishment of a new
stand of seedlings.
Renewable diesel - Defined in the Internal
Revenue Code (IRC) as fuel produced from
biological material using a process called
"thermal depolymerization" that meets the
fuel specification requirements of ASTM D975
(petroleum diesel fuel) or ASTM D396 (home
heating oil). Produced in free-standing
facilities.
200
Renewable energy resource: An energy
resource that can be replaced as it is used,
including solar, wind, geothermal, hydro, and
biomass. Municipal solid waste (MSW) is also
considered to be a renewable energy
resource.
Renewable Fuel Standards - Under the
Energy Policy Act of 2005, EPA is responsible
for promulgating regulations to ensure that
gasoline sold in the United States contains a
minimum volume of renewable fuel. A
national Renewable Fuel Program (also known
as the Renewable Fuel Standard Program, or
RFS Program) will increase the volume of
renewable fuel required to be blended into
gasoline, starting with 4.0 billion gallons in
calendar year 2006 and nearly doubling to 7.5
billion gallons by 2012. The RFS program was
developed in collaboration with refiners,
renewable fuel producers, and many other
stakeholders.
Renewables Portfolio Standards/Set Asides Renewables Portfolio Standards (RPS) require
that a certain percentage of a utility's overall
or new generating capacity or energy sales
must be derived from renewable resources,
i.e., 1% of electric sales must be from
renewable energy in the year 200x. Portfolio
Standards most commonly refer to electric
sales measured in megawatt-hours (MWh), as
opposed to electric capacity measured in
megawatts (MW). The term "set asides" is
frequently used to refer to programs where a
utility is required to include a certain amount
of renewables capacity in new installations.
Reproduction — (a) The process by which
young trees grow to become the older
trees of the future forest. (b) The process
of forest replacement or renewal through
natural sprouting or seeding or by the
planting of seedlings or direct seeding.
Reserve margin: The amount by which the
utility's total electric power capacity exceeds
maximum electric demand.
Residual Stand — Trees left in a stand to
grow until the next harvest. This term
can refer to crop trees or cull trees.
Residues - Bark and woody materials that are
generated in primary wood-using mills when
roundwood products are converted to other
products. Examples are slabs, edgings,
trimmings, sawdust, shavings, veneer cores
and clippings, and pulp screenings. Includes
bark residues and wood residues (both coarse
and fine materials) but excludes logging
residues.
Residues, biomass: By-products from
processing all forms of biomass that
have significant energy potential. For
example, making solid wood products
and pulp from logs produces bark,
shavings and sawdust, and spent pulping
liquors. Because these residues are
already collected at the point of
processing, they can be convenient and
relatively inexpensive sources of
biomass for energy. OR Byproducts that
have significant energy potential from
processing all forms of biomass.
Return on investment- (ROI) The interest rate
at which the net present value of a project is
zero. Multiple values are possible.
Return on investment (ROI): The interest rate
at which the net present value of a project is
zero. Multiple values are possible.
Rotation: Period
of
years
between
establishment of a stand of timber and the
time when it is considered ready for final
harvest and regeneration. OR The number of
years required to establish and grow trees to
a specified size, product, or condition of
maturity.
Rotten tree: A live tree of commercial species
that does not contain a saw log now or
prospectively, primarily because of rot (that
is, when rot accounts for more than 50% of
the total cull volume).
Rough tree: (a) A live tree of commercial
species that does not contain a saw log now
or prospectively primarily because of
roughness (that is, when sound cull due to
such factors as poor form, splits, or cracks
accounts for more than 50% of the total cull
volume) or (b) a live tree of noncommercial
species.
Roundwood products: Logs and other round
timber generated from harvesting trees for
industrial or consumer use.
201
Saccharide: A simple sugar or a more complex
compound that can be hydrolyzed to simple
sugar units.
Saccharification: A conversion process using
acids, bases, or enzymes in which long-chain
carbohydrates are broken down into their
component fermentable sugars. OR The
process of breaking down a complex
carbohydrate, such as starch or cellulose, into
its monosaccharide components.
Salvable dead tree: A downed or standing
dead tree that is considered currently or
potentially
merchantable
by
regional
standards.
Salvage Cutting — Removal of trees that have
dead, damaged, or are expected to die,
generally as a result of natural disaster, pest
infestation, or disease infestation.
Sanitation Cut — Removal of dead and
weaker trees in an overstocked stand to
reduce the danger of natural disasters.
Saplings: Live trees 1.0 inch through 4.9
inches dbh.
Saturated
steam: Steam
at
boiling
temperature for a given pressure.
Screen analysis: Method for measuring a
proportion of variously sized particles in solid
fuels. The sample is passed through a series of
screens of known size openings. Biomass fuel
screen sizes usually range from 5 to 100
openings per inch.
Scrubber: An air pollution control device that
uses a liquid or solid to remove pollutants
from a gas stream by adsorption or chemical
reaction.
Secondary wood processing mills: A mill that
uses primary wood products in the
manufacture of finished wood products, such
as cabinets, moldings, and furniture.
Seed-tree Harvest — A silvicultural system in
which all trees are harvested except for a
small number of selected trees are retained
for seed production for natural regeneration.
Shaft horsepower: A measure of the actual
mechanical energy per unit time delivered to
a turning shaft. See also horsepower.
Shelterwood Harvest — A silvicultural
system in which trees are removed in a series
of two or more cuts, leaving those needed to
produce sufficient shade to produce a new
forest in a moderated microenvironment.
This method produces an even-aged forest.
Short
Rotation
Intensive
Culture (SRIC): Growing tree crops for
bioenergy or fiber, characterized by detailed
site preparation, usually less than 10 years
between harvests, usually fast-growing hybrid
trees, and intensive management (some
fertilization, weed and pest control, and
possibly irrigation).
Short-rotation Woody Crops — Fast
growing species, such as willows and
poplars, which are grown specifically for
the production of energy.
Shredder — A machine that tears material
apart by shearing.
Silviculture: Theory and practice of controlling
the establishment, composition, structure,
and growth of forests and woodlands. OR
Science and art of managing the
establishment, growth, composition, and
quality of forest stands and woodlands for the
desired needs and values of landowners and
society on a sustainable basis.
Site Index — See Site Productivity.
Site Productivity — Combination of soil
and climatic factors contributing to plant
growth and development; may be
measured as biomass accumulation per
unit of time.
Skidder — Machinery used to pull logs
from their stump to a landing. Logs
are pulled with a grapple, cable-winch,
or clam-bunk.
Slagging - The coating of internal surfaces of
fireboxes and in boilers from deposition of
ash particles.
Slash — (a) Tree tops, branches, bark, or
other residue left on the ground after
logging or other forestry operations. (b)
Tree debris left after a natural
catastrophe.
Slow pyrolysis: Thermal conversion of
biomass to fuel by slow heating to less than
842°F (450°C), in the absence of oxygen.
Softwood (conifer): Generally, one of the
botanical groups of trees that in most
cases have needle-like or scale-like
leaves; the conifers; also the wood
produced by such trees. The term has no
202
reference to the actual hardness of the
wood. The botanical name for softwoods
is gymnosperms. OR A tree belonging to
the order Coniferales. Softwood trees are
usually evergreen, bear cones, and have
needles or scale-like leaves.
Soil Fertility — The total availability,
concentration, and amount of essential
plant nutrients.
Soil Function — The role that soils play in
the
environment
and
managed
landscapes.
Soil Productivity — The capacity of a soil
to contribute to the production of a crop,
whether it is agricultural crops or forest
biomass.
Sound dead: The net volume in salvable dead
trees.
Species: A group of organisms that differ from
all other groups of organisms and that are
capable of breeding and producing fertile
offspring. This is the smallest unit of
classification for plants and animals. OR This
notation means that many species within a
genus are included but not all.
SRIC - Short rotation intensive culture - the
growing of tree crops for bioenergy or fiber,
characterized by detailed site preparation,
usually less than 10 years between harvests,
usually fast-growing hybrid trees and
intensive management (some fertilization,
weed and pest control, and possibly
irrigation).
Stand — A group of trees of similar ageclass, composition, and structure
growing on a site of uniform quality.
Stand density - The number or mass of trees
occupying a site. It is usually measured in
terms of stand density index or basal area per
acre.
Stand (of trees): Tree community that
possesses
sufficient
uniformity
in
composition, constitution, age, spatial
arrangement,
or
condition
to
be
distinguishable from adjacent communities.
Starch: A molecule composed of long chains
of a-glucose molecules linked together
(repeating unit C12H16O5). These linkages occur
in chains of a-1,4 linkages with branches
formed as a result of a-1,6 linkages (see
below). This polysaccharide is widely
distributed in the vegetable kingdom and is
stored in all grains and tubers. OR A naturally
abundant nutrient carbohydrate, found
chiefly in the seeds, fruits, tubers, roots, and
stem pith of plants, notably in corn, potatoes,
wheat, and rice, and varying widely in
appearance according to source but
commonly prepared as a white amorphous
tasteless powder.
Steam turbine: A device for converting energy
of high-pressure steam produced in a boiler
into mechanical power. This power can then
be used to generate electricity.
stocked pine forest may have a basal area
of 80 to 120 square
Stocking — A description of the number of
trees, basal area, or volume per acre in a
forest stand compared with a desired level for
balanced health and growth. Most often used
in comparative expressions, such as wellstocked, poorly stocked, or overstocked.
Stover: The dried stalks and leaves of a crop
that remain after the grain has been
harvested.
Streamside Management Zones — Buffer
zones in which cover is retained in riparian
areas adjacent to surface water and aquatic
habitat.
Structural chemical analysis: The composition
of biomass reported by the proportions of the
major structural components: cellulose,
hemicellulose, and lignin. Typical ranges are
shown in the table below.
Stumpage — The value or volume of a tree or
group of trees as they stand uncut in the
woods (on the stump).
Substrate: The base on which an organism
lives or a substance acts upon (as by an
enzyme).
Sulfur Dioxide (SO2) - Formed by combustion
of fuels containing sulfur, primarily coal and
oil. Major health effects associated with
SO2include asthma, respiratory illness, and
aggravation of existing cardiovascular disease.
SO2 combines with water and oxygen in the
atmosphere to form acid rain, which raises
the acid levels of lakes and streams, affecting
the ability of fish and some amphibians to
survive. It also damages sensitive forests and
203
ecosystems, particularly in the eastern part of
the US. It also accelerates the decay of
buildings. Making electricity is responsible for
two-thirds of all Sulfur Dioxide.
Superheated steam: Steam that is hotter than
boiling temperature for a given pressure.
Surplus electricity: Energy produced by
cogeneration equipment in excess of the
needs of an associated factory or business.
Sustainability — The capacity of forests to
maintain their health, productivity,
diversity, and overall integrity, in the long
run, in the context of human activity and
use. Sustainability can apply to single
forest or ecoregions.
Sustainable Forest Management — Forest
management that ensures that forest
resources will be managed to supply goods
and services to meet the current demands of
society while conserving and renewing the
availability and quality of the resource for
future generations.
Sustainable: An ecosystem condition in which
biodiversity, renewability, and resource
productivity are maintained over time.
Sustained Yield — A forest management
strategy in which the net growth and yield
are balanced.
Switchgrass - Panicum virgatum, is a native
grass species of the North American Praries
that has high potential as an herbaceous
energy crop. The relatively low water and
nutrient requirements of switchgrass make it
well suited to marginal land and it has longterm, high yield productivity over a wide
range of environments.
Syngas — A gas mixture that contains varying
amounts of carbon monoxide and hydrogen
generated by the gasification of a carbonbased fuel to a gaseous product with a heating
value.
Synthetic ethanol - Ethanol produced from
ethylene, a petroleum by-product.
Syringyl: A component of lignin, normally only
found in hardwood lignins. It has a six-carbon
aromatic ring with two methoxyl groups
attached.
Systems benefit charge - A small surcharge
collected through consumer electric bills that
are designated to fund certain "public
benefits" that are placed at risk in a more
competitive industry. Systems benefit charges
typically help to fund renewable energy,
research and development, and energy
efficiency.
Tar: A liquid product of thermal processing of
carbonaceous materials.
Therm: A unit of energy equal to 100,000 Btus
(= 105.5 MJ); used primarily for natural gas.
Thermal NOx - Nitrous Oxide (NOx) emissions
formed at high temperature by the reaction of
nitrogen present in combustion air. cf. fuel
NOx.
Thermochemical conversion: The use of heat
to chemically change substances to produce
energy products.
Thinning — A tree removal practice that
reduces tree density and competition
among remaining trees in a stand.
Timber Product Output Database Retrieval
System (TPO): System developed in support
of the 1997 Resources Planning Act (RPA)
Assessment System, acting as an interface to
a standard set of consistently coded TPO data
for each state and county in the United
States. This national set of TPO data consists
of 11 data variables that describe for each
county the roundwood products harvested,
the logging residues left behind, the timber
otherwise removed, and the wood and bark
residues generated by its primary wood-using
mills.
Timber Stand Improvement (TSI) —
Improving the quality of a forest stand by
removing or deadening undesirable
species to achieve desired stocking and
species composition. TSI practices include
applying herbicides, burning, girdling, or
cutting.
Timberland: Forest land that is producing, or
is capable of producing, crops of industrial
wood and that is not withdrawn from timber
utilization by statute or administrative
regulation. Areas qualifying as timberland are
capable of producing more than 20 cubic feet
per acre per year of industrial wood in natural
stands. Currently inaccessible and inoperable
areas are included.
Tipping fee: A fee for disposal of waste.
Tolerant Species — A species of tree that
204
has the ability to grow in the shade of
other trees and in competition with them.
Ton (tonne): One U.S. ton (short ton) = 2,000
pounds. One Imperial ton (long ton or
shipping ton) = 2,240 pounds. One metric
tonne (tonne) = 1,000 kilograms (2,205
pounds). One oven-dry ton or tonne (ODT,
sometimes termed bone-dry ton/tonne) is the
amount of wood that weighs one ton/tonne
at 0% moisture content. One green ton/tonne
refers to the weight of undried (fresh)
biomass material - moisture content must be
specified if green weight is used as a fuel
measure.
Topping and back pressure turbines: Turbines
that operate at exhaust pressure considerably
higher than atmospheric (noncondensing
turbines). These turbines are often multistage
types with relatively high efficiency.
Topping cycle: A cogeneration system in
which electric power is produced first. The
reject heat from power production is then
used to produce useful process heat.
Total lignin: The sum of the acid soluble lignin
and acid insoluble lignin fractions.
Total solids: The amount of solids remaining
after all volatile matter has been removed
from a biomass sample by heating at 105ºC to
constant weight. (Source: Ehrman, T.
Standard Method for Determination of Total
Solids in Biomass. NREL-LAP-001. Golden, CO:
National Renewable Energy Laboratory,
October 28, 1994.)
Toxics: Substances including benzene, 1, 3
butadiene, formaldehyde, acetaldehyde, and
polycyclic organic matter, as defined in the
1990 Clean Air Act Amendments.
Transesterification: A process that includes
chemical reactions of alcohols and
triglycerides contained in vegetable oils and
animal fats to produce biodiesel and glycerin.
Transmission: The process of long-distance
transport of electrical energy, generally
accomplished by raising the electric current to
high voltages.
Transpiration Drying — The natural
drying that occurs when leafy
biomass material is left on the tree.
Traveling grate: A type of furnace in which
assembled links of grates are joined together
in a perpetual belt arrangement. Fuel is fed in
at one end and ash is discharged at the other.
Tree-length — Trees felled, delimbed,
and topped in the stump area and
processed at the landing.
Triglyceride: A combination of glycerol and
three fatty acids. Most animal fats are
comprised primarily of triglycerides.
Trommel screen - A revolving cylindrical sieve
used for screening or sizing compost, mulch,
and solid biomass fuels such as wood chips.
Tub grinder - A shredder used primarily for
woody, vegetative debris. A tub grinder
consists of a hammermill, the top half of
which extends up through the stationary floor
of a tub. As the hammers encounter material,
they rip and tear large pieces into smaller
pieces, pulling the material down below the
tub floor and ultimately forcing it through
openings in a set of grates below the mill.
Various sized openings in the removable
grates are used to determine the size of the
end product.
Turbine: A machine used to convert energy,
such as converting the heat energy in
steam or high temperature gas into
mechanical energy. OR A machine for
converting the heat energy in steam or high
temperature gas into mechanical energy. In a
turbine, a high velocity flow of steam or gas
passes through successive rows of radial
blades fastened to a central shaft.
Turn down ratio: The lowest load at which a
boiler will operate efficiently as compared to
the boiler's maximum design load.
Two-pass Method — A harvest
practice where roundwood and
biomass are recovered in separate
passes. Biomass removal can precede
or follow the conventional product
harvest.
Ultimate analysis: The determination of the
elemental composition of the organic portion
of carbonaceous materials. See elemental
analysis. OR A description of a fuel´s
elemental composition as a percentage of the
dry fuel weight.
Understory — (a) The layer formed by the
crowns of smaller trees in a forest. (b) The
trees beneath the forest canopy
205
Uneven-aged Management — A
regeneration
and
management
technique that removes some trees in
all size classes either singly, in small
groups, or strips in order to maintain a
multi-aged stand.
Unmerchantable wood - Material which is
unsuitable for conversion to wood products
due to poor size, form, or quality.
Urban Residues — Wood and yard waste;
construction and demolition debris from an
urban source.
Urban wood waste - Woody biomass
generated from tree and yard trimmings, the
commercial tree care industry, utility line
thinning to reduce wildfire risk or to improve
forrest health, and greenspace maintenance.
Uronic acid: A simple sugar whose terminal CH2OH group has been oxidized to an acid,
COOH group. The uronic acids occur as
branching groups bonded to hemicelluloses
such as xylan. (Source: Milne, T.A.; Brennan,
A.H.; Glenn, B.H. Sourcebook of Methods of
Analysis for Biomass Conversion and Biomass
Conversion Processes. SERI/SP-220-3548.
Golden, CO: Solar Energy Research Institute,
February 1990.)
Vacuum distillation: The separation of two or
more liquids under reduced vapor pressure;
reduces the boiling points of the liquids being
separated.
Value-added — Payments made by
industry to workers, interest, profits, and
indirect business taxes.
Volatile matter - Those products, exclusive of
moisture, given off by a material as a gas or
vapor, determined by definite prescribed
methods that may vary according to the
nature of the material. One definition of
volatile matter is part of the proximate
analysis group usually determined as
described in ASTM D 3175.
Volatile matter: Those products,
exclusive of moisture, given off by a
material as a gas or vapor,
determined by definite prescribed
methods that may vary according to
the nature of the material.
Volatile organic compounds (VOC) - Nonmethane hydrocarbon gases, released during
combustion or evaporation of fuel.
Volatile: A solid or liquid material that easily
vaporizes.
Waste streams: Unused solid or liquid byproducts of a process.
Water Quality — Suitability of the water
coming from ground and surface water
supplies for drinking water, recreational
uses, and as habitat for aquatic organisms
and other wildlife. OR Timing and total yield
of water from a watershed.
Water-cooled vibrating grate: A boiler grate
made up of a tuyere grate surface mounted
on a grid of water tubes interconnected with
the boiler circulation system for positive
cooling. The structure is supported by flexing
plates allowing the grid and grate to move in a
vibrating action. Ashes are automatically
discharged.
Watershed: The drainage basin contributing
water, organic matter, dissolved nutrients,
and sediments to a stream or lake.
Watt: The common base unit of power in the
metric system. One watt equals one joule per
second, or the power developed in a circuit by
a current of one ampere flowing through a
potential difference of one volt. One Watt =
3.412 Btu/hr. See kilowatt and megawatt.
Wet scrubber: An air pollution control device
used to remove pollutants by bringing a gas
stream into contact with a liquid.
Wheeling: The process of transferring
electrical energy between buyer and seller by
way of an intermediate utility or utilities.
Whole tree chips: Wood chips produced by
chipping whole trees, usually in the forest, so
that the chips contain both bark and wood.
They are frequently produced from the lowquality trees or from tops, limbs, and other
logging residues.
Whole-tree chips - Wood chips produced
by chipping whole trees, usually in the
forest. Thus the chips contain both bark
and wood. They are frequently produced
from the low-quality trees or from tops,
limbs, and other logging residues. OR
Trees are felled and transported to
roadside with branches and top intact.
206
Processing occurs at the deck or landing.
OR A harvesting method in which the
whole tree (above the stump) is removed.
Willstatter lignin: Lignin obtained from the
lignocellulosic complex after it has been
extracted with hydrochloric acid.
Wood Ash — Ash recovered from the
combustion of woody biomass; may
be used as fertilizer or soil liming
agent to reduce soil acidity.
Wood Processing Residue — The unused
portion of materials generated during
wood processing or by-products created
during the pulping process.
Wood: A solid lignocellulosic material
naturally produced in trees and some shrubs,
made of up to 40%–50% cellulose, 20%–30%
hemicellulose, and 20%–30% lignin.
Woody Biomass — The trees and woody
plants, including limbs, tops, needles,
leaves, and other woody parts, grown in a
forest,
woodland,
or
rangeland
environment that are the byproducts of
proper forest management.
Wort: The liquid remaining from a brewing
mash preparation following the filtration of
fermentable beer.
Xylan: A polymer of xylose with a repeating
unit of CHO, found in the hemicellulose
fraction of biomass. Can be hydrolyzed to
xylose.
Xylose (C5H10O5): A five-carbon sugar. A
product of hydrolysis of xylan found in the
hemicellulose fraction of biomass.
Yarding : The initial movement of logs
from the point of felling to a central
loading area or landing, particularly by
cable or helicopter.
Yeast: Any of various single-cell fungi capable
of fermenting carbohydrates.
207
PRACTICAL NO.01
PRACTICAL
208
IDENTIFICATION OF IMPORTANT FUEL WOODS AND PETRO-CROPS.
IDENTIFICATION OF IMPORTANT FUEL WOODS AND PETRO-CROPS.
PRACTICAL NO.02
STUDY OF DIFFERENT PROPERTIES OF BIO FUELS USED IN PAKISTAN.
209
STUDY OF DIFFERENT PROPERTIES OF BIO FUELS USED IN PAKISTAN.
PRACTICAL NO.03
DETERMINATION OF CALORIFIC VALUE, MOISTURE AND ASH CONTENT IN BIOMASS.
210
DETERMINATION OF CALORIFIC VALUE,
The gross calorific value (GCV) and, in particular, the net calorific value (NCV) are fundamental physical parameters in
the use of energetic biomass. The method of measurement and the calculation of the GCV, defined by CEN/TS 14918, is
rather complex and, in many cases, has a time and cost importance. In literature there are some studies in which the
empirical correlations between GCV and the element composition have been calculated. In these contribution some of
the most significant correlations in literature are tested and compared to others obtained from statistical processing of
data from analysis on 200 samples of biomass carried out in the laboratory and with standard CEN methods. The study
shows how the very simplified correlations based on the calculation of carbon and hydrogen content have
performances that are similar to those of more complex ones based on the greater number of parameters. In particular,
the empirical correlation (GCV=297.6+389.7C) produced from this work has errors that are comparable to those of the
better correlation highlighted by literature (GCV=5.22C2-319C-1647H+38.6C.H+133N+21028).
Biomass is becoming increasingly important as a renewable source of energy, by incineration as well as production of
liquid biofuels, e. g. biodiesel or bioethanol. Compared to the incineration of fossil fuels the overall CO2 balance is
considerably less affected by the usage of biomass. Typical biomass materials used for energy production are wood and
so-called energy grass. Special types of cereals have a century old tradition in (bio-)alcohol production, recent
developments also consider cereal incineration.
An important property of a fuel is its heating value. The so called "higher heating value" (HHV) is the enthalpy of
complete combustion of a fuel with all carbon converted to CO2, and all hydrogen converted to H2O. The higher heating
value is given for standard conditions (101.3 kPa, 25 oC) of all products and includes the condensation enthalpy of
water; it is generally used in the USA. In European countries the "lower heating value" - not used in this study - is more
common. It does not include the condensation enthalpy of water.
Direct determination of the heating value requires time-consuming calorimetric experiments, which hardly can be
automated. Empirical equations have been
K. Varmuza, B. Liebmann, A. Friedl published that relate the heating value of a fuel to its elemental composition.
Elemental analysis requires tedious laboratory work too, but can be automated. Early mathematical models for coal
date back to the late 19th century. Recently, modern chemometric methods have been applied for prediction of heating
values of plant biomass from elemental composition.
Determination of calorific values of some renewable biofuels
Jothi V. Kumar *, Benjamin C. Pratt
Department of Chemistry, North Carolina A & T State University. Greensboro,
North Carolina, 27411, USA
Received 16 October 1995; accepted 3 January 1996
The determination of the calorific values as well as the percentages of C, H,N, S, and 0 of biofuels are important in
considering their suitability as environmentally safe energy sources. The biofuels tested such as the common milkweed,
dogbane, kudzu, and eucalyptus tree can be replenished, unlike fossil and petroleum-based fuels. They are fast-growing
renewable energy sources with recovery periods for harvesting ranging from less than a year [l-3] for the weed and
vine-type plants [4,5], and up to seven years for eucalyptus tree [6]. The above biomass materials can be converted to
synthetic liquid fuels [7,8] and chemical feedstocks [9, lo]. Other benefits of these plants are that they can be used to
stop erosion and can be utilized in heating.
Currently, about two percent of the U.S. energy consumption comes from woods, agricultural crops with their residues,
and municipal and animal wastes plus other sources of biomass [ll, 121. The majority of the energy from biomass comes
from its use in the forest industry [13,14]. By the year 2000 up to twenty percent of the U.S. energy consumption could
be furnished by biomass [15].
Thermal methods such as differential scanning calorimetry (DSC) and elemental analysis (EA) were employed to
determine calorific values of biofuels either directly or indirectly. The biofuels tested were the common milkweed,
dogbane, kudzu, and eucalyptus tree. All the biofuels tested were mainly composed of lignocellulosic polymers
(hemicellulose, cellulose, and lignin). The milkweed and dogbane contained some latex (liquid hydrocarbons) while
kudzu and eucalyptus contained high molecular weight resins and oils respectively.
The direct determination of calorific values of fuel materials by differential scanning calorimetry (DSC) was introduced
by Fyans in 1977 [16]. This technique measures heat flow as a function of temperature with the total area under the
curve being proportional to the heat of combustion. A typical thermocurve shows a two-step decomposition with the
211
first peak relating to the combustion of volatiles and the second to the fixed carbon in the sample. Earnest has reported
calorific values for coal samples that are in close agreement with the values published by ASTM [17,18]. Earnest and
Fyans [19,20] determined the calorific values of coal and coke specimens from the percentage of volatile matter and
fixed carbon using a thermogravimetric technique.
A method for calculating the calorific values from the elemental composition has been introduced by Culmo [21].
Percents of carbon, hydrogen, oxygen, sulfur, moisture and ash were used to calculate the calorific values from the
Dulong equation. Giazzi and Colombo introduced a modification of this equation for calculating gross and net heat
values [22]. Calorific values of standard coal samples determined by DSC and elemental analysis in our laboratory were
compared to ASTM values of the same samples. The biofuels were analyzed under the same conditions as the standard
coal samples and the calorific values of direct and indirect determinations were compared.
2. Experimental
2.1. Instruments and materials
A Mettler DSC 20 with measuring cells containing medium-sensitivity sensors was used to determine calorific values of
standard coal samples and biofuels. The instruments were calibrated as per the instructions in the manuals.
Determination of C/H/N/S/O was made on a Carlo Erba Elemental Analyzer (EA), Model 1106.
A microbalance, Cahn C-31, and an IBM computer were interfaced with the instrument. Eager 100 software of Carlo
Erba was used for operating the system and data analysis. The Mettler TG-50 Thermogravimetric Analyzer was used to
dry the samples.
All gases used were 99.9% pure or better from National Speciality Gases, a division of National Welders Supply.
Transparent traps filled with anhydrone and ascarite were added to the lines to absorb traces of moisture and CO 2.
Nitrogen used for drying was purified with a Supleco High Capacity Heated Carrier Gas Purifier, catalogue # 2-3802. The
standards, sulfanilamide for C/H/N/S and dextrose for oxygen analysis, were provided with the instrument for the
standardization and calibration of the instrument. Chemicals to pack the combustion and pyrolysis reactors and other
consumables like tin containers were obtained from Erba Company. The coal standards from National Bureau of
Standards (NBS) (numbered 2684) a set of 8 premium coal samples from Argonne National Laboratories (ANL), and
dextrose sugar were used throughout this work. Due to the decomposition of coal samples after the exposure to
atmospheric conditions, a synthetic standard made of microanalytical chemicals was used to calibrate the elemental
analyzer. Magnesium oxide, lead chromate (Analytical Reagent, Mallinckrodt), silver oxide (Baker and Adamson),
praseodymium oxide, copper oxide (certified ACS, Fisher), and lead dioxide (Fisher) were used as received.
2.2. Sample collection and preparation
Plants were collected in Winston-Salem, Kernersville, Greensboro, and Hillsborough, North Carolina. Coal standards
were acquired from NBS and the Premium Coal Samples came from ANL. Several whole green plants of milkweed,
dogbane, kudzu, and eucalyptus were selected. They were dried separately in a gravity oven (70-120°C for several
hours), ground in a Waring blender, and sieved to obtain 100 mesh size samples. The portions that did not pass 100
mesh were kept as coarse ground. Leaves of the biofuels were cut into small pieces for analysis.
2.3. Procedure
The Mettler TG-50 was used to dry about 10 mg of the sample in a tared platinum container in the furnace with dry,
oxygen-free nitrogen flowing at 300 ml min-I. The sample was dried by slowly heating from 35 to 135°C and held
isothermally for either 2 or 5 min depending on the moisture content. If the thermocurve indicated insufficient drying,
the isothermal drying was repeated. The samples were then stored in nitrogen atmosphere for further analysis.
A screening procedure recommended in the instrument manual for determining the calorific values by DSC was stored
on the TC-I OA processor. This included a 10°C min-I heating rate from room temperature to 600°C. The experimental
conditions were optimized using a standard coal sample as outlined in Table 1. The sample holders are 40 ul in capacity
and each hole is about 0.50 mm in size. Sample weights of about 0.50 mg of coal samples (200 mesh) and biofuels (100
mesh) were integrated over a baseline starting at 105°C to the end of the run. Among the additives (catalysts) tested. a
1: 1 (by weight) magnesium oxide to silver oxide mixture improved the calorific values of both coal and the biofuels (Fig.
1).
A Carlo Erba Elemental Analyzer was used to simultaneously analyze the samples for carbon (C), hydrogen(H),
nitrogen(N), and sulfur(S). Due to the large differences in the elemental composition of sulfanilamide standards, a
synthetic standard was made and used for calibration. The elements, C,H,N and S, were combusted to their respective
oxides first. The nitrogen oxides were then reduced to nitrogen and sulfur trioxide to sulfur dioxide by metallic copper in
212
the reactor. The gas chromatographic separation of N2, CO2, H2O and SO2 is shown in Fig. 2. After separation, the gases
pass through a detector which sends a signal to an integrator. The integrated values
Table 1
Effect of DSC variables on the accuracy of heat value (using a demineralized
bituminous coal standard, h.v. of 35672 J g-t-I)
Exp. conditions
Variable studied
HV/Jg-I
-I
Heating rate/C min
Mass approx. 1 mg, open 1
25844
container, and 80 ml min-I 0, flow 2.5
25114
rate
5
28130
10
27316
25
23712
50
21294
Holes in container cover
Mass approx. 0.75 mg, 10°C min-I 1 holes
27737
-I
heating rate, and 80 ml min flow 2 holes
29282
rate
4 holes
30489
7 holes
28604
8 holes
29885
No cover
27191
Sample mass/mg
10°C min-I heating rate, 80 ml 1.092
27316
min-I flow rate, no cover
0.830
28604
0.432
34287
0.393
30702
-I
0, flow rate/ml min
Mass approx. 0.8 mg, heating 40
32392
rate 10°C min-I, no cover
80
27191
240
31370
320
29404
were used to prepare the calibration curves which were then used to calculate the percentages of the various elements
present. The analysis of oxygen was carried out in an inert gas stream with the pyrolysis of sample over a catalytic layer
of nickel-plated carbon. The oxygen was converted to carbon monoxide (CO) and was separated from any nitrogen on a
chromatographic column, Fig. 3. The signal was recorded and integrated as above. Dextrose was used as a standard for
oxygen. The gross heat value (GHV) of both coal standards and biofuels were calculated using the equation
recommended by Giazzi and Columbo (Table 2). The effect of particle size of the biofuels on the calorific values was also
studied to choose the best mesh size of the sample, Table 3.
3. Results and discussion
The Mettler TG-50 equipped with TClO TA controller/processor was used for drying the coal samples and biofuels. The
Mettler processor was changed from TClO to
213
Fig. la. DSC curves of a standard coal sample.
Fig. lb. DSC curves of common milkweed
TClOA and connected to an IBM/PC. This modification made the storage of raw data feasible and reduced the 4 linked
methods to 2. This processor was tested with standard premium coal samples from ANL and then used for the biofuels.
The samples were dried as described in the procedure and then used in DSC and EA.
The optimized experimental conditions for DSC, based on the data on Table 2 are: 5°C min -I heating
Fig. 2. Simultaneous determination of C, H, N, S
214
Fig. 3. Determination of oxygen by pyrolysis.
and 40 ml min-I oxygen flow rate. Four holes were better than one because more holes allowed sufficient oxygen to
enter into the container for better combustion. Since it took several hours to complete one analysis at a heating rate of
5°C min-It, the experimental conditions were slightly modified to a heating rate of 25°C min-I with
Table 2
Elemental analysis of standard coal samples and biofuels
Sample ID
%C
ASTM
65.7
75.5
86.7
66.2
65.8
ANL# 3
ANL#4
ANL# 5
ANL#7
ANL#8
Milkweed
Dogbane
Kudzu
a
Sample ID
Milkweed (C)
Milkweed(F)
Milkweed(L)
Dogbane (C)
Dogbane (F)
Dogbane (L)
Kudzu (C)
Kudzu (F)
Kudzu (L)
Eucalyptus Gr(LF)
Eucalyptus Gr.(C)
Eucalyptus CA.(L)
a
E.A
64.4
75.0
85.7
66.3
65.7
46.1
48.4
48.4
%N
1.45
2.17
4.91
1.78
1.75
4.10
1.49
3.26
4.72
1.66
0.62
2.53
%H
ASTM
4.2
4.8
4.2
4.2
4.4
E.A
1.2
5.0
4.4
4.3
4.4
6.1
6.0
5.8
%N
ASTM
1.2
1.5
1.3
1.3
1.0
E.A
1.4
1.5
1.2
1.2
0.9
1.8
1.8
2.0
%S
ASTM
4.8
2.2
0.7
0.7
0.8
E.A
4.5
2.2
0.7
0.7
0.9
%O
ASTM
E.A
42.47
38.77
42.23
-1
Jg
ASTM
27798
31701
34946
27470
25588
Table 3
Effect of particle size of the biofuels on the caloritic value
%C
45.81
46.46
45.89
48.50
49.07
45.54
45.91
45.76
44.63
47.90
48.43
49.59
%H
6.00
6.08
6.23
6.05
6.16
6.37
5.86
5.84
5.99
5.41
5.80
6.87
%O
43.46
39.55
34.98
39.26
38.37
37.06
42.64
35.98
35.82
39.33
43.30
35.41
E.A
27130
31829
34946
27607
25556
17298
18201
17273
-1
Jg
16354
17392
18238
18094
18606
17947
16333
11452
18082
17043
16982
20336
C, coarse ground > 100 mesh; F, fine ground cc 100 mesh; L, leaf section; LF, leaves ground to < 100 mesh; Cr., Grandis; GI., Globulus.
one hole in the cover. Varhegyi et al. [23] showed that DSC curves reveal considerably less energy release than the true
heat of combustion due to experimental conditions. To correct this problem they proposed the use of catalysts as aids
to combustion in DSC.
In an effort to improve the DSC techniques for our samples, several metal oxides alone and in mixtures of various
proportions were tested with a standard coal sample. Among the choices, 1: 1 magnesium oxide (MgO) to silver oxide
(Ag,O) (by weight) proved to be the best mixture. Magnesium oxide aids the combustion of the volatile matter and also
catalyzes the oxidation of carbon monoxide (CO) to carbon dioxide (CO,). Silver oxide catalyzes the combustion of fixed
carbon in the sample as well as converting any CO to CO,. Formation of CO, releases approximately four times the
215
amount of heat as the formation of CO from the same amount of carbon [24]. The effect of the catalyst on a coal
sample and a biofuel is presented in Fig. 1.
The simultaneous determination of C, H, N, and S in organic compounds [25] and oxygen [26] has been done by Pella
and Colombo using a Carlo Erba Elemental Analyzer, Model 1106. Sadek and deBot [27] have determined C, H, N, and S
simultaneously along with oxygen (0) in coal samples using the same Model 1106 Elemental Analyzer whereas we used
it for biofuels. A typical gas chromatographic separation is shown in Fig. 2. The Eager 100 computer program on an IBM
personal computer interfaced to the Elemental Analyzer was used to run the instrument, calculate and store the results,
as well as give the actual time plot showing the quality of the chromatographic separation. The regressional analysis for
C, H, N, S, and 0 was done by the computer using the Eager program. Also, the program uses a modified Dulong
equation introduced by Giazzi and Colombo to calculate the gross and net heat values of each sample. The calculated
calorific values were then compared to the ASTM values derived using a bomb calorimeter. The results show good
agreement with those
Table 4
Comparison of heat values (J g-I) from DSC and EA
Sample ID
DSCa
EA
Difference
ANL#3
27798
27130 + 668
ANL#4
31331
31829 -498
ANL#7
27470
27607 -137
ANL#8
25588
25556 +32
Milkweed
18236
17815 +421
Dogbane
18566
18201 + 365
Kudzu
17480
11273 + 207
Eucalyptus gl. [e] 17052
17652 -600
a
With MgO/Ag,O 1: 1 mixture.
generated by ASTM methods as presented in Table 2. The presence of sulfur was found to be below 0.20% or the limit
of detection of the instrument and so considered to be negligible.
The results listed in Table 3 reflect the effect of particle size on the calorific values. The finely ground sample (with
larger surface area) reacted with the catalyst more effectively and released more heat than the coarse and leaf samples.
At the same time, the fine grinding resulted in a loss of some heat and made the sample vulnerable to air oxidation.
4. Summary and conclusion
The calorific values of the ANL premium coal samples as well as the biofuels determined by direct (DSC) and indirect
(EA) methods (Table 4) are within f 668 J g-I. The difference is below the ASTM specified range of k 837 J g-I ( f 360
Btu/lb) for repeatability. Since the same methods and instruments were used to study the biofuels, the calorific values
determined are considered to be accurate and reliable. The addition of the catalyst, 1: 1 (by weight) MgO : Ag,O
mixture, improved the calorific values of the samples. The standard deviation of the elemental analysis of the biofuels
ranged from 0.42 to 0.89 indicating that the results generated are reliable.
MOISTURE AND ASH CONTENT IN BIOMASS.
Overview
Use of woody biomass such as mill residues and forest residues is not a new practice by any stretch of the
imagination. There is a long and widespread tradition of the use of woody biomass in energy appli- cations such as a
boiler fuel, and it represents a very large fraction of the total renewable energy produced in Wisconsin and across the
United States. Interest in increased use of woody biomass has grown signifi- cantly in recent years, particularly in the
Lake States, with increased conversion or replacement of fossil fuel fired boilers to the use of woody biomass and
with consideration of woody biomass as a feedstock for the production of biofuels. While many sectors within the
forest industry, such as sawmills, veneer operations, chip mills, pulp mills and all types of sec- ondary manufacturers
routinely deal with moisture content of wood, other sectors of the industry such as loggers and practicing foresters
have typically had much less need to concern themselves with moisture content determination. Additionally, the
basis and methods of determining moisture content are quite variable depending on the products being dealt with
and the sector of the industry being represented.
With the expanded use of woody biomass, loggers, foresters and others within the industry (and some people
216
from outside the industry) are now being forced to understand and deal with wood moisture content issues. For
example, loggers or foresters that may have sold woody biomass on a green ton basis may soon need to
understand the practical aspects of selling the same woody biomass on a dry ton basis. Also boiler operators
outside of the industry need an understanding of wood moisture determination in
fuel acquisition and testing. This paper is designed to serve as a practical guide for anyone in the Wisconsin
industry in understanding the issues related to deter- mination of moisture content of woody biomass and
reasonable methods that can be used to determine moisture content of woody biomass in an industrial setting.
Woody biomass can be composed of wood (in the form of some kinds of mill residues such as sawdust, trim
ends, etc.), or bark (typically that has been removed in a debarking process), or a combination of wood and bark
(such as cull logs or bolts, chipped tree trimmings etc.). Also the forms of the material can vary considerably,
ranging from roundwood of various sizes and lengths, slabs, edgings, sawdust, hogged fuel, and whole-treechips and also in the form of recovered residue such as branchwood that may include some fraction of needles.
For purposes
of simplicity in this paper, the term “wood” in discus- sion will be used as a generic term for woody biomass in all its
various forms in calculations and discussions for which the calculation would be the same for wood (xylem) or woody
biomass.
The basis on which moisture content % is determinded (i.e. MC as a % of what?)
There are two common ways in which the moisture
content percentage (MC%) of wood is
routinely expressed.
GREEN BASIS: In the green or wet basis (usually ab- breviated “Green basis”) method, the percent mois- ture in the
wood is expressed as a percentage of the TOTAL weight of the wood, including both the dry wood material and the
water. This method is most commonly used for pulp chips and hogged fuel and this method is generally the method
used to deter- mine the MC of woody biomass. It is computed as follows:
methods
of determining moisture content are appropriate and are commonly
It is important to note that both of these
used. There is good reason to use the ovendry basis for measuring moisture content in solid wood products. For
example, where calculations may need to be made regarding changing moisture contents over time using periodically
measured sample pieces (such as sample board in a dry kiln), in using the ovendry basis method, the denominator in the
equation would not change for the piece for the string of calculations to estimate moisture content at various times in
the drying process. In a similar vein, there is good reason to use the green basis method for pulp chips and fuel, where it
is used for a one-time point estimate of what fraction of the whole is usable fiber (or fuel) and what fraction is wa ter. As
you will note, in the example provided above,
MC% (Green basis) = (weight of water) * 100
217
218
weight of water + dry weight of wood
OVENDRY BASIS: In the ovendry basis (usually ab- breviated “OD basis”) method, the %
moisture in the wood is expressed as a percentage of the dry weight of wood. This method is
the standard method used
in this country to express moisture content for solid wood products of all kinds including
lumber, veneer, plywood, OSB, particleboard and other panel products.
the OD basis moisture content can (and will) exceed 100% on occasion – this is NOT an error –
it simply reflects that the weight of water in the sample exceeds the weight of dry material (this is quite
common in
many circumstances in Wisconsin, such as with aspen in the winter, and for many softwoods and
some
lower density hardwoods). In any context regarding the expression of moisture content of woody
biomass in an industrial setting it is essential that all parties concerned understand the basis on
which
the moisture content is determined and expressed.
MC% (OD basis) = (
weight of water
dry weight of wood
)* 100
For this reason, it is highly desirable (if not essential) to clearly express the basis on which the
moisture content was determined. It is so easy to succinctly, In terms of an example, assume you
have taken a
sample of woody biomass equal to 100 grams in
total weight, and you are able to determine that the
sample consists of 49 grams of dry woody biomass
material (after water equal to 51 grams is removed),
the moisture contents would be calculated as follows:
51
MC% (Green basis) =(100 )* 100 =51% MC (Green basis)
And, for THE SAME SAMPLE:
49
51
MC% (OD basis) = ( )* 100 = 104% MC (OD basis)
219
clearly and accurately express “MC (OD basis)” or “MC (Green basis)” - which are two very
different things – that it would be utterly foolish to simply express “moisture content” or “MC”
(without any expressed basis) and create the potential for con- fusion. This potential for confusion
(and contract disputes, disagreements etc.) can largely be avoided by simply specifying the basis
being used to express the percentage moisture content. In almost all cases in transactions regarding
woody biomass it will prob- ably be the case that using the Green basis moisture content would be
used – but there are circumstances
where MC may be determined using the OD basis and
conversion could be required, prompting confusion.
TO CONVERT OVENDRY BASIS %MC TO GREEN BASIS %MC: In the ovendry basis method, as indicated prior, the %MC in the wood is expressed as a percentage of the dry weight of wood. As long
as this dry basis MC is known, this is all that is needed to establish the equivalent green basis %MC,
because the %MC on the dry basis is a surrogate for the weight of water and the ovendry weight
would be equivalent to 100% (relative to the weight of water), therefore, to convert from OD basis
%MC to Green basis %MC the calculation is as follows:
)100%
( MC
% (OD basis)
+ MC% (OD basis) * 100
MC% (Green basis) =
TO CONVERT GREEN BASIS %MC TO OVENDRY BASIS %MC: In the green basis method, as indicated
prior, the %MC in the wood is expressed as a per- centage of the total weight of dry wood plus
water combined. As long as this green basis MC is known, this is all that is needed to establish the
ovendry basis
%MC, because the %MC on the green basis is a surro- gate for the weight of water and the ovendry
weight would be equivalent to subtracting this same % MC green basis from 100% to create a
surrogate for the proportional dry weight, therefore, to convert from Green basis %MC to OD basis
%MC the calculation is as follows:
)100%
(MC
% (Green basis)
- MC% (Green basis) * 100 MC% (OD basis) =
It should be noted that in each case the conversion is simply accomplished by an appropriate
adjustment to the denominator in the equation. This is very simple with a little practice.
220
Common methods of moisture content determination and what is most suitable for woody
biomass of various types
There are several common ways in which the mois- ture content percentage of wood is
routinely estimat- ed. All of these have a purpose and place and there are often practical
reasons (cost, convenience, time, practicality, etc.) that a given method of estimating moisture
content may have an advantage over other methods. The precision level for the methods that
are commonly used to estimate moisture content
of woody biomass should not be assumed to be any
greater than to the integer level (i.e. to the nearest
1%) and with a precision level of from +/- 1%, so calculated moisture contents should be rounded to the
nearest integer value (i.e. the calculation should be
rounded to the nearest 1%)
The oven-drying method
Overview of the oven-drying method: The primary oven-drying method (this is “Method A –
Oven-Drying Primary” as detailed in ASTM D4442-07) is intended
as the sole primary method and is structured for research purposes where the highest
accuracy or degree of precision is needed and requires a specific oven type (i.e. a vented
forced convection oven), closed weighing jars, and the performance of addi- tional special
procedures. The oven-drying method most practically suited for use in determining the
moisture content of wood biomass that is typically or most commonly in the forest industry
is often simply referred to by most people in forest indus- try as “the oven-drying method”
(this is actually “Method B – Oven-Drying Secondary” and is also detailed in ASTM D444207 which provides detail regarding calibration and standardization details for
both methods). This oven-drying method is appropri- ate for use with woody biomass
samples regardless
of moisture content, and although it takes some time to complete the test (usually about 24
hours, and possibly more), the time spent in dealing with each of the individual samples is
minimal, and given a large drying oven, a fairly large number of samples can be handled at
one time. For these reasons, the oven- drying method is the method that is most commonly
used, and other methods (while also suitable) are typically compared to the results of the
oven-drying method to ensure their accuracy.
The oven-drying method procedures: The oven being
used must be capable of maintaining temperatures of
103°C +/- 2°C (or holding between 101°C to 105°C)
near the drying endpoint (this is the same as holding
between about 214°F and 221°F). The sensitivity of
the balance (scale) that is being used to weigh the
samples must be to within a minimum of 0.1% of the
weight of the sample being tested (for example, if
samples being tested are expected to be about 100
grams in weight when dry, the scale should be able to
read to at least 0.1 gram (or a tenth of a gram) –
this would be the minimum sensitivity allowable, but
221
a somewhat greater sensitivity, such as a sensitivity of 0.01 gram (or a hundredth of a gram) would
be preferred in this situation. Samples collected for
moisture content determination are to be kept in
individual vapor-tight containers if there is any delay
between the collection of the sample and the initial
weighing which will determine the “green weight”
that is the weight of wood and water combined.
(Note: If the sample is placed, kept and weighed in
a container, such as a small aluminum pan typically
used to hold chips or sawdust in drying ovens, the
weight of the empty pan needs to be known and
subtracted from all numbers in the calculation, or else
the balance needs to be tare weighted to eliminate
the pan’s weight from what is recorded with each
weighing.) After initial weighing, the sample is placed
in the oven and kept there until the endpoint has
been reached and is then removed and reweighed
as soon as possible. It is known that the endpoint is
reached when there is no appreciable change in the
final weight at approximately 4 hour intervals. The
weight of the sample at endpoint is a direct measurement of the dry weight of wood in the sample, which
is subtracted from the green weight of the sample
(from the initial weighing) to calculate the weight
222
of water. The weight of water is then divided by the green weight of the sample (from the initial
weighing) to calculate the Green basis moisture content of the sample (round to the nearest 1%).
In most cases the oven-drying method can be com- pleted in about 24 hours of testing, assuming
the materials contained in the samples being tested are not very large in size (e.g. in testing samples
of chips and smaller material, these samples can typically be processed within a 24 hour period in a
good forced- convection oven that is properly vented and is not overloaded). If relatively large sizes
of material are included as part of the samples being tested, or if a very large volume of highmoisture material is placed in the oven at one time, this can result in the samples requiring a longer
time in the oven to reach end- point. In using an oven in testing various types of samples over time,
an operator who has appropriate- ly tested for endpoints when running samples of vari- ous types
and moistures (and with various loads in
the oven and during various climatic conditions) could typically be expected to reasonably estimate
the time to endpoint for the samples being tested relative to the conditions at hand. It should be
obvious that it is important to get the samples to endpoint in using the oven-drying method of
moisture calculation or the recorded dry weight for the sample will be overstated (i.e. what is
recorded as dry weight of wood will be
too high as it will have a residual water fraction) and consequently the resulting moisture content
calcula- tion will then understate the moisture content (i.e. the calculated moisture content from the
test will be less than the actual moisture content of the sample). In the circumstance where woody
biomass is pur- chased on a dry ton basis, this failure to reach end- point in drying of samples and
resulting understate- ment of moisture content will overstate the dry tons of material actually
received by the purchaser and will result in an overpayment to the supplier – con- sequently it is not
an error a purchaser can afford to make in a significant way on a regular basis. For this reason it is
important for the purchaser to use good procedures and to ensure the samples being tested reach
endpoint.
Determining moisture content using a microwave oven
Overview of determining moisture content using
a microwave oven: A microwave oven may be used
in determining the moisture content of particulate
wood (as detailed in ASTM E1358-97), such as would
be represented in many forms of woody biomass
samples being tested for moisture content. The
advantage of the procedure in using a microwave
oven is that the test is relatively quick, typically
requiring only about ten to fifteen minutes to
perform. This aspect of timely results is generally
what makes the procedure appear to be an attractive
option. The negatives associated with the procedure
are what generally reduce it to being a procedure
more suited for occasional versus primary use in the
eyes of most potential users. Two minor negatives to
the procedure is that for all practical purposes only
one sample may be tested in the oven at any given
time, and that the testing of the sample needs to
be closely monitored. A major negative to using the
procedure is the risk of combustion of the sample
during testing which is at least in part why the ASTM
E1358-97 standard indicates: “This standard does not
223
purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the
user of this standard to establish appropriate safety
and health practices and determine the applicability of regulatory limitations prior to use.” Where a
microwave oven is to be used in determining the
moisture content of wood it is essential to have a
plan and appropriate mechanisms and materials to
deal with the fires that will occur with testing.
Procedures for determining moisture content using a microwave oven: The microwave oven to be
used can be any standard commercial microwave oven that has a power output of at least 600 W.
The sample size to be tested is to be approximately 50 grams, so the sensitivity of the balance (scale)
that is being used
to weigh the samples should have a minimum sen- sitivity of 0.01 gram (or a hundredth of a gram).
The approximately 50 g sample of the wood to be tested
is placed on 3 sheets of standard paper towels placed
224
on top of each other, the weight of which (towels) has been recorded. The sample with the
towels is weighed, the sample (on the towels) is then placed in the oven and is heated on full
power for a heating interval, it is then removed from the oven after the
heating interval, reweighed and stirred and returned to the oven for another heating interval.
This is continued until endpoint, where the weight change after a drying interval is less than
0.5 g. The weight of the sample minus the weight of the towels (recorded prior) is the dry
weight of wood for the calculation, and the weight of the original sample and towels minus
the weight of the towels is the green weight of the sample for the moisture content
calculation.
An appropriate schedule of intervals of heating times (after which the sample should be
reweighed and stirred before further heating) for higher moisture mixed woody biomass in
particulate form would be something on the order of a first heating interval of
2 minutes, followed by two 1 minute intervals and then 30 second intervals thereafter. For
lower mois- ture material (such as woody biomass well seasoned prior to chipping) it would
be recommended to use a process cycle of three 1 minute intervals and then 30 second
intervals thereafter. For drier materials still, a process cycle of two 1 minute intervals and
then 30 second intervals thereafter would be more appropri- ate. The short intervals of
heating times are very important to ensure that the sample is not overdried. When in doubt, shorter intervals are preferred.
If material larger in size than normal chips or hogged fuel is included in the sample this does
not simplify the situation, rather an even greater care must be exercised. Continuing the
microwave heating of larger pieces of wood for too long will easily result in the sample
starting on fire, and it will typically burn from the inside of the piece giving little early visual
indica- tion of combustion (and perhaps no obvious indica- tion of combustion on the surface,
but on cutting the piece a charred center would be obvious). For this reason, using a
microwave in moisture content deter- mination of larger samples (such as rounds cut from
logs or large materials from a grinder) is not recom- mended. It is difficult for most people to
believe how easy it is to have a sample of wood start on fire by overheating it in the
microwave until they experience it themselves in testing, but the wood will catch fire
if it is heated in the microwave long enough. The first indication of combustion is usually
smelling smoke and then realizing that what appeared to be water vapor or steam leaving the
piece was actually smoke. Pouring water on a larger sample will not likely immediately extinguish the fire as it will almost certainly be burning in the center, so for safety
sake it is desir- able to have a container of water that is large enough to easily hold the sample,
and a means of holding it under the surface of the water is also desirable. (The sample could
also be tossed outside if safe to do so – it will produce smoke for a long time.)
Determining moisture content of chemically treated biomass
Overview of determining moisture content of treated material: Although the oven-drying
method is generally considered the standard to which other methods should be compared –
none of oven-drying
225
methods of any kind (including Method A – Oven-Drying Primary” as detailed in ASTM D4442-07, Method
B – Oven-Drying Secondary” as also detailed in
ASTM D4442-07, or the practice of moisture content
determination using a microwave oven, as detailed
in ASTM E1358-97) are appropriate for use with any
material that may have been chemically treated or
impregnated. Any kind of an oven-drying procedure
(conventional or microwave) may produce incorrect
results in estimation of moisture content (beyond
an acceptable margin of error) due to the potential
concomitant removal of the treatment carrier (and/
or chemical itself) along with the moisture, resulting
in an overestimation of moisture. More importantly
such a practice should be considered inherently
dangerous due to increased potential for increased
safety risks related to fire or explosion, and for health
226
risks related to the potential for respiratory and other related exposure to chemicals in the sample
being handled and volatilized in the drying process. DO NOT USE AN OVEN-DRYING METHOD OF
ANY KIND TO DETERMINE MOISTURE CONTENT OF CHEMICALLY TREATED OR IMPREGNATED
MATERIAL. Combustion of chemically treated materials can have special prob- lems or concerns,
such as those related to stack emis- sions and ash disposal, and should not be undertaken without
appropriate planning. Consideration regard- ing the moisture content determination of chemically
treated biomass is just one aspect of a large potential problem that needs to be carefully considered
before opportunities to use treated biomass can be
exploited.
Procedures for determining moisture content of treated material: The Distillation method (“this is
Method C - Distillation (secondary) method —as de- tailed in ASTM D4442-07) is the appropriate
method of determining the moisture content of chemically treated or impregnated material. This
procedure re- quires special laboratory equipment and some basic level of knowledge and expertise
related to chemistry lab practices. The detailed discussion of this method
is beyond the scope of this paper.
Determining moisture content using an electric moisture meter
Overview of determining moisture content using
an electric moisture meter: Electric moisture meters
may be used in determining the moisture content of
woody biomass in certain circumstances, but such
use is inappropriate in other circumstances. Electric
moisture meters are reasonably priced, portable,
quick and easy to use, and already have widespread
use in the forest industry and the building trades.
Most people are more familiar with hand-held versions of these meters, but there are also stationary
versions of these meters that can monitor material
on a conveyor (and are often used to monitor veneer
or lumber in manufacturing). Almost all of the handheld electric moisture meters readily available are conductance type meters which are able to
operate using the relationship between moisture content and direct current conductance where
direct cur- rent conductance increases with moisture content. (These are also sometimes called
“resistance type” meters – resistance being the reciprocal of conductance.) There are also other types of moisture meters that use the relationship between moisture
content and the dielectric loss factor of the wood (sometimes called the “power-loss type”) or
which use the rela- tionship between moisture content and the dielectric constant of the
(sometimes called the “capacitance type”). The publication “Electric Moisture Meters
for Wood” (USDA - Forest Service Forest Products Laboratory General Technical Report FPL-GTR-6)
by William James provides excellent information on the performance and limitations of these
devices. The key element of concern for use of electric moisture meters with woody biomass is
related to the mois- ture content of the piece being tested needing to
be within the moisture content range at which the device may be reasonably expected to give a
reason- ably accurate reading.
Procedures for determining moisture content using an electric moisture meter: Since
227
manufacturers of stationary meters would establish the appropriate procedures and parameters
for use of their equip- ment, this discussion is more specific to hand-held devices. Hand-held pin
type moisture meters are useful for determining moisture content of some forms of woody
biomass, such as edgings, slabs,
scrap lumber and similar materials within appropriate
moisture contents, and specialized hand-held meters are also made for sampling fine woody biomass
(such as sawdust) also within appropriate moisture
content ranges. Moisture meters are generally suited
to giving quantitative measures of moisture content
between about 7% and 30% MC on the ovendry basis
(or about 6% to about 23% on the green basis). Most
pin type meters readily available in the U.S. market
indicate moisture content on the ovendry basis, but it
is important to verify the basis (i.e. ovendry or green)
on which the device you use is indicating moisture
content. For higher moistures (i.e. anything above
228
about 30% MC on the ovendry basis) a conductance type device may be expected to provide
a qualita- tive indication of high moisture but the quantitative reading indicated cannot
usually be trusted – what this means is, just because the meter might indicate
40% or 50% or 60% MC, doesn’t really mean anything except that the piece is significantly
above 30% MC. It must be understood that just because a meter gives an indication above
30% MC on the ovendry basis does not mean the meter is accurate at that reading (assume it is not). In a similar way, do not expect explicit accuracy for readings below
about 6% or 7% MC on the ovendry basis.
Temperature, moisture distribution and species affect the accuracy of readings for the meters,
along with other factors. Temperature correction is actually a function of both moisture
content and temperature, so a supplier provided correction table is preferred, but as a rule of
thumb, you can correct the reading by subtracting 1 % MC for every 20°F above the calibration temperature and adding 1 % MC for every 20°F below the calibration temperature for (the
most com- mon) conductance type meters. Some meters have correction buttons for use of
the meter with
different species, while others may have
correction tables (corrections are usually less than 2%
for U.S. species). Uneven moisture distributions can
also give readings that will deviate from a true average (usually overestimating by reading along the lines
of higher moisture).
For determining moisture content of some types of solid woody biomass (such as partially
dried slabs, edgings, etc.) the common, inexpensive hand-held pin-type electric
(conductance) moisture meters are
useful tools that should be on hand. Also, some of the newer meters that sample sawdust and
other small particle residues are worth consideration of having on hand for anyone who
purchases fine woody biomass residues that are below fiber saturation point of
about 30% MC on the ovendry basis. These devices for particle materials generally work by a
conduc- tance measurement of a small sample of sawdust or other fine material that has
been compressed to a constant pressure of about 0.2 MPa. In using a pin type meter, it is
desirable to have the pins oriented along the grain versus across the grain as a general
practice (and this is more important as moisture con- tents increase towards the higher end of
the working range – where failure to do this can result in lower than actual readings).
Chemical treatments and glues can lead to inaccurate readings (usually higher than actual).
Using a pin type meter, the pins should be inserted in the piece to a depth of about one fifth
to one fourth of the thickness of the piece of wood be- ing measured, and where there is
significant variabili- ty expected in the piece (e.g. due to rapid drying from the ends) it would
be advisable for multiple reading
to be made on the piece being sampled.
Determining moisture content using specialized devices
Overview of determining moisture content using specialized devices: Commercially
produced bench- top devices are made for the express purpose of moisture measurement of
wood or woody biomass. Usually these devices require a small sample that is tested in a
process by the machine with the moisture content directly indicated. Different types of these
devices have existed for a long time, and it is safe to assume that new products will continue
229
to be devel- oped. These are generally well suited to purposes where very small samples are
acceptable and the results are required fairly quickly, and where running one sample at a
time is practical. Many people like these devices and are satisfied with the price paid,
the results obtained, and the volume of material they can handle – while other people prefer
the more conventional tools and practices. These specialized devices are something that for
some people may be worth examining – where that is the case it would probably be prudent
to carefully examine what is available on the market, and if possible to try to talk to people
who use the equipment and to understand how they use the equipment in terms of type of
materials tested and number of samples tested
in a day.
230
Sampling practices suitable for use with woody biomass of various types
Overview of sampling practices for moisture con- tent determination of woody biomass: The
sampling practices and the sample selection processes to be used to determine the moisture
contents of woody biomass of various types, being delivered by various suppliers, from various
locations, at different times of the years is something which deserves considerable thought and
planning, with regard to how the sam- ples will be collected, labeled, stored and processed, and
also what should be the required frequency of sampling. In doing this, the practical aspects of sampling that must be considered would include safety considerations, the form of the material as
received,
if the material will be immediately staged for use as received, or stored for drying (such as being
held for drying in roundwood form prior to use), the volume of material coming from various
suppliers, the vari- ability regarding moisture content for the material being received from the
various suppliers, and the physical constraints and the costs of testing samples need to be
considered at a minimum.
First and foremost – it must be remembered that consideration of human safety is the most
important consideration in developing sampling and testing practices. No woody biomass sample is
worth anyone risking significant injury or death in sample collection or processing. Each circumstance is somewhat different, so each place of work must be
carefully evaluated with an eye toward safety in developing sampling and testing practices.
Particular concern should be given to developing practices that elimi- nate or at least greatly
minimize the possibilities of serious injury or death, such as anyone being crushed or struck or by
machine or material movement, and the risk of falling off of loads or piles. In the testing
of material, particular concern should be given to proper venting of volatiles released from samples
in drying ovens, prohibition of oven-drying test method of treated and/or contaminated materials
and an eye towards fire safety.
With regard to the frequency of sampling from vari- ous suppliers, consideration must be given to
the costs associated with sampling and testing overall, the variability expected in the moisture
content of
material being received from various suppliers (at any particular point in time and over time), and
physical constraints associated with sampling collection and processing, as well as having an eye
towards overall costs and efficiency in the overall sampling process.
Sampling practices for woody biomass in particle form – for oven-drying testing: In sampling
most woody biomass in particle form (such as chips and sawdust); a sample volume that is
roughly twice the desired average weight at endpoint is generally ap- propriate. For example,
assuming a dry sample size of approximately 100 grams is desired for oven testing; an appropriate green sample of about 200 grams (slightly less than half a pound) would be
desirable in sampling high-moisture residues such as most woods residues. If material being tested
is known to be at significantly lower moisture content, then a roughly equivalent volume of sample
of similar type of par- ticle material (having proportionately lower weight) would be appropriate for
drier material. In practice
it will quickly be recognized that samples should be large enough relative to the need for
appropriate levels of precision in consideration of the equipment being used, however, overly large
samples quickly take up the limited capacity of drying ovens. In a
practical sense, the system for testing woody biomass in particle form needs to be considered on a
holistic basis wherein the capacity of drying ovens available is sufficient to reasonably accommodate
the material to be tested in a given time period, considering both the space required for the pans
and the overall volume of material to be tested (and associated volume of water needing to be
231
removed).
A sample selected to be tested in oven drying can be an individual sample selected specifically for
that pur- pose, or can be obtained as a reduction from a gross sample (i.e. a sample from a gross
sample) with that gross sample being simply a larger sample that is systematically collected over
time. In terms of
232
example, the sample to be tested may be a sample selected to represent the moisture
content of a truckload of material from a supplier who occasion- ally delivers a truckload of
biomass – or in contrast, for a major supplier, it may be desirable to collect a gross sample,
wherein a sample from each truckload of material
delivered by that supplier from a particular job site may be collected and aggregated
together in an airtight container as a gross sample, with the sample (or multiple samples)
that is to be tested then being taken from the gross sample, and representing multiple
truckloads for that job that are represented in the gross sample. Generally, the size of a
gross sample should be fairly large, such as at least 10 kilograms (about 22 pounds) in green
weight, and
the removal or selection of the sample to be tested from the gross sample needs to follow an
appropri- ate procedure (as detailed in ASTM E 871 – 82). The selection of the sample from
the gross sample is most easily done by use of a riffle (such as a coal riffle) that progressively
divides the gross sample into parts,
from which one part is retained for further division, and that division continues until an
appropriate size sample for testing remains. In terms of example, if a gross sample of about
10 kilograms in weight is pro- gressively divided into halves, with one half retained for
division and the other half discarded (e.g. with the first division by half of the 10 kilos of the
gross sample, about 5 will remain; with the 5 kilos divided in half, about 2.5 kilos will
remain, etc.), in about six divisions by half, you will end up with a sample of about 200
grams.
In a practical application, where the woody biomass
material being tested is in the form of some types
of forest residues that has been run through a tub
grinder, there will likely be considerable variability in
the size of the material delivered. In proper sampling
this larger material will represent itself in the gross
sample (note: you should not arbitrarily reject larger
material from the sample or selectively chose material of a size desired). Where this is the case that you
have larger material in the sample than the size of
material that is desired for testing, from a practical standpoint it may be desirable (if not
neces- sary) to accomplish some gross reduction in the size of material in the sample (such as
running it through a hammermill) at least prior to oven testing and it may be necessary to
perform a reduction on the
entire gross sample itself, or at some point fairly early in the division process if very large
pieces of material could represent a problem in sample division. Very large pieces of material
in the sample may not easily be accommodated in the drying pans and if they do,
it is possible they may delay the sample reaching end- point as they would not lose moisture
as easily
as smaller particles having greater surface area rela- tive to their mass. If a microwave oven is
being used in the testing, the particle size in the sample being tested would obviously
become even more impor- tant, due to the differences in rate of drying and the smaller
sample size, consequently it may be desirable to generally reduce microwave samples to a
smaller size particle than typical for testing in a conventional oven.
As indicated prior, the material being collected for the gross sample needs to be held in an
airtight container until the sample for testing is to be drawn from the gross sample. That
sample for testing, and any individual samples selected from it for testing also need to be
233
held in an airtight container of some type until their initial weighing in the testing process to
determine green weight of the sample. If this is not done, the sample to be tested may be
expected to lose moisture to the atmosphere, and this loss of
moisture in the sample will result in the calculation of a moisture content that is lower than
would accu- rately represent the load or loads being represented by that sample. (Or the
reverse could occur if very dry material was being received and tested, but this is un- likely.) In
a practical sense it will quickly be recognized that containers for the collection and storage of
gross samples that could easily weigh more than 25 pounds could be any of a number of
durable, larger airtight storage containers readily available from a variety of sources. For
holding an individual sample for testing until it is ready to begin to be processed, both larger
“zip-loc” type food storage bags and reusable small, durable air-tight containers work well.
12
234
The physical collection of woody biomass samples should be done by a regular process – which as
noted prior – gives key concern to safety. The sample may
be physically taken by hand or by some collection device (such as a small container on a pole), and
the sample for a load may be taken from one or more parts of the load (depending on what may
be practi- cal or physically possible). Reasonable consideration should be given to not sampling
primarily or solely from what would clearly be atypical for the load
as a whole. For example, if biomass is transported in a truck with a rear screen on a rainy day or
dur- ing a late or early snowfall, a very small layer of the load against that screen could pick up
considerable moisture in the haul – and in a similar vein, a small portion of the load exposed by
such a screen to hot, dry air could be expected to lose moisture in a long haul. In either case,
although these extremes would indeed represent a very small part of the load, the extremes
would not represent a reasonable average
for the load from which the material was taken, if the extreme area of unusually higher or lower
moisture was all that was selected from as a sample for the load. Where possible, sampling
somewhere near the middle of the load as a regular practice should rea- sonably be expected to
work best over time and to be most fair to both buyer and seller.
Sampling practices for woody biomass in solid
form – oven-drying testing: The sampling of woody
biomass in larger solid form – such as from cull logs
– presents some special problems. Where the form
of the biomass as received has each component
element that is huge relative to the desired size of a
sample for testing in oven-drying, so clearly it is not
possible to simply take samples by hand from the material received. To accomplish appropriate sampling
of such material in the woods can be a relatively easy
but time consuming process, wherein from a selected
representative sample tree at the time of harvest,
thin disks of uniform thickness (e.g. about one inch
in thickness) may be cut from the stem as each bolt
or log is bucked from the tree, such that the disks
considered in total would provide a sample giving a
weighted average for the stem as a whole, and the
sample could be tested in its entirety (or each disk could be reduced by hand with a proportional
pie-cut fraction retained, such as retaining a disk equal to a pie cut from outer surface to center, of
equal propor- tion, such as a half, or a quarter, and that sample could be tested in its entirety), or
the sample of disks could become a gross sample that could be reduced
in a hammermill and then reduced in a riffle to provide a smaller sample for testing.
However, in normal circumstances where such cull logs are received on a truck with no real
opportunity to sample at the point of harvest, the possibility of maintaining the integrity of sample
trees is lost. Disk collection from a sample of logs could still be an acceptable mechanism for
collection of a gross sam- ple; however, there is a problem with cutting disks from woody biomass
logs or boltwood as received for moisture content sampling. Once cut into logs or bolts, the logs
will rapidly begin to dry longitudinally (from the ends), such that the wood at the ends would
typically be at a lower moisture content than
would be typical or average for the log. Cutting a disk
from near the middle of the log would be expected
to be a much better representation of the average
235
moisture content for the log – and this would be a
good testing practice if it is practical – but in many
cases this will not be practical. Increasingly some
purchasers of woody biomass in roundwood form are
purchasing the material and holding it for seasoning
for a significant time (in many cases from six months
to a year) in an effort to reduce moisture content of
the material. In this circumstance in particular, and in
other circumstances as well, bucking bolts or logs to
retrieve sample disks for moisture measurement is
not a practical alternative due to problems it will create further handling and storage of the logs.
Sampling from near the (longitudinal) center of logs or bolts using an increment borer is a practical
alter- native to the cutting of sample disks. The appropriate procedure for such sampling on a log
would be to place the borer perpendicular to an imaginary plane on the tangential face of the log
and bore to the center of the log (i.e. to the pith). The problem in
such a sampling procedure is that the small cylinder
236
of wood removed is of equal diameter throughout (i.e. from the bark surface to the pith),
and the sam- pling as such would tend to greatly over-sample the center half of the log
(nearer the pith) and to under- sample the outer area of the log, relative to the proportional volumes of these areas. Given the expecta- tion of typical differences in the
moisture content of heartwood versus sapwood, and also a significant understatement of
the bark fraction in sampling,
this creates some significant problems. A very simple solution to this is that in addition to
taking the initial sample bore from bark surface to the pith (half the diameter or the radius)
on a given log, two additional sample cores are then taken in the same approximate location
and in the same way, except in taking those two additional cores, they are taken to a depth of
only one half of the depth of the initial sample. This would entail taking a total of three cores
in total from one general location (near the longitudinal center)
on a given log being tested – the first being one sample core all the way from the bark
surface to the pith (half the diameter) and two additional cores in the same general location
but only going to half the depth of the original (i.e. to only one-fourth of the diameter or half
the radius). This is a slight additional effort but represents a much better overall sample
because it makes an adjustment to better propor- tionately sample the log’s volume in inner
and outer fractions.
For an understanding of why this differential sam- pling is important, consider a circle of
any diameter representing the cross-section of a log. Two paral- lel lines placed close
together extending from the center of the circle to the perimeter could be used to
represent a sample of the circle removed by an
increment core. This type of sampling would equally represent the portions of the circle
represented in the area contained in the inner half of the radius and the outer half of the
radius, however, the actual area represented with the inner “half” of the circle in the
form of a smaller circle with the same center and half the original radius would only represent
about one- third of the volume contained in the outer “half” of the circle (which is
represented as a ring around the half-diameter circle). This would mean that about one fourth
of the total area would be represented in the smaller (half-full diameter) inner circle, while
about three fourths of the total area would be represented in the outside ring around that
small circle, where
the thickness of the ring is equal to half the radius of the larger circle and equal to the radius
of the smaller circle. Essentially in using the increment core in the first extraction to the pith
sample, half of the core will come from the inner circle and half from the outer ring – the two
additional half-depth (or half full diameter) cores adjust the total sample to be representative of representing approximately three fourths of the total cores being taken from the
outer “half” (outer ring) and one fourth from the inner “half” (half full diameter circle). The
three cores are combined
to form a sample for that log. In sampling a load, the three core sampling procedure may be
applied to sampling multiple logs (taking three cores from each), with the sampling process
mixing species and sizes as appropriate. All cores can then be combined to rep- resent a
sample for testing representing an individual load or used in developing a form of a “gross
sample” of cores across a number of loads that may be used
to collect a volume of material suitable to represent a lab sample (that could be tested in
total without divi- sion by a riffle or other means).
The sampling of woody biomass in the form of asym- metrical high-moisture residual material
(such as un- seasoned slab wood or edgings obtained from small mills) presents some
difficulties as compared to the testing of logs, as the three core procedure described for logs
237
is not suited to this material being tested.
This is because of the cross-section of these materi- als is not circular, rather it represent a
fraction of a circle or an irregular shape. The problem is further exacerbated where the
material may still be at quite a high moisture overall, but having a much greater surface area
than is typical for logs, and some or all pieces of material may have had some seasoning
processes begun (with associated loss of moisture)
in short term storage and hauling. In sampling such materials, the use of an increment borer
is still likely
to be one of the best practical options, but the person
238
taking the samples needs to be cognizant of the fact there is likely to be considerable variation in
moisture content, that could be directly related to size (i.e. material with greater thickness in crosssection might be expected to have higher moisture content ) , and also that there is likely to be a
significant moisture profile in many pieces where the moisture content of the core may be expected
to be significantly greater than the outer perimeter. Keeping these factors in mind can help
underscore the need for selecting samples from a representative mix of materials in the load having
different thicknesses and cross section. Also where these pieces would typically be fairly thin
(compared to cull logs), sampling completely through the thickness of material may be a practical
way of capturing a representative sample from pieces with a significant moisture profile.
Sampling practices for well-seasoned or dry woody biomass in solid form: In circumstances where
woody biomass in solid form is delivered in a well-seasoned or dry condition, this permits the use of
a simple
hand-held pin-type electric (conductance) moisture meters to collect moisture measurements. This
would be a realistic possibility where all (or virtually all)
of the load could be expected to be at an average moisture content that is low enough to permit
testing with an electric moisture meter. This is a reasonable and practical alternative where the
moisture content of the material being received does not exceed about
23% MC on the Green basis (or about 30% MC on the OD basis). Such very low average moisture
contents should almost never be expected for woody biomass in roundwood form, but can be quite
common for woody biomass in the form of well-seasoned slabs and edgings from smaller sawmills
(that could typi- cally be at moisture contents close to the upper limit) and also in the form of dry
solid wood residuals from secondary manufacturers that could be at quite low moisture contents
(even possibly near the lower limit for accurate readings using such equipment). Where
it is possible to use such a hand-held moisture meter for sampling an incoming load of material, it
is a very quick and easy process to sample a number of pieces to estimate an average moisture
content for the load, sampling near the longitudinal center of the longer pieces, as with other
processes, to limit the effect of excessive moisture loss from the ends. In the case of well-seasoned
slabs at such low moisture contents, in many cases bark will have sloughed off or will be sloughing
off, but where firmly fixed, both wood and bark should be sampled.
In sampling materials such as seasoned slabs and edgings that are likely at the upper end of
moisture contents suitable for this process (e.g. well-seasoned slabs) if in about twenty to twenty
five readings taken from different pieces yield no moisture readings
so high that there is reason to mistrust any of the readings as being more likely reflective of a
qualita- tive versus a quantitative nature, then an average
of the readings may be used to represent an aver- age for the load. If one or two of the readings
taken indicate moistures somewhat above 23% MC on the Green basis (or about 30% MC on the OD
basis), then additional readings should be taken (on additional pieces) to attempt to confirm that
there is not too large a number higher-moisture pieces such that
the use of a moisture meter for sampling may be inappropriate. As long as no more than 5 or 10%
of pieces sampled reflect moisture contents above 23% MC on the Green basis, the average of all
displayed moisture content readings should represent a suit- able representative average for the
load, however,
if a significantly large number of pieces sampled are at a moisture where the reading is more
qualitative versus quantitative, the average of the meter read- ings cannot be trusted to provide
something that can confidently be projected as a true average for
the load and testing better suited to higher moisture material (such as the oven-drying method)
should be employed. In rare circumstances (usually in the win- ter) dry solid wood residuals
received from secondary manufacturers could be at very low moisture con- tents such that for some
239
pieces the readings reflect
a moisture content of something less than 6% which is at the lower limit for accuracy in using a
hand-held pin-type electric (conductance) moisture meters. Where that is the case, there is no
particular problem in simply averaging the readings taken as the possible
240
error introduced by inclusion of a few such readings
is minimal where the range of difference between
the true moisture content and the indicated moisture
content on the meter is so small.
Sampling practices for well-seasoned or dry woody biomass in particle form: In circumstances
where woody biomass in solid form is delivered in a dry con- dition in particle form (such as sawdust
or other fine particles), that permits use of an inexpensive hand- held meter that can sample sawdust
and other small particle residues this is likely to be the tool of choice for quickly sampling the
occasional truckload of such material. Where larger suppliers might routinely ship truckloads of such
material, it will probably be the case that the moisture contents of the material as received will be
quite uniform, and the hand-held meter is simply used to confirm that knowledge. One or two
samples of material per truckload delivered would be an appropriate sample in most cases. Any
reading that indicates a moisture content that is above, at (or even very close to) the upper limit of
the devices capability should be an indication that testing better suited to higher moisture material
(such as the oven-drying method) should be used for the material.
Moisture content of wood in equilibrium with stated
temperature and relative humidity (on the
OVENDRY basis)
Moisture content (%) on the OVENDRY basis at various relative
Temperature
humidity values
°C
°F
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
55%
60%
-1.1
40
10
15.6
21.1
26.7
32.2
37.8
43.3
48.9
54.4
60
65.6
71.1
76.7
82.2
87.8
93.3
98.9
104.4
110
115.6
121.1
126.7
132.2
30
1.4
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
1.4
2.6
1.4
1.3
1.3
1.3
1.2
1.2
1.1
1.1
1
0.9
0.9
0.8
0.7
0.7
0.6
0.5
0.5
0.4
0.3
0.3
0.2
0.2
0.1
2.6
3.7
2.6
2.5
2.5
2.4
2.3
2.3
2.2
2.1
2
1.9
1.8
1.6
1.5
1.4
1.3
1.1
1
0.9
0.8
0.6
0.4
0.3
0.1
3.7
4.6
3.6
3.6
3.5
3.5
3.4
3.3
3.2
3
2.9
2.8
2.6
2.4
2.3
2.1
1.9
1.7
1.6
1.4
1.2
0.9
0.7
0.5
0.2
4.6
5.5
4.6
4.6
4.5
4.4
4.3
4.2
4
3.9
3.7
3.6
3.4
3.2
3
2.8
2.6
2.4
2.1
1.9
1.6
1.3
1
0.7
0.3
5.5
6.3
5.5
5.4
5.4
5.3
5.1
5
4.9
4.7
4.5
4.3
4.1
3.9
3.7
3.5
3.2
3
2.7
2.4
2.1
1.7
1.3
0.9
0.4
6.3
7.1
6.3
6.2
6.2
6.1
5.9
5.8
5.6
5.4
5.2
5
4.8
4.6
4.3
4.1
3.8
3.5
3.2
2.9
2.6
2.1
1.7
1.1
0.4
7.1
7.9
7.1
7
6.9
6.8
6.7
6.5
6.3
6.1
5.9
5.7
5.5
5.2
4.9
4.7
4.4
4.1
3.8
3.4
3.1
2.6
2.1
1.4
7.9
8.7
7.9
7.8
7.7
7.6
7.4
7.2
7
6.8
6.6
6.3
6.1
5.8
5.6
5.3
5
4.6
4.3
3.9
3.6
3.1
2.5
8.7
9.5
8.7
8.6
8.5
8.3
8.1
7.9
7.7
7.5
7.2
7
6.7
6.4
6.2
5.9
5.5
5.2
4.9
4.5
4.2
3.5
2.9
9.5
10.4
9.5
9.4
9.2
9.1
8.9
8.7
8.4
8.2
7.9
7.7
7.4
7.1
6.8
6.5
6.1
5.8
5.4
5
4.7
4.1
10.4
11.3
10.3
10.2
10.1
9.9
9.7
9.5
9.2
8.9
8.7
8.4
8.1
7.8
7.4
7.1
6.8
6.4
6
5.6
5.3
4.6
11.3
12.3
11.2
11.1
11
10.8
10.5
10.3
10
9.7
9.4
9.1
8.8
8.5
8.2
7.8
7.5
7.1
6.7
6.3
6
241
from table 3-4 of the USDA Wood Handbook - reprinted with permission
METHODS FOR ESTIMATING BIOMASS DENSITY FROM EXISTING DATA
3.1 APPROACH 1: BIOMASS DENSITY BASED ON EXISTING VOLUME DATA
3.2 APPROACH 2: BIOMASS DENSITY BASED ON STAND TABLES
3.3 BIOMASS ESTIMATES OF INDIVIDUAL
3.4 BIOMASS ESTIMATES FOR PLANTATIONS
3.5 BIOMASS OF OTHER FOREST COMPONENTS
This primer discusses two approaches for estimating the biomass density of woody
formations based on existing forest inventory data. The first approach is based on the use of
existing measured volume estimates (VOB per ha) converted to biomass density (t/ha) using
a variety of "tools" (Brown et al. 1989, Brown and Iverson 1992, Brown and Lugo 1992,
Gillespie et al. 1992). The second approach directly estimates biomass density using biomass
regression equations. These regression equations are mathematical functions that relate ovendry biomass per tree as a function of a single or a combination of tree dimensions. They are
applied to stand tables or measurements of individual trees in stands or in lines (e.g.,
windbreaks, live fence posts, home gardens). The advantage of this second method is that it
produces biomass estimates without having to make volume estimates, followed by
application of expansion factors to account for non-inventoried tree components. The
disadvantage is that a smaller number of inventories report stand tables to small diameter
classes for all species. Thus, not all countries in the tropics are covered by these estimates. To
use either of these methods, the inventory must include all tree species. There is no way
to extrapolate from inventories that do not measure all species.
Use of forest inventory data overcomes many of the problems present in ecological studies.
Data from forest inventories are generally more abundant and are collected from large sample
areas (subnational to national level) using a planned sampling method designed to represent
the population of interest. However, inventories are not without their problems. Typical
problems include:
 Inventories tend to be conducted in forests that are viewed as having commercial value, i.e., closed
forests, with little regard to the open, drier forests or woodlands upon which so many people
depend for non-industrial timber.
 The minimum diameter of trees included in inventories is often greater than 10 cm and
sometimes as large as 50 cm; this excludes smaller trees which can account for more than
30% of the biomass.
 The maximum diameter class in stand tables is generally open-ended with trees greater than
80 cm in diameter often lumped into one class. The actual diameter distribution of these large
trees significantly affects aboveground biomass density.
 Not all tree species are included, only those perceived to have commercial value at the time
of the inventory.
242
 Inventory reports often leave out critical data, and in most cases, field measurements are not
archived and are therefore lost.
 The definition of inventoried volume is not always consistent.
 Very little descriptive information is given about the actual condition of the forests, they are
often described as primary, but diameter distributions and volumes suggest otherwise (e.g.,
Brown et al. 1991, 1994).
 Many of the inventories are old, 1970s or earlier, and the forests may have disappeared or
changed.
Despite the above problems, many inventories are very useful for estimating biomass density
of forests. In the next two sections, details of the methods for using existing forest inventory
data for biomass density estimation are presented.
3.1 APPROACH 1: BIOMASS DENSITY BASED ON EXISTING VOLUME DATA
3.1.1 GENERAL EQUATION
3.1.2 VOLUME-WEIGHTED AVERAGE WOOD DENSITY (WD)
3.1.3 BIOMASS EXPANSION FACTOR (BEF)
3.1.4 EXAMPLES OF CALCULATIONS OF BIOMASS DENSITY
3.1.5 ADJUSTMENTS TO APPROACH USING VOLUME EXPANSION FACTORS
(VEF)
3.1.6 USE OF INVENTORIES OF OPEN FORESTS AND WOODLANDS
The method presented here is based on existing volume per ha data and is best used for
secondary to mature closed forests only, growing in moist to dry climates. It should be used
for closed forest only because the original data base used for developing this approach was
based on closed forests. The primary data needed for this approach is VOB/ha, that is
inventoried volume over bark of free bole, i.e. from stump or buttress to crown point or first
main branch. Inventoried volume must include all trees, whether presently commercial or
not, with a minimum diameter of 10 cm at breast height or above buttress if this is higher. If
the minimum diameter is somewhat larger, the VOB/ha information can be used with some
adjustments as shown below. However, such adjustments to the primary data introduce larger
errors in the estimate.
3.1.1 GENERAL EQUATION
Biomass density can be calculated from VOB/ha by first estimating the biomass of the
inventoried volume and then "expanding" this value to take into account the biomass of the
other aboveground components as follows (Brown and Lugo 1992):
(Eq. 3.1.1)
243
Aboveground biomass density (t/ha) = VOB * WD * BEF
where:
WD = volume-weighted average wood density (1 of oven-dry biomass per m3 green volume)
BEF = biomass expansion factor (ratio of aboveground oven-dry biomass of trees to oven-dry
biomass of inventoried volume)
3.1.2 VOLUME-WEIGHTED AVERAGE WOOD DENSITY (WD)
Wood density here is defined as the oven-dry mass per unit of green volume (either tons/m3
or grams/cm3). Wood densities for trees of tropical American forests tend to be reported in
these units. In contrast, few data on wood density for trees in tropical Africa and Asia are
expressed in these units (Reyes et al. 1992). Rather, wood density is expressed in units of
mass of wood at 12% moisture content per unit of volume at 12% moisture content. A
regression equation was developed by Reyes et al. (1992) to convert wood density based on
12% moisture content to wood density based on oven-dry mass and green volume (Eq. 3.1.2).
(Eq. 3.1.2)
Y = 0.0134 + 0.800 X
(r2= 0.99; number of data points n = 379)
where:
Y = wood density based on oven-dry mass/green volume
X = wood density based on 12% moisture content
Ideally, a weighted average (based on dominance of each species as measured by volume)
wood density value is best used here, calculated as follows.
(Eq. 3.1.3)
WD = {(V1/Vt *WD1 + (V2/Vt) *WD2 +........... (Vn/Vt)* Wdn
where:
V1, V2,.... Vn = volume of species 1, 2,.. to the nth species
Vt = total volume WD1 WD2,..... Wdn = wood density of species 1, 2,...... to the nth species
However, sufficient wood density data of forest species to do such calculations are not
always available. In these situations it is best to estimate a weighted mean wood density
based on known species, using an arithmetic mean from the table below for unknown species.
Wood density data for 1180 tropical tree species are given in Appendix 1.
244
The arithmetic mean and most common wood density values (t/m3 or g/cm3) for tropical
tree species by region
Tropical region No. of species Mean Common range
Africa
282
0.58
0.50-0.79
America
470
0.60
0.50-0.69
Asia
428
0.57
0.40-0.69
(from Reyes et al. 1992)
3.1.3 BIOMASS EXPANSION FACTOR (BEF)
Broadleaf forests: Biomass expansion factor is defined as: the ratio of total aboveground
oven-dry biomass density of trees with a minimum dbh of 10 cm or more to the oven-dry
biomass density of the inventoried volume. Such ratios have been calculated from inventory
sources for many broadleaf forest types (young secondary to mature) growing in moist to
seasonally dry climates throughout the tropics. Sufficient data were included in these
inventory sources to independently calculate aboveground biomass density and biomass of
the inventoried volume (Brown et al. 1989). The reported inventoried volume in the studies
was based on the definition given above. Analysis of these data show that BEFs are
significantly related to the corresponding biomass of the inventoried volume according to the
following equations (Brown and Lugo 1992):
(Eq. 3.1.4)
BEF = Exp{3.213 - 0.506*Ln(BV)} for BV < 190 t/ha
1.74 for BV>=190t/ha
(sample size = 56, adjusted r2 = 0.76)
where:
BV = biomass of inventoried volume in t/ha, calculated as the product of VOB/ha (m3/ha)
and wood density (t/m3)
Conifer forests: No model for calculating biomass expansion factors for native conifer
forests is available at present because of the general lack of sufficient data for the type of
analysis performed for the broadleaf forests. However, one would expect that BEFs for
tropical pine forests would vary less than for broadleaf forests because of the generally
similar branching pattern exhibited by different species of pine trees. Biomass expansion
factors have been calculated based on a limited data base of 12 stands of Pinus oocarpa
growing in Guatemala (Peters 1977) and the methodology given in Brown et al. (1989). The
inventoried volume in this case was defined as volume over bark/ha from the stump to the tip
of the tree; i.e. main stem based on total height. Volumes of these stands ranged from 64 to
331 m3/ha. The BEFs based on biomass of the main stem ranged from 1.05 to 1.58, with a
mean of 1.3 (standard error of 0.06). No significant relationship between BEF and main stem
biomass was obtained. Until additional data become available, a BEF of 1.3 can be used, with
caution, for biomass estimation of pine forests.
245
3.1.4 EXAMPLES OF CALCULATIONS OF BIOMASS DENSITY
To demonstrate the application of this methodology, aboveground biomass density is
calculated for the following examples:
Example 1.
Broadleaf forest with a VOB = 300 m3/ha and weighted average wood density; WD = 0.65 t/m3
Step 1 Calculate biomass of VOB: = 300 m3/ha x 0.65 t/m3 = 194 t/ha
Step 2 Calculate the BEF (Eq. 3.1.4): BV > 190 t/ha, therefore BEF = 1.74
Step 3 Calculate aboveground biomass density (Eq. 3.1.1): = 1.74 x 300 x 0.65
= 338 t/ha
Example 2.
Broadleaf forest with a VOB = 150 m3/ha and weighted average wood density, WD = 0.55 t/m3
Step 1 Calculate biomass of VOB: = 150 m3/ha x 0.55 t/m3 = 82.5 t/ha
Step 2 Calculate the BEF (Eq. 3.1.4): BV < 190 t/ha, therefore BEF = 2.66
Step 3 Calculate aboveground biomass density (Eq. 3.1.1): = 2.66 x 150 x 0.55
= 220 t/ha
As can be seen from these two examples, although there is a two-fold difference in VOB/ha,
there is only a 1.5-fold difference in aboveground biomass density.
3.1.5 ADJUSTMENTS TO APPROACH USING VOLUME EXPANSION FACTORS (VEF)
Forest inventories often report volumes to different standards, e.g., to minimum diameters
greater than 10 cm. These inventories maybe the only ones available, and thus it is important
that a means to unify the volume data to some kind of standard be developed so that these
inventories can be used to estimate biomass density.
In an attempt to unify data on inventoried volume measured to a minimum diameter greater
than 10 cm, volume expansion factors (VEF) were developed (Brown 1990). After 10 cm, a
common minimum diameter for inventoried volumes ranges between 25-30 cm. Data from
inventories that reported volumes to minimum diameters in this range were combined into
one data set to obtain sufficient number of studies for analysis. The VEF is defined here as
the ratio of inventoried volume for all trees with a minimum diameter of 10 cm and above
(VOB10) to inventoried volume for all trees with a minimum diameter of 25-30 cm and above
(VOB30). The uncertainty in extrapolating inventoried volume based on a minimum diameter
of larger than 30 cm to inventoried volume to a minimum diameter of 10 cm is likely to be
246
large and is not suggested. Estimates of the VEFs were based on a few inventories from
tropical Asia and America which provided sufficient detail for this analysis (see Brown
1990). Volume expansion factors based on these inventories ranged from about 1.1 to 2.5,
and they were related to the VOB30 as follows:
(Eq. 3.1.5),
VEF = Exp{1.300 - 0.209*Ln(VOB30)} for VOB30 < 250 m3/ha = 1.13 for VOB30 > 250
m3/ha
(sample size = 66, adjusted r2 = 0.65)
To demonstrate the use of this correction factor to estimating biomass density, consider the
following example:
Broadleaf forest with a VOB30 = 100 m3/ha and weighted average wood density; WD = 0.60
t/m3
Step 1 Calculate the VEF from Eq. 3.1.5: = 1.40
Step 2 Calculate VOB10: = 100 m3/ha x 1.40 = 140 m3/ha
Step 3 Calculate biomass of VOB10: = 140 m3/ha x 0.60 t/m3 = 84 t/ha
Step 4 Calculate the BEF from Eq. 3.1.4: BV < 190 t/ha, therefore BEF = 2.64
Step 5 Calculate aboveground biomass density (Eq. 3.1.1): = 2.64 x 140 x 0.60
= 222 t/ha
3.1.6 USE OF INVENTORIES OF OPEN FORESTS AND WOODLANDS
No general approach for estimating aboveground biomass density of open forests and
woodlands based on inventoried volume has been developed because of the general lack of
suitable data. The method described above for closed forests is not generally applicable
because trees have different branching patterns (often multi-stemmed) and inventoried
volume of open forests and woodlands is usually measured to different standards than for
closed forests. For example, inventories done in open forests and woodlands generally report
inventoried volume per ha to minimum diameters less than 10 cm, and also often include
branch volume. Earlier work suggested that total aboveground biomass density of open
forests could be up to three times the inventoried volume (Brown and Lugo 1984), however
further field testing would be needed to confirm this. It is recommended that the approach
described in section 3.2 (next) for estimating aboveground biomass density be used for open
forests and woodlands.
3.2 APPROACH 2: BIOMASS DENSITY BASED ON STAND TABLES
247
3.2.1 BIOMASS REGRESSION EQUATIONS
3.2.3 PROBLEMS WITH REGRESSION APPROACH
Another estimate of biomass density is derived from the application of biomass regression
equations to stand tables. The method basically involves estimating the biomass per average
tree of each diameter (diameter at breast height, dbh) class of the stand table, multiplying by
the number of trees in the class, and summing across all classes. A key issue is the choice of
the average diameter to represent the dbh class. For small dbh classes (10 cm or less), the
mid-point of the class has been used (e.g., Brown et al. 1989). The quadratic-mean-diameter
of a dbh class would be a better choice, particularly for wider diameter classes. If basal area
for each dbh class is known, the quadratic-mean-diameter (QSD) of trees in the class, or the
dbh of a tree of average basal area in the class, should be used instead. To calculate the QSD,
first divide the basal area of the diameter class by the number of trees in the class to find the
basal area of the average tree. Then the dbh = 2 x {square root (basal area/3.142)}. For
example, the dbh of a tree of basal area of 707 cm2 = 2 x {square root (707/3.142)} = 30 cm.
3.2.1 BIOMASS REGRESSION EQUATIONS
The biomass regression equations for broadleaf forests were developed from a data base that
includes trees of many species harvested from forests from all three tropical regions (a total
of 371 trees with a dbh ranging from 5 to 148 cm from ten different sources; see Appendix 2;
equation 3.2.2 in the table below was developed by Martinez-Yrizar et al. (1992)). The
biomass regression equations can provide estimates of biomass per tree. The data base was
stratified into three main climatic zones, regardless of species: dry or where rainfall is
considerably less than potential evapotranspiration (e.g. <1500 mm rain/year and a dry season
of several months), moist or where rainfall approximately balances potential
evapotranspiration (e.g. 1500-4000 mm rain/year and a short dry season to no dry season),
and wet or where rainfall is in excess of potential evapotranspiration (e.g. >4000 mm
rain/year and no dry season). These rainfall regimes are just guides, and generally apply to
lowland conditions only. As elevation increases, as in mountainous areas, temperature
decreases as does potential evapotranspiration and the climate zone becomes wetter at a given
rainfall. For instance, an annual rainfall of 1200 mm in the lowlands would be the dry zone,
but at about 2500 m it would be the wet zone. Therefore, judgement should be used in
selecting the appropriate equation.
Figure 1 - Relationship between oven-dry biomass of tropical trees and dbh for (a) biomass
regression equations by all climatic zones and trees with dbh between 5 to 40 cm, and (b)
equations for moist and wet zones for trees in the full range of dbh. The equations are given
in Section 3.2.1.
(a) All zones
248
(b) Moist and wet zones
Biomass regression equations for estimating biomass of tropical trees. Y= biomass per
tree in kg, D = dbh in cm, and BA = basal area in cm2
Equation
Climatic
Equation
Range in
Number of Adjusted
249
Number
3.2.1
zone
DRY a
3.2.2
3.2.3
MOIST b
3.2.4
3.2.5
WET c
Y = exp{1.996+2.32*ln(D)}
Y =10^{-0.535+log10
(BA)}
Y = 42.6912.800(D)+1.242(D2)
Y = exp{2.134+2.530*ln(D)}
Y = 21.2976.953(D)+0.740(D2)
dbh (cm)
5-40
trees
28
r2
0.89
3-30
191
0.94
5-148
170
0,84
0.97
4-112
169
0.92
None of the regression equations should be used for estimating the biomass of trees whose
diameter greatly exceeds the range of the original data.
a
Eq. 3.2.1 revised from Brown et al. (1989) for dry forest in India, and Eq. 3.2.2 from
Martinez-Yrizar et al. 1992 for dry forest in Mexico (original equation based on BA). For dry
zones with rainfall less than 900 mm/year use equation 3.2.2 and for dry zones with rainfall >
900 mm/year use equation 3.2.1. "exp" means "e to the power of".
b
Both equations are based on the same data base; A. J. R. Gillespie, pers. comm. based on a
revision of equation in Brown et al. (1989).
c
From Brown and Iverson (1992)
Analysis of the data bases implied that the trees within the dry and wet zones could be
grouped together within a zone (Brown et al. 1989). Within the moist zone, the analysis
indicated that different data bases were not statistically homogeneous and theoretically could
not be grouped. For practical purposes, however, the moist zone was considered to be the
population of interest and the different data bases were considered to be subsamples from this
population. Thus a combined regression for the pooled data sets was developed (Brown et al.
1989).
Biomass regression equations for several species of pines combined into one data base was
also developed. A simple method for estimating the biomass of palms was also developed
(Frangi and Lugo 1985).
Broadleaf forests: Details of the: (1) evaluation of several linear, nonlinear, and transformed
nonlinear regression equations, (2) the testing of the behavior of the equations, and (3)
selection of the final equations are given in Brown et al. (1989). A listing of the original data
are given in Appendix 2.
The behaviour of all these regression equations as a function of dbh is illustrated in Figure 1.
Application of all five regression equations for smaller diameter classes shows that for a
given dbh biomass is highest for trees in the moist zone (Fig. 1a; Eq. 3.2.3 and 3.2.4),
followed by trees in the wet zone (Eq. 3.2.5), and trees in the dry zone (Eq. 3.2.1 and 3.2.2).
250
The regression equation for dry zone trees given by Eq. 3.2.1 gives higher biomass per tree
for a given diameter than the regression developed for the Mexican dry zone (Eq. 3.2.2; see
Fig. la). As tree diameters increase, the difference becomes larger so that by diameter 40 cm
(the upper limit for the data bases) the biomass per tree based on Eq. 3.2.1 is about 1.7 times
higher than that based on Eq. 3.2.2. The main reason for this trend is that the trees used for
developing Eq. 3.2.1 grow in a dry deciduous forest zone of India that receives about 1200
mm/year of rainfall in contrast to the dry deciduous forests in Mexico where rainfall averaged
about 700 mm/year. The result of this difference in rainfall regime is that the Mexican trees
are shorter than those in India, and thus biomass for a given diameter is less. For example,
height for the Mexican trees commonly ranged between 4 to 9 m, with an average height of
about 7 m (Martinez-Yrizar et al. 1994), whereas those in India had heights up to about 15m
(Bandhu 1973).
The tropical dry forest zone describes areas where rainfall is less than 1500 mm/year or so.
For a dry zone where rainfall is similar to that for the dry deciduous zone of Mexico (about
700 to 900 mm/year or less), Eq. 3.2.2 could be used. For dry zone 'forests at the wetter end
of the zone, i.e., rainfall greater than 900 mm/year, Eq. 3.2.1 should be used. However,
because of the high variability of tree biomass with rainfall in the dry zone, it is
recommended that local biomass regression equations be developed, or at least a few trees
harvested to test how well the two equations presented here fit the local conditions.
The moist zone equations (Eq. 3.2.3 and 3.2.4) give essentially the same biomass estimates
for trees with dbhs up to about 80 cm (Fig. 1b). After this diameter limit, estimates of the
biomass per tree diverge markedly. However, the estimates from Eq. 3.2.4 are closer to the
original data (cf. Appendix 2) and the r2 of the regression equation is higher than for Eq. 3.2.3
(0.97 versus 0.84). It is not recommended that any of the regression equations be used for
estimating the biomass of trees whose dbh greatly exceeds the range of the original data.
However, if trees with dbh greater than 160 cm or so are encountered in an inventory, it is
recommended that Eq. 3.2.3 be used for these trees as the function behaves better in these
larger classes. Equation 3.2.4 is an exponential function and biomass per tree increases
rapidly at large diameters. In the ideal situation where many trees with dbhs larger than 150
cm are encountered, some new field measurement of their biomass should be made (see
section 4.).
It is important that the biomass of trees with large dbh be estimated as accurately as possible
because their contribution to the biomass of a forest stand is much more than their number
suggests. For example, in mature moist tropical forests, the biomass in trees of dbh greater
than 70 cm can account for as much as 40% of the stand's biomass density, although the
number of these trees corresponds to less than 5% of all trees (Brown and Lugo 1992, Brown
1996).
The regression equation for trees in the wet zone (Eq. 3.2.5) matches the original data well
and behaves well at larger diameters. As with the moist equation however, caution should be
taken in using the equation much beyond the original data.
Palm trees: In many tropical moist and wet forests, palms are sometimes common.
Estimating their biomass is difficult as few studies have been made on this topic.
Furthermore, many different species exist with different forms, different proportions of their
mass in leaves, and different stem densities. To estimate the biomass of palms, height
251
measurements as well as diameter measurements will be needed. A simple way to estimate
their biomass is to compute the volume of the stem as a cylinder (basal area x stem height)
and then multiply this by an estimate of the density. Wood density of palms varies
considerably by species and within the stem of the same species, and it can range from about
0.25 to almost 1.0 t/m3 (Rich 1987). The biomass of the leaves also has to be added, which in
total may range from 10 to 65% of the stem biomass (Frangi and Lugo 1985, Rich 1986). An
alternative approach is to use a regression equation developed for the palm Prestoea
montana, a common species in the moist forests of Puerto Rico. Two regression equations
were developed, based on either total height or stem height as follows (from Frangi and Lugo
1985):
(Eq. 3.1.6)
Y (biomass, kg) = 10.0 + 6.4 * total height (m); n=25, r2=0.96
(Eq. 3.1.7)
Y (biomass, kg) = 4.5 + 7.7 * stem height (m); n=25, r2=0.90
An example is given here to demonstrate the variation in the estimates from the three
different methods. For a palm of 15 cm diameter, 15 m total height, and 12 m stem height, the
biomass estimates are:
Method Based on volume: stem volume = 0.21 m3, wood density = 0.25 t/m3; stem mass =
53.0 kg; assume leaves are 65% of stem, total biomass = 87 kg
1
Method Based on Eq. 3.2.6: total biomass = 86 kg
2
Method Based on Eq. 3.2.7: total biomass = 97 kg
3
The three methods give similar values. Unless the forest is composed mostly of palms, any of
these methods would be suitable for estimating biomass of palms scattered throughout moist
or wet forests. However, the variation in wood density by species must be taken into
consideration; higher wood density estimates need to be used for denser species. In the case
of forest stands where palms are dominant, local biomass regression equations would need to
be developed, or at least measurements of wood density of dominant palm species would
need to be measured (see section 4.).
Conifer forests: Few data on the biomass of conifer trees for tropical zones exist. To develop
a preliminary biomass regression equation, data on the biomass of harvested pine trees from
eight literature sources, including pine forests from the southeastern USA, India, and Puerto
Rico were compiled. Several species of pine included in these sources were combined into
one data base and analyzed as was done for the broadleaf forests. The resulting equation is:
(Eq. 3.1.8)
Y(kg) = exp{-1.170+2.119*ln(D)}
252
D = dbh, cm; range in dbh = 2-52 cm; number of trees =63; adjusted r2=0.98
For most situations where an estimate of the biomass density of pine forests is needed, Eq.
3.2.8 can be used. However, if time and resources are available, a local biomass regression
equation should be developed.
Below is an example of how to use the biomass regression equations with stand tables. The
stand table example is for a moist forest in Ghana. Biomass density of this forest was
estimated using the moist equation, Eq. 3.2.3. Maximum diameters are at about the upper
limit for this equation (about 150 cm).
Use if the biomass regression equation, an example
Diameter class (cm)
5-20 20-40 40-60 60-90 90-120 120-150
>150
1. Number trees/ha
794
161
25.2
12.3
3.3
1.05
0.23
a
2. Mid-point of class, cm
12.5
30
50
75
105
135
155 b
3. Biomass of tree at mid-point of class using Eq. 3.2.3; kg
70.5
646
2353 6563
15375
29038
41 187
4. Biomass of all trees, t/ha = (product of rows 1 and 3)/1000°
56
104
59.3
80.7
50.8
30.5
9.5
Total aboveground biomass = sum of row 4 = 391 t/ha
a
As no additional information was available the mid-point of the diameter class was assumed to
represent the class; as the classes are wide this could overestimate the biomass density estimate.
b
Assumed to be diameter of largest class; choice of this upper limit when no additional data
are present is problematic (see section 3.2.4).
c
To convert kg to t
Although the approach presented here has emphasized the use of regression equations with
stand tables, the regression equations can also be used with individual tree measurements
from stands. Using individual tree measurements overcomes the problem of choosing the
diameter of the class.
3.2.3 PROBLEMS WITH REGRESSION APPROACH
Several problems exist with this method, namely: (1) the small number of large diameter
trees used in the regression equations (e.g., for the moist equation, the largest dbh was 148
cm, with only five trees >100 cm diameter), (2) the open-ended nature of the large diameter
classes of the stand tables, (3) wide and often uneven-width diameter classes, (4) selection of
the appropriate average diameter to represent a diameter class, and (5) missing smaller
diameter classes (i.e., incomplete stand tables to minimum diameter of 10 cm). To overcome
the potential problem of the lack of large trees (problem 1), equations were selected that were
253
expected to behave reasonably up to 150 cm or so or upon extrapolation somewhat beyond
this limit (Brown et al. 1989). Rarely are stand tables encountered that contain trees much
larger than the maximum dbh used in the regression.
The problem with open-ended large diameter classes is knowing what diameter to assign to
that class. Sometimes additional information is included that educated estimates can be made,
but this is often not the case. Clearly, further improvements in reporting the distribution of
the largest diameter trees in stand tables would improve the reliability of the biomass density
estimates as it is often these large trees that account for significant proportions of the total
biomass density (Brown and Lugo 1992, Brown 1995). In the above example, the
approximately 1.3 trees greater than 120 cm constitute about 70% of the biomass represented
by the 794 trees in the smallest class.
Many inventories often report stand tables with wide and/or uneven-width classes. The most
unbiased biomass density estimate is obtained when diameter classes are small, about 10 cm
wide or smaller, and are even-width for the whole stand table. This problem is illustrated by
the following example for a moist forest where in Example A the classes are 10 cm wide and
in Example B two classes are combined to make them 20 cm wide.
Example A
Diameter class (cm)
10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 100-109 110-119 >120
Number of stems/ha
183 80 35.1 11.8 4.7 2.3 1.5 0.9 0.5
0.4
0.2
0.5
Biomass/tree (kg) at mid-point of class(Eq. 3.2.3)
112 407 954 1 802 2995 4570 6563 9008 11936 15375 19354 23900
Biomass of trees (product of rows 1 and 2), t/ha
20.5 32.6 33.5 21.3 14.1 10.5 9.8 8.1 6.0
6.2
3.9
12.0
Total biomass density =178 t/ha
Example B
Diameter class (cm)
10-29 30-49 50-69 70-89 90-109
>110
1. Number of stems/ha
263
46.9
7.0
2.4
0.9
0.7
2. Biomass/tree (kg) at mid-point of class(Eq. 3.2.3)
232
1 338 3732 7727
13590 21 555
3. Biomass of trees (product of rows 1 and 2), t/ha
60.9
62.7
26.1
18.5
12.2
15.1
Total biomass density =196 t/ha
The biomass density in Example B, based on the 20 cm wide classes, is about 10% higher
than that in Example A, based on the 10 cm wide class. In general, wider classes will
254
overestimate the biomass density. However, regular estimation of biomass density as part of
inventory analysis or accessibility to the field data should not encounter these problems
because original inventory data generally includes details down to individual trees.
Estimating the biomass of individual trees in inventory plots directly would overcome
problems (2) to (4) given above. Foresters have wide experience in these type of calculations
as they are basically no different from estimating volumes from volume equations.
To overcome the problem of incomplete stand tables, an approach has been developed for
estimating the number of trees in smaller diameter classes based on number of trees in larger
classes (Gillespie et al. 1992). It is recommended that the method described here be used for
estimating the number of trees in one to two small classes only to complete a stand table to a
minimum diameter of 10 cm. It is also emphasized that this method should only be used
when no other data for biomass estimation are available.
The method is based on the concept that uneven-aged forest stands have a characteristic
exponential or "inverse J-shaped" diameter distribution. These distribution have a large
number of trees in the small classes and gradually decreasing numbers in medium to large
classes. Pull details of the theory behind the approach and of the different methods tested are
given in Gillespie et al. (1992). The best method was the one that estimated the number of
trees in the missing smallest class as the ratio of the number of trees in dbh class 1 (the
smallest reported class) to the number in dbh class 2 (the next smallest class) times the
number in dbh class 1. This method is demonstrated in the following example:
1 Assume that: the minimum diameter class is 20-30 cm and we wish to estimate the number of
trees in the 10-20 cm class.
2 The number of trees in the 20-30 cm class equals 80, and the number in the 30-40 cm class
equals 35.
3 The estimated number of trees in the 10-20 cm class is the number in the 20-30 cm class x
(number in 20-30/number in 30-40); this equals 80 x (80/35) =183.
To use this approach, diameter classes must be of uniform width, preferably no wider than
10-15 cm, and should not be used for estimating numbers of trees in more than two "missing'
classes.
3.3 BIOMASS ESTIMATES OF INDIVIDUAL
The regression equations reported above can be applied to inventories of individual trees
planted in lines, as living fence posts, for dune stabilization, for fuelwood, etc. Biomass
estimates for individual trees are particularly useful in drier regions where the trees are grown
for all the aforementioned products and services. However, as discussed above, the regression
equations for dry zone trees are based on a small data base. Furthermore, trees grown in lines
or in more open conditions generally display different branching patterns and are likely to
have more biomass for a given diameter than a similar diameter tree grown in a stand.
Although the above regression equations could be used where no other data exist for rough
approximations, new regression equations need to be developed for trees growing in open
conditions.
255
3.4 BIOMASS ESTIMATES FOR PLANTATIONS
Estimating the biomass density of plantations can be done using techniques similar to those
for native forests as described above. Inventoried volume can be converted to aboveground
biomass density using Eq. 3.1.1 outlined in Section 3.1. However, the equation for BEFs (Eq.
3.1.4) would not necessarily work in the case of plantations of broadleaf species because tree
form is likely to be different in managed forests and definitions of inventoried volumes are
also likely to be different. It is recommended that BEFs be locally derived. The biomass
regression equations for broadleaf species (Eq. 3.2.1-3.2.5) could also be used for plantations,
but once again caution should be taken with their use. Direct biomass measurements of
representative plantation trees should be made to check the validity of the regression
equations, or even better local biomass regression equations should be developed. See
Section 4 for further details on methods.
For plantations of conifer species, the average BEF of 1.3 given for pine forests in Section
3.1.3 could be used if measured volume was based on the total stem. In the case where
diameters of individual plantation trees or diameter distributions are given, Eq. 3.2.8 could be
used, taking the same precautions as for broadleaf species. Kadeba (1989) developed biomass
regression equations for plantations of Pinus caribaea trees growing in the savanna zone of
Nigeria with annual rainfall ranging from 1250 to 1800 mm/year. However, the data base
spanned a small diameter range, about 15-25 cm, and each equation was based on 12 trees
only. For situations that mimic the conditions of Kadeba's study, the reader is referred to his
work.
In situations where lack of resources prevent the development of local biomass regression
equations for plantations, use of any or the above approaches would give a reasonably good
estimate of the aboveground biomass density.
3.5 BIOMASS OF OTHER FOREST COMPONENTS
This primer does not include methods or approaches for making biomass density estimates
for (1) understorey (including e.g., bamboo or rattan), (2) belowground woody biomass such
as fine and coarse roots, (3) forest floor fine litter (e.g., dead leaves, twigs, fruits, etc.), nor
(4) lying and standing dead wood. Most efforts on biomass estimation to date have generally
focused on the aboveground tree component because it accounts for the greatest fraction of
total biomass density and the methods are straightforward and generally do not pose too
many logistical problems. Commonly reported ranges of biomass density estimates for these
other components are given below, although they must be used with caution as the data base
on which they are built is limited.
Summary of estimates of biomass density of other forest components, expressed as a
percent of aboveground biomass in trees
Component
Percent of aboveground! biomass of mature forest!
Understorey
3
Belowground (roots)
4-230
Fine litter (dead plant material)
5
256
Dead wood
5-40
(sources of these data are given in the text)
The amount of biomass in understorey shrubs, vines, and herbaceous plants can be variable
but is generally about 3 percent or less of the aboveground biomass of more mature forests
(Jordan and Uhl 1978, Tanner 1980, Hegarty 1989, Lugo 1992). However, in secondary
forests or disturbed forest, this fraction could be higher (e.g., up to 30%; Brown and Lugo
1990, Lugo 1992) depending on age of the secondary forest and openness of canopy. Palms
are common in many tropical moist forests and they are also often ignored in forest
inventories. Their contribution to total biomass density can be very variable, from nearly 100
percent to less than a few percent (see section 3.2.1 above for more details on estimating the
biomass of this component).
The biomass of roots varies considerably among tropical forests depending mainly upon
climate and soil characteristics (Brown and Lugo 1982, Sanford and Cuevas 1996). Root
biomass is often expressed in relation to aboveground biomass, such as a root-to-shoot ratio
(R/S ratio). A recent review of the literature gives the R/S ratios (from Sanford and Cuevas
1996) shown in the table on the next page.
These estimates of R/S are based on only a few studies (about 30) and not all of them are
consistent with respect to depth of sampling and nor whether coarse roots were included. It
seems clear from this discussion that more studies of root biomass and their relationship with
other factors such as aboveground biomass, climate and soil, are needed.
The amount of dead plant material in a forest, or detritus, is composed of fine litter on the
forest floor, (leaves, fruits, flowers, twigs, bark fragments, branches less than 10 cm diameter,
etc.), standing dead trees and snags, and lying dead wood greater than 10 cm diameter. The
biomass density of fine litter ranges from about 2 to 16 t/ha (average of 6 t/ha or less than 5%
of aboveground biomass), with higher values generally in moist environments although no
clear trend is apparent in the data base (Brown and Lugo 1982). The amount of fine litter on
the forest floor represents the balance between inputs from litterfall and outputs from
decomposition, both of which vary widely across the tropics.
The amount of dead wood in tropical forests is poorly quantified but extremely variable. It is
potentially a large pool of organic matter, perhaps accounting for an amount equivalent to
less than 10 percent to more than 40 percent of the aboveground biomass of a forest
depending upon forest age and climatic regime (Saldarriaga et al. 1986, Uhl et al. 1988, Uhl
and Kauffman 1990; Delaney et al. 1997). Lack of data on this significant forest component
obviously can lead to underestimates of the total amount of biomass in a forest.
It is clear from the above discussion that ignoring these other forest components can seriously
underestimate the total biomass of a forest by an amount equivalent to about 50 percent or
more of aboveground biomass. Although beyond the scope of this primer, it is apparent that
logistically and economically feasible methods and approaches must be developed to estimate
this significant quantity of biomass and its range of uncertainty, especially for improving
estimates of terrestrial sources and sinks of carbon and biogeochemical cycles of other
elements.
257
Forest type
Range of R/S Average R/S
Moist forest growing on spodosols
0.7 - 2.3
1.5
Lowland moist forest
0.04 - 0.33
0.12
Montane moist forests
0.11 - 0.33
0.22
Deciduous forests
0.23 - 0.85
0.47
(e.g., tropical dry and seasonal forests)
PRACTICAL NO.04
258
STUDY VISITS
STUDY OF ENERGY CONSUMPTION PATTERN IN RURAL AND URBAN AREAS THROUGH
SURVEY. VISIT TO NEARBY BIO-ENERGY UNITS.
259
REFERENCES