NTNU
Norwegian University of
Science and Technology
TPG 4140 NATURGASS
Comparison of biomass and natural gas
Group11:
Mirtha Ortega
Per Åkesson
Hilde Dyrbeck
Silje Fosse Håkonsen
Trondheim November 2004
Abstract
This report gives a description and comparison of bioenergy and natural gas as energy
sources. Cost and environmental aspects are considered from production to end-users
in Sweden and partly Norway.
Both natural gas – and biomass fired power plants offer a good alternative to existing
coal, oil and nuclear power plants. Commercialised technologies are available, and the
choice is dependent on economical and environmental aspects as well as political.
The report can not conclude with one alternative being better than the other. It all
depends on location and existing power production. Bioenergy is not a completely
“clean” energy source, there are many environmental aspects regarding this that needs
to be recognised and considered. On a long term basis there will be no net emission of
CO2 from biomass, but with a large increase in the number of biomass power plants
the short-term effect is unclear.
ii
Index
Abstract ..........................................................................................................................ii
Index ............................................................................................................................ iii
1 Introduction ................................................................................................................. 1
2 Emissions .................................................................................................................... 2
2.1 CO2-emissions ..................................................................................................... 2
2.2 NOX-emissions ..................................................................................................... 3
2.4 International agreements....................................................................................... 4
2.4 Environmental consequences when growing short rotation forests ..................... 5
3 Natural Gas ................................................................................................................. 7
3.1 Transportation of natural gas ................................................................................ 7
3.2 Power production – combined heat and power .................................................... 9
3.3 Economical analysis – electricity and heat from natural gas.............................. 11
4 Bioenergy .................................................................................................................. 14
4.1 Benefits of bioenergy.......................................................................................... 14
4.2 Taxes and subsidies ............................................................................................ 15
4.3 Combined heat and power from biomass ........................................................... 15
5 Social cost analysis ................................................................................................... 17
5.1 Method and assumptions .................................................................................... 17
5.2 Production cost analysis ..................................................................................... 18
5.3 Environmental cost analysis for forest residues ................................................. 19
5.3 Total social cost .................................................................................................. 23
6 Discussion ................................................................................................................. 25
7 Conclusions ............................................................................................................... 28
References .................................................................................................................... 29
Appendix 1 Possible natural gas pipe line routes ........................................................ 32
Appendix 2 Development in natural gas prices ........................................................... 34
iii
1 Introduction
The world’s population is presently increasing by more than 90 million people a year
and the world’s 6 billion people today is expected to grow to 10 billion in 2050 before
it will reach stability. 95% of the growth is forecasted to be in developing countries
(Miljøstatus, 2004a). This increase in the world’s population in addition to the
globalisation of the world economy will greatly add to the global energy demand.
According to IEA (International Energy Agency) world-wide energy demand is set to
grow by 2.4% per year to 2030 (EU energy, 2003). This sets high requirements for
pollution control and will lead to many environmental challenges.
Bioenergy is a renewable energy source and can be defined as a material that can be
derived directly or indirectly from plant photosynthesis. If biomass was grown at the
same rate as it was consumed, the net contribution to atmospheric CO2 would be zero.
This is not the case for fossil fuels, which will increase the concentration of CO2 in
the atmosphere. Bioenergy is not included in the Kyoto Protocol and is thus not in the
CO2-accounts. In other words, the combustion of e.g. biopellets will not affect the
emission quotas distributed via the Kyoto Protocol.
This project will look further into the use of bioenergy versus the use of natural gas in
Sweden and partly in Norway. Is bioenergy as environmentally friendly as it is
claimed to be? A comparison between bioenergy and natural gas will be given, from
production to end-users. Both environment and cost will be emphasised.
1
2 Emissions
Combustion of natural gas or bioenergy results in large emissions of carbon dioxide
and nitrogen oxides, which in different ways pose threats to the environment.
However, unlike coal and oil, both natural gas and bioenergy contains only small
amounts of sulphur so the emissions of sulphur dioxide are relatively negligible in
comparison.
2.1 CO2-emissions
The world’s climate has always shifted between warm and cold periods. However, the
observed increase in the earth’s yearly mean temperature is caused by emissions of
greenhouse gases. The UN Intergovernmental Panel on Climate Change (IPPC) has
concluded that our emissions have already influenced the climate to be more than
0.5C warmer than during the 19th century (Naturvårdsverket, 2003). Figure 1
presents the deviation in global mean temperature in the period of 1861 – 2001.
Figure 1: Deviation in the global mean temperature in the period of 1861 to 2001
(Source: DNMI/University of East Anglia).
2
A change in the global climate will have serious consequences for our environment
and social economy, especially if the natural ecosystem does not manage to adapt to
the change fast enough. Regional temperature change and changes in rainfall patterns
will alter conditions for farming and can result in reduced food production with a
subsequent loss in income for farmers. A rise in temperature may also affect our
health as diseases such as malaria may spread into new regions. Another cause of
concern is that extreme weather may become more frequent and more violent leading
to great humanitarian disasters. The sea level will rise due to ice-melting and thermal
expansion of the sea, drowning low-lying land and increase the risk of flooding. This
will seriously influence the life in the coastal zone (Miljøstatus, 2004a).
2.2 NOX-emissions
NOX is generated in all combustion reactions. To some extent, NOX originates from
the nitrogen content of the combustibles, but the greater part are formed as a result of
atmospheric nitrogen and oxygen at the high temperatures obtained during reaction.
Emissions of nitrogen oxides cause several environmental problems. Sulphur dioxide
(SO2) and NOX are the main contributors to acidification, which leads to widespread
damage to vegetable and animal life in forests and lakes. In addition, NOX contributes
to the formation of ground-level ozone, which has negative effects on vegetation and
human health.
Even though serious attempts have been made to reduce the extent of NOX emissions,
goals have not been yet reached (Naturvårdsverket, 2004a). Figure 2 shows the
emissions of NOX in Sweden from 1980.
3
Figure 2: NOX emissions in Sweden from 1980 to 2002.
2.4 International agreements
Year 1992 in Rio de Janeiro the industrial countries of the world were signing a
convention saying that all industrial countries should prepare to reduce their
emissions of green house gases and report their figures to UN. But soon they realised
that they had to be more restrictive and in 1997 the Kyoto protocol, which regulates
emissions of CO2 and other green house gases during 2008-2012 for the OECDcountries, was established. According to the protocol EU has to reduce its emissions
with 8 % compared to the level of 1990.
The countries inside EU have agreed in a national level for each country, depending
on the industrial structure and BNP of the country. Norway has committed to
stabilising the emissions at 1% above the 1990 emission level in the period from 2008
to 2010 (Miljøstatus, 2004b). Sweden has agreed to stabilise the emissions at 4%
above 1990 emissions in the same period. Between 1991 and 2001 Sweden has
decreased their emissions with 6%, while Norway has increased emissions with
approximately 40%. (Statens Energimyndighet, 2003a) To meet the emission quotas
established by the Kyoto Protocol will be difficult for many countries. The protocol
has therefore opened up for some flexible mechanisms that make it possible for the
countries to trade with the carbon dioxide emissions (UNFCC).
4
Vladimir Putin signed the Kyoto agreement the 5. November 2004. After Russia
ratified this agreement it will finally become operative the 16. February next year
(2005) (VG, 2004).
The Gothenburg Protocol treats the emissions of sulphur dioxide, nitrogen oxides,
ammonia and volatile organic compounds. The first breakthrough for this protocol
came in 1979 when 30 European countries, USA and Canada endorsed the UNConvention on Long-range Transboundery Air Pollution (CLRTAP). In this protocol
the problems of acidification were recognised and the signatories agreed to co-operate
to reduce their emissions of acidifying substances.
The Gothenburg Protocol was signed in 1999 and will be used to control emissions of
i.a. nitrogen oxides in Europe up to 2010. Norway has agreed to reduce its emissions
of nitrogen oxides to a maximum of 156 000 tonnes in 2010. This corresponds to a
reduction of 28% compared to 1990 level (Miljøstatus, 2002).
2.4 Environmental consequences when growing short rotation forests
In Sweden willows are grown on farmland and used in short rotation forestry with the
aim to produce biomass for energy. There are several environmental influences when
growing willows as for any cultivated crop. These need to be recognized and
evaluated.
Energy crop production is proposed to be performed in land currently used for
agricultural production (Ranney&Mann, 1994). In this way wild nature is spared, but
at the same time energy crop production will compete with agricultural production.
Chemicals are used in connection with energy crop production. Fertilizers, herbicides
and pesticides are used in varying extent for nutrition, weed control and insect
control. If energy crops replace row crops, the use of fertilizers and herbicides are
expected to be lower, and thus water quality should improve. If energy crops replace
pasture, hay land and close crops such as wheat, water quality effects are expected to
be mixed (Ranney&Mann, 1994).
5
Short rotation forestry plantation with willows will not lead to acidification of the soil
if the grower follows the management recommendations. A liming effect on the soil
will be achieved if the ashes from the willows are recycled, as is the intention in the
future (Ledin, 1998).
Willow crops have a relatively large uptake of cadmium from the soil which can be
used to clean the soil from cadmium. This possibility can only be taken advantage of
if the cadmium can be separated from the ash at low cost and in an environmentally
sound way. However, more research is needed to explore the process of cadmium
cleaning (Ledin, 1998).
High dust and pollen emissions can be expected to be a problem in willow crop
production (Ranney&Mann, 1994). This can cause serious problems and discomfort
for allergics and asthmatics.
It is estimated that the degree of erosion will be approximately the same for energy
crop production as for hayland or pasture if it was not for the establishment phase.
Thus, erosion is
of concern when establishing energy crop
production
(Ranney&Mann, 1994).
Willows will grow to 6-7 meters in height before harvest. This will change the
landscape significantly if for example energy crops are replacing row crops. An
earlier open landscape will therefor be changed to forest (Ledin, 1998). If this
influences the landscape in a good or bad way is a case of personal opinion.
6
3 Natural Gas
Sweden consumes approximately 0.8 BCM of natural gas per year (BP, 2003), which
correspond to about 2% of the total energy use in Sweden. The natural gas is imported
from Denmark, and is transported up the west coast from Malmö to Gothenburg in a
300 km long high-pressure pipeline. The focus in this report will be on the
Stockholm-region, which is estimated to have a potential of 3 BCM natural gas per
year, 2 BCM for power production in a combined heat and power plant and 1 BCM
for industry (Guðmundsson, 2004).
3.1 Transportation of natural gas
There are several alternatives for transportation of natural gas, and figure 3 shows a
scheme that can be used to assess the different options. Because of the large amounts
of natural gas needed, there are mainly two options for transporting the natural gas to
the Stockholm region, as high-pressure gas in a pipeline or as LNG in boats. They
each have different advantages, and the choice is usually a trade-off between capital
cost and running expense, based on the amount natural gas needed and the distance
from the field to the market (Guðmundsson and Graff, 2003).
Figure 4 shows the correlation between capital expenditure and distance for different
natural gas transportation options.
Building a pipeline is a major investment, and is probably only possible with cooperation with the government. A pipeline is a necessity for realising a natural gas
fired power plant in the Stockholm region.
7
Figure 3: Technology choices for transportation of natural gas at different capacities
and distances (Guðmundsson and Graff, 2003).
Figure 4: Capital cost plotted against distance for different natural gas
transportation systems (Guðmundsson and Graff, 2003).
There are proposed two different routes for gas transportation to Sweden and the
Stockholm area, the Mid-Nordic gas pipe (Stamgass) and the Scandinavian gas ring
(Statnett). Sketches of both are shown in Appendix 1.
8
3.2 Power production – combined heat and power
When describing power production from natural gas, one usually refers to the
combined gas- and steam turbine process. A power plant with both steam- and gas
turbines is called a combined cycle power plant (CCPP). A principle sketch of a
CCPP is given in figure 5. Compressed air (10-30 bar) is mixed with natural gas in the
combustion chamber, and the exothermic combustion reaction causes a rapid increase
in temperature. The exhaust gas (1400-1500˚C) is expanded in the turbine, and the
mechanical work is transformed to electric energy in the generator. Some of the
expansion work is used for driving the compressor. After the gas turbine, the exhaust
gas (500-600˚C) is heat exchanged with the closed steam cycle to produce highpressure steam (110-120 bar, 550-600˚C). The steam is expanded in the steam turbine,
to as low as 0.03-0.07 bar, and then condensed and pumped back into the steam boiler
(Bolland, 2004).
Figure 5 : Combined cycle power plant (Bolland, 2004).
9
The planned combined heat and power (CHP) plant at Rya south in Sweden is used as
a basis for the estimates in this work. In addition to a CCPP it has a district heating
system, see figure 6. It has a efficiency of approximatly 0.9 , with ηel = 0.5 and ηheat =
0.4, and will deliver 1459 GWh heat and 1250 GWh electricity each year. It will have
three gas turbines and one common steam turbine (Göteborg Energi).
Figure 6 : Co-production of heat and power (Göteborg Energi).
The exhaust gas from the natural gas combustion drives a gas turbine connected to an
electric generator. The exhaust gas is then heat exchanged with the closed steam
cycle, and the hot steam operates the steam turbine with another generator. Finally,
the remaining heat is taken out into the district heating system through a condenser.
The effect of the plant is 260 MW electricity and 290 MW heat (Göteborg Energi).
The plant will use 300 million Nm3 natural gas per year. The key numbers are
summarised in table 1.
10
Table 1: Key numbers for Rya power plant.
Electricity
Heat
Effect
260 MW
290 MW
Energy production
1250 GWh/year
1450 GWh/year
Efficiency
0.5
0.4
Load factor
55%
57%
The emissions of CO2 from a CCPP is estimated to approximately 350 g/kWh
electricity produced (Furuholt, 2004; Bolland, 2004). The amount of NOx emitted is
dependent on the burner characteristics in the combustion chamber, and can become
very low with contemporary low-NOx burners. At the Rya power plant the
requirements say that emissions should be less than 30 mg NOx/MJ fuel, and with
normal operation the emissions should be less than 10 mg NOx/MJ fuel (Göteborg
Energi). The amount of CO and particles in the exhaust gas should not exceed 30 ppm
and 1 mg/nm3, respectively.
3.3 Economical analysis – electricity and heat from natural gas
The most important factors in assessing the cost of the plant is capital expenditure,
operating expenses, the price of natural gas and taxes on CO2 and NOx emissions.
According to Swedish law, the taxation on energy from natural gas is 1861 SEK per
1000 m3. Of this sum 233 SEK per 1000 m3 come from an energy tax, and 1628 SEK
per 1000 m3 come from carbon dioxide taxation. Natural gas has no taxation for
sulphur dioxide because the sulphur content is considered to be negligible (Svenska
Gasföreningen).
A Swedish study by Sundberg and Henning (Sundberg and Henning, 2002) estimates
the investment cost as a combination between a fixed cost and one part dependent on
the size of the power plant. The study also estimates operational costs, and all
numbers are shown in tables 2 and 3.
11
Table 2: Capex for a natural gas fired CHP (Sundberg and Henning, 2002).
Fixed investment Size dependent
cost (MSEK)
investment cost
(SEK/kWe)
110
5200
Table 3: Opex for a natural gas fired CHP (Sundberg and Henning, 2002).
Fuel price
CO2-tax
Energy tax
Operation and
(SEK/MWh)
(SEK/MWh)
(SEK/MWh)
maintenance
(SEK/MWh)
110
37
6
5
Total
(SEK/
MWh)
158
In another Swedish analysis, estimates are made for both production cost and
environmental cost, and the sum of the two are called total social cost (Miranda and
Hale, 2001). Table 4 summarises the numbers for four different natural gas fired
power plant technologies. The environmental costs mainly consist of emissions from
processing and transport (NOx, SO2 CO, CO2, particulate matter and hydrocarbons)
and emissions from the combustion (NOx, CO, CO2, and hydrocarbons). The concept
of total cost analysis is explained in chapter 5.
Table 4: Total social costs for natural gas based energy production systems
(SEK/MWh) (Miranda and Hale, 2001).
Costs
Production
Environmental Total
Small heating plants
93-113
8-49
104-162
Large heating plants
86-103
8-49
94-152
Condensing plants
130-159
8-49
138-208
CHP plants
151-183
8-49
159-232
Natural gas fired power plants
12
A cost diagram for a combined cycle power plant is shown in figure 7 (Bolland,
2004). It is for a 400 MW power plant, and shows the variation in electricity prices
due to variation in natural gas prices. It can be seen that a prospective CO2–tax will
have a large influence on the economic viability of the project.
Figure 7: Electricity production cost at different natural gas prices for a CCPP
(Bolland, 2004).
From figure 7 it can be concluded that price on natural gas is very important for
whether the project will be economic profitable. A prospective CO2-tax will also
influence the electricity production cost, note that the number in the figure is only an
example.
13
4 Bioenergy
Bioenergy can be regarded as one of the most important renewable resources in future
energy systems. Biomass is stored sun energy and can be upgraded to solid or liquid
fuels. The northern part of Sweden has abundant supply of forests but much heat and
power is needed in the southern parts. An increase in demand for bioenergy in the rest
of Europe is also expected. This means that the biomass has to be transported over
long distances and this result in an increased level of emissions and increased energy
input. Is this a sustainable system that can compete with other energies in the future?
4.1 Benefits of bioenergy
The benefit of using bioenergy is that the combustion does not provide the
atmosphere with any net CO2. The plants on Earth build up biomass with carbon from
the CO2 in air and when being combusted the CO2 is released and can be used by the
plants to build new biomass. The same amount of CO2 would have been released
when decomposing, but during a longer time period and without letting us take
advantage of the energy stored in the biomass. If the use of biofuels is to be
sustainable in the future, it is necessary to return the nutritive substances and minerals
back to the forest.
An increased use of bioenergy also creates new jobs, often in areas with low
employment. The raw materials have to be refined and transported, and equipment has
to be manufactured. Bioenergy creates a chain of activities that generates jobs. Svebio
has made the appraisal that every TWh of new produced bioenergy in Sweden can
create about 300 new jobs (Svenska Bioenergiföreningen, 2003). When new lasting
jobs are being created the society earns money from salary and employment taxes.
The costs for unemployment benefit decrease at the same time. Theoretically there
can be a yearly profit for the society of nearly 65 million SEK for every new TWh
from bioenergy (Svenska Bioenergiföreningen, 1998).
14
4.2 Taxes and subsidies
In 1991 taxes on CO2 emissions was introduced in Sweden, and is to be paid for
emissions from all fuels except biofuel and peat. In Sweden the CO2-tax has
contributed to a more profitable development and usage of biofuels and to a
substantial reduction of CO2-emissions. Biofuels have become very competitive for
production of district heating. Today the Swedish CO2-tax is 0,76 SEK/kg (Statens
Energimyndighet, 2003b). All fuels used for electricity production are declared
exempt from energy- and CO2-tax.
The producers of renewable energy (wind, CHP with biofuel and water power in
small-scale) is supported by being allotted electricity certificates from the Swedish
government, one for every produced MWh. The electricity suppliers are forced to buy
certificates in ratio to the electricity they use. During 2003 they were forced to buy
seven certificates for every hundred MWh they had used. The ratio will raise from
year to year in order to stimulate investments in the electricity production from
renewable sources, from 7.4% in 2003 to 16.9% in 2010. The goal is to increase the
electricity from renewable sources with 10 TWh from 2002 to 2010. Norway has
chosen not to introduce electricity certificates because they think this leads to too big
fluctuation in prices and uncertain conditions for investments in power plants.
4.3 Combined heat and power from biomass
In a CHP plant heat is produced in addition to electricity. Heat is distributed to the
consumers in a district heating system. There are several different biomass
combustors, the most popular ones are either stoker-fired or fluid bed designs. In
stoker-fired combustors the biomass feed burns as it moves through the furnace,
resting on a stationary or moving grate.
15
Fluid bed designs burn the feed in a turbulent bed of inert material that is fluidised by
combustion air flowing through it from underneath. Fluid bed boilers are
commercially available in different technical configurations. Bubbling fluid bed
reactors are used for low capacities and circulating fluid beds are reported over the
entire capacity range.
Fluid bed combustors are rapidly becoming the preferred alternative, because of their
low NOx emissions (Bridgwater et.al., 2002).
16
5 Social cost analysis
5.1 Method and assumptions
In this study an analysis for the full social costs has been made to explore the
attractiveness for different bioenergy producing systems in Sweden. Similar studies
have been done before and have proved how important it is to consider the full social
costs, not just the economical (Miranda and Hale, 1997). Full social cost analysis
includes production costs (e.g. transport, capital, operation and maintenance costs)
which producers pay, as well as environmental costs (e.g. air and water pollution),
typically borne by society. The social costs for harvesting is neglected since it would
occur regardless of the ultimate use of forest residue.
This study focuses specifically on forest residues. The estimated data in this report
derives from a larger study made for Studieförbundet Näringsliv och Samhälle
(Miranda and Hale, 1998). The social cost analysis of energy production is made on
two forms of forest residues; wood chips (chip, limbs and tops, sawdust, bark) in
bales, and refined residue (biopellets). The reason for baling the wood chips is to
increase the density to facilitate storage and transportation.
The energy production is categorised in four different systems typically for Sweden:
small heating plants (1-10 MW), big heating plants (>50 MW), condensing plants
which produce electricity, and combined heat and power plants (CHP plants) which
produce both heat (hot water or steam) and electricity. Heating and CHP plants have
the possibility to use flue gas condensation (FGC) technology. Wood chips contain a
large amount of water (30-50%) and generate substantial amounts of steam when
combusted. Flue gas condensation is a technique used to recover the steam at the end
of the pipe during biomass combustion. This technology requires an increased capital
but gives increased energy efficiency (Joanneum Research, 2001). It must also be
considered that during combustion, forest residue fuel produces a significant amount
of ash. The ash could either be disposed of (landfill option) or be reapplicated to the
forest (reapplication option). For the landfill option deposition in monofills is
assumed – a landfill with only one type of waste (Miranda and Hale, 1998).
17
5.2 Production cost analysis
Production costs for forest residue energy production includes costs in removal of
residue extraction, processing, transport combustion and ash disposal/reapplication
(see Table 5).
Table 5: Steps in energy production based on forest residues(Miranda and Hale,
1998).
Removal of forest residue
Combustion
Disposal
Harvesting
Combustion
Monofill or
Chipping or refining
Ash processing
Transport
Ash application
Table 6 estimates the production costs for the forest residue energy production for
different combustion systems (SEK/MWh). This includes the costs incurred in residue
extraction, processing, transport (Energimyndigheten, 2004), combustion (Börjesson
et al., 1995) and ash disposal/reapplication (Ericson et al., 1994).
Table 6: Comparison of production costs (SEK/MWh) (Miranda and Hale, 1998).
Fuel
Small heating
Large heating
Condensing
CHP plants
plants
plants
plants
(el. & heat)
Wood chips w/o FGC 203-240
155-191
194-231
199-240
Wood chips w/ FGC
202-238
171-219
N/A
209-257
Refined forest residue 268-302
220-253
139-293
264-302
Wood chips w/o FGC 202-240
154-191
193-232
198-204
Wood chips w/ FGC
201-239
170-220
N/A
208-258
Refined forest residue 268-302
220-253
259-293
264-302
Landfill options
Reapplication option
18
5.3 Environmental cost analysis for forest residues
Environmental costs include impact on the environment for residue extraction,
emissions from the processing – combustion – waste chain, and ash reapplication or
disposal.
Forest harvesting for industrial use has a major impact on the environment. Since this
occurs regardless of the later use of the biomass, it is not included in this report. But
of course it has negative effects on the soil, water, air, biota and future productive
potential of the forest. Comparing the environmental impacts from residue removal
with a situation when the residues are left on site shows interesting information. With
mechanical harvesting methods the residue are left in rows or piles. In these piles
unnaturally high levels of nitrogen and potassium forms and could easily leak out to
the surrounding soil. Indeed, high levels of nitrogen have been measured at these
types of sites (Samuelsson and Bäcke, 1997). In contrast, the nitrogen of natural
decomposed residues are volatile and leaves only 10% redeposited as nitrogen oxide
and ammonia. Thus, certain soils and watersheds will be significally negatively
affected, even though the residues remains on site (Miranda and Hale, 1998).
Harvesting residues are rich in nutrients that the tree originally extracted from the soil.
Under natural circumstances these nutrients return to the soil during decomposition.
Harvesting disturbs the balance and remove nutrients form the soil. This results in
compositional changes in the soil, pH, productivity losses and changes in biota.
Further, residue removal also results in air emissions.
Table 7 shows an estimated cost calculation for environmental impact associated with
the removal of forest residues and energy production. The largest cost comes from the
loss of nutrient in the soil. The damage is estimated in a Norwegian study which
proves cost functions for water and forest damage from NOX and SO2 (Alfsen and
Brendemoen, 1992).
19
Table 7: Estimated costs for environmental impacts of residue removal (SEK/MWh)
(Miranda and Hale, 1998).
Impact
Assumption
Cost
Soil acidification Acidification is equal to acid precipitation
5–7
Nutrient export
Fertilizer will be needed to replace the nutrient
Unknown, but
loss
likely
Possible reduction, especially considering
Unknown, but
changes in soil mycorrhizae – more study needed
likely
Possible effects – long term study needed
Unknown, but
Productivity
Flora & fauna
likely
Nitrogen export
In southern Sweden N export results in net
-5 – 2
benefit; in northen Sweden, in net cost
Total
11-20
Mycorrihzae is a type of fungus that grows in association with plant and tree roots,
improving the ability of roots to absorb nutrients from the soil (Svampguiden).
Residue removal, chipping and transport to combustion plants all involve motordriven vehicles and machinery. Both harvesting equipment and chipping machines
runs on diesel fuel. Air emission controllers for this type of motors tends to be less
restrictive then for normal combustion motors although diesel motors have a
significant high level of NOX emissions. The chip delivery from harvesting site to
combustion plants usually occurs by truck, train or ship. Compared to train and ship,
trucks have the highest level of air emissions. CO2 emissions from the supply system
are relatively small compared with the amounts from combustion. Since CO2
emissions from combustion origin from the fuel, the supply system is responsible for
most of the CO2 net emission. Emissions levels can be reduced by using biobased
fuels or improved fuel efficiency (Börjesson et. al., 1995).
The decision on what means of transportation to use depends primarily on the
distance. Trucks are less expensive on short distance (<150 km) while train and ship
are preferred for longer distances or when there is a depot or harbour close by.
20
Further, only refined forest residue fuels are considered to be economically profitable
for long distance transportation (Börjesson and Gustavsson, 1996). Table 8 shows
estimated costs for air emissions from harvesting and transportation. For wood chips
trucks are assumed and for refined fuels train or ship are assumed (Börjesson and
Gustavsson, 1996).
Table 8: Estimated costs for air emission from fuel processing and transportation
(SEK/MWh) (Miranda and Hale, 1998).
Impact
Estimated emission
Cost
Wood chips
Incl. NOX, SO2, CO, CO2, HC and
3 – 23
PM
3 – 19
Refined fuels
As for all forms of combustion, wood fuel emits air pollutants. The amount and type
of pollutant depend both on the specific combustion process, as well as the extent of
controlled burning. In Sweden, large heating plants must have permits for emissions,
although small plants have less strict regulation and therefore emit more pollutants per
MWh (Börjesson and Gustavsson, 1996).
The dispute concerning the role of CO2 emission in global climate requires further
studies. Many consider CO2 emission from biomass fuels irrelevant because carbon
from forest residues is a part of the natural carbon cycle. Based on this, the Swedish
government has decided not to levy carbon taxes on energy production based on
biomass fuels. However, the carbon uptake by growing biomass occurs much slower
than carbon release during combustion. Studies have been made to investigate this
time difference and the net emission for CO2 to the atmosphere from forest residue
combustion is calculated. It has been estimated that 13% of the emissions released
from combustion remains in the atmosphere after 80 years (Börjesson, 1996)
Table 9 shows the estimated environmental costs for air emissions from combustion
of different types of combustion systems. The largest contributing factors are NO X
21
and particle emissions. Since smaller heating plants have less strict regulations, they
have increased environmental costs.
Table 9: Estimated costs for air emissions from combustion (SEK/MWh) (Miranda
and Hale, 1998).
Source
Estimated pollutant
Wood
Refined fuels
chips
Small heating plants
NOX, SO2, CO, CO2, HC, Cd, 9-79
6-69
Pb, Hg and PM
Large heating plants
6-37
4-34
Condensing plants
4-18
4-18
CHP plants
4-24
3-21
Environmental costs associated with landfilling combustion ash origin primarily from
air emissions and water leachate. Generally it is assumed that monofills has a
negligible environmental costs (Miranda and Hale, 1997). But since ash from biomass
combustion contains most of the nutrients which have been removed from the forest
soils, it is a natural consequence to reapplicate the ash. Therefore, ash reapplication is
considered to be a completion of the nutrient cycle. Further, acidified soil benefits
from the liming effects of the ash. In loose form the ash is very basic, pH 11-13,
which could have a more negative effect than a positive if it is applicated directly to
the soil (Samuelsson and Bäcke, 1997). Instead, the ash has to be modified
(hardening, granulation, pelletization) to slow the release of nutrients, heavy metals
and the liming effect. Although this process increases the economical costs, it
dramatically decreases the negative environmental impacts (Ericson et al., 1994).
Generally ash reapplication results in a net benefit, but it has significant geographical
variations. Research shows that the extent of the increase in pH from ash reapplication
is similar to the reduction caused by removal of forest residues.
22
5.3 Total social cost
To analyse the competitiveness of every energy production system, the total social
cost has to be calculated. The social cost combines the production cost with the
environmental cost. This type of analysis provides a more complete picture over the
real costs in an energy system (Miranda and Hale, 2001).
Table 10 shows the total social cost from the earlier estimated production and
environmental costs. Two of the systems is based on wood chips; one with FGC and
one without. Both systems are assumed to use trucks as a mean of transportation. The
third system is based on refined fuels and assumes to use ship as a mean of
transportation.
Refined biofuel has somewhat lower environmental costs than wood chips. This
derives primarily from transportation costs. Refined fuels contain more energy per
mass unit than wood chips due to a lower content of moisture. Thus, fewer trucks are
needed to transport the same amount of energy. As a result of the lower moisture
content, ship or train, which both have a lower negative environmental impact than
truck transport can transport refined fuels (Miranda and Hale, 2001). Table 10 also
shows that the use of FGC technology results in lower environmental costs, primarily
due to differences in emissions from combustion.
Generally, systems using ash reapplication are more economical. This particularly
applies to central and southern Sweden, which receives the greatest reward from the
liming effects of ash (Samuelson and Bäcke, 1997). Wood chips also seem to be a
more attractive option than refined fuels.
23
Table 10: Total social costs for wood chip based energy production systems with and
without FGC and for refined biofuel based energy production systems (SEK/MWh)
(Miranda and Hale, 1998).
Costs
Production
Environmental Total
Small heating plants
202-238
20-112
222-350
Large heating plants
171-219
18-77
189-296
CHP plants
209-257
17-64
226-321
Small combustion plants
201-239
-5-96
196-335
Large combustion plants
170-220
-8-62
162-282
CHP plants
208-258
-8-49
200-307
Small heating plants
203-240
22-122
225-362
Large heating plants
155-191
20-80
175-271
Condensing plants
194-231
18-61
212-292
CHP plants
199-240
18-67
217-307
Small heating plants
202-240
-3-107
199-347
Large heating plants
154-191
-6-64
148-256
Condensing plants
193-232
-7-46
186-278
CHP plants
198-240
-8-51
190-291
Small heating plants
268-302
20-108
288-410
Large heating plants
220-253
17-73
237-326
Condensing plants
259-293
17-57
276-350
CHP plants
264-302
17-60
281-362
Small heating plants
268-302
-5-92
263-394
Large heating plants
220-253
-8-58
212-311
Condensing plants
259-293
-8-41
251-334
CHP plants
264-302
-8-45
256-347
Wood chip based energy production systems with FGC
Landfill option
Reapplication option
Wood chip based energy production systems without FGC
Landfill option
Reapplication option
Refined biofuel based energy systems
Landfill option
Reapplication option
24
6 Discussion
Comparing the numbers in tables 4 and 10, some conclusions can be drawn about the
economies of the different scenarios. Looking first at the production cost, energy
production from the natural gas option is less expensive for all the plant options
considered. The main reason for this is probably the investment cost, because natural
gas power plants are cheaper to build. This would maybe not be the case if the plant
had to be build with a CO2 separation unit, but that is unlikely to happen and will not
be considered here.
The other main contributor to the production cost is the fuel price. The market and
political decisions regarding taxes affect the price on biomass. Sweden has a
satisfactory supply of biomass, and a study made by Sundberg and Henning shows
that it is possible to double the withdrawal without affecting the production price
(Sundberg and Henning, 2002). The price on natural gas is, amongst other things,
dependent on the oil price, and is therefore not very stable (see appendix 2). This
implies that natural gas systems are more sensitive to fluctuations in fuel price
(relative to investment cost) than biomass options. This increases the risk for the
natural gas options, but the lower capital cost acts opposite and partly reduces the risk.
The environmental cost does not vary all that much, especially if only the CHP plants
are considered. The numbers for natural gas and biomass reapplication option are very
equal, so on the basis of this analysis there is no foundation to claim that biomass is
more environmentally friendly than natural gas.
Table 11 shows the total amount emission per MWh from the bioenergy systems.
Compared to the numbers given in chapter 3.2 the bioenergy systems have lower CO2
emissions, so a unique conclusion can not be given without a further investigation.
25
Table 11: Total emissions from the bioenergy systems (Forsberg, 2000).
Emission
Wood chips
Refined biomass
fuels
CO2 (kg/MWh)
29
27
CO (g/MWh)
206
243
NOX (g/MWh)
781
1110
N2O (g/MWh)
16
17
SOX (g/MWh)
116
110
PM (g/MWh)
268
424
HC (g/MWh)
Small amounts
Small amounts
For biofuels, systems based on woodchips with FGC technology outperform systems
based on wood chips without FGC, which in turn outperform systems based on
refined fuels.
If biomass is considered a viable substitute for nuclear power in the future, care must
be taken in this transition. There is still not enough knowledge on the environmental
impacts of growing short rotation forests. This transition needs to be done gradually
with careful monitoring. The problem with depletion of the soil is especially of
concern since no economical viable solutions exist for cleaning the ash enough for it
to be returned to the forests.
Giving that transportation of bioenergy and natural gas depends strongly on distance,
amounts and which means of transportation are used (Bioenergy - boats, trucks etc.
Natural gas – pipe, LNG, CNG etc.), it is difficult to give an exact comparison of
emissions and costs. Transportation of bioenergy with trucks or boats and natural gas
as LNG and CNG give emissions due to combustion of diesel etc. Transporting
natural gas through a pipeline gives no emissions except for at construction and
maintenance. This form of transportation is however only economically viable if the
distance from production to end-user is not too long.
26
A comparison of social costs between bioenergy and natural gas is very complicated
seeing that it is dependent on whether the fuel is replacing an existing source of
energy (e.g. nuclear power in Sweden or hydropower in Norway) or it is a “new” fuel.
It also depends on which region is considered. For example is bioenergy an abundant
resource in Sweden thus making it more favourable to use here than in Norway.
While in Norway natural gas is the most obvious choice of the two due to large gas
resources. However, even local considerations have to be made. In Sweden for
example, the west coast has a gas grid and the forests are mainly present in the north.
Compared to power production from coal and oil both these alternatives seem
environmentally favourable, with low emissions. On the other hand nuclear power is
virtually emission free, but other aspects make it seem unwanted (risk of accidents,
negative reputation).
During this project it has been observed that coal often is used as standard of
reference when discussing bioenergy in for example Sweden. In this way bioenergy
stands out as the evident choice for energy source. However, only very small amounts
of the energy consumed in Norway and Sweden come from coal fired plants. This can
raise questions if coal is considered only for bioenergy to gain popularity. If
bioenergy is to be compared rightfully with other energy sources, it should be with
sources that are regarded as alternatives.
27
7 Conclusions
Compared to traditional fossil fuel power plants, especially coal fired, both
alternatives discussed here will have a positive impact on carbon mitigation problems.
Biomass fired CHP plants already exist in Sweden (e.g. in Eskilstuna), and a natural
gas fired plant is under construction in Rya. So the technology is available, and it is
most of all dependent on the energy policy of the Swedish government what will be
the trend in the future. High electricity price and heavily taxed natural gas in
combination with cheap biomass fuel may make a biomass fired plant more profitable
in the future.
Forest fuels constitute a reasonable replacement for the energy currently produced by
nuclear power in Sweden, but it is not the full solution. Forest residues are especially
attractive due to the national and international desire to reduce the CO2 emissions. But
regardless, attention should be paid to the complete environmental impact for energy
production by using forest residues. Since it is and will remain unknown, Sweden
should proceed with caution.
It is difficult to conclude with one alternative being better than the other. It all
depends on location and existing power production. Bioenergy is not a completely
“clean” energy source, there are many environmental aspects regarding this that needs
to be recognised and considered. On a long term basis there will be no net emission of
CO2 from biomass, but with a large increase in the number of biomass power plants
the short-term effect is unclear.
28
References

Bridgwater, A.V. , Toft, A.J., Brammer, J.G.;A techno-economic comparison of
power production by biomass fast pyrolysis with gasification and combustion,
Renewable and Sustainable Energy Reviews ,6, 181–248 (2002)

Börjesson P, Gustavsson L, Johanssom B, Svenningsson P. Reducing CO2
emissions by substituting biomass for fossil fuels. Energy 20:11, 1097-113
(1995).

Börjesson P, Gustavsson L. Regional production and utilization of biomass in
Sweden. Energy 21:9, 747-764 (1996).

Börjesson P. Emissions of CO2 from biomass production and transportation in
agriculture and forestry. Energy Convers. 37:(6-8), 1235-1240 (1996).

Energimyndigheten. Prisblad för biobränslen, torv m.m. No3/2004. Statens
energimyndighet, 2004. Home page,
www.stem.se/web/biblshop.nsf/FilAtkomst/pb3_04w.pdf/$FILE/pb3_04w.pdf?Op
enElement

Ericson SO, Lundborg A, Oskarsson R. Ash in forests: accumulatd experience and
knowledge from the forest power project. Vattenfall and SÖDRA (1994).

EU Energy, 2003 IEA puts global energy tab to 2030 in the trillions, EU Energy,
70, 21, (2003)

Forsberg, G. Biomass energy transport: Analysis of bioenergy transport chains
using life cycle inventory method. Biomass and Bioenergy 19, 17-30 (2000)

Guðmundsson, J.S.: Natural gas in Norway and the Mid-Nordic Gas Pipeline
Study, (2004)

Gustavsson, L., Madlener, R. CO2 mitigation costs of large-scale bioenergy
technologies in competitive electricty markets. Energy 28 1405-1425 (2003)

Göteborg Energi: Home Page, www.goteborgenergi.se

Joanneum Research. District heating with biomass (2001). Home page,
www.bmvit.gv.at/biomasse/e/p6.htm

Ledin S.: Environmental Consequences when Growing Short Rotation Forests in
Sweden, Biomass and Bioenergy, 15(1), 49-55, (1998).

Miljøstatus, 2002 http://www.miljostatus.no/templates/themepage____2366.aspx

Miljøstatus, 2004a http://www.miljostatus.no/templates/themepage____2143.aspx
29

Miljøstatus, 2004b
http://www.miljostatus.no/templates/PageWithRightListing.aspx?id=2142

Miranda ML, Hale B. Protecting the forest from the trees: the social costs of
energy production in Sweden. Energy 26, 869-889 (2001).

Miranda ML, Hale B. Using the forest for the trees: production and environmental
costs of production energy from forest residues in Sweden. SNS occasional paper,
81(1998).

Miranda ML, Hale B. Waste not, want not: the private and social costs of wasteto-energy production. Energy Policy 25:6, 587-600(1997).

Naturvårdverket, 2003
http://www.naturvardverket.se/dokument/hallbar/klimat/snabbkurs/snabbkurs.htm

Naturvårdverket, 2004
http://www.naturvardsverket.se/dokument/fororen/kalka/forsur.html

Ranney J.W. and Mann L.K.: Environmental Considerations in Energy Crop
Production, Biomass and Bioenergy, 6(3), 211-228, (1994).

Samuelsson H, Bäcke J-O. Effekter av skogsbränsleuttag och askåterföring – en
litteraturstudie. Skogsstyrelsen, Rapport 6 (1997).

Stamgass (2001): Naturgasleden i Mitt-Norden, (information brochure),
www.stamgass.com.

Statens Energimyndighet, Energiläget 2003, 40, Energimyndighetens förlag,
Eskilstuna (2003b)

Statens Energimyndighet, Energiläget 2003, 50, Energimyndighetens förlag,
Eskilstuna (2003a)

Sunberg, G., Henning, D. Investments in combined heat and power
plants:influence of fuel price on cost minimised operation. Energy Conversion
and Management 43 639-650 (2002)

Sund, K., Statnett (2004) : Scandinavian Gas Ring: En mulig integrering av
skandinavisk gassinfrastruktur?, GO-samarbeidets seminar om gass og energi, 19
august 2004: ”Gass gir GO energi”(viewgraphs).

Svampguiden. Home page, www.svampguiden.com/ordlista.asp?nr=103

Svenska Bioenergiföreningen, Faktablad Nr 3 1998, Energimyndighetens förlag,
Eskilstuna (1998)

Svenska Bioenergiföreningen, Fokus Bioenergi Nr 1 2003, 2003
http://www.svebio.se/Fokus%20Bioenergi/Fokus%20Bioenergi_sv1webb.pdf
30

Svenska Gasföreningen: Naturgas och skatter på miljö och energi,
www.gasforeningen.se

UNFCC http://unfcc/kyoto_mechanisms/items/1673.php

VG, 2004 http://www.vg.no/pub/vgart.hbs?artid=255066
31
Appendix 1
Possible natural gas pipe line routes
Two different proposals for natural gas pipe line routes are shown in figure A1.1 and
A1.2.
Figur A1.1: Phase three of the Scandinavian Gas Ring. Green lines indicate existing
pipes, while red lines are planned/proposed gas pipes.(Statnett)
32
FigureA1.2: The Mid-Nordic gas pipe (Stamgass)
33
Appendix 2
Development in natural gas prices
Figure A2.1 shows the development in natural gas price in the European Union, 19852001. The figure is excerpted from an article by Gustavson and Madlener (Gustavson
and Madlener, 2003), and the numbers are based on BP Statistical Review of World
Energy.
Figure A2.1: Natural gas price development (Gustavson and Madlener, 2003).
34