Sustainable Community Development Using Plasma Arc Gasification of Municipal Solid Waste
by
Celerick Stephens
A Thesis Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degrees of
MASTER OF ENGINEERING SCIENCE AND
MASTERS OF SCIENCE IN MANAGEMENT
Approved:
_________________________________________
Dr. David Rainey, Thesis Adviser
_________________________________________
Dr. Ernesto Guiterrez-Miravette, Thesis Adviser
Rensselaer Polytechnic Institute
Hartford, Connecticut
August 2011
© Copyright 2011
by
Celerick Stephens
All Rights Reserved
CONTENTS
CONTENTS ....................................................................................................................... i
LIST OF DEFINITIONS .................................................................................................. iv
LIST OF SYMBOLS ........................................................................................................ vi
LIST OF TABLES ........................................................................................................... vii
LIST OF FIGURES ........................................................................................................ viii
ACKNOWLEDGMENT ................................................................................................... x
ABSTRACT ..................................................................................................................... xi
1. Introduction.................................................................................................................. 1
1.1
The need for electrically sustainable communities ............................................ 3
1.2
The need for waste sustainable communities ..................................................... 4
1.3
Distributed Power .............................................................................................. 7
1.4
Reuse of matter .................................................................................................. 7
1.5
The synergism of waste recycling and distributed power generation ................ 9
2. Application of the Technology .................................................................................. 10
2.1
2.2
Plasma gasification........................................................................................... 10
2.1.1
Plasma, the charged gas ....................................................................... 10
2.1.2
Gasification, the gaseous conversion of stored energy ........................ 11
2.1.3
Plasma gasification, the charged gas conversion of energy ................. 11
Plasma gasification for the conversion of waste .............................................. 13
3. Methodology and Theory .......................................................................................... 15
3.1
3.2
Distributed scale plasma gasification ............................................................... 15
3.1.1
Municipal solid waste collection and disposal ..................................... 17
3.1.2
Tailored waste stream .......................................................................... 19
Plasma Arc Gasification Analysis .................................................................... 22
3.2.1
Synthesis Gas Production..................................................................... 29
3.2.2
Municipal Solid Waste Constituents .................................................... 29
i
3.3
3.2.3
The Boie Estimation ............................................................................. 23
3.2.4
Constituents and Products Analysis ..................................................... 29
SynGas Conversion .......................................................................................... 29
3.3.2
3.4
Gas Turbine SynGas Analysis ............................................................. 29
Waste Heat Recovery ....................................................................................... 29
3.4.1
Process Heat ......................................................................................... 29
3.4.2
Community Heat .................................................................................. 29
3.5
System Design .................................................................................................. 29
3.6
Community Layout .......................................................................................... 29
3.7
Tenement Analysis ........................................................................................... 29
3.8
Suburban Analysis ........................................................................................... 29
3.9
Waste Delivery System .................................................................................... 30
3.10 Community/Urban Planning ............................................................................ 30
3.11 Exergy Analysis ............................................................................................... 30
3.12 Traditional Community Analysis ..................................................................... 30
3.12.1 Waste Delivery System Analysis ......................................................... 30
3.12.2 Landfill System Analysis ..................................................................... 30
3.12.3 Inadvertent Hazardous Waste Production ............................................ 30
3.12.4 Community Energy Consumption........................................................ 30
3.12.5 Waste Collection and Conversion Exergy Analysis ............................ 30
3.13 Plasma Conversion Community Analysis ........................................................ 30
3.13.1 Waste Delivery System Analysis ......................................................... 30
3.13.2 Plasma Waste Conversion Analysis ..................................................... 30
3.13.3 Waste Carbon Production .................................................................... 30
3.13.4 Inadvertent Hazardous Waste Production ............................................ 30
3.13.5 Waste Collection and Conversion Exergy Analysis ............................ 31
4. Results and Discussion .............................................................................................. 32
ii
5. Conclusions................................................................................................................ 33
6. References.................................................................................................................. 34
7. Appendices ................................................................................................................ 37
7.1
Defining the unsustainable growth of the worldwide middle class ................. 37
7.1.1
Worldwide middle class population rise .............................................. 37
7.1.2
Middle class electrical power consumption ......................................... 39
7.1.3
Middle class waste production ............................................................. 41
7.2
Plasma Gasification Reaction Program ............................................................ 48
7.3
Source Reduction with Plasma Waste Gasification ......................................... 48
iii
LIST OF DEFINITIONS
Distributed power - generation of power on a where-needed and, often when-needed,
basis
Gasification - a process by which a hydrocarbon-based substance undergoes a thermochemical conversion from a solid to a gas
Globalization - the “fundamental changes in the spatial and temporal contours of social
existence, according to which the significance of space or territory undergoes
shifts in the face of a no less dramatic acceleration in the temporal structure of
crucial forms of human activity” (1)
Landfill(ing) - gathering wastes in aggregate and allowing generally natural processing
to decompose the matter over time (landfilling is the process thereby)
Leachate – typically hazardous liquid composed primarily of water and contaminated
salts, present due to the transmission of water through waste
Middle class – a segment of the population determined on the basis of an income (between $6,000 US and $30,000 US) that, on the worldwide aggregate year 2007
purchasing-power parity, provides household disposable income
Municipal solid waste – Refuse or discard from a local populace that is in nature composed of consumable, non-biologically generated matter
OECD – Organization for Economic Cooperation and Development, an international
group of 50 generally affluent nations with the mission to promote international
and local policies to improve the socioeconomic situation of the world’s population
Plasma - a state of matter comprised of a charged fluid which is characterized by having
nearly equal concentrations of electrons and positively charged ions
Purchasing Power Parity – theory in economics that seeks to set an equivalent exchange
rate by adjusting for the purchasing power of the exchanged currencies. This exchange is typically among national currencies and is relatable to the “law of one
price,” which states that barring fair trade vehicles (e.g. tariffs), the goods sold in
any country would be the same cost of the identical goods sold in any other country (2)
Refuse Derived Fuel (RDF) – processed stream of waste matter that is useful for the
production of energy
iv
Sanitary landfill – designed areas of open waste decomposition that by way of hydrological and geological technologies prevent the emission of hazardous materials into
the environment
Sustainable (sustainability) – a process that continues or progresses at a rate that promotes the repletion of resources that are consumed or changed by the process;
this ensures the process, or others that depend upon its input or output, may continue without threat of decline
Vitrification – a process in which amorphous materials are heated to a molten state and
cooled rapidly forming a glass. In the sense of this research it is used as a process by which non-gassifiable solids are encapsulated in glass by the process
described.
Waste – material remaining after the transformation or extraction of the most readily
available or most useful content or energy contained within that material
v
LIST OF SYMBOLS
vi
LIST OF TABLES
Table 6.1:The growth of the world middle class compared to the growth of the world
population: a compilation of data from the Goldman Sachs* (15) and the U.S.
Census Bureau** (16).......................................................................................... 38
vii
LIST OF FIGURES
Figure 1.1: Growth of the worldwide middle class from 1960 to 2010, with projections
to 2030. The total world middle class population is read on the left axis, while
the percentage is read to the right. Sources: US Census Beaureau (17), Goldman
Sachs (15). ............................................................................................................. 3
Figure 1.2: Worldwide middle class electrical energy consumption, with data from 1960
to 2008 and projections to 2030. Compilation of sources: Goldman Sachs (15),
U.S. EIA (2), The World Bank (20). ..................................................................... 4
Figure 1.3: Worldwide middle clas waste generation per year showing, with a
conservative projection that refuse generation rates are constant that more than
2.2 billion tons of waste may be generated by the middle class people of the
world. The methodology and rationale for this projection is detailed in Appendix
6.1. ......................................................................................................................... 5
Figure 6.1: Excerpt from Goldman Sachs report on the expanding middle class showing
a pareto of the per capita income in 2007 and comparing it to the world
projection in 2050. The chart on the right shows a swell of middle class income,
particularly in the nations known as the BRIC’s. ................................................ 37
Figure 6.2: World population growth showing the growth of the middle class. Data
sources: Goldman Sachs* (15) and the United States Census Bureau** (21). ... 39
Figure 6.3: The projected world electricity consumption against the projected middle
class population growth showing close linear correlation between the global
middle class and power consumption. ................................................................. 40
Figure 6.4: World electrical energy consumption on the basis of the world population.
This chart shows correlation to Figure 6.2, where the increase in the world wide
middle class correlates to the growth of the world projections of energy
consumption. ........................................................................................................ 40
Figure 6.5: IPCC unrecycled waste generation data showing minimum annual rates of
carbon storage in landfills from 1971 to 2002. (5) .............................................. 42
Figure 6.6: OECD waste generation in kg/capita/year for the period between 1980 and
2005. As all OECD countries are represented in the legend, only several are
listed. (6) .............................................................................................................. 43
Figure 6.7: IPCC graphical representation of post-consumer waste generation between
1971 and 2002. (5) ............................................................................................... 43
viii
Figure 6.8: U.S. EPA data showing municipal solid waste generation of the United
States between 1960 and 2008 (in million tons). (17) ......................................... 44
Figure 6.9: U.S. EPA data showing municipal solid waste recycling (in million tons).
(17) ....................................................................................................................... 45
Figure 6.10: United States waste generation as determined independently by the United
States EPA (17) and the OECD (6). .................................................................. 46
Figure 6.11: Waste generation as a function of the population of the world wide middle
class. This figure is analytically generated based upon data and projections from
the U.S. EPA (17), the OECD (6), and Goldman Sachs (15). See also Figure 1.3.
............................................................................................................................. 47
ix
ACKNOWLEDGMENT
Type the text of your acknowledgment here.
x
ABSTRACT
The growth of a worldwide middle class and the electrification of mobility are
factors stressing the current standards in electrical power generation. In developed
countries, electrical power is produced in mass at central locations and delivered over
large distances to communities. This produces significant electrical distribution losses,
approaching 7% of the produced power.
Growing electrical demand coupled with
inherent grid losses will ultimately require additional points of generation, further
promoting the consumption of valuable resources in power plant construction and
operation.
Further, as middle-class communities continue to grow, the amount of waste
generated also increases, promoting the problems associated with waste disposal. The
proliferation of inexpensive consumer electronics also ensures that a significant percentage of the generated waste stream becomes inorganic and biologically harmful, and the
innocuous disposal and treatment of post-consumer waste is a growing concern.
The foundation of this proposal addresses both of these concerns by investigating
a means of converting waste into energy. Though waste-to-energy conversion is a
mundane technology, the peculiar benefit being proposed by this work is that energy
may be produced by the reduction of the waste stream on a local basis to advance
sustainable communities. The research and analysis presented develops a case for using
plasma gasification of municipal solid waste—a clean method of converting waste into
useful synthesis gas—to generate distributed power for individual communities. The
analysis conducted uses the principles of thermodynamic and economic systems analysis
to determine the benefit and feasibility of a distributed power plasma arc municipal solid
waste gasification system. The distributed production of energy on a community basis
will significantly reduce electrical delivery losses and waste equating to an overall net
energy savings.
xi
1. Introduction
Sustainability is an area of research of focused attention, made ever more important due to the growth the world population and the finite resources by which to
support it. However there is a global phenomenon outstripping the resource pressures
caused by population growth: it is the growth of the worldwide middle class. The
worldwide middle class currently is a minority, but a person of this minority group
consumes resources and produces wastes many times that of the average person of the
world’s population. Globalization—the “fundamental changes in the spatial and temporal contours of social existence, according to which the significance of space or
territory undergoes shifts in the face of a no less dramatic acceleration in the temporal
structure of crucial forms of human activity”1—is a factor supporting that growth.
Globalization allows for larger pool of human resources that can provide goods and
services to distant regions conveniently (with little loss in time) and, due to economic
disparity in the costs of those rendered goods and services, attractively on a global scale.
In turn, the compensation for those rendered goods and services provide for previously
impoverished people to afford not only wealth to meet their needs, but also wealth to
satisfy their desires. Also as the aforementioned definition of globalization implies, this
growing middle class is technologically driven; meaning that a greater and growing
percentage of the population enjoys the benefits of technology, especially the magic of
electrification. This places upon the established methodologies of energy delivery and
production stresses previously unmatched.
Scientists and engineers are attacking the
issue by pursuing renewable power generation, giving life to new technologies in solar,
wind, biofuel, and tidal energy technologies. Conservationists are also pushing for more
efficient means of utilizing energy by pursuing advances that reduce power consumption, while preserving the comforts that electrical consumption afford.
1
It is this definition offered by Scheuerman that demonstrates globalization and the
significance it has upon the world middle class population growth. This definition
highlights that the globalization is directly fueled by technology, which decreases the
significance of distance by decreasing the time by which physical and/or intellectual
goods or services subtend that distance. (25)
1
A major sector of the environmental movement that has the potential to significantly influence both energy production and energy (and resource) conservation is not as
popularly discussed: waste generation. The growth of the world middle class is an
increase in world resource consumption. The law of conservation of energy (the first
law of thermodynamics) then dictates that the waste generated by this increased consumption middle class is also increasing: the space in which to dispose of the waste is
not. Expanding one’s purview beyond the bounds of general thought, one may see
clearly that the waste associated with waste disposal is significant. The generated waste
must be disposed of, and that process requires the expenditure of energy—the waste is
generally transported to a destination and repeatedly agitated or treated to accelerate its
decomposition, as evidenced in landfilling operations. Reductions in the energy required
to dispose of waste is conventionally realized through recycling, but this constitutes a
fraction of the overall waste stream. The remainder (the majority) of the waste is
deposited in a landfill, with a small percentage used to generate heating and electrical
power. Because of environmental concerns however, waste-to-energy conversion is
used primarily where land is a constraint.
The global middle class is also stressing the systems that deliver electrical power.
Even with the most advanced utility systems, significant losses are incurred in the
transmission of electrical power from the point of generation to the point of use. This
loss of electrical power through resistance and power transformation is compounded
with the distance over which that electrical power must travel. Again, referring to
Scheuerman’s definition of globalization, it is easy to see that the speed at which technology enables the flow of ideas and materials effectively promotes the physical
disbursement of people, because the time-based perception of distance is decreased. The
points of electrical consumption are thus more widely distributed. The energy lost in
transmission is thus increased.
This body of work addresses waste disposal and its associated resource consumption, electrical power generation, and electrical power transmission with one unifying
technology.
The unifying technology utilizes the process of plasma gasification to
convert municipal solid waste into energy. This technology is ecologically responsible
in that it reduces concentrations of both immediately hazardous and potentially hazard2
ous waste products, and the technology is sustainable as it requires a “renewable resource,” waste, as its fuel.
The purpose of this work is to explore plasma conversion
technology as a means of reducing the human waste stream and producing distributed
electrical power to promote sustainable communities in an ecologically benign manner.
1.1 The need for electrically sustainable communities
The need for sustainable communities is apparent. Though the rate of growth of the
world population is projected to be in decline for the coming decades, the rate of growth
of the middle class shows a progressive trend. Compared with only 16% of today’s
world enjoying prosperity levels to the extent that some income is disposable, in the year
2030 it is projected that 43% of the world’s population may be deemed to be within the
middle class2
3
(this
trend is depicted in
Figure 1-1).
This
equates to 3.6 billion
people in the year
2030
consuming
electrical
power
at
levels in excess of
projected
capacity4
(3) (see Figure 1-2).
Such an electrification growth rate is
nearly
the
quintu-
Figure 1-1: Growth of the worldwide middle class from 1960 to 2010, with
projections to 2030. The total world middle class population is read on the
left axis, while the percentage is read to the right. Sources: US Census
Beaureau (24), Goldman Sachs (1).
The definition of the “middle class” is determined on the basis of an income (between
$6,000 US and $30,000 US) that, on the worldwide aggregate year 2007 purchasingpower parity, provides household disposable income (1).
3
Middle class percentage statistics are compiled from worldwide population statistics
from the United States Census Bureau (24) and the Goldman Sachs Economics Research
Group (1), respectively
4
This analysis was conducted based upon worldwide energy consumption data (22) (3)
and the projections of the middle class growth rate (1).
3
2
pling, in less than twenty years, the current electrical power generation rate of the United
States (4).
Figure 1-2: Worldwide middle class electrical energy consumption, with data from 1960 to
2008 and projections to 2030. Compilation of sources: Goldman Sachs (1), U.S. EIA (3), The
World Bank (22).
1.2 The need for waste sustainable communities
The growth of the worldwide middle class also influences waste production. In
2007, Americans alone produced 254 million tons of trash at a rate of about 4.6 lbs. per
individual per day (5). The effect of this is noted by research by the Intergovernmental
Panel on Climate Change (IPCC) which directly relates the rate of municipal solid waste
generation to prosperity and population (6).
Assuming that the growing worldwide
middle class may be represented by the consortium of primarily majority middle class
nations known as the Organization for Economic Cooperation and Development
(OECD), the world’s middle class may generate municipal waste at a rate of 3.4 lbs. per
day (7). Though this waste generation rate is substantially lower than that of the United
States, projecting this over the growth of the world’s middle class indicates that 2.2
4
billion tons of refuse may be
discarded per annum in the year
2030, as shown in Figure 1-3.
The amount of waste generated in
one year in 2030, based upon this
potentially conservative projection5, would be enough to bury
New York City in six feet of
trash6.
Governmentally
imposed
regulation, and a shift in awareness in OECD countries, has led
to the significant reduction in
disposed waste because of waste
source
reduction,
recycling
Figure 1-3: Worldwide middle class waste generation per
year showing, with a conservative projection that refuse
generation rates are constant that more than 2.2 billion tons
of waste may be generated by the middle class people of the
world. The methodology and rationale for this projection is
detailed in Appendix 7.1.
efforts, and conventional waste to energy—incineration—technologies.
Still by the
process described in Figure 1-4, 54% of the waste generated in the predominantly
middle class OECD nations is deposited in open waste decomposition sites called
landfills (5). These decaying landfills cause further environmental damage due to the
release of carbon dioxide and ground water pollution. Because of the dangers of open
waste decomposition, many nations have implemented regulations to allow for sanitary
landfills only. In these designed areas of open waste decomposition, hazardous materials emission is limited by the implementation of hydrological and geological technology
(8).
5
See Section 7.1.3
The rate of waste generation in 2030 is 2.2 billion tons, or 8.9 billion cubic yards based
upon the mass to volume relationship of municipal solid waste in collection vehicles
presented by Tchobanoglous (8).
5
6
Figure 1-4: Waste stream processing showing the reduction of landfill waste from the point of generation.
Source: U.S. EPA Department of Solid Waste an Emergency Response (5)
The emissions from landfills (both toxic and environmental) are significant. However, the process of disposing waste in a landfill is arguably more damaging. Municipal
waste vehicles travel to more than 79 million American homes, a 25,000-mile journey
each year for the average waste collection vehicle. With 179,000 waste collection
vehicles in operation in the United States alone, the consumption on a fuel basis exceeds
1.5 billion gallons of fuel each year (9)7.
The solution for ensuring sufficient resources exist to support the world demands is
multifaceted. Conservation, recycling, and the use of renewable resources for power
generation (wind, solar, and wave energy) are all important improvements in our energy
dependent society, but recycling is the predominate technology assisting in waste
reduction. The definition of sustainability should be augmented to not only address
power consumption and conservation but also waste generation and waste reduction.
Establishing waste and energy sustainable communities could significantly reduce
harmful emissions and improve resource conservation.
7
Municipal waste collection vehicles consume on average one gallon of fuel for every
three miles traveled due to the repetitive acceleration cycle on waste collection routes (9)
6
1.3 Distributed Power
The majority of the power generated in the developed world is pumped onto an
electrical grid, which is a means of distributing power over large expanses. The benefits
of this technology is that power can be generated where the resources are present,
economical, and as a human matter, convenient. The detriment is that there is a significant amount of power loss associated with large power distribution grids.
Line losses are a primary symptom of grid-distributed power. Seven-percent of the
electrical power generated in the United States is expended prior to consumption solely
due to transmission and distribution inefficiencies (10). This equates to 261 million
kilowatt-hours of electrical power, or enough to sustain 20,000 American homes with
electrical power per year8 (10). With growing demand and improved efficiencies, the
transmission and distribution loss fraction is not expected increase significantly. However the required, costly, and resource intensive expansion of the electrical grid will be
necessary to support the growth in electrical demand.
A better solution may exist, the distributed production of power. Distributed power
production is the generation of power on a where needed (and often times, when needed)
basis. Distributed power production reduces line losses merely due to the reduced need
for power transformation for long-distance transmission, as the power is generated near
the source of consumption. For this to be feasible, a local source of fuel and a local
means of converting it to electrical power is necessary. It would be of prime benefit if
that local fuel source were sustainably generated and transformed into electrical energy
with low ecological impact.
1.4 Reuse of matter
All living organisms consume “useful matter” and expel “wastes.” Both useful
matter and wastes are in quotations as it is apparent in nature that the by-products
(wastes) of a given organism promote the continued life of another organism as a source
of fuel or habitation (useful matter). With the technologically advanced human organ8
In 2005, the average American single family detached home consumes electricity at the
rate of 13,162 kW-hrs. (3).
7
ism, however, more byproduct is produced than what is readily recyclable by natural
means. Because of this disproportionate cycle, humans are faced with the interesting
quandary of how to dispose of waste.
Though recycling and waste to energy methods have been used to reduce the waste
footprint of the developed world, the dominate means of waste disposal is landfilling.
Simply, the process of landfilling gathers wastes in aggregate and allows generally
natural processing to decompose the matter over time. Landfills in actuality are much
more complicated, and require a significant energy input. Firstly, the landfill must be
created. With environmental regulations to control the flow rate of biologically damaging leachates from landfills, wastes can no longer be openly discarded. Instead, landfills
are ecologically and geologically designed and constructed in a process known as
sanitary landfilling. Once the landfill is operational, the waste must be collected from
the points of generation and delivered to the site of disposal. To speed the process of
decomposition, increasing the useful life of the landfill, waste agitation is put into effect.
This process of using earthmovers to churn the wastes periodically results in yet more
fuel consumption. Upon attaining the limit capacity of a sanitary landfill, the landfill is
capped, a process by which organic materials (soils, grasses, other forms of vegetation,
and man-made inorganic materials) are placed on top of the landfill to render the site less
harmful.
Recycling in its various forms has a lower ecological impact and because of this fact
has been promoted worldwide. Thirty-three percent of the wastes that would be bound
for a sanitary landfill are recovered or immediately reused as otherwise useful materials
(11). Typically for the products that are in high demand, the reclamation of these
materials is even more economical and environmentally friendly than farming the
materials from the earth. Increased emphasis is being placed upon composting as well.
In composting, organic materials are combined in such a way that the natural decomposition of the materials is relatively fast. The byproducts are also nutrient rich, allowing
for an environmentally friendly soil generation method. Though recycling and composting currently make up a significant percentage of the recoverable waste, vigilance and
education are still required to ensure that the appropriate materials are placed in the
recycling and composting waste streams.
8
1.5 The synergism of waste recycling and distributed power
generation
Efforts have been made to utilize wastes efficiently. Incineration and landfill gas
recovery are means of waste reduction while generating electricity as a by-product.
Both cases however have undesirable results. In incineration, the wastes (after significant processing) are simply combusted as fuel. The byproducts of combustion however
are environmentally unsafe. Combustion methods have been found to release dioxins
and other potentially carcinogenic compounds into the atmosphere.
Moreover, the
release of greenhouse gases (carbon dioxides and other gases) is undesirable. For the
collection of natural gas (methane) from decomposing matter, land (a precious resource)
must be occupied in great measure, and as previously discussed significant controls are
required to preclude the release of potentially hazardous materials into the ecosystem.
Posited in this research is that a synergism in methods of power generation and
waste stream reduction may exist. Imagine if the wastes generated in a locale were
directly used to generate the power requirements of that locale, with the resulting
byproducts being heat and innocuous building materials. Each of the processes required
for this synergism currently exists.
Plasma arc gasification, a process that has been proven in industry, is a means of
recovering non-toxic and toxic waste streams into heat (useful for community and
process heating), process gases (which can be used for power generation), and inert
building materials. This research further speculates that there is an optimum combination of plasma arc waste gasification and distributed power generation. In this solution,
the wastes that are locally generated fuel the process that generates local power. Moreover, this research posits that a more macroscopic benefit is also at play. Infrastructure
reduction, fuel and energy consumption, and electrical wastes are all significantly
reduced on a more global basis if more power were generated locally. Small-scale
plasma arc gasification of municipal solid wastes could be a key enabler of more sustainable communities in the developed world.
The benefits may be yet more far
reaching in the undeveloped worlds, enabling electricity production on an efficient basis,
where currently no or limited energy resources exist.
9
2. Application of the Technology
2.1 Plasma gasification
Plasma gasification is a process of converting typically organic materials into energetically useful substances, such as liquid or gaseous fuels. Though the industrial use
of plasma in material conversion is a relatively young technology, the discovery of
plasma has its roots in electric lighting. In 1927 an American chemist, Irving Langmuir,
found that an electrified fluid can transport electrons and ions in a similar manner as
blood plasma carries red and white blood cells. He stumbled upon this discovery while
attempting to prolong the life of the tungsten filament in a light bulb, and from this
discovery he was able to leverage his theories of this ionized gas to not only improve the
light bulb, but also to introduce a new branch of physics (12). It is upon the discovery of
plasma physics in which the root of this research is planted.
2.1.1 Plasma, the charged gas
The generally accepted scientific definition of plasma is a charged fluid, which is
characterized by having nearly equal concentrations of electrons and positively charged
ions. The physical characteristics of this matter is generally complex and not readily
described by the solid, liquid, or gaseous states of matter—plasmas have also been
termed the fourth state of matter for this reason. Although the discovery of plasma is
recent, it is considered the most abundant state of matter in the universe, as it is the very
material composing our sun and countless other stars and celestial bodies in the universe.
On earth, we typically see plasma in the mundane forms of lightning and open flames,
and confined within fluorescent bulbs.
High-temperature plasmas that are formed by gases in electric arcs have also
found industrial uses. By passing high velocity gasses in a highly charged electric arc,
streams of high-energy electrons and ions emit intense amounts of heat at temperatures
exceeding 11,000 degrees Fahrenheit (13).
Devices that perform this function are
plasma torches, and at the exit conditions of a plasma torch, materials undergo rapid
pyrolysis in the case of organic materials or, in the case of inorganic materials, rapid
10
melting. It is this useful function of high temperature plasma that is the basis of the
technology described in this body of work.
2.1.2 Gasification, the gaseous conversion of stored energy
The other side of the technology presented is gasification. Gasification is a process
by which a hydrocarbon-based substance undergoes a thermochemical conversion from
a solid to a gas. This conversion allows for energy in a typically solid form to be transformed into a more useful form (either for transport, energy density, or utility).
Described as an “ancient art” by Higman and Van der Burgt due to its roots in woodfueled fires (14), the gasification typically described in engineering processes employs
pyrolysis, the heated and near-anaerobic conversion of a hydrocarbon to a useful,
combustible gas. The more modern development of gasification was employed in the
early 1800’s as a means of turning coal into a form of gas. This “town gas” was widely
distributed for various uses ranging from industrial power and heat generation, to public
and private lighting, heating and cooking, in much the same way that natural gas is
currently delivered and utilized.
Because of the town gas origins of gasification and because of the widespread availability of the fuel source, coal gasification continues to be the most widespread
application of the technology. However, the quest for clean and renewable sources of
fuel spurred along with the discovery of liquid fuel processing using the Fischer-Tropsch
method of converting gas into liquid fuel (easing its transport and increasing its energydensity) has led to the gasification processing of other hydrocarbon feed stocks such as
biomass, including human wastes.
2.1.3 Plasma gasification, the charged gas conversion of energy
It is upon the convergence of the two technologies, plasma and gasification, that this
work is based. Generally, the process described here is hydrocarbon gasification. The
hydrocarbon is provided as the fuel source for the reaction and is derived from a solid
waste stream. The process of gasification is enhanced using high-energy plasma gas as
the pyrolysis catalyst. Both technologies, as described earlier, are proven in theory and
in practical application.
Also the combination of the two processes (using plasma
11
torches to gasify refuse) has recently made the transition from the laboratory and controlled environments to industry implementation. The former and the latter reveal that
plasma thermal processing of human refuse is sufficient for the gasification of waste into
a useful, energy rich gas (synthesis gas) with about one-half the heating value of methane.
The combination of plasma and gasification differs significantly from waste incineration. Incineration processes are low-temperature thermal processes. Though the flue
gases generated by combustion often have sufficient free carbon (soot), hydrocarbons,
and carbon oxides (particularly carbon monoxide) to be combustible, the main product
of interest from incineration is heat. It is the heat from the combustion process that
provides steam to generate electrical power through steam turbine generators and
process or municipal heating. Further, incineration is typically an environmentally toxic
process.
As wastes are destroyed at low temperature and in typically atmospheric
conditions, fly-ash, containing harmful substances, often escapes the process due to their
buoyancy and difficulty of processing. Further, the low-temperature recombination of
products of partial combustion results in the production of polychlorinated dibenzo-pdioxins, human carcinogens (15), and colloquially termed dioxins. To limit the production of toxic byproducts, incineration facilities employ extensive waste filtering and
recycling to remove potentially toxic products from the incoming waste stream and
extensive environmental monitoring and flue gas and ash processing to remove harmful
impurities from the exhaust.
Conversely, plasma gasification is regarded in industry as a clean process for the
thermal conversion of waste to fuel.
Because of the extremely high temperatures
involved and the oxygen starved environment under which the process takes place,
municipal solid wastes can be nearly instantly converted into a combustible and useful
fuel with significantly fewer potentially harmful agents being generated (16). Further,
conventional gas scrubbing technology may be used to process clean the synthesis gas
while reprocessing the syngas contaminants through the plasma gasifier. The resulting
synthesis gas with a heating value about half that of natural gas is immediately useful for
the clean production of steam for steam power generation, directly in a Brayton cycle, or
as a fuel source in a fuel cell. There is only one other form of waste product from
12
plasma gasification. The inorganic materials, which would generally become fly ash in
an incineration process, become molten materials due to the high process temperature.
These molten materials are vitrified, encapsulating even potentially harmful substances
in an inert silica or alumina glass, while other hazardous materials at these process
temperatures form harmless oxides, which are also vitrified (17). This innocuous glasslike material is useful in construction materials, without any subsequent cleaning.
2.2 Plasma gasification for the conversion of waste
Plasma gasification is a technology that can be applied to a range of input fuels.
In fact, because byproducts of plasma gasification have low harmful substance percentages and potentially hazardous solids are vitrified, plasma conversion is regarded as a
means of transforming hazardous wastes (primarily biological and nuclear wastes) into
more benign forms. In these processes, the goal is the reduction of waste and the
benumbing of any hazardous byproducts. Though one of the outputs of the conversion is
synthesis gas, the high concentrations of inorganic matter in these waste streams prohibit
the production of significant quantities of gas for effective energy production. However
hazardous waste is minimized and nearly eliminated, therefore the overall cost associated with the application of plasma technology to the conversion of this hazardous waste is
justifiable (18).
Coal conversion using plasma was among the first explored uses of plasma gasification for the production of energy. It provides a clean process gas for electricity
production while reducing dioxin and carbon emissions. The plasma conversion of coal
also vitrifies the trace contaminants in coal (sulfur, metals, stone and sand) into a useful
construction material. It comes as well with the benefit of facilitating the retrofit of
existing coal-fired power plants while reducing upgrade costs (19). Coal gasification has
a significant side effect: the coal that is to be used in the process needs to be delivered
from its place of origin to the point of power production. Moreover, at the place of
origin, large amounts of energy are expended for the extraction of coal. With an overall
consideration, the use of coal for the production of energy using plasma gasification is a
net energy loss.
13
The use of plasma gasification presented here may be considered of three purposes. The primary area of focus is sustainable power production. The secondary focus
also builds upon the premises of the first, the elimination of waste at the source of the
waste. Finally, by generating the power at the place of necessity, significant reductions
in power transmission can be realized, and by consuming waste locally to generate
power locally, significant reductions in waste energy expenditures are also attainable.
14
3. Methodology and Theory
3.1 Distributed scale plasma gasification
The process of plasma conversion of municipal solid wastes (detailed in Figure
3-1) starts with the community generated waste stream. The waste stream is composed
of post-consumer and post-industrial materials with perceived low residual value. In the
common culture of the developed world, the low value waste is easily discarded, either
by separating the contents of the waste stream to remove those components of higher
residual value by recycling, and either incinerating or landfilling the majority of what is
remaining. In both cases—recycling and discarding—the waste is centrally gathered,
necessitated by economics, legal and environmental controls, and public desire9. The
plasma gasification process presented here begins at the point of generation. Instead of
gathering waste and transporting it to a central processing facility, the waste is transported only a short distance to a distributed collection facility, which processes then only a
fraction of the waste that would be generated by a municipality.
The second step in the gasification process is waste stream conditioning. The
waste stream is filtered for content that ultimately detracts from the desired result, the
production of synthesis gas and heat. The need for this step in the process resulted from
a macroscopic optimization showing the desirable products of the process (electricity
and heat generation and waste reduction) significantly benefit from conditioning the
waste stream. Recycling materials and removing moisture from the waste stream are
both aspects of waste stream conditioning. The process presented attempts to maximize
electrical output by balancing the moisture content and constituents of the waste stream.
This processed waste stream then becomes fuel (known in industry as a refuse-derived
fuel) for the plasma convertor.
9
Waste collection is a highly regulated industry. Sanitary and environmental concerns
have led to legislation that specifically zones where and how waste will be stored. This
is also driven by public desire to not have waste collection facilities in close proximity to
developed areas. The importance of these factors will become apparent as they may be
detractors to the adoption of a distributed power generation scheme similar to that
described in this research.
15
The refuse-derived fuel is then passed into the plasma convertor. In the plasma
convertor, the waste fuel is thermally converted at extremely high temperatures resulting
in a gas which, when controlled in its cooling, produces a combustible fuel.
Another
byproduct of the plasma converter is a molten slag which is process cooled in a controlled manner to ensure vitrification, the result of which is an inert solid that needs no
further processing. Finally, due to the heat input into the waste stream by the plasma
torch and the energy rejection from the synthesis gas and vitrification processes, significant amounts of residual heat is generated. This byproduct can be fluid transferred for
use in waste conditioning (reducing moisture content) and community heating (for
heated water, process heat, or for air-conditioned living spaces). It is the primary
byproduct, synthesis gas, which is of significant interest as it becomes the main source
of energy for the plasma process.
16
Figure 3-1: Plasma gasification process showing waste consumption and power production cycle. The
waste is first community generated, and proceeds through a recycling stream prior to being converted into a
refuse derived fuel. The RDF is then converted to heat and waste gas in the plasma gasifier. The waste gas
is finally converted into electrical energy to sustain the plasma process and supplement power for the
community. In this figure are symbols describing the constituents of the waste stream and waste gas that
will be discussed in detail in sections 3.2 and 3.3.
3.1.1 Municipal solid waste collection and disposal
The conventional collection and transportation of municipal refuse is a cycle that
itself generates significant waste. In most municipalities in the United States and other
developed nations, refuse vehicles transit neighborhoods and businesses to collect wastes
at the point of generation and deliver them to a more centralized disposal location. In
2007, the United States had a daily refuse collection vehicle fleet (including recycling
vehicles) numbering 136,000. The operation or duty cycle of these vehicles requires the
constant acceleration and deceleration associated with making frequent stops. Mostly
powered by diesel fuel and hydraulic mechanisms for pick-up and waste compaction,
17
even the stop cycle of these large trucks requires large (typically diesel) engines to idle
continuously. This results in an overall fuel efficiency of 2.8 miles per gallon of diesel
fuel (9). Considering the average refuse vehicle travels 25,000 miles per year, the
ecological implications of municipal waste collection are great. Collecting and transporting waste in the United States equates to the consumption of 1.5 billion gallons of
fuel each year, which is enough fuel to power 2.2 million commuting vehicles10.
Though there are recent efforts worldwide to address the environmental impact of
waste collection vehicles, they are primarily aimed towards hybrid technologies and
alternative fuels such as natural gas and hydrogen combustion vehicles. Recently in
China, even battery electric vehicles have been introduced to address the need to reduce
fuel consumption. Efforts to reduce fuel consumption in refuse vehicles (and in general
large vehicular diesel engines) are being regulated by legislation. In the United States in
2010, heavy-duty engine emissions standards were implemented specifically to address
this concern. It is estimated that if 50% of waste collection vehicles in the United States
were converted to alternative energy, the savings could amount to an energy reduction of
14.3 million barrels of oil each year.
Regardless of the potential savings in reducing the oil consumption of refuse vehicles, the collection and transportation of waste perpetuates the waste of resources for the
sole purpose of disposing of waste. Another solution to the problem is to diminish the
need for the collection and transportation of waste. By consuming the waste locally, at
or very near the point of generation, significant reductions in overall fuel consumption
may be realized. For a typical waste stream in the United States, more than 58% of the
waste by mass11 is plastic, paper, and organic non-food wastes (wood, leather, textiles,
and rubber). Local plasma gasification could remove these wastes from the waste
stream, resulting in a highly recyclable mix of glass and metals. Accordingly, the energy
consumption associated with waste transportation and collection of the remainder of the
waste stream is more than halved. This opportunity is addressed in the distributed power
10
The calculations are based upon the American average fuel economy of 17.2 miles per
gallon and the American average commuter vehicle mileage of 11,900 miles for the year
2007. (28)
11
A mass basis is considered due to the assumption that compaction reduces the volume
of trash collected.
18
aspect of plasma waste gasification explored in this research, as most of the waste
generated could be locally consumed in a small, local plasma gasification facility.
3.1.2 Tailored waste stream
Detractors of plasma waste gasification argue that the technology is detrimental in
that it promotes the waste generation mentality while also degrading recycling efforts.
The argument is posed that if all waste is recoverable there is no benefit in waste reduction, because waste is a source of fuel in the new paradigm. Also the advantages of
recycling are obsoleted because paper and plastics wastes are even better fuels for
plasma gasification. There is truth in these claims, and a thorough review of the application of distributed plasma gasification also promotes recycling, as well as waste
reduction12.
This research shows that a tailored waste stream creates a more energy rich synthesis gas. Elementarily, one can come to this conclusion by considering the constituents of
a gas with a high recoverable energy. On the basis of the higher heating value of a fuel,
hydrogen is the most energy rich, with a heating value of 61,000 BTU/lb. A more
abundant natural gas, methane, is a hydrocarbon with a chemical composition of CH4
and has a heating value of nearly 24,000 BTU/lb. When organically derived components
of the waste stream are subjected to plasma conversion the result is the generation of
hydrogen and low heating value hydrocarbon gases, while the inorganic portions of the
waste stream only debits the net energy generation of the process. In fact, the most
energy productive plasma waste processing would completely recycle out all metals and
non-organic wastes in favor of dry hydrocarbons—such as paper, plastics, rubber,
textiles, and wood. It should be noted in the previous statement that dry hydrocarbons
are preferred: the process of converting water into its gaseous form in plasma gasification only consumes energy with no significant benefit—water effectively only changes
its form without releasing valuable byproducts by the plasma process. For this reason
wet organic wastes such as food wastes only subtract from the net valuable energy of
12
Source reduction as it pertains to waste-to-energy methods such as plasma gasification
is addressed in the Appendix in Section 7.3.
19
plasma gasification of waste. Since one of the goals of plasma gasification is the production of the highest energy synthesis gas for the production of electricity, recycling on a
plasma waste conversion basis simplifies the waste stream into the simple categories of
food waste, metals, and everything else.
It is this simplification of the recyclable waste stream that continues to promote
plasma gasification. To reduce the costs of recycling collection, and to promote recycling collection from the private and corporate sectors, many municipalities have
transitioned to single-stream recycling. In single-stream recycling, all post-consumer
content is aggregated at the time of collection. The public remains uneducated about
what is acceptable as recyclable materials, and this method has resulted in more contaminated recycling streams, as inappropriately separated materials degrade the quality of
recycled input leading to material losses13. While loss rates for metals and glass are low
(7% to 12%) loss rates for plastics and paper derived products are 20% to 40% (20).
The contaminated wastes are ultimately incinerated (conventionally) or land-filled.
However, in the plasma gasification model, those wastes with high reclamation rates
(metals and glass) are still recycled, while the wastes that are more easily contaminated
(plastics14 and paper) are plasma converted into synthesis gas and the contaminants are
inconsequential to the process.
Using plasma gasification for waste allows for an
improved recycling methodology in this respect.
Another cost of recycling is also averted by converting waste to energy using plasma gasification on a local basis. In most municipalities, recycling input is collected in
the same way as municipal waste—large waste transfer vehicles are employed to
13
For example, in multi-stream recycling there is no differentiation in paper products, so
all articles from copier paper to milk cartons are bundled together at the single-stream
recycling centers (or material recovery facilities) and then sold to pulp and paper mills.
Though this is in theory beneficial, large amounts of what is thought to be recyclable is
actually discarded at the pulp facilities due to contamination as the single-stream papers
include plastic and wax coated papers (e.g. as from plastic view windows in postal
envelopes, plastic coated newsprint, and modern milk and juice cartons which are wax
coated with the plastic pour spouts and caps).
14
Plastics recycling initiatives result in significant wastes due to contamination. Because the public remains unaware of the necessity to empty thoroughly the plastic
containers to be recycled, quantities of food wastes, oils, cleaning fluids and medications
pollute the potentially recyclable plastics stream.
20
transport the waste to a central processing facility. Where single stream recycling
collection is employed, the waste is mechanically (and even manually) separated into the
various recycling streams at the expense of additional resource consumption. By reducing the recycling to glass and metals, only 30% of what is currently recycled or
composted would need to be transported to a central processing facility (21).
From these two counterarguments, we see then that recycling in waste management
is not degraded, but instead is newly defined15. Plastics and dry paper wastes (regardless
of contamination rates16) are desirable in the waste stream. Metals (of all constituencies), glass17, and wet organics (such as yard clippings, food wastes) are then considered
undesirable. The multi-stream recycling is then reduced to three streams, compost,
metals, and glass. All other forms of waste provide direct high-energy input for the
plasma gasification reaction. The robust nature of this recycling scheme precludes
public education and accidental recycling stream contamination, and for this reason
plasma waste conversion of post-consumer waste products may be viewed as enhanced
recycling—a recycling method that generates the ultimate starting state of the matter
15
Source reduction is an important consideration in waste management and is discussed
in the Appendix section 7.3.
16
In plasma waste conversion, the most destructively contaminated constituents of a
recycling stream are desirable in their combination. All paper based constituents provide
the needed hydrocarbon contents for a high-heating value synthesis gas to be created, as
well as contributing to the operating temperature of the reaction. Plastics, however,
being hydrocarbons of significantly lower moisture content provide even more heat
energy while also boosting synthesis gas generation rates and raising syngas heating
values. Even the scenario of plastic or paper based containers retaining other products
(from inadequate cleaning or emptying of containers) is addressed in that the plasma
temperatures are sufficiently high to gasify the container and the residual contents while
vitrifying constituents that do not gasify. It is possible that paper and plastic wastes with
high moisture contents (as in a container of water being introduced in the plasma convertor) to reduce the net energy output from the plasma recycling process, but the only
consequence in such a scenario is the net loss in power; no waste is created. This also
holds true for other recycling and non-recycling content that may be introduced into the
waste stream.
17
Glass and silicates typically comprise 5% of a municipality’s waste stream (21). In the
ideal case, all of this too would be recycled, however reality requires some small amount
of this to be present in the plasma processing because it is the substance that allows for
the vitrification of solids (both toxic and non-toxic).
21
being consumed: energy. For its benefits to recycling, plasma gasification of waste
might be considered plasma enhanced recycling.
3.2 Plasma Arc Gasification Analysis
The key differentiator of waste to energy in this research is the use of plasma
conversion. It is this process that heats the waste stream so quickly and to such high
temperatures that the waste is not burned. The plasma torch leads to the decomposition
of the primarily hydrocarbon waste without the combination of oxygen that would
promote combustion. Also, the temperatures are so high that inorganic wastes (metals
and silicates) are melted allowing for vitrification of potentially harmful substances.
Separating plasma pyrolysis from lower temperature pyrolysis is the significant reduction in the formation of carbon, soot or char. The analysis of this process is of prime
importance in the plasma gasification of waste because it generates the synthesis gas that
makes this process ecologically and economically feasible.
The plasma furnace (also referred to as the plasma convertor, as it changes waste
into useful byproducts) is the fundamental component in the high-temperature pyrolysis
of the waste stream. This process generates the clean and useful product, synthesis gas,
as well as useful waste heat and a vitreous product, which entrains potentially hazardous
compounds into an inert solid. The analysis of the process starts with the input waste
stream. The waste stream is municipal solid wastes, but the contents of the waste stream
are selected through recycling to provide the highest heating value (highest net energy
output) through its conversion. The process for determining the optimum waste input
for energy conversion is an optimization based upon a chemical ultimate analysis. The
products of the ultimate analysis are the gases that are used to then generate electrical
power, which is in turn used to power the plasma torch. The residual electrical power is
then used to supplement the power requirements of the community. The residual heat
from the plasma torch is used to dry the input waste (reducing the moisture content and
increasing the energy output) and can be used for hot water production.
22
3.2.1 Community Waste Generation
The analysis begins with the input waste stream. As a part of the optimization as
well, it is important to understand the amount of waste a community typically generates
to determine the minimum size of the community that can be supported with the plasma
gasifier. Recall that the significance of this research is to create a basis for waste consumption and power generation on a distributed basis, reducing the impact of waste and
electrical power transportation.
In the United States, 4.65 lbs of waste is generated per day per person excluding
recycling efforts18. This generation rate is used as a global estimate of the middle class
waste production rate and intentionally does not include the reduction of waste due to
recycling efforts as the paper and plastic content is key in increasing the energy output of
the gasification cycle. It is important to understand the constituents of the waste stream
and the chemical composition for determining the products of gasification.
In 2006, the United States population generated 251 million tons of waste. The
content of that waste stream was quantified in research presented by Shoo-Yuh Chang
and is shown in Figure 3-2. It is also important to note the trend in the waste generated.
Chang’s work shows that from 1960 to 2006, plastics have grown as a disproportionate
piece of the waste stream (due in large part to product packaging and electronics). Paper
has in recently remained unchanged or is on a slight decline as a percentage of the
overall waste stream. The importance of this trend is that plastics and paper provide the
highest calorific benefit in the plasma conversion of waste. As a part of the optimization, it may also be determined that the presence of plastics provides for the higher
production of synthesis gas.
18
Section 7.1.3 details waste and recycling statistics used in the determination of the
waste and recycling habits of the worldwide middle class.
23
Figure 3-2: The waste stream constituents of waste generated in the United States in 2006
United States Waste Content from 1960 to 2005
45%
40%
Paper and Paperboard
35%
Glass
Waste Content
30%
Metals
25%
Plastics
20%
Rubber and Leather
Textiles
15%
Wood
Food Waste
10%
Yard Waste
5%
Other
0%
1950
1960
1970
1980
1990
2000
2010
Year
Figure 3-3: Trends in the constituents of the municipal solid waste stream of the United States from 1960
to 2006.
Obviously missing from the constituent analysis of the waste stream is the presence of water. This is accounted for in the typical content of moisture inherent in the
24
constituents, as helped by the relationship developed by Tchobanoglous (22) and summarized in Table 3-1. The content of moisture will be important not only for accounting
for the water present in the waste stream, but also for determining the amount of drying
that may help optimize the production of synthesis gas and in the raising of the temperature of the plasma reaction. The basis for determining water used in this analysis is
simply the product of the constituent mass and the typical moisture content. Research
presented consistently implies that this method is an underestimate of the moisture
content of the waste stream. It must be noted that in this analysis, the presence of
externally provided water in the waste stream (from the collection of rainwater and
waste water) is expected to be minimized, as the waste will be locally generated and
disposed. Water that enters the waste stream from large scale collection methods can be
discounted. As such, the starting input moisture of the waste stream is nearly 20%, as
opposed to the 28% – 35% moisture content documented in the prevailing research.
Further, the conditioning of the waste stream (primarily in the composting or other
disposal of organic wastes) will drop the moisture content of the waste stream to 7%.
This reduction of the moisture content of the waste stream at the point of generation is very significant point: the presence of water decreases the temperature of
pyrolosis (or conversely stated, increases the input energy required to maintain a given
pyrolosis temperature). Less energy will be required for electrical torch operation and
waste stream drying. There is a balance involved as well, however. Water is required to
aid in the formation of hydrogen, methane, and other low-energy gases that comprise the
syngas, which will ultimately be providing electrical power for the reaction and for
power generation.
Table 3-1: Constituents in municipal solid waste showing the typical moisture content of constituents (8).
*The water weight of the waste presented is calculated from the data presented and is not present in the
original source.
Material
Paper & Paperboard
Glass
Metals
Plastics
Weight
Generated
77.42
12.15
20.85
30.05
Percentage
Generation
31%
5%
8%
12%
25
Typical
Moisture
Content
6%
2%
0%
2%
Water
Weight
of
Waste *
4.65
0.24
0
0.60
Rubber & Leather
Textiles
Wood
Other Organic Wastes
Other Inorganic
Wastes
Total
7.41
12.37
16.39
64.69
3%
5%
7%
26%
15%
6%
35%
60%
1.11
0.74
5.74
38.81
8.28
249.61
3%
0%
0
51.8934
Finally, because the optimization of power generation from the waste stream is
dependent upon the energy of the input fuel, we need a means of relating the contents of
the waste to the chemical constituents of the waste stream. A chemical elemental
analysis of the waste stream generates this data. As it is beyond the scope of this research to perform the ultimate analysis in a laboratory environment, again the research
documented by Tchobanoglous is used, and compared with the works of Boie and
Qinglin [Develop this point with Excel evaluation of the waste stream presented and
compared in research to the others]. Techobanoglous breaks down on an elemental basis
the predominant contents of a municipal solid waste stream as shown in Table 3-2.
Table 3-2: Elemental contents of components of a typical municipal solid waste stream (22). The
categories highlighted are the values of the represented constituents of the waste stream in this analysis.
**Mixed textiles are not a category found in Techobanoglous text, but is averaged here for the simplification of the waste stream analysis.
Type of Waste
Food and Food Products
Fats
Food wastes (mixed)
Fruit wastes
Meat wastes
Carbon
Percent by weight (dry basis)
Hydrogen
Oxygen
Nitrogen
Sulfur
Ash
73.0
48.0
48.5
59.6
11.5
6.4
6.2
9.4
14.8
37.6
39.5
24.7
0.4
2.6
1.4
1.2
0.1
0.4
0.2
0.2
0.2
5.0
4.2
4.9
Paper Products
Cardboard
Magazines
Newsprint
Paper (mixed)
Waxed cartons
43.0
32.9
49.1
43.4
59.2
5.9
5.0
6.1
5.8
9.3
44.8
38.6
43.0
44.3
30.1
0.3
0.1
<0.1
0.3
0.1
0.2
0.1
0.2
0.2
0.1
5.0
23.3
1.5
6.0
1.2
Plastics
Plastics (mixed)
Polyethylene
Polystyrene
Polyurethane
60.0
85.2
87.1
63.3
7.2
14.2
8.4
6.3
22.8
-4.0
17.6
-<0.1
0.2
6.0
-<0.1
-<0.1
10.0
0.4
0.3
4.3
26
Polyvinyl chloride
45.2
5.6
1.6
0.1
0.1
2.0
Textiles, rubber, leather
Textiles
Rubber
Leather
Textiles (mixed) **
48.0
69.7
60.0
59.2
6.4
8.7
8.0
7.7
40.0
-11.6
25.8
2.2
-10.0
6.1
0.2
1.6
0.4
0.7
3.2
20.0
10.0
11.1
Wood, trees, etc
Yard wastes
Wood (green timber)
Hardwood
Wood (mixed)
Wood chips (mixed)
46.0
50.1
49.6
49.5
48.1
6.0
6.4
6.1
6.0
5.8
38.0
42.3
43.2
42.7
45.5
3.4
0.1
0.1
0.2
0.1
0.3
0.1
<0.1
<0.1
<0.1
6.3
1.0
0.9
1.5
0.4
Glass, metals, etc.
Glass and mineral
Metals (mixed)
0.5
4.5
0.1
0.6
0.4
4.3
<0.1
<0.1
---
98.9
90.5
Miscellaneous
Office sweepings
Oils, paints
24.3
66.9
3.0
9.6
4.0
5.2
0.5
2.0
0.2
--
68.0
16.3
This is further backed by an ultimate analysis that further refines the waste
stream into a heating value, a measure of the potential calorific energy of the refuse
derived fuel. Measuring this would require the use of a bomb calorimeter in a controlled
laboratory environment. Instead, the optimized (conditioned) waste stream that results
from the optimization process will be compared to that presented in research ensuring
the analysis remains valid over the range of conditions being evaluated. Primarily the
Boie methodology is employed to provide this assurance.
3.2.2 The Boie Estimation of the Heating Value of Waste
To determine the theoretical synthesis gas production, the method by A.
Mountouris was originally employed. However, because Mountouris’ work focuses
mainly upon an analyzed waste stream (the heating value of the particular input waste
stream was empirically derived in a laboratory environment) another method of determining the calorific value of the variable waste stream function used in this optimization
was required.
Schuster, Loffler, Weigl and Hofbauer were presented with a similar
problem in understanding biomass steam gasification. The answer in their research was
27
the Boie relationship. The Boie relationship is an empirical derivation developed in
1953 to estimate of the lower heating value of carbonaceous compounds. Though other
relationships exist, such as the Dulong equation, the Grummel and Davis relationship,
and the Mott and Spencer methodology, Boie is applicable in oxygenated and moist
environments. It also takes into account the significant presence of nitrogen and sulfur.
The presence of these constituents is important in this analysis as the gasification process
from the plasma torch is in a natural air furnace to reduce the cost of the plasma furnace
and to reduce the complexity of operation.19 The accounting for dry ash is also important
as the ash in the process is also vitrified in the slag produced from the plasma process.
The Boie relationship is generally applied to fuel oils, coal, and younger fuels
such as biomass. Siegle, et al., vetted the Boie relationship in research presented by
determining the heating value of biomass using a bomb calorimeter and by performing
the ultimate analysis using Boie’s formula (22). His work showed that Boie’s method
employed in an ultimate analysis produces sufficiently precise determination of the
lower heating value of biomass which is, on an average basis, 2.5% of the empirically
determined upper heating value.
Without laboratory testing, the works of Mountouris and Boie allow for the understanding of the applicability of this method to the amalgamated municipal solid waste
stream. To gain confidence in this method, the constituents of the waste stream must
first be compared to that of the
19
While an atmospheric environment of the plasma furnace promotes inexpensive
facilities and allows for the simplicity of operation, it is noted that the facility will
generate more ash and require more frequent maintenance. The useful life of the plasma
torch is also reduced due to oxygenated erosion of the electrode.
28
3.2.3 Municipal Solid Waste Constituents
3.2.4 Constituents and Products Analysis
3.2.5 Synthesis Gas Production
3.3 SynGas Conversion
3.3.1.1 Theoretical Energy Production
3.3.1.2 Gas Conversion
3.3.2 Gas Turbine SynGas Analysis
3.3.2.1 Theoretical Energy Production
3.3.2.2 Combustion Byproduct Analysis
3.3.2.3 Gas Turbine Cycle Analysis
3.3.2.4 Turbine Cycle Optimization
3.4 Waste Heat Recovery
3.4.1 Process Heat
3.4.1.1 Gas Turbine Pre-heat
3.4.1.2 Fuel Cell Pre-heat
3.4.2 Community Heat
3.4.2.1 Output
3.4.2.2 Delivery System
3.5 System Design
3.6 Community Layout
3.7 Tenement Analysis
3.8 Suburban Analysis
29
3.9 Waste Delivery System
3.10 Community/Urban Planning
3.11 Exergy Analysis
3.12 Traditional Community Analysis
3.12.1 Waste Delivery System Analysis
3.12.1.1
Energy Consumption
3.12.1.2
Carbon Production
3.12.2 Landfill System Analysis
3.12.2.1
Energy Consumption
3.12.2.2
Carbon Production
3.12.3 Inadvertent Hazardous Waste Production
3.12.4 Community Energy Consumption
3.12.5 Waste Collection and Conversion Exergy Analysis
3.13 Plasma Conversion Community Analysis
3.13.1 Waste Delivery System Analysis
3.13.1.1
Energy Consumption
3.13.1.2
Carbon Production
3.13.2 Plasma Waste Conversion Analysis
3.13.2.1
Energy Consumption
3.13.2.2
Energy Production
3.13.3 Waste Carbon Production
3.13.4 Inadvertent Hazardous Waste Production
30
3.13.5 Waste Collection and Conversion Exergy Analysis
31
4. Results and Discussion
32
5. Conclusions
33
6. References
1. Wilson, Dominic and Dragusanu, Raluca. The Expanding Middle: The Exploding
World Middle Class and Falling Global Inequality. Goldman Sachs Economics
Research Group. New York : Goldman Sachs, 2008.
2. Krugman, Paul R. and Obstfeld, Maurice. International Economics - Theory &
Policy. Boston : Addison Wesley, 2009. HF1359.K78 2009.
3. U.S. Energy Information Administration. International Energy Outlook 2010.
Office of Integrated Analysis and Forecasting, United States Department of
Energy. Washington, DC : U.S. Energy Information Administration (EIA), 2010.
DOE/EIA-0484(2010).
4. International Energy Agnecy. World Energy Outlook 2009 Fact Sheet. Paris :
International Energy Agency, 2009.
5. United States Environmental Protection Agency. Municipal Solid Waste in The
United States: 2001 Facts and Figures. Office of Solid Waste and Emergency
Response (5305W). Washington, D.C. : United States Environmental Protection
Agency, 2003.
6. Bogner, J., et al., et al. Waste Management, In Climate Change 2007: Mitigation.
Contribution of Working Group III to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change. Cambridge : Cambridge University
Press, 2007.
7. Environment Directorate. OECD Environmental Data: Compendium 2006-2008 -Waste. Environmental Performance and Infomration Division OECD. Paris :
Organization for Economic Cooperation and Development, 2008.
8. Tchobanoglous, George, Ph.D. Solid Waste Management. [book auth.] Joseph A.
Salvato, Nelson L. Nemerow and Franklin J. Argardy. Environmental
Engineering. Hoboken, New Jersey : John Wiley & Sons, Inc., 2003.
9. Cannon, James S. Greening Garbage Trucks: Trends in Alternative Fuel Use, 20022005. New York : Inform, Inc., 2006.
10. U.S. Energy Information Administration. State Electricity Profiles 2009.
Washington, D.C. : U.S. Department of Energy--Energy Information
Administration, 2011. DOE/EIA-0348(01)/02.
11. United States Environmental Protection Agency. Municipal Solid Waste
Generation, Recycling, and Disposal in the United States: Facts and Figures for
2008. Washington, D.C. : United States Environmental Protection Agency, 2009.
EPA-530-F-009-021.
34
12. Fitzpatrick, Richard. The Physics of Plasma. Austin : University of Texas at
Austin, 2008. pp. 6-10.
13. Gasification of municipal solid waste in the Plasma Gasification Melting process.
Zhang, Qinglin, et al., et al. 2011, Applied Energy, p. 7.
14. Higman, Christopher and van der Burgt, Maarten. Gasification. Burlington :
Elsevier Science, 2003.
15. Schecter, Arnold. Dioxins and Health. New York : Plenum Press, 1994.
16. Quapp, William J. General Description of the Plasma Enhanced Melter. Richland :
Integrated Environmental Technologies, LLC, 2002. p. 19.
17. Noyes, Robert. Unit Operations in Environmental Engineering. Norwich : William
Andrew Publishing, 1994.
18. Moustakas, D., et al., et al. Demonstration Plasma Gasification/Vitrification System
for Effective Hazardous Waste Treatment. Journal of Hazardous Materials. 123,
2005, Vol. B, 038.
19.
Westinghouse Plasma Coal Gasification and Vitrification Technology.
Westinghouse Plasma Corporation. Hersey : Westinghouse Plasma
Corporation, 2002. Power Generation Conference. pp. 17-18.
20. U.S. Environmental Protection Agency. Waste Reduction Model (WARM) Version
12. [Software Documentation] Washington, D.C. : s.n., 2012.
21. Kutz, Myer. Environmentally Conscious Materials Handling. Hoboken : John
Wiley & Sons, Inc., 2009. ISBN 978-0-470-17070-0.
22. Siegle, Volker, Spliethoff, Hartmut and Hein, Klaus R.G. Characterization and
Preparation of Biomass for Co-Combustion with Coal. Dallas : American
Chemistry Societly, 1998.
23. The World Bank. World dataBank--World Development Indicators (WDI) &
Global Development Finance (GDF). The World Bank--World Databank.
[Online] 2011. [Cited: 02 19, 2011.] http://data.worldbank.org/topic/energy-andmining.
24. Yaws, Carl L. Chemical Properties Handbook. New York : McGraw-Hill, 1999.
25. International Data Base - Region Summary - U.S. Census Bureau. International
Data Base (IDB). [Online] December 28, 2010. [Cited: January 30, 2011.]
http://www.census.gov/ipc/www/idb/region.php.
35
26. Scheuerman, William. Globalization. Stanford Encyclopedia of Philosophy (Spring
2011
Edition).
[Online]
2011.
http://plato.stanford.edu/archives/spr2011/entries/globalization/.
27. Burnley, S. J. The Use of Chemical Composition Data in Wast Management
Planning - A Case Study. Waste Management. May 2, 2006, pp. 327-336.
28. United States Census Bureau. International Programs Total Midyear Population for
the World: 1950 - 2050. U.S. Census Bureau - International Programs . [Online]
June
27,
2011.
[Cited:
September
6,
2011.]
http://www.census.gov/population/international/data/idb/worldpoptotal.php. IDB
Version: Data:11.0620 Code:11.0615.
29. United States Department of Transportation; Research and Innovative
Technology Administration: Bureau of Transportation Statistics. National
Transportation Statistics. Washington, DC : Research and Innovative
Technology Administration (RITA): U.S. Department of Transportation (US
DOT), 2012.
36
7. Appendices
7.1 Defining the unsustainable growth of the worldwide
middle class
In determining the need for a waste-to-energy solution, research was conducted
concerning the world’s electrical energy consumption, the world’s waste production, and
the rate of growth presented by each. These were then contrasted with the world’s
capability to produce sufficient energy or consume sufficient waste with the rate of
growth projected.
7.1.1 Worldwide middle class population rise
Invaluable sources of data were revealed in this research. The economic report by
Goldman Sachs entitled “The Expanding Middle” (1) provided a reasonable basis from
which to base the research. In this report Dominic Wilson and Raluca Dragusanu
document two transformative and related trends: power in spending is shifting from the
richest nations to those of predominately middle income, and the purchasing power of
people of a middle class income is overtaking the purchasing trends of the very rich due
primarily to the explosive growth of the middle class population segment.
For their study, Wilson and Dragusanu relate the middle class in the economic
Figure 7-1: Excerpt from Goldman Sachs report on the expanding middle class showing a pareto of the
per capita income in 2007 and comparing it to the world projection in 2050. The chart on the right shows
a swell of middle class income, particularly in the nations known as the BRIC’s.
37
terms of purchasing power parity to settle differences in currency valuations and purchasing power (2). In the terms of the United States Dollar, Wilson and Dragusanu
deem the middle class population of the world to earn between $6,000 and $30,000,
roughly equivalent to the median incomes of the OECD nations (1). It was in reviewing
the wage range of the middle class to per capita income projections that the burgeoning
growth of the purchasing power of the middle class became evident, especially among
Brazil, Russia, India, and China, and other developing nations—a rapidly growing
grouping of countries known in economics by the acronym BRIC, as shown in Figure
7-1. Using the Goldman Sachs expanding middle class data and correlating it with the
United States Census Bureau projections on world population growth show the signifi-
Table 7-1:The growth of the world middle class compared to the growth of the world
population: a compilation of data from the Goldman Sachs* (15) and the U.S. Census
Bureau** (16).
Year
1960
1968
1972
1980
1990
2000
2004
2008
2010
2020
2030
World Population**
3,042,445,344
3,562,353,760
3,867,338,018
4,452,942,594
5,289,040,477
6,089,648,784
6,393,741,245
6,700,983,106
6,852,472,823
7,592,888,345
8,248,535,284
World Population at
Middle Class Lev el*
500,000,000
750,000,000
800,000,000
1,000,000,000
1,010,000,000
1,100,000,000
1,350,000,000
1,550,000,000
1,800,000,000
2,750,000,000
3,600,000,000
World Population
w ithin Middle Class
Status
16%
21%
21%
22%
19%
18%
21%
23%
26%
36%
44%
cance of the middle class, the staggering growth of this power population segment is
apparent in Error! Reference source not found..
When comparing the worldwide growth of the middle class population (Figure 7-2)
an interesting trend is visible. Between the years 2004 to 2008, a significant increase is
seen in the growth rate of the worldwide middle class, with no correlating growth rate
increase in the world population projections. The growth rate of the middle class is even
seen to be similar to the growth rate of the world population for the years between 2010
and 2030.
38
Figure 7-2: World population growth showing the growth of the middle class. Data sources: Goldman
Sachs* (1) and the United States Census Bureau** (27).
7.1.2 Middle class electrical power consumption
It may be assumed that with the increasing middle class population comes an increased electrical power demand. To test this claim, aggregated data from The World
Bank World Databank of Energy Consumption (22) and projections of energy usage
from the United States Energy Information Administration International Energy Outlook
(3) were combined and correlated to the worldwide population and worldwide middle
class projections from the U.S. Census Bureau and the Wilson and Dragusanu report on
the “Expanding Middle” for the correlating years. Upon visual inspection of the compilation of this data, the trend of the increasing rate of energy consumption matches the
rate of worldwide middle class expansion, even to the same period of its upswing, as
shown in Error! Reference source not found.. As the data in worldwide electricity
consumption arrives from two different sources and show parity for overlapping years,
the existence of a trend is more evident, and this trend is interrogated further by linearly
39
Figure 7-4: World electrical energy consumption on the basis of the world population. This chart
shows correlation to Figure 6.2, where the increase in the world wide middle class correlates to the
growth of the world projections of energy consumption.
correlating the projection of the worldwide electricity production to the prediction of the
worldwide middle class population between the years 2010 to 2030.
This analysis is a major tenet to the claim of Figure 1-2 in that it relates the key influencing factor in future electrical demand being a growing global class of people of
Figure 7-3: The projected world electricity consumption against the projected middle class population
growth showing close linear correlation between the global middle class and power consumption.
40
middle income. From the same analysis presented in Figure 1-2, it may be argued that
there is no actual correlation to the growth of the middle class and global electrical
power consumption. Refuting this argument is the Wilson and Dragusanu report by
Goldman Sachs indicating that the size and thus purchasing power parity of the global
middle class prior to the year 2004 was such that even large swings in middle class
consumption had a small influence on key global indicators, but the recent and explosive
expansion of this population group is shifting the balance of economic power to the
global middle class. One need only review Error! Reference source not found. to see
that by 2010, more than 25% of the world’s population exists at the middle class level, a
trend that grows to 46% only twenty years later.
The question still remains, “can the world support such growing demand for electrical power?” Because the natural resources exist to sustain such growth20, the answer is
largely economic (3). The International Energy Agency (IEA) states that an additional
4,800 gigawatts of electrical power will be needed to support the demand in the year
2030 at the cost of 35 billion dollars per year if capital investments were to have started
in 2008. This is no small investment, and the current rate of infrastructure growth and
improvements worldwide will still leave 1.3 billion people without electrical power in
2030 (4).
7.1.3 Middle class waste production
Applying the law of conservation to the macrocosm of the global middle class
indicates that with increased consumption comes increased waste. The data to support
such an argument however is mired in uncertainty. In fact, Jean Bogner’s environmental
waste management research team concluded
“The availability and quality of annual data are major problems for the
waste sector. Solid waste and wastewater data are lacking for many coun“The world’s energy resources are adequate to meet the projected demand increase
through to 2030 and well beyond. But these Reference Scenario trends have profound
implications for environmental protection, energy security and economic development.
The continuation of current trends would have dire consequences for climate change.
They would also exacerbate ambient air quality concerns, thus causing serious public
health and environmental effects, particularly in developing countries.” (4)
41
20
tries, data quality is variable, definitions are not uniform, and interannual
variability is often not well quantified.” (6)
The team did continue on to describe industry accepted methodologies for determining waste output and understanding trends.
These methodologies (the use of
internationally collected survey data and statistics, estimates on the basis of population
dynamics, and the use of demographic and economic indicators) are also employed in
this research.
Bogner’s team provides the first insight towards a potential link between the
growing worldwide middle class and the waste generation rates. In Figure 7-5, a signifi-
Figure 7-5: IPCC unrecycled waste generation data showing minimum annual rates of carbon storage in
landfills from 1971 to 2002. (6)
cant trend is notable: throughout the time scale, the rate of waste generation in Latin
America, South East Asia, North and Sub-Saharan Africa and the Middle East are
significantly higher than the countries in the developed world. Possibly of greater
interest is the step change in waste production in 1994, with a steadily growing trend
thereafter. This trend appears to roughly relate with the same period as the rise of the
middle class and the previously noted changes in electrical generation. Further illustrating this trend, Bogner relates the waste generation rates graphically, reproduced in
Figure 7-7. Visually coinciding with the growing middle class is the waste characteristic
in the BRIC nations.
42
Providing an objective measure to this waste trend is of the most interest in the argument that waste projections increase dependent upon the increase in the middle class
population.
To this end, environmental data from the Organization for Economic
Cooperation and Development is employed—a
convenient
relational
source of data, as Wilson
and Dragusanu related the
OECD nations as the
upper bound of the global
middle class (1).
OECD
The
Environmental
Data Compendium Report
Figure 7-6: OECD waste generation in kg/capita/year for the period
between 1980 and 2005. As all OECD countries are represented in the
legend, only several are listed. (7)
of 2006-2008 provides
un-recycled
municipal
solid waste data for the
participating nations from 1980 to 2005 in two useful forms: on a total (aggregate) basis,
and on a per capita basis. The data shows for the period that the rate of waste generation
was large in the 1990’s, but tapered significantly—and actually declined—from the year
2000 to the year 2005, as depicted in Figure 7-6. Understanding that most of the participating countries are considered developed nations with middle-class majorities provides
Figure 7-7: IPCC graphical representation of post-consumer waste generation between 1971 and 2002.
(6)
43
some insight to this trend.
The United States Environmental Protection Agency documents that efforts in
awareness, governmental regulation, and improved recycling solutions have resulted in a
decline in the per capita waste generation rate (11). This point is further illustrated in
Figure 7-8, which may indicate that waste generation rates may have peaked at 4.65
pounds of waste per person per day. The timing of this occurring also corresponds to the
Figure 7-8: U.S. EPA data showing municipal solid waste generation of the United States
between 1960 and 2008 (in million tons). (11)
OECD countries waste generation rates as described in Figure 7-6. The U.S. EPA data
also gives insight as to the reason for this decrease in waste generation, as depicted in
Figure 7-9 where recycling is shown to have achieved rates of 33% of the generated
waste stream. Showing that the relation amongst the OECD and U.S. EPA findings are
more than anecdotal is Error! Reference source not found.. This relation demonstrates, though the magnitude of the generated waste estimate is underestimated by the
OECD, the general trend of increasing waste production rate to the eventual leveling of
44
the rate of production from 1980 to 2005 is essentially the same. The difference in the
data being a scalar is within 1%, showing high correlation despite the offset21.
It is the leveling off of the waste generation rate that forms the basis of an important
assumption in the sustainability analysis for waste production. Based on the trends
noted in both the OECD data and the U.S. EPA data, which the amount of waste produced by predominantly middle class developed nations is curbed by recycling and
government enforced regulation, the assumption is formed that the production of waste
in a developed nation is asymptotic to a constant. Otherwise stated, there may exist a
natural limit to the amount of waste generated per middle class person per day. Conservatively, a constant22 (assuming that the United States represents the highest extreme of
the global middle class) given by the OECD rate of waste generation from 2004 to 2010
Figure 7-9: U.S. EPA data showing municipal solid waste recycling (in million tons). (11)
21
The offset may be due to a variety of factors as mentioned in the assumptions of waste
generation rates and differences in definitions (11) (7).
22
The conservatism in assuming the waste generation rates as a constant is due to the
factors that contribute to the leveling seen in the waste generation data. It is noted that
regulation in the developed countries have helped curb discarded waste and have helped
with the establishment of recycling centers and programs. If a developing nation were
not to institute such regulation or otherwise encourage conservation and recycling, the
rate of waste generation of the global middle class may mimic the waste generation rates
of the developed nations in the years prior to 2000.
45
is used: 3.38 lbs. of municipal solid waste generated per person each day. Because the
rate of waste generated is assumed constant for the middle class, the projected amount of
waste generation tracks linearly to the growth of the global middle class, depicted in
Figure 7-11. This leads to the staggering number of 2.2 billion tons of waste generated
per annum by the year 2030.
Otherwise accounted, Tchobanoglous’ relationship of
roughly 500 lbs. of municipal solid waste per cubic yard23 (8) gives 8.9 billion cubic
yards of waste or, distributing that evenly to a depth of three feet, enough to bury New
York City in only six months.
Again, the question remains as to whether this amount of waste generation is sustainable. The answer on the basis of available land on a worldwide basis is yes.
However, the definitive answer may be largely economic and political, as the environmentally sound most preferred method of waste management, landfilling, is expensive
and, in every locale, publicly undesirable.
Figure 7-10: United States waste generation as determined independently
by the United States EPA (11) and the OECD (7).
23
Estimate based upon the average mass to volume relationship for as received waste at
a landfill from a waste compactor truck.
46
Figure 7-11: Waste generation as a function of the population of the world wide middle class. This
figure is analytically generated based upon data and projections from the U.S. EPA (11), the OECD
(7), and Goldman Sachs (1). See also Figure 1-3.
47
7.2 Plasma Gasification Reaction Program
The program used to predict the plasma gasification reaction (including tailoring
the waste stream and estimating the synthesis gas output) is documented here. The code
is written for Mathematica Version 6.0.1. This program is adapted from the program
developed by A. Mountouris denoted as “GasifEq,” provided courtesy of A. Mountouris
for the purpose of this thesis as a Microsoft Excel spreadsheet with an optimization
macro. The program is inline commented for documentation; however the full methodology of the program and differences from A. Mountouris’ work is defined in Section 3
of this document.
7.3 Source Reduction with Plasma Waste Gasification
It is important to address source reduction in the discussion regarding any wasteto-energy method, such as plasma gasification. The conversion of waste into energy
using plasma gasification technology requires waste as an input; however this should not
be seen to conflict with efforts to reduce the sources of waste. Instead, the technology
should be seen as a synergistic means to an end: as long as waste is generated, its benign
disposal and residual energy recovery are necessary. Never should waste be generated
as a means to create electrical power.
High-energy waste is also desirable for plasma gasification. As mentioned in Section Error! Reference source not found., paper, plastics, and any petroleum or oil
based product (e.g. rubbers, latex, and Styrofoam) promotes the production of a higher
energy synthesis gas. However, directly recycling these products is also highly desirable
as the costs and materials (as well as the energy) to regenerate products from these forms
are high. If plasma gasification of waste is pursued in mass, it cannot be at the expense
of plant matter (paper based) and petroleum (oil based) products because the recycled
material reclaimed in plasma gasification is energy, not material. Since the basic input
materials are not being recycled, source reduction is of significant importance. Means of
reducing the amount of paper and petroleum based products consumed is still fundamental in a comprehensive sustainability model.
48