EPA/530/SW-130
MARKETS AND TECHNOLOGY
FOR RECOVERING ENERGY FROM SOLID WASTE
U.S. ENVIRONMENTAL PROTECTION AGENCY
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MARKETS AND TECHNOLOGY
FOR RECOVERING ENERGY FROM SOLID WASTE
This publication (SW-130) was written
for the Federal solid waste management programs
by STEVEN J. LEVY
U.S. ENVIRONMENTAL PROTECTION AGENCY
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CONTENTS
INTRODUCTION 1
SOLID, LIQUID, AND GASEOUS FUELS 3
Marketability 3
Potential Market Opportunities 4
Steam electric power plants 5
Industrial operations 5
Systems for Producing Fuels from Solid Waste 6
Prepared solid waste as a supplemental fuel 6
Pyrolysis 9
Oil pyrolysis 9
Gas Pyrolysis 9
Methane production 12
STEAM AND ELECTRICITY 13
Marketab i1i ty of Steam 13
Market Opportunities for Steam 15
District heating for steam 15
Industrial plants 17
Steam electric power plants 17
Systems for Producing Steam 18
Waste heat boilers 18
Waterwall incinerators 20
Refuse-fired support boilers 20
Markets for Electricity 20
Systems for Producing Electricity 21
ANALYSIS AND CONCLUSIONS 21
Comparison of Market Opportunities 23
Comparison of Energy Forms 23
Comparison of Technological Alternatives 2k
Selecting an Alternative 25
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APPENDIX - DEMAND FOR CONVENTIONAL SOURCES OF ENERGY 27
Coal 27
Oil 27
Gas 27
Electrical Generation 27
REFERENCES 30
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Markets and Technology for Recovering Energy from Solid Waste
In J973, energy consumption in the United States grew by 4.8
percent, and experts predicted that energy demand would double between
1970 and 1990. This increasing consumption and the announced goal of
achieving independence from foreign energy supplies have created pressures
to find new fuel sources.
Municipal solid waste is one raw material currently being discarded
that can be "mined" for its energy content. In the United States in
1971, 125 million tons of solid waste from residential and commercial
sources were discarded with no attempt to recover energy.3 Since solid
waste has a heat value of approximately 9 million Btu per ton, this
represents some 1,100 trillion Btu per year, the energy equivalent of
500,000 barrels of oil per day. Of course, not all of this solid waste
would be available for recovery, but some 75 percent of it is concentrated
in major metropolitan areas, where processing plants could be large
enough to be economically feasible. Industrial, agricultural, and
forestry wastes represent the equivalent of an additional 2 million
barrels of oil per day,5 although collection and transportation problems
may restrict their use.
Many different approaches to recovering the energy value of refuse
are presently being examined. Waterwall incinerators are currently
generating steam in a number of U.S. cities. A new waterwall incinera-
tor will be completed in Nashville, Tennessee in mid-197i». In Baltimore,
Maryland, a pyrolysis system that will generate steam is nearing comple-
tion. St. Louis is currently demonstrating a system that uses the
shredded, combustible portion of solid waste as a coal substitute in a
utility boiler. Many communities are considering similar systems and
extension of the concept of oil-fired boilers, as well as use of wet-
pulped and/or pelletized solid waste as a fuel. Pyrolysis systems are
being developed to convert solid waste into liquid and gaseous fuels.
Two of the most promising of these systems are the Garrett Research and
Development County's system for producing oil, which is being demon-
strated in San Diego County, California, and Union Carbide's system for
producing a gaseous fuel, which is being tested by that company at its
plant in South Charleston, West Virginia. The recovery of methane from
landfilled solid waste is being practiced in a pilot plant in Los
Angeles. Electrical power generation is being explored in a research
project conducted by the Combustion Power Company with support from the
U.S. Environmental Protection Agency. The demonstration projects in
Baltimore, St. Louis, and San Diego are also EPA-supported.
These technologies enable solid waste to be converted into a
number of different energy forms, including gaseous, liquid, and solid
fuels as well as steam and electricity. The energy recovery system
that should be employed in any particularly community depends upon the
market for the output product.
2, Tables C and E.
\- P- 3-
", p. II.
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The value of a solid waste energy product should be equivalent,
on the basis of heat produced to the value of the fuel which it replaces,
less .any additional costs incurred in its use. The current fuel crisis
has significantly increased the value of these products and reduced
the need to provide special incentives to enhance their marketability.
To be marketable, though, the solid waste energy products must
have qualities acceptable to the user. Steam and electricity produced
from solid waste are equivalent to those products from other sources,
but fuels produced from solid wastes are physically and chemically
different from their fossil fuel counterparts. Characteristics such as
ash content, heat value, corrosiveness, viscosity, and moisture content
have to be acceptable to the user. For all energy products derived
from solid waste, such factors as reliability, quantity, and availability
are also important.
This paper reviews the characteristics of the major energy products
recoverable from solid waste, the marketability of these products, the
potential markets, and the status of the technology for recovery. The
first section considers the f uel s--sol id, liquid, and gaseous — that can
be created out of solid waste. The second section examines steam and
electricity, two other forms in which the energy from solid waste can
be sold. In the final section, the various systems and energy products
are compared.
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SOLID, LIQUID, AND GASEOUS FUELS FROM SOLID WASTE
Solid, liquid, and gaseous fuels can be producted from solid waste
using a number of systems currently under development. These fuels can
be used as a supplement to their fossil fuel counterparts: coal,
petroleum, and natural gas. (The characteristics and uses of the
fossil fuels are discussed in the Appendix.)
Marketabi1ity
Fuels derived from municipal solid waste will have physical and
chemical properties different from those of conventional fuels and,
therefore, will have different handling and combustion characteristics.
In order to analyze the potential markets for the solid waste fuels,
it is necessary to identify their characteristics and evaluate the
constraints they will place on using the fuel products.
There are a number of general characteristics that determine the
marketability of fuels derived from solid waste whether they are solid,
liquid, or gaseous. These include:
Quantity of fuel produced. Enough of the product must be available
to justify any expenses that the user will incur in modifying his
facility to accept this new fuel source.
Heating value. The heat value of each fuel must be high enough to
minimize the effect of the fuel on boiler or furnace efficiency.
Also the costs of transporting, storing and handling the fuel go up
as the heat value goes down since a greater quantity of fuel has to
be handled in order to obtain the same amount of energy.
Reliabi1ity. A high degree of reliability in the supply of the
fuel increases its value because the user does not need to maintain
standby equipment or fuel.
Quali ty. The better the product, in terms of handling, stability,
aesthetics, etc., the more it is worth because the customer's cost
to use the product is reduced.
Solid fuels derived from solid waste are currently being used as a
supplement to coal in suspension-fired utility boilers. They are also
being considered for use in conjunction with oil-fired units and as a
fuel supplement in cement kilns. Some factors that influence the
marketability of these solid fuels are:
Particle size. Particles must be small enough to permit complete
combustion when burned in suspension. This size will vary with the
type of unit used to burn the fuel. Small particle size particu-
larly important if there are no burnout grates at the base of the
combustion chamber.
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Residue content. Residue should be kept to a minimum in order to
prevent errosion of the furnace walls and the fuel firing system.
Also high amounts of residue can overload the ash removal system
and may restrict the value of the coal ash.
Moisture content. Moisture content will affect the heat value of
the fuel. If it is high enough it will reduce the combustion
efficiency of the unit.
The Garrett Research and Development Company pyrolysis system is
producing a heavy, oil-like liquid fuel from solid waste. This liquid
fuel can be used as a supplement to No. 6 fuel oil in large industrial
or utility boilers. Factors which will influence its marketability
include:
Viscosity. If viscosity is too high the costs of storing and
pumping can be excessive. High viscosity can also cause plugging
of fuel 1ines.
Volumetric heating value. The volumetric heat value (Btu per
gal Ion) influences the cost of transporting and storing the fuel.
Chemical stabi1ity. If the fuel undergoes chemical change, this
will restrict the length of time it can be stored.
Special handling problems. The need to maintain separate storage
and firing systems for the solid waste fuel, and to purge the
firing systems after the fuel has been burned, places an extra
burden on the user which may minish its value.
Most gaseous fuels produced from solid waste have a lower heating
value than natural gas because they contain significant quantities of
carbon dioxide and, in some systems, nitrogen. The distance they can be
transported is limited by the cost of compressing and pumping the gas.
As the Btu value goes down this cost becomes prohibitive.
Potential Market Opportunities
Most markets for solid waste fuels would be large utility or industrial
users who could blend 20 to 30 percent of solid waste fuel with conven-
tional fuels and still use sufficient quantities of the solid waste
fuels to justify the costs of special storage and firing facilities.
Steam electric power plants because of their large fuel needs and pro-
ximity to urban areas, represent an attractive market opportunity for
solid waste fuels. Major industrial operations (such as cement plants,
steel mills, and paper mills) and central heating/cooling plants also
represent potential market outlets.
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Steam Electric Power Plants
Electric utilities operating steam electric plants fired by fossil
fuels are the most promising market for solid waste fuels for several
reasons: they use very large quantities of fuel; electricity demand
is influenced by the same factors that influence solid waste generation--
population and industrial and commercial activity; and the utility's
generating plants are often located in close proximity to the urban area
where the solid waste is generated. Also the quasi-public structure of
the electric utility tends to make it more conscious of community prob-
lems and more receptive to accepting the costs and risks associated with
using these fuels.
Economic gain is the overriding factor influencing a utility's
decision to use solid waste fuels. Although savings from using solid
waste fuels can amount to only a small fraction of the utility's total
fuel costs, other indirect economic gains can be realized through
improved community relationships, if local governments build incentives
into this means of waste disposal. For instance, a utility may gain
approval of a new power plant site more easily if it is part of a solid
waste/energy recovery program.
Savings in the cost of a solid waste fuel would be effectively
passed on to the utility's customers, since most rate structures include
automatic adjustments to reflect changes in the cost of fuel.
Industrial Operations
Many industrial operations are ideal markets for fuel produced from
solid waste. Fuel from several hundred tons of solid waste or more a
day could be readily utilized in all but the smallest cement plants,
papermills, and steelmills, for example.
A typical paperboard mill uses about 25,000 pounds of steam to
produce 1 ton of boxboard.6 A small plant producing 360 tons of box-
board per day would require 400,000 pounds of steam per hour, the equiva-
lent yield of 1,200 tons of solid waste per day.
Most papermills currently burn their own bark and wood waste in
boilers as a supplement to conventional fuels. Although this might
reduce somewhat the capacity of this market for solid waste fuels, it
should ease the marketing task because the industry is already accustomed
to burning waste fuels.
Feasibility studies are currently being done to examine the possi-
bility of using solid waste as a fuel in cement manufacturing kilns.'
The solid waste would supplement the coal or other fuel being used, and
any ash remaining would be incorporated into the final product. Cement
kilns require about 8 million Btu of fuel per ton of cement produced.
P.27-K
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Plants range in capacity from 1,000 to 3,000 tons or more per day.
Therefore, using refuse as 20 percent of the fuel load, even a small
plant could handle the fuel produced from AOO tons of solid waste per
day.
Systems for Producing Fuels From Solid Waste
The technology for converting solid waste into fuel is very new and
is developing rapidly. All of the systems under consideration today
were conceived since 1968. Nevertheless, several full-scale demonstra-
tion projects are presently in operation and others soon will be.
Furthermore, many communities are proceeding to implement full-scale
systems on the basis of these demonstrations.
Prepared solid waste as a supplemental fuel. The city of St.
Louis, with demonstration grant assistance from EPA is producing a dry,
shredded solid waste fuel which is used to supplement pulverized coal in
an existing Union Electric Company suspension-fired boiler. Solid
waste fuel provides 10 percent of the energy used in the boiler. At
this rate, the 125-megawatt boiler is capable of burning 350 tons of
prepared solid waste fuel per day. The project engineers are under-
taking experiments to increase the solid waste fuel to 20 percent of the
boiler feed.
The process is divided into two distinct operations--preparation
and firing. A fuel transportation system is also required in St. Louis
because the fuel is prepared 18 miles from the power plant. At the
processing plant municipally collected solid waste is shredded in a
horizontal hammermill and fed into an air classifier which separates the
material into heavy (dense) and light fractions. The heavy fraction is
passed over a magnetic belt to remove ferrous metals. The light, mostly
combustible material is stored temporarily in a bin and is then transferred
to 75-cubic-yard transfer trailers for the trip to the power plant
(Figure 1). At the power plant the prepared fuel is transferred to a
smaller bin from which it can be pneumatically blown into the boiler
(Figure 2).
Similar systems are already being implemented in several other
communities, even though the concept is still being tested. The Union
Electric Company has announced a 70-mi11ion-dollar program to expand its
demonstration operation to serve the entire metropolitan St. Louis
area.y In Ames, Iowa, a prepared fuel will be used in a municipally
owned power plant, u and in Chicago it will be used by the Commonwealth
Edison Company.11 In East Bridgewater, Massachusetts, Combustion
Equipment Associated is preparing a solid waste fuel for use by the
Weyerhaeuser Company J2
Other studies are investigating other possibilities for solid fuel •
using it as a supplemental fuel in oil-fired boilers; preparing it bv a'.
wet-pulping method developed by the Black-Clawson Company; and pelletiz-
mg it for use in grate-fired boilers.
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PROCESSING PLANT FOR SOLID WASTE, ST. LOUIS PROJECT
AIR CLASSIFIER
Cyclone separator
STORAGE AND TRANSPORTATION
HAMMERMILL
Packer truck
RAW REFUSE DELIVERY
Nonmagnetic metals, glass, and waste
to further separation or to landfill
Ferrous metals hauled to steel mill
FERROUS METAL RECOVERY SYSTEM
Figure 1. In the system being demonstrated by Union Electric Company in St. Louis, fuel and ferrous metal are recovered from municipal
solid waste that has been shredded and air classified.
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POWER PLANT USING SOLID WASTE FUEL, ST. LOUIS PROJECT
UNLOADING OPERATION
Receiving bin
Trailer truck f
FIRING SYSTEM
Tangentially-fired boiler
oo
Figure 2. In the St. Louis project, the shredded solid waste fuel is delivered to the power plant,
where it is fired pneumatically into boilers as a supplement to coal.
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Pyrolysis. Pyrolysis is the thermal decomposition of materials in
the absence or near absence of oxygen. The high temperature and the
"starved air" situation cause a breakdown of the materials into three
parts: (1) a gas consisting primarily of hydrogen, methane, and carbon
monoxide; (2) a liquid fuel that includes organic chemicals such as
acetic acid, acetone, and methanol; (3) a char consisting of almost pure
carbon, plus any glass, metal, or rock that may have been processed.
The design of the individual system controls which of these outputs will
be the predominant product. '•* Two systems currently under development
show promise of producing fuels of sufficient quality and yield to be
marketable. The Garrett Research and Development Company's "Flash
Pyrolysis" system which is undergoing EPA demonstration in San Diego County,
California will produce a liquid fuel. A gaseous fuel will be pro-
duced in a Union Carbide System that the company is testing in South
Charleston, West Virginia.15
Oil Pyrolysis. The demonstration plant for "Flash Pyrolysis" will
produce an oil-like liquid which will be used by the San Diego Gas and
Electric Company as a supplemental fuel in an existing oil-fired boiler.
This fuel, which is produced at the rate of 1 barrel per ton of solid
waste, has a heating value of about 9^,000 Btu per gallon. This is
about 65 percent of the heating value of No. 6 fuel oil, on a volumetric
basis. This oil has a higher moisture content and a higher viscosity
than No. 6 oil.
The Garrett process consists of a complex preparation system
followed by a relatively simple pyrolysis reaction (Figure 3). To
prepare the solid waste for the reactor it must first be shredded. An
air classifier than separates out a light combustible fraction which,
after being dried, is shredded again, this time to a particle size of
one-sixteenth of an inch. This material, now resembling the material
caught in a vacuum cleaner bag, is then introduced into the reactor,
where it is mixed with hot glowing char in an inert atmosphere. The
material is pyrolyized in less than a second, at a temperature of 900F.
The resulting gas is condensed to recover the oil. The process char is
recirculated as the energy source to pyrolyze the incoming material.
Gas Pyrolysis. The Linde Division of the Union Carbide Corporation
is building a 200-ton-per-day test facility to generate a gaseous fuel
product.
The key element of the system is a vertical shaft furnace (Figure
A). Refuse is fed into the top of the furnace. Oxygen entering at the
base of the furnace reacts with the char that is one of the end products
ultimately formed from the refuse. This reaction generates a tempera-
ture high enough to melt and fuse the ash, metal, and glass; this molten
material drains continuously into a water-filled tank, where it solidi-
fi,es as a hard granular material.
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OIL PYROLYSIS OF SOLID WASTE
PRIMARY
SHREDDER
AIR
CLASSIFIER
SECONDARY
SHREDDER
FROTH
FLOATATION
FINE SHRED
PYROLYSIS
REACTOR
MAGNETIC
RECOVERY
NONFERROUS
TO STEEL
COMPANY
MIXED COLOR
GLASS
TO GLASS
COMPANY
TO UTILITY
RESIDUALS
PRODUCT
RECOVERY
FUEL OIL
TO LANDFILL
Figure 3. The Garrett process produces an oil-like liquid fuel from solid waste by means of
pyrolysis.
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GAS PYROLYSIS
REFUSE
FEED HOPPER
SEAL—•
FEEDLOCK
SEAL
SHAFT
FURNACE
OXYGEN
COMBUSTION
ZONE
MOLTEN
MATERIAL
WATER QUENCH
FUEL GAS
PRODUCT
GAS CLEANING
SYSTEM
RECYCLE
WASTE WATER
.GRANULAR
RESIDUE
Figure 4. The key element of the Union Carbide pyrolysis process is a vertical shaft furnace.
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The hot gases formed by reaction of the oxygen and char rise up
through the column of refuse and pyrolyze the refuse, transforming it to
gas and char. In the upper portion of the furnace, the hot gas also
dries the incoming refuse. The gases produced from the pyrolyzed refuse
exit the furnace at a temperature of about 200F. This exhaust gas
contains considerable water vapor, some oil mist, and minor amounts of
other undesirable constituents, which are removed in a gas-cleaning
system.
The resultant gas is a clean-burning fuel comparable to natural gas
in combustion characteristics, but with a heating value of about SOO^Btu
per cubic foot which ts 30 percent of the value of natural gas. It is
essentially free of sulphur compounds and nitrogen oxides and burns at
approximately the same temperature as natural gas. This gas can be
substituted for natural gas in an existing facility; the only plant
modification necessary would be to enlarge the burner nozzle so that the
volumetric flow rate could be increased.
One limitation on use of this gas is the cost of compressing it for
storage and shipment. Since a larger quantity of this gas is required
to yield the same amount of energy as natural gas, compression costs per
million Btu will be 3.1 times greater than for natural gas. As a result,
markets for this gas will have to be within 2 miles of the producing
facility and only short-term storage can be contemplated.
Methane Production. When solid waste decomposes in an anaerobic
(oxygen-free) environment, it produces methane and carbon dioxide.
Programs are currently underway to recover the methane that is produced
by the natural decomposition of solid waste in a sanitary landfill^°> '7
and by the accelerated decomposition of solid waste in a mechanical
digester used to digest sewage sludge.
In the sanitary landfill recovery program, a well is drilled
through the fill and lined with perforated pipe. The gases are pumped
out of the fill and the carbon dioxide is removed using membrane filtra-
tion or cryogenic separation techniques. The NRG NuFuel Company is
installing gas recovery systems in landfills operated by the County of
Los Angeles and the City of Phoenix. Both of these sites possess very
specific characteristics which are necessary for the process to be
feasible, and any potential site must be examined to determine whether
this process is practicable there.
The National Science Foundation is currently supporting a research
effort by the Dynatech Corporation to examine the feasibility of com-
bining solid waste with sewage sludge for digestion in a mechanical
digester.'° Pipeline quality gas, with a heat value of 900 Btu per
cubic foot, would be recovered at the rate of 3,700 cubic feet per ton
of waste.
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STEAM AND ELECTRICITY
Steam can be thought of as the medium of transportation in an
energy network, in the sense that chemical energy of the fuel is trans-
ported by the steam as thermal energy to the user, who may convert it to
other forms of energy. Steam can be sold for use in three basic energy
forms: (1) it can be used to transmit heat directly- for example, to
heat buildings in a district heating system; (2) it can be mechanically
converted into electricity by the use of steam turbines, which is what
happens in a steam electric power plant; (3) its mechanical energy can
be used to drive machinery in various industrial processes, or to
operate a condensing unit in a district cooling system. A municipality
may elect to^produce the steam from its solid waste and sell it to a
utility, or it may take the process one step further, converting the
steam to electricity and selling it in that form.
In a steam electric power plant, the furnace is lined with tubes
filled with water. The fuel burned in the furnace releases heat and
converts the water to steam. The steam is then piped to a turbine where
it^gives up its heat energy by driving a generator that produces elec-
tricity. Due to practical limitations on the efficiency with which heat
can be transferred to the steam and can later be extracted from it,
about 10,000 Btu of fuel energy are required to produce one kilowatt-
hour (kwh) of electricity, which is equal to only 3,412 Btu of energy.'9
Steam temperatures generally range from 250F to 1.050F and pressures
range from 150 pounds per square inch (psi) to 3,500 psi. The strength
of the materials used to construct the system places limitations on
temperature and pressure. In electric power plants the greatest effi-
ciency is achieved at the highest temperatures and pressures. In steam
distribution systems, however, temperatures are kept as low as possible
to minimize heat loss in the delivery system, and pressures are kept as
low as possible to reduce the cost of the system and minimize danger
from bursting pipes.
In system that use solid waste as the sole or primary fuel, the
steam is usually produced at 600 psi or less in order to minimize
slagging and corrosion of the boiler tubes. The steam can be further
processed in separate units to bring it to the pressure at which it will
be used.
Marketability of Steam
Unlike fuels derived from solid waste, steam produced from solid
waste is indistinguishable from steam from any other source.
To be marketable this steam must meet the specific needs of the
user. When designing a solid waste disposal/steam recovery system some
factors which must be considered are:
'9, p.IV-19.
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Proximity to Customer. The facility must be close enough to
economically serve the steam market. Steam can be transported only
about 2 miles, and in congested areas expensive pipeline installa-
tion problems may further restrict this distance.
Va 1 ue. The cost at which the steam is delivered must be competi-
tive with the costs of the customers alternate energy sources.
Quantity. The amount of steam supplied must be compatible with the
customer's needs. If peak loadings cannot be supplied entirely by
burning refuse then standby, fuel-fired boilers will be needed.
Operating Schedule. The steam-producing facility must be set up
on an operating basis that satisfies the operating schedule of the
steam customer.
Availability of Refuse. The municipality must insure that it has
enough refuse to meet its steam output commitments.
Steam Quality. The temperature and pressure at which the steam is
produced must be a function of both the optimal performance of the
unit and the limits acceptable to the customer.
Reliabi1ity. The system must include sufficient backup facilities
to meet the level of reliability of supply agreed upon. This may
include contingency plans to burn fossil fuels when the solid waste
unit is out of service. The cost of building and operating these
facilities must be considered in the economic evaluation of the
system.
Excess Steam. The facility must be designed to serve the community's
disposal needs, even if there is an interruption to the steam
market. Condensing units or a backup sanitary landfill may be
necessary.
Timi ng. The steam must be available when it is needed. Unantici-
pated delays in construction of the facility could force a steam
customer to find another source of steam.
Steam can be marketed in two ways: as a guaranteed supply, or as a
limited supply that requires a backup system. In the first case,
the municipality provides a complete and reliable supply, and assumes
the responsibility of providing steam from other sources if there is
an interruption in the production of steam from solid waste. If the
municipality is supplying steam which the customer does not otherwise
have the capability of producing, then the municipality must guarantee
the reliability of the supply. Although the municipality's costs go
up, the value of the steam also goes up, for this steam has a value
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15
equivalent to what the customer would have to spend to produce it
himself. In the second case, the utility buys all of the steam the
municipality produces from solid waste, but the customer carries the
burden of producing additional steam in the event that this supply
is interrupted or is not adequate to meet its demand. In this case,
the value of the steam is lower (it is limited to the value of the
fuel saved by the customer) but the municipality assumes less risk and
respons ibi1ity.
Market Opportunities for Steam
Most metropolitan areas have one or more major outlets for steam.
Yet, despite the fact that proven technology exists for generating steam
from municipal solid waste, constraints on its use have made the market-
ing of steam very difficult.
District Heating and Cooling Systems. There are about 450 commercial
and campus district steam heating systems operating in this country.20
Many of these systems also distribute chilled water for cooling build-
ings during warm weather. A number of cities have steam systems serving
their central business or industrial areas (Table 1). The fuel crisis
has encouraged other cities to consider such systems in an effort to
make more efficient use of limited and increasingly costly fuels.
TABLE 1
SELECTED CITIES WITH DISTRICT HEATING/COOLING SYSTEMS*
Akron, Ohio Hartford, Conn.
Allentown, Pa. Houston, Tex.
Atlanta, Ga. Indianapolis, Ind.
Baltimore, Md. Los Angeles, Calif.
Birmingham, Ala. St. Paul, Minn.
Boston, Mass. Nashville, Tenn.
Cheyenne, Wyo. New York, N.Y.
Cleveland, Ohio Oklahoma City, Okla.
Dayton, Ohio Omaha, Nebr.
Denver, Colo. Philadelphia, Pa.
Detroit, Mich. Pittsburg, Pa.
Eugene, Oreg. San Diego, Calif.
Grand Rapids, Mich. Seattle, Wash.
Harrisburg, Pa. Tulsa. Okla.
International District Heating Association, 1973 Rate Reference Book.
Pittsburg, 1973- 15 P-
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16
In these systems, steam is distributed at a low pressure, generally
in the neighborhood of 250 psi, which can be easily provided by a solid
waste disposal facility. Unlike the demand for electricity, which has
certain peak periods, steam demand is fairly constant throughout the day
and from day to day. Seasonal variations can be significant, but if the
utility also distributes chilled water it can operate its chilling plant
with a steam-driven turbine. In any event, the demand for steam can be
sufficient to accommodate a constant amount of steam produced in an
energy recovery plant during most, if not all, of the year.
Because steam cannot be transported for more than about 2 miles,
the solid waste plant must be located close to the steam users; usually
this will mean in or near the central part of the city. Although land
costs may be higher, solid waste hauling costs will probably be minimized,
because of the proximity of the plant to the waste generators.
When the steam produced in a solid waste disposal facility is sold
to a district heating utility, its value is equivalent to the price the
utility would pay for the fuel needed to produce the steam. However, if
by purchasing this steam, the utility is able to expand its service to
customers whom it previously lacked the capacity to serve, then the
steam would have a higher value equivalent to the utility's own total
cost for producing steam.
In a city where no steam distribution network exists, the munic-
ipality can consider installing a complete solid waste steam-generating
incinerator and a steam distribution network. To minimize the costs,
this might be tied to a major urban renewal project or to the construc-
tion of a large industrial park or complex. Although the municipality
would then be able to sell the steam at a much higher price, it would
also be responsible for a much higher capital investment. Because it
would be the only source of supply for its customers, it would also have
to assume the responsibility for total reliability. A backup system
would be needed to provide steam when the incinerator was out of service
or if there were an interruption in the delivery of refuse to the
faci1ity.
Two systems currently under construction will produce steam for
utility distribution. The first system, being built in Baltimore with
grant assistance from EPA, will produce steam for sale to the local
utility.1 The utility will use the steam in its existing steam dis-
tribution loop. Revenue from the sale of steam will amount to at least
$3-50 per ton of refuse.
In the second project, the city of Nashville, Tennessee, created
an independent, non-profit authority that will sell steam and chilled
water to commercial and government office buildings in downtown Nashville,
using refuse-fired waterwal1 incinerators as the primary steam source.20
Fossil-fuel-fired backup boilers will also be available. Steam
revenues will amount to $10 per ton of refuse. This price, nearly
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17
three times the price paid for Baltimore's steam, reflects the construc-
tion cost of the complete steam generation and distribution system.
Chilled water, which is sold at a much higher price, will provide an
even greater amount of revenue about $25 per ton of refuse.
Industrial Plants. Large industrial facilities such as papermills,
food processors and major manufacturing plants are also steam customers.
Industrial customers who operate their facilities 2k hours a day are
preferred because a waterwall incinerator is designed for round-the-
clock operation. Some industrial users may specify the quantities of
steam to be delivered at certain given times, and then will most likely
specify the temperature and pressure. These factors must be identified
and incorporated in the design of the incinerator.
Although it is impossible to predict the long-term effect of the
energy shortages on industrial needs, fuel shortages should improve
the marketability of a reliable steam supply.
Many cities have single industries large enough to utilize all
the steam that a large solid waste facility can produce. In Saugus,
Massachusetts, a 1,700-ton-per-day waterwall incinerator is being
built that will handle 1,700 tons of refuse per day. All of the steam
produced in this plant (about 350,000 pounds per hour) will be used in
an adjacent General Electric Company plant for heating and cooling,
electric power generation and a variety of manufacturing and testing
operations. 2
Steam Electric Power Plants. Although steam electric power plants
use tremendous quantities of steam it may be difficult to develop
satisfactory marketing arrangements in this sector.
One problem is that the cost of accommodating an outside steam
source may exceed the value of the expected fuel savings. Modification
of the pressurized components of the power plant could involve costly
construction operations and could require that the power plant be kept
out of service for a long time. Also, using supplementary steam may
cause a boiler to operate at a lower efficiency so that additional
fuel will be needed to obtain the same energy output.
Another marketing problem results from the fact that the total
demand, or the amount of electricity that a utility must produce, varies
considerably throughout the day and from day to day. The utility's
most efficient plants are used continuously to supply the minimum
demand (baseload), while the less efficient or otherwise more costly
plants are used during peak demands. Thus each power plant within a
utility system, and in fact each boiler within a plant, will have a
different rate of utilization (or load factor) depending on its
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18
relative operating efficiency. The utility would be able to buy steam
only when the boiler which has been modified to accept outside steam
is operating. This would be 75 percent or more of the year for a base-
load unit, but it could be 25 percent or less for a peakload unit.
One way to overcome the problems of retrofitting an existing unit
would be to build a new baseload turbine and generator unit especially
to take steam produced in the solid waste facility. The Florida Power
and Light Company suggested such an arrangement as part of a plan to buy
energy from a proposed solid waste processing facility in Dade County.23
According to their proposal, the company building the solid waste
facility would also build the generating facility. Florida Power and
Light would then buy the steam, and also buy the generating facility,
paying for it on the basis of the units of electricity produced. This
arrangement requires that the municipality provide the capital invest-
ment, and the municipality, rather than the utility, assumes the financial
risk since reimbursement is tied to production.
Systems for Producing Steam
Systems available for the generation of steam from solid waste include
waste heat boilers, waterwall incinerators, and refuse-fired support
boilers.
Waste-heat boilers. A waste heat boiler package is one that is
placed in the flue following the secondary combustion chamber of a
conventional refractory-1ined, mechanical grate incinerator. In addi-
tion to being used in many industrial processes, waste-heat boilers
were used in the early design of heat recovery incinerators in this
country. The poor operating characteristics of refractory-1ined
incinerators have made this approach obsolete. ^
A waste heat boiler is employed quite effectively, however, as part
of the new pyrolysis system being built in Baltimore. The plant,
designed by Monsanto, has the boiler following a pyrolysis kiln (Figure 5).
Heat cannot be recovered from the kiln directly because it is used to
accomplish the pyrolysis of the solid waste. Once the pyrolysis gases
are formed they are combusted in a separate afterburner and the heat
that is released is then recovered as steam using a package type,
waste heat boiler. Two hundred thousand pounds per hour of steam
will be recovered from processing 1,000 tons of solid waste per day.
The steam will be transmitted by pipeline three-fourths of a mile to
an existing steam distribution system which is operated by the local
ut i1i ty.
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COMBINED PYROLYSIS AND STEAM RECOVERY SYSTEM
STEAM
JGAS r-rr^
SCRUBBER M
\
1
LSJ
STACK
FAN
WATER CLARIFIER
RESIDUE
WATER
QUENCHING
MAGNET
FERROUS
METAL
Figure 5. This schematic drawing of the main components of the Monsanto system in
Baltimore shows how it recovers steam with a waste heat boiler following the pyrolysis of
municipal solid waste.
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20
Waterwall incinerators. Waterwall furnaces have almost entirely
replaced refractory-1ined combustion chambers in current incinerator
design. In this type of construction, the furnace walls are constructed
of vertically arranged metal tubes joined side-to-side with metal fins.
Radiant energy from the burning of refuse is absorbed by water passing
through the tubes. Additional boiler packages, located in the flue,
control the conversion of this water to steam of a specified temperature
and pressure.
This construction is also advantageous because it acts as an
efficient method of controlling the temperature of the unit. The heat
released by combustion is transferred to the water, so less air is needed
to keep the operating temperature of the incinerator at an acceptably^
low level. This in turn reduces the size of the combustion unit and its
air pollution control equipment. In fact, the volume of gas entering the
air pollution control equipment will be only about 25 percent that of
an air-cooled, refractory unit. So effective is this means of tempera-
ture control that this type of construction has become standard even in
incinerators not designed for every recovery.
Refuse-fired support boilers. In Europe many municipalities
combine waterwal1 refuse units with separate fossil-fired boilers in
one facility.25 Steam from the two separate units is integrated to
drive one turbine/generator system.
One reason this concept is widely used in Eurpoe but not used at
all in this country is that many European municipal governments unlike
their American counterparts are responsible for solid waste disposal
but also for power generation, distribution of steam for district
heating, and the operation of electrically powered transportation
systems.
Markets for Electricity
Like steam, electricity produced from solid waste is indistin-
guishable from electricity produced by any conventional method. The
problem in marketing electricity, though, is that it usually can be
sold only to the electric utility serving the area, because within that
service area the utility is generally exempt from competition. The only
exception are municipally owned utilities but these account for only
10 percent of the nation's generating capacity. '9
The price that a utility will pay for electricity depends on
whether it is used to satisfy baseload or peakload demand. Although
peakload marketing commands a much higher price, a municipality needs
to sell electricity on a continuous basis (i.e., as baseload) in order
to maintain a continuous solid waste disposal operation.
19, p. Ill-it.
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21
A municipality considering the sale of electricity to a utility
should seek to establish a floating price for the electricity, whereby
the price per kilowatt-hour rises as the demand on the utility increases.
Thus, the price would be a function of the incremental direct costs the
utility incurs in producing the electricity needed to meet increased
demand.
Systems for Producing Electricity
The systems for producing fuel and steam discussed above can be
extended to include power generation. An economic analysis would have
to be undertaken to determine whether the revenue produced from the sale
of the electricity would be enough to offset the additional capital and
operating costs of the equipment needed to produce it.
The direct generation of electricity from solid waste combustion
is being explored through a research project funded by EPA.2° The
Combustion Power Company has developed a completely integrated solid
waste combustion-power generation system (Figure 6). A 100-ton-per-day
pilot plant is currently in the shakedown phase.
Incoming municipal refuse is shredded and air classified to remove
noncombustibles. Metal and glass are further separated for recovery.
The combustible fraction is pneumatically transported to an intermediate
storage facility and from there into a pressurized fluid bed combustor.
The hot, high-pressure gases from the combustor pass through several
stages of air cleaning equipment (separators) to remove particulates.
The cleaned gases are then passed through a gas turbine that drives a
1,000-kilowatt generator. Although the pilot plant operates at only
^5 pounds per square inch guage (psig), commercial plants would operate
at pressures in excess of 100 psig.
Performance problems have caused accelerated deterioration of the
turbine blades and have thus slowed the development of this process.
This deterioration and other problems must be solved before this is a
technically and economically feasible system for energy recovery.
ANALYSIS AND CONCLUSIONS
The key to successful implementation of a solid waste energy
recovery program is to select a system which is compatible with the
energy market as well as the community's solid waste disposal require-
ments. Once a suitable market has been identified, an appropriate system
can be designed which will convert the solid waste energy potential into
a marketable form.
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DIRECT GENERATION OF ELECTRICITY FROM SOLID WASTE
N>
Figure 6. The CPU-400 system, being developed by the Combustion Power Company,
produces electricity from the combustion of solid waste in a high-pressure fluidized bed.
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23
Comparison of Market Opportunities. It is most important that the
market for fuels and energy produced from solid waste be large and
favorably located. The size of the market is very important because
the customer may have to absorb the cost of process changes needed to
accommodate the new energy source. This is particularly true with
regard to producing an oil or a solid prepared fuel because special
storage and firing facilities are needed and these fuels are fired only
as a small percentage of the total fuel load.
Steam and gas can be transported only very short distances and
although the dry and liquid fuels can be transported farther, trans-
portation costs should be minimized wherever possible. Therefore, the
preferred market would be a facility located near the point of solid
waste generation.
Steam electric power plants are the most promising market. The
fact that most utility systems consist of several power plants increases
the probability that an acceptable market can be found. The potential
energy value of all solid waste generated amounts to between 5 and 10
percent of the total of fossil fuels used for electric power generation.
Steam distribution systems are also a good prospective market. The
scarcity and rising cost of fuels is creating a demand for new or
expanded systems. These systems are centrally located in order to
serve the greatest concentration of customers, so haul distance is
minimized. There is less fluctuation in load than in electric power
plants, and the lower operating temperature and pressure is compatible
with the constraints of a refuse-fired system.
Comparison of energy forms. The key to marketing energy from solid
waste is to produce an energy form that can be sold and used without
regard to its derivation. In addition, the type of fuel produced
should be storable and transportable so the solid waste facility
will be independent of the fuel market.
Steam and electricity satisfy the first objective, but neither
can be stored and steam can be transported only very short distances.
The solid and liquid fuels can be transported and stored for brief
periods of time (several days to several weeks). However, both
fuels require the user to install special storing and firing
facilities. In addition, the user must follow special handling pro-
cedures to minimize problems of air pollution and corrosion.
Gaseous fuels are less likely to require special handling or
separate facilities for storage and firing, but those currently being
produced cannot economically be compressed for extended storage and
shipment. The best of the gaseous fuels cannot be shipped more than
2 miles.
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2k
Comparison of technological alternatives. Municipalities require
solid waste disposal systems that are reliable and involve a nimimum of
technical risk. Furthermore, the system must meet acceptable environ-
mental standards at an economical cost, though not necessarily at the
least possible cost.
Risk and reliability are usually evaluated by examing full-scale
systems in actual operation. A number of energy recovery systems which
are currently being proposed to cities, however, have not had this long-
term operating experience. These systems have generally been developed
by private companies which hold patent rights to the process. The risk
of procuring such systems can be reduced by a turnkey arrangement,
whereby the contractor builds the system and turns it over to the city
only when it meets detailed performance specifications. A municipality
can also minimize risk and avoid large capital investments by entering
into a long-term contract for private ownership and operation of a
solid waste disposal/energy recovery system.
Waterwall incinerators are already in widespread use in this
country. While there is little risk of technical failure, the long-
term reliability of these systems has not yet been established. Water-
wall incinerators are usually the most costly of the energy recovery
systems, on the basis of both capital and operating costs.
The system expected to be the least costly of the energy recovery
options is the use of dry shredded waste as a prepared fuel. One
full-size plant has been in operation for over 2 years in St. Louis,
and several others are presently under construction. This system has
been particularly attractive because energy can be recovered with a
minimum amount of processing.
The 1,000-ton-per-day pyrolysis and steam recovery system in
Baltimore wi11 be in full operation in late 197^. It is being built
under a turnkey, fixed-price contract with guarantees on the daily
throughput, the amount of air emissions, and the extent of burnout.
Oil and gas recovery through pyrolysis, as well as direct con-
version to electricity, are undergoing demonstrations at less than
full size. Further technological developments will be needed before
widespread utilization can be expected.
In summary, the energy recovery options available for implementation
now are waterwall incineration and prepared refuse fuel systems,
although neither has been completely evaluated. Steam recovery through
pyrolysis should be available soon for full-scale systems, but the other
options will not be ready for full-scale use until the late 1970s.
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25
Some acceleration of this can be expected if the companies producing
the systems assume the development risk through direct ownership of
the facility or by offering them to local governments initially on a
no-risk basis.
Selecting an Alternative. Implementing a solid waste energy recovery
program is more complex than just selecting a technology. The first
and most important consideration is to secure a reliable and realistic
market.
All aspects of the market must be carefully understood by both the
user of the fuel or energy and the municipality supplying it. The
constraints of the market will indicate the technical aternatives
available. Once the various major markets for solid waste energy and
the possible energy forms that can satisfy those markets are examined
(Table 2), the possible alternatives will be narrowed to just one or a
few technologies. The final selection of a system will depend on the
relative technical risk and the estimated net operating cost.
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26
TABLE 2
MARKETS FOR ENERGY FROM SOLID WASTE
Conventional
energy source
Coal
Oil
Gas
User
Industrial boilers
and furnaces
Power plants"
Industrial boilers
and furnaces
Power plants*
Industrial boilers
Sol id
Prepared Liquid
fuel fuel
X X
X X
X
X
waste energy
Gas Steam
X X
X
X X
X
X X
form
Electricty
Steam
Electricty
and furnaces
Power plants»
District
heating/cool ing
Uti1ity d istribution
Industrial plants
Municipal 1ighting
Mass transit systems
x
x
X
X
" Electric or steam utility plants.
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27
APPENDIX
DEMAND FOR CONVENTIONAL SOURCES OF ENERGY
In examining the prospects for marketing solid waste fuels, it is
helpful to review the forms and uses of conventional fuels. Total energy
demand in the U.S. in 1970 was 67.8 quadrillion Btu.27 This is equivalent
to 32.5 million barrels of oil per day.- This energy is supplied by
three major fossil fuel sources--oi1, coal, and gas--and by hydroelectric,
geothermal, and nuclear power. Transportation, industrial operations,
and residential and commercial needs account for the major uses of energy
(Figure 7)•
Coal. Coal has been the staple of the American energy supply. In
addition to being abundant, coal is the cheapest source of energy currently
available. Unfortunately, when coal is burned its high sulfur and ash
contents contribute to air pollution. Coal's predominant use in this
country is in large industrial and utility furnaces or boilers where the
cost of adequate air pollution control equipment can be economically
absorbed. Other environmental problems associated with coal are
strip mining and the water pollution it causes. The Btu content of
American coals range from 11,000 to 14,000 Btu per pound.
Oil. In 1970 the U.S. consumed 13-9 million barrels of oil per day.
Of this, 3-5 million barrels were imports. All further increases in oil
consumption were also projected to come from imports, mostly from the
Middle East. ' Since this supply has become politically vulnerable,
new sources of oil will be needed to satisfy our increasing demand.
Crude oil is processed, by various refining operations, into more
than 100 different products. The lighter (lower density) fuels are
gasoline, diesel fuel, and jet fuels. These fuels are characterized
by good vaporization and burning properties, low quantities of impurities
and good storage stability. ' They account for more than 50 percent of
the liquid fuel market and are utilized primarily for transportation.
Heating oils are heavier than the fuels used for transportation and
are required to meet less stringent performance and quality characteris-
tics. These fuels are graded from No. 1 to No. 6, with the higher num-
bered grades having higher viscosities and lower purity requirements.
Grades No. 5 and 6, which require pre-heating facilities for pumping and
storing the fuel, are used in large industrial boilers and furnaces
where additional costs for handling and firing facilities can be
accommodated. The heating value of liquid fuels varies from 110,000
to 150,000 Btu per gallon with the heavier fuels having the higher Btu
contents.
•• Calculated by converting the energy produced from other forms of
•fuel to the equivalent amount of oil needed to produce the same
amount of energy.
*7, P. 16.
27, P. 273-
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1970 ENERGY SUPPLY AND CONSUMPTION
HYDROELECTRIC
GEOTHERMAL —
NUCLEAR
(IMPORTS)
GAS
DOMESTIC
LOST
ENERGY
ELECTRICAL
ENERGY
GENERATION
RESIDENTIAL
&
COMMERCIAL
7.5
CO
Co
(Each unit represents 1 million barrels of oil per day or its equivalent in energy)
Figure 7. Coal, gas, and oil are the major sources of the nation's energy, which is used for industry, transportation, and residential and
commercial purposes. Source: U.S. Congress JOINT COMMITTEE ON ATOMIC ENERGY. Understanding the "national energy dilemma."
Washington, Georgetown University, The Center for Strategic and International Studies, 1973. Tables C and E.
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29
Gas- The demand for gasous fuels currently exceeds the avilable
supply. Gas is a particularly popular fuel because price regulations
make it cheaper than most other fuels. It is easily stored, shipped,
and fired, and burning causes no pollution.
The major gaseous fuel is natural gas, an odorless, colorless
substance that accumulates in the upper part of oil or gas wells. It
consists chiefly of methane, and has a heating value between 1,000 and
1,100 Btu per cubic foot.
Propane and butane are produced in the process of refining petro-
leum. Their heating values are considerably higher than natural gas.
Because they are easily liquefied under pressure, they are usually
"bottled" in steel cylinders or shipped in large pressurized tanks.
They are used either as standby supplies for users of natural gas or
as fuel for stoves, trucks, buses, etc.
There are also many types of manufactured gas which are produced
by heating various solid fuels under specific controlled conditions.
These gases are referred to as coal gas, coke-oven gas (or coke), pro-
ducer gas, blast-furnace gas, water gas, etc. The heating value of
these gases ranges from 100 to 750 Btu per cubic foot. In many instances
they are used by the industry producing them because their heating
value is low and it is not generally economical to compress them for
shipment or storage.
Electrical generation. The electric utility industry is a supplier
of energy to consumers and, at the same time, is itself a major consumer
of fuels. In 1970, in fact, 25 percent of the energy used in the U.S.
was consumed by the electric generating industry. More than half of
this fuel input came from coal, with gas comprising 2k percent and oil
15 percent. Nuclear energy supplied only 2 percent of the industry's
needs in 1970. Although nuclear generating plants are expected to
supply 53 percent of the total utility load by 1990, the use of coal and
oil is also projected to increase but at a less rapid rate.
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30
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The Center for strategic and International Studies, 1973- 24 p.,
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31
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