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FROM THE U&EPk
Office of Solid Waste Management Programs
A REVIEW OF ENERGY RECOVERY
TECHNOLOGIES
By
Steven j. Levy and Stephen A. tingle
Techniques of solid waste disposal which incorpo-
rate energy recovery are being considered by virtually
every sizable community reviewing its waste man-
agement situation. What are the options available?
What is their status of development? These and re-
lated questions are addressed in an EPA publication
just released entitled Resource Recovery Plant Im-
plementation: Guides for Municipal Officials-
TECHNOLOGIES." Some brief highlights of this pub-
lication are summarized here.
Resource Recovery Technologies
Waterwall Combustion Systems (Mass Burning).
Combustion of unprocessed solid waste on mechan-
ical grates in waterwall furnaces to recover steam or
generate electricity is the most thoroughly proven re-
source recovery technology. However, most of the
experience has been in Europe rather than the United
States. Approximately 200 of these systems have
been installed in Europe. An additional 50 or so exist
in Japan, Brazil and elsewhere.
Six waterwall combustion systems are now operat-
ing in the United States. Market and institutional ar-
rangements in the past have been less attractive here
than other countries. For example, both landfills and
Steven J. Levy is the manager of the Technology
Demonstration and Evaluation Program of the
Technology and
Markets Branch,
USEPA. Levy is
also affiliated with
the Resource Re-
covery Division
and the Office of
Solid Waste Man-
agement Pro-
grams (OSWMP). Stephen A. Lingle is Chief,
Technology and Markets Branch, and edits the "Up-
date" series.
energy generally have been more available and less
costly here. Municipal steam markets have been more
available in Europe than in the United States. How-
ever, changes in these factors are now creating a
significantly expanded interest in this technology in
this country.
Although this is a proven technology, it is somewhat
complex relative to conventional solid waste disposal
methods. Some improperly designed, or improperly
operated units have experienced problems such as
boiler corrosion and inadequate air pollution control.
Thus, examples of both successful and unsuccessful
units can be found. Proper design and operation,
based on experience of the most successful opera-
tions is the key to success.
Waterwall Combustion Systems (Bern/suspension
Burning). A recent variation of the standard mass
burning waterwall combustion system involves size
reduction of waste followed by burning in an on-site
waterwall stoker boiler to produce steam. Waste is
first shredded or pulped for size reduction, then may
also be classified to remove noncombustibles. The
waste is mechanically, or pneumatically thrown into a
furnace and burned on a moving grate as the sole
boiler fuel to produce steam.
At least three of these systems are operating now,
and others are scheduled for construction in the near
future. This is a relatively recent alternative to energy
recovery from municipal solid waste, thus operating
experience is somewhat limited. However, the basic
boiler technology is similar to mass burning waterwall
boilers. Also, similar boilers have been used to burn
bark and other waste.
Small Modular Incinerator. One approach to energy
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recovery from waste which is particularly applicable to
small communities (producing 100 tons or less of
waste per day) is the use of small modular in-
cinerators coupled with waste heat boilers. These
factory-built combustion units have been in use for
many years, especially among larger industrial and
commercial complexes. However, recovery of steam
has been incorporated relatively recently. Each indi-
vidual unit can handle up to one-ton-per-hour. By in-
stalling multiple units, it is feasible to build plants as
large as 100 tons-per-day. The quantity of steam pro-
duced is best suited for sale to a single industrial cus-
tomer where it can be used to supplement his own
fuel-fired boiler system.
Several of these units have been built in the past
two years. There is currently some information avail-
able on commercially operating units. However, com-
prehensive long-term operating data on modular in-
cinerators with heat recovery still have not been com-
piled.
Refuse Derived Solid Fuel Systems (RDF). This
technology includes size reduction of solid waste and
removal of non-combustibles to produce a
supplementary fuel for use in coal-fired steam boilers.
The type of RDF produced can vary significantly.
Needs of the user (i.e., type of boiler in which the RDF
is to be fired) would determine the type of RDF to be
produced.
Emphasis to date has centered on producing an air
classified "fluff" RDF (of 1 to 1Vz inch particle size) for
burning in a suspension-fired boiler as a supplement
to coal. Other variations of RDF include: coarsely
shredded (i.e., 3 to 6 inch) waste for burning in a
grate-fired boiler; fine powdered waste called "dust"
RDF for use in suspension-fired boilers; wet pulped
and classified waste for drying and use in suspension
or other boilers; and densification of all of the above to
form pellets or briquettes for cofiring with coal in
grate-fired boilers.
The commercial operating experience of this
technology is limited. Much of the experience stems
from a demonstration plant (St. Louis, Mo.) where fluff
RDF was burned in a suspension-fired boiler with pul-
verized coal. In addition, a commercial facility has
been operational in Ames, Iowa since late 1975. Fluff
RDF from this plant has been burned primarily in
grate equipped spreader-stoker boilers. Several other
facilities are currently under design or construction.
Two 1000-ton-per-day facilities will begin operation in
early 1977. In these plants, "fluff" RDF will be pre-
pared and burned in suspension-fired boilers as a
supplement to coal. Experience with other RDF forms
includes a recently constructed dust RDF plant in E.
Bridgewater, Mass., which will soon begin operation,
and several production and firing tests of densified
RDF.
Based on these experiences, the basic technical
feasibility of size reduction and classification of waste
is generally accepted. However, it should be noted
that the design and operating parameters have not yet
been determined for the most cost-effective approac
to RDF production, storage and transportation. Alsc
some operational difficulties may be expected, partict
larly in the early months of operation.
Markets for the RDF are critical factor in the suc-
cess of this technology. Experience with the RDF
demonstration project in St. Louis convinced many
electric utility officials that RDF can be burned in
combination with coal, at rates of 5 to 20 percent of
total heat input, without measurably affecting boiler
operation and short term maintenance requirements.
However, while the indications are positive in this re-
gard, there is still the uncertainty associated with lack
of experience in burning this material. Thus, in any
agreements to buy RDF, most potential users cur-
rently would require firing test periods of at least sev-
eral months to allow them to evaluate the effects of
RDF firing and estimate the possible need for
changes in pollution control equipment. The purchase
agreements required by such buyers usually would
allow them to terminate the contract if sufficient prob-
lems are found to make use of the RDF economically
unattractive. This can be a significant problem in se-
curing a market.
Pyrolysis Systems. Pyrolysis is a broad term given to
a variety of processes that decompose processed
waste or unprocessed waste by the action of heat in
an oxygen-deficient atmosphere. The fuels produced
by these pyrolytic processes can be either combusti-
ble gases or liquids, depending on operating condi-
tions. These products may either be burned im-
mediately to produce steam or, in some cases, they
can be transported and sold to other users.
Several pyrolysis systems are currently being de-
veloped. One pyrolysis system produces a low energy
gas that is converted to steam on-site. It is being
demonstrated at the 1000-ton-per-day scale in Balti-
more, Maryland. This plant is currently undergoing ex-
TABLE 1
PRODUCTS PRODUCED BV MAJOR
ENERGY RECOVERY TECHNOLOGIES
Steam or Electricity
generated "on-site"
for sale
Waterwall combustion system (mass
burning)
t'odular incinerator
Waterwall combustion system
(seim-suspension)
Fyrolysis to low BTU gas, burned
in an afterburner
3'c-conversion to a gas, burned
ip £n afterburner
Gaseous or liquid
Ref-se-Dsrived Solid Fuel (RDSF)
SVst=~l
?J'TC^S;S to a medium BTU gas
Pyrclysis to a liquid
Bio-conversion to medium BTU gas
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tensive modifications to correct problems which arose
during its initial start-up period. An assessment of the
systems' availability cannot be made until the modifi-
cations are completed and their performance is
evaluated.
A 200-ton-per-day demonstration plant of another
pyrolysis process is under construction in San Diego,
California and will begin operations in the spring of
1977 to produce an oil-like liquid fuel. The fuel will be
sold to an electric utility for use as a supplement to oil.
A third pyrolysis process has already operated at
200-tons-per-day in South Charleston, W. Virginia, as
a pilot operation. This plant uses oxygen to produce a
medium-energy gaseous fuel. This fuel, like the
pyrolysis oil, may be suitable for transport off-site for
use. It is also viewed as a possible feedstock for
synthesis of chemicals.
In Europe (Luxembourg,) one 200-ton-per-day
pyrolysis plant is nearing start-up as a commercial
facility. Two other units are soon to be constructed.
This system produces a low BTU gas for combustion
on-site to produce steam. An earlier demonstration
plant was operated in Orchard Park, New York.
Finally, a pyrolysis system suitable for small-scale,
or even mobile application, has been successfully
tested at the pilot scale at the Georgia Institute of
Technology. This system can produce a solid or
gaseous fuel. It has been tested extensively on ag-
ricultural waste.
In addition, a number of other pyrolysis systems are
being developed or evaluated at the pilot scale. How-
ever, the extent of testing is generally less than those
described above.
No pyrolytic system has operated on a regular basis
as a part of a community solid waste system. How-
ever, at least two companies feel that their
technologies are ready to advance from pilot to com-
mercial stage, and are marketing them to
municipalities. Thus, some communities are consider-
ing pyrolysis for implementation, realizing that the lack
of operating experience implies technological uncer-
tainties that generally exceed those for technologies
which have operated commercially.
Biological Conversion Systems. Biological conversion
involves the decomposition of solid waste by bacterial
action to produce combustible gases. Recovery of
methane from sanitary landfills is one type of bio-
conversion. It is possible when certain site conditions
(such as age and depth of fill, soil characteristics, rain-
fall, etc.) are appropriate. Although the technology is
not complicated, long-term monitoring is necessary to
determine projected yields over extended periods of
time. Also, more information is needed to define the
parameters necessary to predict yields, and thus, sys-
tem economics.
Anaerobic digestion in controlled reactors is another
means of bio-conversion of solid waste. This technol-
ogy is presently being pursued at the research level,
and thus is not currently ready for commercial applica-
tion.
TABLE 2
EilERGY RECOVERY TECHHGLOGY A'lB PRODUCTS
(Status as of 11/7M
TECHNOLOGY
JMATSBIALL
COMBUSTION
(MASS BUStllKG)
(SOU-SUSPENSION)
;j| SOLID FUEL (RDF)
J( '
°l
GASIFICATION
LOW BTU
MsBMtcjrt.fi T iC)
Key Questions in Technology Selection
A decision to implement resource recovery and
select technology are complicated endeavors. There
are two key questions which must be addressed:
Is there a market for the product?
The most important factor for a city to remember
when assessing resource recovery technology is that
the system must be able to produce marketable prod-
ucts. Technology selections should not be made until
potential markets have been identified, and the mar-
ket requirements specified. Some communities will
find that there is only one technical approach that can
simultaneously meet their needs and the require-
ments of their markets. Most cities, however, will have
the flexibility to choose from two or more technologies
that meet their market requirements. Table No. 1 re-
lates the primary energy products available from solid
waste to the technologies that can produce them.
What is the status of development of the technology?
The level of operating experience is one important
factor in determining the technological uncertainty of
each process. With the exception of waterwall com-
bustion systems, all of the energy recovery
technologies are relatively new. Little or no commer-
cial operating data exists. Thus, use of these
technologies naturally entails some technological un-
certainty. A community contemplating construction of
a resource recovery system must understand the na-
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ture of its technological uncertainties.
Technological uncertainty ius in turn related to risk,
but the two are not the same. Risk refers to the poten-
tial of economic loss resulting from technological fail-
ure. Risks associated with technological uncertainty
need not be fully assumed by cities. The private com-
panies marketing these technologies should assume
a significant portion of the risk through performance
guarantees, and financial (i.e., cost) guarantees. Such
guarantees can be extremely important in shifting risk
from a city. For example, even a system with good
operating history, if not properly designed or backed
by performance or cost guarantees, could entail signif-
icant risk for a city. Conversely, a technology without
extensive operating history can entail an acceptable
level of risk if it is properly designed and warranted by
a qualified vendor. Thus, both operating history and
performance warranties are important.
Most resource recovery technologies are still i
relatively early stage of application and, thus, er
uncertainties. Furthermore, the technologies tenc
be complex and require highly competent design,
gineering and operation. A city, therefore, must ca
fully examine the competence of prospective vend
and designers.
However, uncertainties need not lead to high ri:
Uncertainties do not make implementation prematu
They simply must be realized and understood so tf
they can be addressee! and approached properly.
so doing, cities need not assume undue risks. Secu
markets, proper design by qualified firms, system We
rantees, and appropriate financial guarantees, c;
shift much of this risk away from a city. Thus, mai
resource recovery technologies can be attractive ar
prudent disposal alternatives today. I
CONCLUSIONS
Information on the various energy recovery
technologies is summarized in Table No. 2. Each
technology is listed with its potential products. Loca-
tions of specific installations are included. The table
also groups technologies according to the level of
operating experience achieved to date.
"Resource recovery plant implementation: guides ft
municipal officials-TECHNOLOGIES. Levy, S. J., an>
Rigo, H. G. Environmental Protection Publication
SW-157.2, Washington, U.S. Environmental Protec
tion Agency, 1976. Other parts of this series are
Planning and Overview (SW-157.1); Markets (SW
157.3); Financing (SW-157.4); Procurement (SW
157.5); Accounting Format (SW-157.6); Risks anc
Contracts (SW-157.7); Further Assistance (SW-
157.8).
Reprinted from Waste Age, November 1976
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