United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/098 Dec. 1 985
oEPA Project Summary
Investigation of Fluid Bed
Combustion of Municipal Solid
Waste
R. H. Eustis, Keith B. Wilson, Lyn C. Preuit, and Maximilian M. Marasigan
A systems study was conducted for a
co-generation, 300-tons/day power
plant to be located on the Stanford
University campus to supply all of the
process steam requirement and as much
of the electrical power as possible. The
size of the plant was determined by the
estimated available processed MSW
supply in 1983. Preliminary design of
components based on the 300-hour
test results and cost estimates were
made. It was estimated that the total
plant investment for the co-generating
plant, 6.7 MWe average and 200,000
pounds per hour of steam average,
would be 23.1 million dollars, exclusive
of fuel processing and transportation
costs.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory. Cincinnati, OH to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
A concept which utilizes fluid-bed
combustion of municipal solid waste was
investigated for application to the power
generation and steam supply at Stanford
University. Preliminary investigation of
the system has shown considerable eco-
nomic promise, although the operation of
an atmospheric fluid bed containing
steam-generating tubes had not been
tested. Therefore, a program was rec-
ommended to the Department of Energy
and the U.S. Environmental Protection
Agency which would involve an exper-
imental program to burn solid waste in a
fluid-bed combustor and to undertake a
more detailed economic study.
An experimental program was designed
to investigate the favorable operating
regimes for a bed with steam-raising
tubes, to determine the combustion cor-
rosion of the tubes, and to investigate the
fouling of the tubes or system internals
caused by the combustion of municipal
solid waste. Two 50-hour preliminary
experiments were run in order to shake
down the equipment and to conduct a
parametric study to specify the most
favorable operating regime for a subse-
quent 300-hour test. All of these exper-
iments were conducted in a 7 ft2 atmos-
pheric fluid bed located at the Combustion
Power Company (CPC) in Menlo Park,
California.
An economic study was also undertak-
en to determine the promise of the system
as defined from the results of the exper-
iments. As described below, a complete
system was envisaged for application to
the Stanford University campus, and the
sizing and performance of the fluid-bed,
solid-waste combustor was based on the
experimental results. The application to
Stanford University was used only as a
specific application and was not neces-
sarily the most favorable one, because of
the wide variety of requirements for
electric power and steam. However, it
was felt that this would be a typical
situation and that there would be con-
siderable benefit in having a study made
to meet definite, realistic requirements.
In the final report, the proposed system
at Stanford University is described, fol-
lowed by the results of the fluid-bed
testing program. The last section of the
final report is a presentation of the
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systems study showing the performance
and economics of a fluid-bed, municipal-
solid-waste combustion system which
incorporates electrical power generation
with process heating.
Proposed System
In order to prevent the present study
from becoming merely an academic exer-
cise, a practical possible application was
defined so that the experimental program
would be conducted under realistic test
conditions and the economic study would
have reference to a specific situation.
Therefore, consideration was given to the
energy requirements of Stanford Univer-
sity. This is a particularly favorable situa-
tion, inasmuch as the University has a
central steam-heating system and an
electrical power requirement. At the
present time the electrical power is
supplied by the local utility, and steam is
generated in the University's boiler sys-
tem with natural gas as the fuel, backed
up by light fuel oil. The balance of the
heating and electrical load is such that
co-generation of electricity and process
heat is feasible and very attractive from a
technical point of view.
The general concept for the Stanford
Solid-Waste Energy Program (SSWEP) is
to process solid waste at a convenient
collection site, where some landfill is
available to handle the non-combustible
part of the stream. The lightly processed
solid waste, which would be processed
only so that it can be fed into the
combustors through a 5"-diameter pipe,
would be transferred to the University
campus with special transfer trucks. The
size of the system is specified by the
available Municipal Solid Waste (MSW),
which is estimated to be 800 tons of
processed MSW per day in 1983. This
corresponds to approximately 1200 tons
per day of raw MSW delivered to the
remote processing site. The plan would
be to feed the processed MSW to fluid-
bed boilers which would be built in a
modular fashion for economy and for
improved turn-down as required for meet-
ing the variable load on the campus.
Superheated steam at a modest pressure
and temperature would be delivered to a
steam turbine, with extraction at a pres-
sure of approximately 170 psia. The
extraction steam would condense in a
heat exchanger and then be returned to
the fluid-bed boiler. The heat exchanger
would transfer heat to the return con-
densate from the Stanford heating sys-
tem to produce 140 psia steam for the
Stanford system. If all of the flow from the
high-pressure turbine was not required
for the heat exchanger, the remainder
would flow to a condensing turbine in
order to generate more electrical power.
A cooling tower would be provided for
cooling the condenser so that the fluid-
bed boiler steam would be self-contained
and could be carefully controlled.
The fluid-bed boiler system involves a
combustion air blower, an air preheater,
and an exhaust clean-up system after the
fluid-bed boiler. The solid waste would be
introduced into the bed pneumatically,
and the present design incorporates
internal recycling of elutriated flyash and
bed material to the bed, as this was found
beneficial in the experimental program.
Most of the system is conventional, with
the fluid-bed boiler being the most novel
and at the same time the most critical
component. Because of this, an exper-
imental program was performed in a 7 ft2
fluid-bed combustor with water-cooled
tubes. Air-cooled tubes were included for
corrosion tests in both the freeboard and
m the active bed, in which test samples
were subjected to the expected temper-
ature of superheater tubes in an actual
application.
Test Results
Two 50-hour runs were made to check
out the system and to determine a
satisfactory operating point for the princ-
ipal experiment of 300 hours' duration.
The test conditions were:
superficial velocity = 4.5 ft/sec
bed temperature = 400 F
freeboard temperature = 1500 F
excess air = 44%
internal recycle of elutriated solids to
bed
The 300-hour test was performed
without incident and terminated on sched-
ule. The combustor and ducting were
clean on inspection after the test, and bed
agglomeration did not occur. A corrosion-
erosion tube placed in the freeboard
showed considerable metal wastage for
carbon and low-alloy steels and some
wastage for stainless steels. Low-tem-
perature carbon-steel water tubes in the
bed showed negligible wastage. It was
concluded that heat-exchanger tubes in
the freeboard require protection from the
high-velocity elutriated solids. Combus-
tion efficiency was greater than 99%, and
pollutants were measured as follows1
Economic Summary
The material from the cost estimates
described in the final report is summar-
ized in Table 1. Each major subsystem is
shown, along with the additional costs
which are recommended for a construc-
tion project such as this by the standards
of the Electrical Power Research Institute.
The total direct cost as estimated is 1 6.7
million dollars, and the total plant invest-
ment, using various contingencies and
sales tax, amounts to $23.1 million. This
figure should be compared to plants
which handle 1 200 tons per day of raw
municipal solid waste and produce both
steam and electrical power. The costs
presented do not include processing or
transporting the processed MSW to the
point of use.
S02
NOx
CO
Hydrocarbons
58 ppm
178 ppm
242 ppm
4.4 ppm
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Table 1. Stanford Solid-Waste Energy Program Total Plant Investment
1 Boiler system
2 Startup system
3. Combustion air system
4 Flue-gas system
5. Bed-maintenance system
6. F/yash-disposal system
7. Fuel-feed system
8 Fuel-receiving bldg., equipment
9 Main steam system
JO Feedwater system
11 Electrical/controls/misc
12 Building, site work, construction, A & E
$ 2.239,700
155,200
798,900
2,382,000
84,100
79,200
457.800
252.400
5.421.000
1,942,600
1,204,100
1,645,000
Total Direct Costs
Undistributed Costs <6%>
16,662.000
999.700
Process Capital
Engineering & Home Office Fees
17,661.700
1.666.700
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R. H. Eustis is with Stanford University, Palo Alto, CA 94105; andK. B. Wilson, L
C. Preuit, andM. M. Marasigan are with Combustion Power Corporation, Menlo
Park, CA 94025.
Michael I. Black is the EPA Project Officer (see below).
The complete report, entitled "Investigation of Fluid Bed Combustion of Municipal
Solid Waste,"(Order No. PB85-242 121 /AS; Cost: $11.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S2-85/098
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