5AN DIEGO COUNTY
DEMONSTRATES
OF PYROLY5IS
50LIP WfQTE
to recover liquid fuel,
metals, and glass
This report (SW-80d.2) on work performed
under Federal solid waste management demonstration grant
No. S-801588 to San Diego County was written by STEVEN J. LEVY.
U.S. ENVIRONMENTAL PROTECTION AGENCY 1975
-------
An environmental protection publication (SW-80d.2)
in the solid waste management series
Mention of commercial products or organizations does not constitute
endorsement by the U.S. Government
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C 20402
-------
foreword
In this time of concern about dwindling supplies of energy and materials,
nearly all of the large amounts of energy and recyclable materials in municipal
solid waste are still dumped or buried. In fact, locating land space for disposal
of the growing waste loads is a serious problem in many cities, and in a num-
ber of places disposal is being carried out in ways that could create health and
environmental hazards. This report describes a project that will recover
energy, ferrous metals, and glass from municipal solid waste and so offer a
means of saving these resources while also reducing the problems of disposal.
The energy recovered will be in the form of a liquid fuel that is suitable for
use in utility boilers.
The pyrolysis process being demonstrated in the San Diego County project
is one of a number of technologies that can be used for resource recovery.
To promote such technological development, the Congress, through the
Solid Waste Disposal Act as amended, enabled the Federal solid waste
management program to assist States and municipalities by assuming part of
the risk of trying new technologies. The result was a significant expan-
sion of the Federal resource recovery demonstration program.
Other grants in this program have been awarded to: Baltimore, Maryland,
to demonstrate the recovery of steam by pyrolysis; the State of Delaware to
demonstrate the use of solid waste as a supplemental fuel in an oil-fired
utility boiler; to Franklin, Ohio, to demonstrate the recovery of paper fiber;
to Lowell, Massachusetts, to demonstrate the recovery of materials from in-
cinerator residue; and to St. Louis, Missouri, to demonstrate the use of solid
waste as a supplemental fuel in a coal-fired utility boiler.
The pyrolysis process described in this report was developed by Garrett
Research and Development Company, Inc., of LaVerne, California, a subsid-
iary of Occidental Petroleum Corporation. Construction ,of the 200-ton-
per-day plant began in 1975 and full-scale operation is scheduled for 1976.
Subsequent reports will follow the progress of the demonstration project,
which will include a full evaluation of the environmental impacts, economics,
and effectiveness of the process.
-ARSEN J. DARNAY
Deputy Assistant Administrator
for Solid Waste Management
11]
-------
-------
DIEGO COUNTY
DEMONSTRATES
PYROLY5IS
OF SOLID WflSTE
The recovery of energy from municipal solid waste has become a well-
established objective. As increasingly sophisticated energy recovery alterna-
tives are developed, the demand increases for systems that can convert solid
waste into a fuel that can be used interchangeably with other fuels. The
marketability of a fuel product is also improved if it can be stored and trans-
ported, because the user need not be located near the solid waste processing
facility, nor must the operating schedules of the user and the processing
facility be similar. The system being built by the county of San Diego is de-
signed to produce a synthetic liquid fuel that, with certain constraints, will
have these qualities of storability and transportability. And results of pilot-
scale research indicate that the fuel produced can be used in conventional fur-
naces or boilers that use heavy residual fuel oil.
Pyrolysis is lie physical and chemical decomposition of organic matter
brought about by the action of heat in the absence of oxygen. When munici-
pal solid waste is heated, the organic fraction (primarily cellulose) is broken
down into compounds of simpler molecular structure, primarily hydrogen,
carbon monoxide, methane, and carbon dioxide. By controlling certain oper-
ating parameters, such as temperature, pressure, operating time, and the pres-
ence of catalysts, it is possible to control what products are formed. For the
San Diego County project, parameters were selected that would result in the
formation of a product which is a liquid at room temperature.
The plant, which will have the capacity to handle 200 tons of waste per
-------
day, will utilize a flash pyrolysis process in which a nearly instantaneous reac-
tion liquifies the organic solids. Incoming waste will first be shredded (Figure
1). The lighter, organic material will then be separated from the heavier, in-
organic material, dried, and reshredded before being fed into the pyrolysis
reactor to produce fuel oil. The heavy fraction will be processed further to
recover ferrous metals and glass.
Objective
The objective of the demonstration project is to test the principles of the
process and to scale up the pilot plant technology under normal operating
procedures using municipal solid waste. Data collected on this plant will aid
in evaluating the technical and economic viability of the process and will pro-
vide a data base for designing larger, optimally sized facilities.
Participants
The U. S. Environmental Protection Agency is supporting the construction
and evaluation of this facility with a $3.5 million grant to San Diego County,
provided under authority of the Solid Waste Disposal Act as amended.
The San Diego County Department of Sanitation and Flood Control, the
agency responsible for solid waste disposal in the county, will be the owner
and operator of the facility. The county is providing almost $2 million to
carry out the program.
The plant is being built in the city of El Cajon and will receive refuse col-
lected in the city and surrounding areas. The 5.3-acre industrial site was ob-
tained from the city of El Cajon under a long-term lease.
The process was developed by the Garrett Research and Development Com-
pany of La Verne, California, the research subsidiary of Occidental Petroleum
Company. Under the provisions of its turn-key contract, Garrett is responsi-
ble for designing, constructing, and starting up the plant, which must be in
fully operational condition when turned over to San Diego County. Garrett
is contributing $3.5 million toward the cost of construction. The detailed de-
sign is being prepared by the Ehrhart Division of Procon, Inc., a subsidiary of
Universal Oil Products, Inc., through a subcontract from Garrett.
The liquid fuel will be used by the San Diego Gas and Electric Company.
Capital for minor modifications needed at the power plant will be provided
by the utility. Following a comprehensive testing period, the utility will
determine the value of the fuel based on its equivalency with other fuels.
Although the utility will pay for the fuel, initial shipments will be credited
against the utility's capital expenditures. After that investment has been re-
tired, the utility will begin paying the county.
-------
CO
CO
CO
UJ
CO
C3
CO
Figure 1. This very simplified diagram shows the main steps in the process that will
be employed by the San Diego project.
-------
Schedule
The project is divided into three major phases: design, construction, and
evaluation (Table 1).
TABLE 1
Project Schedule as of October 1, 1974
Milestone
Date
Grant award
Begin design (start phase 1)
Initiate turn-key contract (start phase 2)
Begin ordering equipment
Begin construction
Complete construction
Complete startup
Begin evaluation (start phase 3)
Complete evaluation (end of project)
September 1972
February 1973
September 1974
November 1974
August 1975
July 1976
August 1976
September 1976
September 1977
f\
: lVPHT7?
"•i jP*-i'^t
ua,
-------
The design phase ended in the summer of 1974 when the turn-key con-
tract was negotiated with Garrett. The second or construction phase will end
when Garrett delivers a fully operational plant to the county.
As soon as the plant is capable of performing according to design specifi-
cations, a 1-year testing and evaluation period will begin; this will be the
third and final phase of the project.
Development of the Process
Garrett developed this process for solid waste as an extension of research
on the liquification of coal. Initial theories were tested on a 3-pound-per-
hour laboratory test unit. This unit has been used to test many different types
of waste, including bark, rice hulls, and waste rubber, in addition to finely
shredded municipal solid waste. It is still being used to test process changes.
A 4-ton-per-day pilot unit was completed in March 1971 (Figure 2). With
this unit, Garrett was able to verify the theoretical processes established in the
laboratory unit and to process enough material to allow definition of design
parameters for a full-size plant. The pilot plant has produced fuel for com-
bustion tests and is still being used for occasional tests using municipal solid
waste and other organic waste materials.
Figure 2. A plant with a capacity of 4 tons
of solid waste per day was operated in Van-
couver, Washington, for pilot testing of the Gar-
rett system. The data from this experience was
used to design the 200-ton San Diego County
plant.
-------
the system
Feed Preparation
Only the organic fraction of the solid waste can be pyrolyzed; therefore,
in order to obtain an efficient operation, the waste is first processed to remove
the inorganic materials. The feed preparation is more rigorous in this system
than in any other energy recovery system currently under development. In
addition to being virtually free of inorganic contaminants, the feedstock must
also be of extremely small particle size and essentially moisture-free.
In the first step of feed preparation, incoming solid waste is fed into a
horizontal shaft hammermill driven by a 1,000-horsepower electric motor
(Figure 3). The hammermiU's heavy metal hammers, which swing on pins
attached to the shaft, shred the waste to a nominal size of 3 inches (90 per-
cent passing a 3-inch screen). Steel grates retain the oversize waste until it is
shredded into particles small enough to pass through the grate openings.
The shredded material is then passed beneath an electromagnet to extract
the ferrous metal, which will be sold to a scrap dealer- The remaining materi-
al goes into a storage bin until it is needed in the next step in the process,
air classification. This storage capability assures that a uniform rate of feed
into the air classifier can be maintained even though the shredder operates
only 8 hours per day while the rest of the plant (except the glass recovery
system) operates on a 24-hour basis.
The air classifier separates the heavier, mostly inorganic particles from the
lighter, organic material. An upward-flowing column of air catches the lighter
material as it is fed into the air classifier and carries it out the top. Heavier
material falls through the air stream and is removed from the base of the clas-
sifier. The heavy fraction is processed further as described under "Glass
Recovery."
The light fraction is dried to a moisture content of 4 percent using heat
from burning either combustible gas produced in the pyrolysis reactor or fuel
oil.
After drying, this fraction is purified further using a series of mechanical
processes. A 0.125-inch screen is used to remove larger particles for secondary
shredding in an attrition mill. In this mill, waste fed between two counter-
rotating disks is ground into extremely fine particles having a nominal size of
minus 14 mesh (that is, 80 percent of the particles could pass through a
screen having 14 openings to the inch). Meanwhile, the particles that fall
-------
CO
CO
CO
CO
Figure 3. Preparation of feedstock for the pyrolytic reactor involves a number of
steps to produce fine particles of moisture-free organic material. The glass recovery sys-
tem results in recovery of about 75 percent of the glass in total incoming waste.
-------
through the 0.125-inch screen are fed onto an air table where a combination
of vibrating motion and air flow separates light organic particles from dense
metal and glass particles. The light particles from the air table are combined
with the secondary shredder output to form the organic feedstock, which is
stored until it is fed into the pyrolysis reactor. The storage bin is large enough
to hold a full day's feed for the reactor.
Glass Recovery
The remainder of the feedstock preparation portion of the system con-
sists of the glass recovery process at this time; Garrett will probably add an
aluminum recovery process at a later date.
There are two sources of glass-rich feedstock: heavy particles coming from
the air classifier underflow and the dense fines recovered from the air table
separator.
The heavy fraction from the air classifier is passed through an inclined ro-
tating cylinder called a trommel. At the head or feed end of the trommel,
%-inch perforations in the wall allow small particles to drop out.
These particles are then further separated using a rake classifier, a screening
device in which a mechanical rake continuously scrapes the oversize parti-
cles from the face of the screen. The particles that fall through the screen are
put through a rod mill (a rotating chamber in which steel rods move about
crushing the friable material) and then passed into the glass recovery processes.
The oversize particles are returned to the storage bin that feeds into the air
classifier.
Back at the trommel, beyond the Vi-inch holes is a section with holes 4 in-
ches in diameter, where the particles larger than % inch but less than 4 inches
fall out. This material will be the feedstock to the aluminum recovery plant,
if it is added; otherwise, this fraction will be disposed of in a sanitary landfill.
Particles greater than 4 inches fall out the end of the trommel and are re-
turned to the front of the plant where they go back through the primary
hammermill.
The second source of feedstock to the glass recovery subsystem, the dense
fines recovered from the air table, require further processing. From the air
table, the fines pass into a flotation cell where the glass is crudely separated
by froth flotation. In this step the mixture is coated with a liquid reagent
that causes the glass to have a greater affinity for air than for water. The flo-
tation cell is filled with water, and air is pumped into it continuously. As the
coated material is pumped into the flotation cell, the glass particles are car-
ried to the surface along with the air bubbles. The glass floats on the surface
while the nonglass material sinks to the bottom of the cell. This "float,"
along with the small particles recovered from the trommel, constitutes the
8
-------
Figure 4. When the organic feedstock is mixed with hot char, it decomposes into a
gas-char mixture. The gas is then immediately cooled to produce the liquid fuel.
-------
feedstock to the glass recovery subsystem.
The glass recovery subsystem consists of a series of froth flotation cells
which, by recirculating both the float and sink fractions several times, is ex-
pected to recover 99 percent of the glass in the glass feedstock at a purity of
better than 99.5 percent. However, the total recovery of glass from the in-
coming solid waste will be only 75 percent because there is loss in various
parts of the process before the feedstock is formed.
Pyrolysis Process
The pyrolysis reactor is a vertical, stainless steel pipe through which the
organic feedstock is pneumatically blown (Figure 4). In the reactor, hot par-
tides of char provide the energy needed to pyrolyze the organic material. The
char, which is actually the solid residue remaining after the pyrolysis reac-
tion, enters the reactor after having been heated to a temperature of 1,400 F
and is mixed turbulently with the organic material. Five pounds of char is
mixed with each pound of organic material. The pyrolysis reaction takes
place as the char-waste mixture proceeds through the reactor. The organic
feedstock is broken down into a gas and char mixture. Because this reaction
is endothermic, that is, requires heat to proceed, the temperature of the mix-
ture falls to about 950 F by the time it leaves the reactor.
A mechanical separator or cyclone is used to remove the char from the gas.
The char, which now consists of the char fed into the reactor as well as that
newly formed by the pyrolysis reaction, is stored for reuse in the reactor.
Before being recirculated to the reactor, this stored char is reheated. Excess
char will be cooled with water and removed for disposal in a sanitary landfill;
it is possible, however, that markets can be developed for this material.
The process gas that has been separated from the char is cooled quickly to
175 F in an oil decanter. In this device, oil is sprayed into the gas stream,
causing it to cool. The cooling must be done very quickly to halt the chemical
reactions taking place in the gas and thus prevent a reduction in the yield of
fuel. The oil used for cooling is a combination of the liquid fuel produced by
the plant and No. 2 fuel oil. After cooling, the liquid fuel settles in the base
of the decanter. Approximately 36 gallons of fuel will be recovered from each
ton of mixed solid waste. (Additional fuel will be recovered if the aluminum
recovery subsystem is added, because this subsystem would allow for the
recovery of organic material left in the feedstock for the aluminum recovery
processes.)
The remaining gas stream goes through a series of cleanup steps and is
compressed for plant use. Part of the gas is used as the oxygen-free medium
for pneumatically transporting both the organic feedstock and the char into
and through the pyrolysis reactor. The rest of the gas is burned to preheat
10
-------
combustion air for the char heater, to preheat the reactor transport gas, and
to preheat dirty gas streams that are produced in various parts of the system.
The dirty gases are then burned along with the fuel gas in the afterburner.
The combustion gases coming out of the afterburner are cooled in the heat
exchanger, cleaned in a baghouse, and then vented to the atmosphere.
The liquid fuel product either goes directly to the oil storage tank or is
passed through a centrifuge if the solids content is too high. Liquid fuel that
does not meet product specifications is burned in a small boiler to produce
steam for heating certain pieces of equipment throughout the plant.
11
-------
energy and
materials balance
Energy Balance
It is expected that each ton of solid waste processed will yield a minimum
of 36 gallons (0.9 barrels) of liquid fuel product plus char and gas. The excess
combustible char will not be suitable for use as a fuel because its high ash
content will make it difficult to bum without producing excessive particulate
emissions. Combustible gas will be used internally in lieu of purchased fuel.
Energy inputs to the system, in addition to the solid waste, will amount to
135 kilowatt hours (kWh) of electricity and 2/3 gallon (5 pounds) of No. 2
fuel oil per ton of solid waste processed. The electricity will be used to
operate the various pieces of equipment. A small quantity of No. 2 fuel oil,
used to quench the process gas stream, will be vaporized and burned with the
uncondensed gas for process heat.
To express net energy yield per ton of solid waste, the energy inputs are
subtracted from the energy recovered and the result is shown as a percent of
total energy present in the waste. The energy value of the liquid fuel prod-
uct less the energy value of the electricity (calculated on the basis that the
average steam electric power plant in the United States uses 10,000 Btu of
fuel to produce 1 kWh of electricity) and No. 2 fuel oil used amounts to
2.66 million Btu of energy per ton of waste.* Since municipal solid waste
Energy out (liquid fuel) - Energy in (electricity, No. 2 oil)
*YJeld =
Total energy in solid waste
(36galX 113,910 Btu)- [(135kWhX 10,000 Btu)+ (5 IbX 19,200 Btu)]
1 ton X 9,200,000 Btu
4,101,000 - (1,350,000 + 96,000)
9,200,000
2,655,000
9,200,000
= 29 percent
= 0.29
12
-------
has an original heat value of about 9.2 million Btu per ton, the net energy
yield is about 29 percent.
The energy efficiency of the process, however, is expected to be more
favorable. This term refers to the fraction of energy recovered from the total
amount of energy put into the system, i.e., energy out divided by energy in.*
The San Diego plant will convert 39 percent of the energy input into useful
energy. Although this ratio is lower than those of most solid waste energy
recovery systems, it compares quite favorably with ratios for other methods
of converting solid fuels into gas or liquid, such as coal gasification and pro-
duction of petroleum from oil shale.
Materials Balance
The plant will process mixed municipal solid waste collected in packer
trucks from residential sources in El Cajon and surrounding communities.
Unfortunately, no composition analysis is available for El Cajon waste. The
analyses presented in this report are based on studies conducted on solid
waste generated in Vancouver, Washington, because this waste was the feed-
stock for most of the pilot plant tests conducted by Garrett during 1972-
73. These studies found that about half of the waste was organic material,
12 percent ferrous metal, 1 percent aluminum, and 7 percent glass (Table 2).
The ferrous metal content of Vancouver waste is relatively high; the percent-
age may well be somewhat lower at El Cajon.
The salable products—glass, ferrous metal, and liquid fuel—represent about
34 percent of the wet weight of incoming materials (Table 3 and Figure 5).
The remaining material is moisture (25 percent), solid residuals (21 percent),
and gaseous emissions (20 percent).
Energy out (liquid fuel)
* Efficiency =
Energy in (solid waste, electricity, No. 2 oil)
36 gal X 113,910 Btu
(1 ton X 9,200,000 Btu) + (135 kWh X 10,000 Btu) • " " 1Q 200 Btu)
4,101,000
9,200,000 + 1,350,000 + 96,000
4,101,000
10,646,000
= 39 percent
-=0.39
-------
TABLE 2
Composition of Municipal Solid Waste*
Component
Organics
Metals
Ferrous
Aluminum
Glass
Other inorganics
Miscellaneous solids
Moisture
Total
Percent
52
12
1
7
2
1
25
100
Tons per day
at plant
104
24
2
14
4
22
50
200
*Based on data from pilot testing conducted at Vancouver, Washington, 1972-73.
TABLE 3
Materials Balance
Input = 200 tons per day municipal
Outputs
Products (dry weight)
Ferrous metals
Glass
Oil
Residue to landfill (dry weight)
Solid residuals
Waste char
Waste gasesf
Moisture
Total
solid waste (150 tons
Percent
of wet weight
12
5
17
16
5
20
25
100
dry weight).*
Tons per day
23.7
10.4
33.8
(172 barrels)
31.5
11.1
39.5
50.0
200.0
the combustible gas which is used as a fuel in the afterburner and
led in the pyrolysis reactor.
-------
< x S
15 ~
oo
Figure 5. Thirty-four tons of liquid fuel, 24 tons of ferrous metal, and 10 tons of
glass will be produced each day from 150 f>ns of municipal solid waste. (All numbers
represent dry weight in tons per 24 hours.)
15
-------
quality
of the products
Liquid Fuel
The fuel product is an oil-like, chemically complex, organic fluid. The
sulfur content is a good deal lower than that of even the best residual oils.
The average heating value per pound of the pyrolytic "oil" is about
10,500 Btu, compared with 18,200 Btu per pound for typical No. 6 fuel oil
(Table 4). The lower heating value is due to the fact that pyrolytic oil is
lower in both carbon and hydrogen and contains much more oxygen. Fuel
oils are generally sold on a volume basis, however, and since the specific
gravities of pyrolytic oil and No. 6 are 1.30 and 0.98 respectively, a compari-
son of heating values is much more favorable to the former when expressed
on a volumetric rather than weight basis. A gallon (or barrel) of oil derived
from the pyrolysis of municipal waste contains about 76 percent of the heat
energy available from No. 6 oil. Each ton of solid waste yields about 4.1 mil-
lion Btu of energy as liquid fuel.
Pyrolytic oil is more viscous than a typical residual. However, its fluidity
increases more rapidly with temperature than does that of No. 6 fuel oil.
Hence, although it must be stored and pumped at higher temperatures than
are needed to handle heavy fuel oil, it can be atomized and burned quite well
at 240 F. This is only about 20 F higher than the atomization temperature
for electric utility fuel oils.
It has been found that pyrolytic oil from municipal waste can be blended
with several different No. 6 oils, although over a period of hours the heavier
pyrolytic oil settles out from the mixture because there is little mutual solu-
bility.
Successful combustion trials were carried out at the Kreisinger Develop-
ment Laboratory of Combustion Engineering, Inc., in Windsor, Connecticut,
with pyrolytic oil blended at 50 percent and 25 percent by volume with
No. 6 oil derived from an Alaskan crude. Combustion Engineering's formal
report on tb° work states:
Pilot-scale laboratory tests indicate that pyrolytic oil or blends of
pyrolytic oil with No. 6 fuel oil can be successfully burned in a
utility boiler with a properly designed fuels handling and atomi-
16
-------
TABLE 4
Typical Properties of Liquid Fuel from Solid Waste
and No. 6 Fuel Oil*
Liquid fuel
product
No. 6
fuel oil
Physical properties (dry basis):
Heating value (Btu/lb) 10,500 18,000
Specific gravity 1.30 0.98
Density (Ib/gal) 10.85 8.18
Volumetric heating value (Btu/gal) 113,910 148,840
Handling properties (at 14 percent moisture):
Pour point (F) 90 65-85
Flash point (F) 133 150
Pumping temperature (F) 160 115
Atomization temperature (F) 240 220
Viscosity (sSu at 190 F) 1,000 90-250
Chemical analysis (dry basis, % by weight):
Carbon
Hydrogen
Sulfur
Chlorine
Ash
Nitrogen
Oxygen
57.5
7.6
0.1-0.3
0.3
0.2-0.4
0.9 ]
33.4 j
85.7
10.5
0.5-3.5
t
0.5
L 2.0
1
*Finney, C. S., and D. E. Garrett. The flash pyrolysis of solid wastes. Presented at
Annual Meeting, American Institute of Chemical Engineers, Philadelphia, Nov. 11, 1973.
p. 18b.
fNot available.
17
-------
zation system. Ignition stability with pyrolytic oil and with the
blends was equal to that obtained with No. 6 alone; and stack
emissions when burning pyrolytic oil or blends indicated negligi-
ble amounts of unburned carbon at excess oxygen levels over
two percent.*
The San Diego Gas and Electric Company has agreed to purchase the fuel
for use in one of its existing oil-fired steam-electric power plants. However,
the fuel will first be put through an extensive testing program to determine
its suitability and to determine a price for it.
Several properties of the fuel are of special concern to the utility:
Corrosion. Because this fuel is more corrosive to metals than natural resid-
ual oils, particularly at high storage and handling temperatures, the use of
corrosion-resistant materials in the storage and handling equipment will be
required.
Temperature degradation. At temperatures above 200 F the fuel begins to
undergo chemical changes which adversely affect its viscosity. It will there-
fore be necessary to store the fuel at a lower temperature and heat it when it
is used.
Mixing. This fuel cannot be mixed with No. 6 oils for extended periods
because it is not soluble, and the great difference in specific gravities (Table 5)
causes rapid separation unless the mixture is thoroughly agitated.
Composition. This fuel has higher ash and nitrogen content than No. 6
oil; this could affect the rate of boiler tube fouling and the emission of partic-
ulates and oxides of nitrogen.
Ferrous Metal
Ferrous metal will be separated magnetically following the primary shred-
ding operation. Ninety-five percent of the ferrous in the waste stream will be
recovered, and the recovered material will be about 95 percent pure ferrous.
Several scrap dealers in San Diego and Los Angeles have expressed a desire to
purchase the ferrous metal.
Glass
Glass will be recovered as a mixed-color cullet. It should be better than
99 percent pure with a moisture content of about 20 percent. The glass prod-
*Borio, R. W. Combustion and handling properties of Garrett's pyrolytic oil Wind-
sor, Conn., Kreisinger Development Laboratory (Department 683), Dec. 4,1972. p.1-2.
18
-------
uct will consist of very small particles (at least 60 percent by weight will be
less than 50 mesh). A tentative market has been established with Glass Con-
tainer Corporation to use the cullet in the manufacture of either green or
amber bottles. Its small particle size will require the user to maintain separate
handling and feeding facilities; it will thus command a somewhat lower sales
price than would normally be expected for glass cullet of this purity.
Char and Gas
In addition to the salable products, two fuel products will be produced for
internal use.
Char produced at the rate of about 110 pounds per ton of solid waste will
be used internally as the heat transfer medium. It will first be heated in the
char heater and then mixed with the solid waste as it is fed into the pyrolysis
reactor. Five pounds of char will be fed into the reactor for every pound of
organic feedstock. Once a stockpile of char has been established, the excess
will be discarded. The discarded char will have a heat value of 9,000 Btu per
pound, but its high ash content (32 percent) will make it unsuitable for sale
as a fuel. Garrett is examining its potential value as a filler for various plastic
products.
Combustible gas will be produced from the solid waste at a rate of 275
pounds per ton. This gas will be used internally as a fuel in the drier, in the
char heater, and in the preheater for combustion air and transport gas.
19
-------
economics
An economic analysis of the 200-ton-per-day facility to be built in El
Cajon has been made on the basis of definitive estimates of the capital cost
and expected operating costs and revenues. It should be kept in mind, how-
ever, that this plant is below the size range normally considered cost-effective.
The capital cost for the facility was estimated in June 1974 to be $6.3 mil-
lion. This includes engineering design, site development, construction, over-
head, and the contractor's profit (Table 5).
Amortization of capital is assumed to be at 6 percent over 20 years.
Annual costs for normal operation, exclusive of a detailed testing and
evaluation program, are projected as follows:
Operating costs
Electric power $.127,000
Other utilities 39,000
Labor (20 positions) 361,000
Maintenance 317,000
Land rent 34,000
Residual transfer and disposal 38,000
Total operating costs 916,000
Capital costs
Amortization of $6,344,000 553,000
(20 years at 6 %)
Total annual cost $ 1,469,000
To estimate the plant's revenues, a dollar value can be assigned to the liquid
fuel based on its energy value to the utility (less an allowance for the utility's
extra handling costs). The actual price to be paid for the fuel will be deter-
mined during the first operating year. Revenues will also be generated through
the sale of ferrous metals and mixed-color cullet.
Total quantities of recovered materials are calculated on the assumption
that the plant will achieve 85 percent of its design capacity on an annual
basis. The plant is designed (and operating expenses are calculated) for 24-
hour-per-day operation, 7 days per week. Throughput will thus be 62,050
tons per year (85 percent of 200 tons X 365 days).
20
-------
TABLE 5
Breakdown of Capital Costs Estimated for
200-Ton-per-Day Pyrolysis Plant
June 1974
ltem estimates
Design $ 777,000
Site development costs 679,000
Construction 3,716,000
Receiving and preparation (through air classifier and trommel)
Equipment 596,000
Installation 885,000
Organic feed preparation
Equipment 317,000
Installation 306,000
Pyrolysis and fuel recovery
Equipment 254,000
Installation 398,000
Glass recovery
Equipment 113,000
Installation 262,000
General and utility (product storage, afterburner, package boiler,
spare parts)
Equipment 312,000
Installation 273,000
Inflation, overhead, and contractor's profit 1,172,000
Total $6,344,000
21
-------
On a wet weight* or as-sold basis, the amounts of revenue-producing ma-
terials are:
Ferrous metal 7,874 tons per year
Glass 4,033 tons per year
Liquid fuel 53,644 barrels per year
Revenues for the various products are calculated on the basis of mid-1974
market values less an allowance for transporting the products to the users'
facilities. Revenues actually produced from the sale of ferrous metal from
this plant may be somewhat less because El Cajon's waste is not expected to
have as high a metal content as the waste samples used in this analysis. An-
nual estimated revenues are:
Ferrous metal (7,874 tons at $47/ton) $370,000
Glass (4,033 tons at $6.40/ton) 26,000
Liquid fuel (53,644 barrels at $4/bbl) 232.000
Total $628,000
Net costs will thus be:
Total annual cost $ 1,469,000
Annual revenues - 628,000
Net cost $ 841,000
This results in a net cost per ton of $13.42. It should be noted that the cost
per ton would be lower in a full-sized plant with a throughput larger than that
of this demonstration unit.
"The weights for the products as shown in the material balance in Table 3 are dry
weights. In actual operations these materials will contain certain amounts of moisture.
Product values are based on the wet weight of the respective materials. Ferrous is
6.64 percent moisture; glass is 20 percent moisture; the fuel is 14.2 percent moisture.
22
-------
environmental impacts
of the system
Conservation of Resources
Using this system, fuel, metal, and glass are recovered from solid waste, all
of which would ordinarily be buried in a landfill. Each ton of waste de-
livered to the facility will provide the equivalent of 27 gallons of No. 6
heating oil; in addition, 237 pounds of ferrous metal and 104 pounds of glass
will be recovered. The amount of waste going to the landfill will be reduced
by over three-fourths.
Also, as a form of disposal the system is free of the health and environmen-
tal hazards sometimes associated with conventional disposal methods; such
hazards include leachate production from disposal sites and subsequent water
pollution, air pollution from open burning and incinerators, dangerous ac-
cumulations of gas in landfills, and harborage of rodents and other vectors.
Atmospheric Emissions
Pyrolysis Plant. In designing the plant careful attention was directed to
minimizing the chance of any adverse impact on air quality. Although air
will be used throughout the system, the equipment will be designed to con-
trol emissions. The air from the drier, air classifier, and pneumatic transport
systems will be used as combustion air in the process heater. All other air
will be recirculated within the system. Exhaust gases from the process heater
will be cooled and then passed through a bag filter, so that when finally re-
leased to the atmosphere, they will be in compliance with Federal, State, and
local standards.
Combustion of Fuel Product. In converting solid waste to a liquid fuel one
of the primary objectives is to produce a fuel that burns cleaner than the
original solid waste and that can economically be made to burn at least as
clean as the fossil fuel it replaces. Limited test data have been collected on
emissions of sulfur dioxide and oxides of nitrogen produced when the pyrolyt-
ic oil is burned. Concentrations of sulfur dioxide in the flue gas were directly
proportional to the sulfur content of the fuel. They ranged from 120-155 parts
per million (ppm) when the fuel was blended with No. 6 oil (having a sulfur
23
-------
content of 0.4 percent), up to 290 ppm when 100 percent pyrolytic oil was
burned. This compares quite favorably to the 380 ppm produced when No. 6
fuel oil having a 1 percent sulfur content was burned. Nitrogen oxide pro-
duction was somewhat higher for the pyrolytic oil than No. 6 heating oil.
Blends of No. 6 and pyrolytic oil produced an average of 420 ppm of oxides
of nitrogen. Additional experimentation with various firing methods is needed
to determine the impact this fuel will have on emissions of oxides of nitrogen.
In order to assess fully the environmental impact of this fuel, the San Diego
Gas and Electric Company has proposed a 21-month test program incor-
porating both laboratory and boiler tests. Flue gas analysis will include partic-
ulates, oxides of nitrogen, oxides of sulfur, hydrochloric acid, carbon mon-
oxide, and visible emissions.
Water
The plant will use 16,800 gallons of water per day. This water will be used
in the glass recovery process, and part of it will be recycled for char
quenching.
Water from the plant will be discharged to the sanitary sewer system fol-
lowing removal of settleable solids. No significant impact on the treatment
plant appears likely as this effluent is equivalent to the waste produced by
less than 200 people.
Land
All residual waste will be disposed of in a sanitary landfill. This amounts
to 42.6 tons per day or about 21 percent of the original quantity of solid
waste.
Odors
Special precautions will be taken to insure that no odors emanate from the
plant. All solid waste will be unloaded in a fully enclosed building, and no
waste will be stored at the site longer than 24 hours. The pyrolysis process
will be contained fully so that there are no emissions.
Air used in air classification will be combined with the combustion gases
and dryer exhaust and will be injected into the process afterburner and heat
exchanger to destroy odors. These gases will then be cooled, scrubbed, and
filtered before being released to the atmosphere.
Noise
Noise can result from truck traffic making deliveries to the plant and from
equipment in the plant. Approximately 35 truckloads of refuse will be de-
24
-------
livered to the plant each day between 8:00 am and 5:00 pm. Unloading will
be done inside the receiving building. Any equipment which would create a
noise disturbance above ambient levels at the property line will be insulated so
as to muffle the sounds.
summary
The San Diego County demonstration plant, now under construction and
scheduled to begin operating around August 1976, will recover at least 36 gal-
lons of liquid fuel (equivalent in heating value to 27 gallons of No. 6 fuel oil)
from each ton of municipal solid waste using the Garrett flash pyrolysis sys-
tem. This system employs a relatively complex fuel preparation process in-
volving two stages of shredding and air classification. The fuel will be pur-
chased by the San Diego Gas and Electric Company for use in its oil-fired
boilers. The pilot tests indicate that the liquid fuel can be stored and trans-
ported, but some modifications in equipment and handling may be necessary
because of its special characteristics.
Ferrous metal and glass will also be recovered, and an aluminum recovery
system may be added later.
The demonstration plant, with a capacity of 200 tons of waste per day, is
not considered large enough to be cost-effective, but the data collected on its
operations will enable evaluation of the process and provide a base for de-
signing larger facilities.
The potential environmental benefits from this system—the resources saved
and the reduction in volume of wastes—are great. In order to control all possi-
ble impacts on the environment, careful attention has been given to this as-
pect of plant design; the emissions from combusting the liquid fuel will be
fully tested.
25
-------
bibliography
General
1. Markets and technology for recovering energy from solid waste,
by Steven J. Levy. Environmental Protection Publication SW-
130. Washington, U.S. Environmental Protection Agency, 1974.
31 p.
2. Resource recovery and source reduction; second report to Con-
gress, by U.S. Environmental Protection Agency, Office of Solid
Waste Management Programs. Environmental Protection Publica-
tion SW-118. Washington, U.S. Government Printing Office, 1974.
112 p.
3. Decision-makers guide in solid waste management, compiled by
Robert A. Colonna and Cynthia McLaren. Environmental Protec-
tion Publication SW-127. Washington, U.S. Government Printing
Office, 1974. 157 p.
Pyrolysis
4. The flash pyrolysis of solid wastes, by C. S. Finney and
D. E. Garrett. Presented at Annual Meeting, American Institute
of Chemical Engineers, Philadelphia, Nov. 11-15,1973. 25 p.
5. Pyrolysis of municipal solid waste, by Steven J. Levy. Waste Age,
5(7): 14-15,17-20, Oct. 1974.
6. Solid waste pyrolysis systems, [by J. Robert Holloway]. Wash-
ington, Office of Solid Waste Management Programs, Resource
Recovery Division, Nov. 1974. (Unpublished list.)
7. Technical report on the Garrett pyrolysis process for recycling
municipal solid waste, by H. F. Bauer. La Verne, Calif., Garrett
Research and Development Company, Inc., Dec. 29, 1972. [104
p.] (Unpublished report.)
26
-------
Other Reports of EPA Demonstrations
8. Energy recovery from waste; solid waste as supplementary fuel
in power plant boilers, by Robert A. Lowe. Environmental Pro-
tection Publication SW-36d.ii. Washington, U.S. Government
Printing Office, 1973. 24 p.
9. Recovering resources from solid waste using wet-processing;
EPA's Franklin, Ohio, demonstration project, by David G. Arella.
Environmental Protection Publication SW-47d. Washington,
U.S. Government Printing Office, 1974. 26 p.
10. Baltimore demonstrates gas pyrolysis; resource recovery from
solid waste, by David B. Sussman. Environmental Protection Pub-
lication SW-75d.i. Washington, U.S. Government Printing Office,
1975. 28 p.
11. The demonstration of systems for recovering materials and energy
from solid waste, by John H. Skinner. Presented at National
Materials Conservation Symposium, National Bureau of Standards,
Gaithersburg, Md., Apr. 29, 1974. [Washington], U.S. Environ-
mental Protection Agency, 1974. 20 p.
Mffll64b
27
-------
------- |