AN OVERVIEW OF SAN DIEGO COUNTY'S

RESOURCE RECOVERY PLANT

ANIL K. CHATTERJEE Acres American, Inc.

Buffalo, New York

YVONNE GARBE Environmental Protection Agency

Washington, D. C.

ABSTRACT

San Diego County's resource recovery plant is designed to process 200 tons per day (181.5 t/day) of municipal solid waste in a flash pyrolysis system to produce 200 barrels of synthetic oil, 15 tons (13.6 t) of ferrous metals, 10.7 tons (9.71 t) mixed colored glass and 1.2 tons (1.09 t) of non­ferrous metals. This paper describes the flash pyrolysis process, including the major system components and their individual functions. Capital outlays, fmancial participation, the plant shakedown, startup and operating data will also be discussed. 1

remaining waste stream. The San Diego Gas & Electric Company has a contract with the County to purchase the pyrofuel and burn it as a supple­mental fuel in one of their existing power boilers. After construction of additional storage and fuel handling equipment at the utility, initial test burns of the fuel will begin in the winter of 1977.

The cost of the project now totals $14.4 million contributed by the following participants:

Occidental Research Corporation

Environmental Protection Agency

San Diego County

- $ 8.2 million

-

-

4.2 million* 2.0 million

$14.4 million INTRODUCTION *Total amount to date.

In September 1972, the County of San Diego, California, accepted a $3.8 million grant from the U.S. Environmental Protection Agency (EPA) to demonstrate a flash pyrolysis process developed by Occidental Research Corporation. The process is designed to extract and pyrolyze the organic fraction of municipal solid waste to produce fuel oil called pyrofuel. Occidental Research Corpora­tion projects that one barrel of pyrofuel will be' produced for each ton of solid waste received at the plant. In addition, ferrous and nonferrous metals and glass will be recovered from the

1 At the time of this writing, the plant was in the early stages of startup and little operating data were available. More information and data will be available by the May 1978 conference.

447

Plant construction began early in 1976 and was completed in December 1976. For the following flYe months, the plant was in shakedown and has been in startup ever since. A recent aerial view of the 5.3-acre (2. 15-hectare) plant is shown in Fig. 1.

PROC ESS D ESCRIPTION

A Simplified process flow diagram is shown in Fig. 2. Domestic municipal solid waste is dropped onto the tipping floor inside the receiving building. A front-end loader pushes the material into a conveyor pit that feeds a 1000 hp horizontal hammermill. The waste is shredded to a nominal 3-in. particle size at the rate of 25 tons per hour (22.7 t/h). From the shredder the material is

passed under an electromagnet to extract ferrous metals. The waste stream is then conveyed onto a rotating stacking conveyor inside a storage room. The stacking conveyor rotates 360 deg. each hour and automatically distributes the shredded material onto the storage room floor below. For 20 min. of each hour during the day shift, the conveyor pauses over a conveyor pit that feeds one-third of the incoming shredded waste to the rest of the plant during the first shift of operation. The remaining two-thirds waste is stored for use during the seconcLand third shifts. At that time, a fron t end loader is used to move the shredded material from the storage room floor into the pit feeding the rest of the plant.

Shredded waste from the storage area is carried to a doffing roll bin2 which meters the material into a new zigzag air classifier designed and tested by Occidental Research Corporation. A unique feature of the air classifier is the recirculation of air in a closed loop. Inside the classifier, the lighter fraction of the waste (mostly organics) is blown off as "overhead flow" while the heavier materials

2 A constant feed bin equipped with drag chain and spiked delumper rolls.

(mostly inorganios, e.g., glass, nonferrous metals, rocks, dirt) are dropped to the bottom as "under­flow" stream.

The light fraction is dried using hot air heated from burning the combustible gases produced in the pyrolysis reactor.

After drying, the material is screened for further removal of residual glass and metal fines before it is shredded to a nominal -14 mesh particle size in a 350 hp attrition mill. Meanwhile, the finer particles (glass and organics) that fall through the screen are fed to an air table where a combination of vibrating motion and air flow separate the light organics from the glass. The glass is directed to the glass recovery subsyst�m. The light organic material is carried back to the shredded organic waste stream and together the waste is stored in a second doffing roll bin that feeds the pyrolysis reactor. The pyrolysis reactor is a refractory lined vertical pipe. There is a con­tinually reCirculating flow of ash at a temperature range of 1350 to 1400 F (732 to 760 C). The organic feedstock is pneumatically transported using oxygen-free recycled gas. At startup condi­tion, nitrogen gas is used to carry the organics to

Occidental Research Corporation's 200 TPD Resource Recovery

Demonstration Center E1 Cajon, San Diego County, CA

FIG.1 AERIAL VIEW OF SAN DIEGO COUNTY'S RESOURCE RECOVERY PLANT

448

B

the reactor. The organic waste is turbulently mixed with the hot ash, absorbing heat from the fluidized ash stream until the optimum pyrolysis tempera­ture range of 850 to 950 F (454 to 510 C) is reached. The process is called "flash pyrolysis" because the distillation operation is performed by rapid and controlled application of heat, the dura­tion of which is measured in seconds.

Three stages of cyclones are used to remove the char from the reactor gases. After char removal,

the pyrolytic vapors are quenched rapidly with a No.2 diesel oil to prevent the large-molecule oil components from cracking further to less desirable elements. The products are then separated into pyrofuel oil, gas and water.

The noncondensing vapors are sent through an acid scrubber and compressed for plant use. Part

of the gas is used for the oxygen-free transport medium. The remaining gas is burned to preheat combustion air for the char heater, to preheat the reactor transport gas, to supply heat to the dryer and to oxidize dirty gas streams produced through­out the system.

The pyrofuel is separated from the quench oil

in a decanter. As the pyrofuel is more dense than No. 2 diesel oil, it settles down to the bottom of the decanter and is then tapped into oil storage tanks.

The remainder of the plant process consists of glass and aluminum recovery subsystems. A glass­rich stream is separated from a nonferrous-rich stream by passing the air classified heavy fraction through a trommel. The glass-rich stream is direct­ed to the glass recovery subsystem where it is washed, reduced to a -20+200 mesh size, and then sent through a series of froth flotation cells to recover the high-purity color-mixed glass prod­uct.

The nonferrous-rich stream dropped out of the trommel screen is directed to the aluminum recovery subsystem. First, the stream is passed under a magnetic belt for removal of tramp ferrous metals and then sent through two stages of

aluminum magnet separators to recover a relatively pure aluminum product. Aluminum recovery is achieved when the incoming waste stream is

carried on a moving belt over a pair of linear

U The San Diego Solid Waste Resource Recovery Project

SIMPLIFIED FLOW DIAGRAM COMPRES SOR

Q.UENC VEN TURI ..,

MAGNET SECONC\o\RY SH R

SHREDDER SCREEI"-�� _--,

AIR TABL

----... FROTH FLOTATION

PYROLYSIS REAC TO

BIN

u= 0 RECYC-AI...

0 0 0 GLASS EDDY CURRENT ..!-.------ ALUMINUM

CHAR BURNER

'----------- FERROUS METAL

FIG.2 SIMPLIFIED FLOW DIAGRAM

449

•

HEAT EXCHANGER

AIR ATMOS.

P'(RQ FUEL

motors. The motors create a magnetic field over the conveyor belt and induce eddy currents in the conductive metals. The charged metals react with the magnetic field and are deflected off the belt into a collection bin.

POLLUTION CONTROL

Any air or gas streams that contain particuJate matter are passed through the bag house before

being vented into the atmosphere. Any gas stream that might contain combustibles and organic hydrocarbons is combusted in the afterburner before being passed to the bag house.

A large quantity of water is used for the glass plant. However, in the glass plant the water is treated, fIltered and recycled over and over again.

Only make-up water is used to balance the water need. Other wash water and cleaning streams are collected in an impound pond, tested and then dis­charged to the city sewer.

The tailings from the glass plant, from the air table, and char from the pyrolysis process are sent to the city land fill area for disposal.

Noise abatement steps have been taken in the glass and aluminum plant areas and regular noise levels are monitored to meet local, state and federal requirements.

OPERATIONS

Plant shakedown began in early 1977. In the follOwing four months, shakedown efforts were concentrated at the front end operations of the plant which includes the primary shredder, storage area, doffmg roll bin, air classifier and trommel operations. The aluminum and glass recovery sub­systems were started up soon after. During this period, minor modifications were made in the process to upgrade the recovered ferrous product, and to reduce noise levels in the aluminum and glass recovery subsystems.

Because of the single stage magnetic separation operation, the separated ferrous metals have been found to contain a fair amount of organic wastes. Steps are being taken to clean up the contaminants by providing a vacuum suction by-pass line to the ferrous metal discharge chute.

Preliminary physical analysis of ferrous metal and aluminum plant products have been made. Table 1 illustrates some of the typical data. It shows that the aluminum content of the aluminum plant product ranges from 81 to 85 percent, and

ferrous metal products contain organic contami­nants ranging from 8 to 9 percent. More physical and laboratory analyses will be performed on the above in the coming year.

Limited performance tests were taken on the Occidental-designed zig-zag air classifier. The test data have been shown in Table 2 and Table 3. For easy understanding, some of the characteristic values have been plotted.

Figure 3 is plotted as MSW feed rate versus doffmg bin drag chain settings. The data were plotted with the bypass damper fully open and half-open conditions. The effect of the fully closed bypass damper was not conclusive. Figure 4 illustrates the ratio of overflow to underflow versus drag chain settings. No conclusion could be derived from Fig. 4 for operation with 70/30 splits of overflow versus underflow of the air classifier. The split between glass plant and aluminum plant feed at various bypass opening conditions as a percent of air classifier feed versus pressure drop across the air classifier is shown in Fig. 5.

Shakedown in the organic feed preparation operations (dryer through second doffing roll bin) began in May 1977. A major problem that developed in this area was severe wear to the secondary shredder discs caused by excessive amounts of glass fines in the organic feed stock. The problem now appears to have been corrected as a result of: (1) readjusting the air classifier over­head flow and underflow ratio to allow more glass

to fall with the heavy fraction; (2) modifying the screening equipment with multiple screens deck; and (3) replacing the shredder discs with discs having harder wearing surfaces.

Other changes in the system include adding a drop-off box in the dryer cyclone return line

450

to remove Circulating organic particles within the recycle system and adding additional safety equipment to the afterburner unit.

At the time of this writing, the pyrolysis had been started up three to four times at 20 percent

capacity, with the longest run lasting 3 he 45 min. Only longer periods of continuous pyrolysis operation will produce a detectable quantity of pyrofuel for sampling.

Future test runs (I 0-12 he duration) are scheduled in November at 20 percent capacity followed by similar runs at 50 percent and 75 per­cent capacity in the next few months. More data and information will be available on pyrolysis by next spring.

PYROFUELTEST BURNS

It is expected that sufficient quantities of pyrofuel will be produced by February 1978 to perform co-firing of pyrofuel with the residual oil

to San Diego Gas & Electric Company's 980,000 lb/hr, 2150 psig @ 1000 F superheated steam boiler. The EPA-sponsored contractor will perform emission measurements to include particulate loading, particle size determination, SOx, NOx, hydrocarbons, and trace metal concentrations. The emission measurements will be made at the full­and part-load conditions of the boiler and at various co-firing ratios of pyrofuel to residual oil. San Diego Gas & Electric Company's engineers will evaluate the combustion characteristics during co-firing of the fuel to the boiler. These results will also be available by spring 1978 presentation.

ECONOMICS

Like most small-scale demonstration plants, the San Diego resource recovery facility is not ex­pected to be economically competitive. It will serve mainly to test the application of this

_

pyrolysis and materials recovery process in solid

12

DOFFING ROLL BIN DRAG CHAIN CALIBRATION

DAMPER POSITION X HALF OPEN -

o OPEN -

waste management, and will define the expected economics of larger-scale systems. A major part of the evaluation to be conducted during the demonstration period will be assessing economic feasibility for constructing and operating larger scales (I ,000 and 2,000 TPD) of this system.

ACKNOWLEDGMENT

This evaluation program is supported by Environmental Protection Agency, Office of Solid Waste's contract with Acres American, Incorpo­rated, Buffalo, New York.

The schematic diagram and related information are extracted from Occidental Research Corpo­ration's brochures.

100

90 r

80 r

r

-

-

RATIO OF OVERFLOW TO UNDERFLOW

VS.

DRAG CHAIN SETTINGS

(DOFFING BIN)

• •

A

0· BY PASS CLOSfD

A' BY PASS HALF OPEN

0- BY f'lISS OPEN-FUll:

I I I I I I I I 0.2 0.6 1.0 1.6

,

DRAG CHAIN SETTING

o

- 10

• 20

-130

-

-

I 1 2.0

FIG.4 RATIO OF OVERFLOW TO UNDERFLOW

2 VERSUS DRAG CHAIN SETTINGS

DRAG CHAIN SETTING

FIG.3 DRAG CHAIN CALIBRATION

1.6 2.0

451

� oJ ... a: w o z �

� o

c w w u. a: w -

u. -II) II) -< ...J U

Ia: -

-< >Ii. I-�

DOFFING �OLt BIN UNDERFLOW VS.t:.P ACROSS THE AIR CLASSIFIER

12 r---------------�========� o GLASS 8. AL UMINUM

10

8

6

4

2

1.2 1.4 1.6 1.8

11 P ACROSS AIR C LASSI FI ER

FIG.5 UNDERFLOWS VERSUS /::;P ACROSS AI R

CLASSIFIER

TABLE 1 SUMMARY OF SHREDDED METAL CHARACTERIZATION

PLANT: ORC RESOURCE RECOVERY CENTER

ORGANIZATION: Acres American , Inc. PERIOD: August 16-17, 1977

TEST NUMBERS

DESCRIPTION 1 2 3 REMARKS

Avg. Bulk Density of Products of aluminum Shredded Aluminum 266.7 254.6 262.7 plant random samplinR lb/cu yd (kg/cu m) (158.2) (151. 0 (155.8)

Avg. Bulk Density of Random sampling Magnetic Separator Material 969.7 937.1 961. 6 lbs/cu yd (kg/cu m) (575.2) (556.1) (570.5)

Character- Aluminum 81. 0 84.4 83.3 Hand sorted physical ization of

Le ad 5.8 6.7 8.0 characterization Shredded Metal Zinc 4.4 5.1 3.4 (% by wt)

Copper 4.4 1.9 5.0

Organic 4.4 1.9 0.3

Characteriza- Hands sorted physical tion of Mag- Met al 90.5 91. 3 91. 9 characterization netic Separa-tor Material

Organics 9.5 8.7 8.1 (% by wt)

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TABLE 2 AIR CLASSIFIER TEST DATA

AIR AIR H2O CLASSIFIER CLASSIFIER t.P DURATION TOTAL FLOW FLOW

RUN A/C PRESS. OF RUN DAMPER PROCESSED OVERHEAD UNDERFLOW RATIO NO. DIFF . (min) POSITION (lb/hr) (lb/hr) (lb/hr) OVER/UNDER

1 1.7 38 Closed 9, 663.2 7, 957. 9 1, 705. 3 82/18

2 1.2 44 Open 10,022.7 7,568.2 2, 454. 5 76/24

3 1.8 30 Closed 14,400.0 12,300.0 2, 100.0 85/15

-1 1.3 Plugged Open - - -- -- --

5 1.2 48 t Open 11,667.5 8,550.0 3, 117. 5 73/27

6 1.8 27 Closed 17,042.2 14, 688.9 2,353. 3 86/14

7 1.8 35 Closed 12, 992.6 11, 108. 6 1, 884. 0 85/15

8 1. 5 26 t Open 21, 150.0 14,561. 5 6,588.5 69/31

9 1. 2 45 Open 10,958. 7 7,840.0 3, 118.7 72/28

10 1.7 57 Closed 7,671.6 6,168.4 1, 503.2 80/20

11 1.2 35 t Open 14, 982.8 10,645.7 10, 645. 7 71/29

12 1.2 50 t Open 8 , 184 . 0 5,484. 0 2, 700.0 67/33

6' 1.8 27 Closed 19,024.4 15,755.5 3, 268. 9 83/17

TABLE 3 AIR CLASSIFIER TEST DATA

I 1b/hr CLASSIFIER CLASSIFIER

TOTAL FEED TO FEED TO GLASS ALUMINUM ALUMINUll GLASS ALUM I NUl!

RUN PLANT ALUMINUM TROMMEL TROMMEL PLANT PLANT PLANT PLANT NO. FEED RECOVERED OVERSIZE MAGNETICS REJECTS FEED (%) (%)

1 710.5 78.9 315.8 78.9 521.1 600.0 7.35 6.21

2 940.9 27.3 1070.4 81. 8 334.1 361.4 9.39 3.61

3 720.0 60.0 80.0 340.0 900.0 960.0 5.00 6.67

4 -- -- -- -- -- -- -- --

5 1025.0 75.0 112.5 155.0 1750.0 1825.0 8.79 15.64

6 733.3 111.1 44.4 86.7 1377.8 1488.9 4.30 8.74

7 600.0 102.8 17.1 101.1 1062.9 1165.7 4.62 8.97 ,

8 1800.0 46.1 3853.8 103.8 784.6 830.7 8.51 3.93

9 893.3 213.3 133.3 118.7 1760.0 1973.3 8.15 18.01

10 494.7 136.8 52.6 50.5 768.4 905.2 6.45 11.80

11 1234.3 154.3 1217.1 154.3 1577.1 1731.4 8.24 11. 56 •

12 780.0 60.0 96.0 72.0 1692.0 1752.0 9.53 21. 41

6' 822.2 -- 2355.5 91.1 -- -- 4.32 - -

Key Words: Fluidized Bed, Gasification, Pyrolysis, Refuse Derived Fuel, Resource

453

Discussion by

Roger S. Hecklinger

Charles R. Velzy Associates

Armonk, New York

This paper has been prepared as a result of an EPA supported evaluation of an EPA supported demonstration plant. The authors acknowledge that much additional information is being gathered which no doubt will be presented at some time in the future. However, the manner in which some of the data is presented here raises questions.

For example: Tables 2 and 3 present perform­ance test data taken on the air classifier. We are told: "For easy understanding, some of the charac­teristic values have been plotted." Figure 5 plots the percent of air classifier feed going to the glass plant and the aluminum plant against pressure drop across the air classifier. The two curves are smooth and indicate a very definite and predict­able response to pressure drop. While the tables include eleven complete data runs, the figure utilizes data for the glass and aluminum plants from just three of the runs plus glass plant data from one other run. None of the remaining data, that is, more than two-thirds of the data, would support the curves plotted on Fig. 5. To illustrate, the data points for 1.2 in. of pressure drop were taken from Run 2 and show feed to the aluminum plant to be less than one half of the feed to the glass plant. Runs 5, 9, 11 and 12, also for 1.2 in. of pressure drop, all show feed to the aluminum plant higher than feed to the glass plant. Perhaps there is a rational explanation for such selective use of data. If so, it should have been carefully explained in the paper.

The final report on the evaluation of this im­portant demonstration project is anxiously await­ed during a comprehensive, well-planned test pro­gram. This paper is not an encouraging harbinger.

Discussion by

Professor A. Buekens

University of Brussels

The presentation on the Occidental Petroleum process and the disasterous experience in Baltimore may lead to the erroneous conclusion that py­rolysis and gasification processes are technically unfeasible. It should be borne in mind, however, that it took 50 years to develop conventional

mass-incineration techniques and that some early incinerator plants, like the von Roll plant near Brussels (constructed in 1958), required extensive modifications before being capable of normal operation.

454

On the other hand, it can be pointed out that several Japanese firms, such as Ebara Mfg. Co. Ltd. and Tsukishima Kikai Co. Ltd., successfully operated dual fluidized bed pyrolysis systems. The latter company operated their demonstration plant continuously for 1200 hr with a total oper­ating time of 4000 hr. The system proved to be flexible, easy to operate, safe and durable.

AUTHORS' REPLY

To Roger S. Hecklinger

To answer Mr. Hecklinger's comment, we have to look into the data gathering circumstance and the prinCiples of air classification.

The data that were reported in the paper were gathered in the early startup stage of the plant. We had very little control over the operation and gathering of data. Emphasis at that time was to try to run the plant. As a result, many of the de­signed test procedures and data gathering activities could not be instituted.

Let us look into the complexities of the Zig Zag air classification process.

The primary shredded MSW entering the air classifier is of mixed sizes, shapes and different specific gravities. The buoyant force acting on the falling refuse particles by the upward moving air stream in the air classifier is a function of: (a) particle shape, 9b) particle density, (c) fluid mass flow rate, (d) particle mass flow rate and (e) void fraction. Due to inherent heterogeneity of the MSW feed to the air classifier, it is difficult to correlate relations of many of the component fractions. The air classifier has two exhaust streams. The overhead (light fraction) stream and the under­flow (heavy fraction) stream. It is easy to collect the overhead stream, weigh it, and perform loss on ignition tests to determine the organic vs in­organic content. However, the underflow stream consists of the following:

1. Glass plant feed. 2. Small ferrous product. 3. Large size ferrous product. 4. Aluminum plant product. 5. Aluminum plant rejects.

6. Oversize material materials. 7. Miscellaneous spills. Unless a controlled design test procedure is

adopted, it is difficult to collect precise data of the underflow stream. Had all the collected data points been plotted, the plotting would reflect a random scattering of data that will show no meaningful correlations. To avoid this, the author attempted to draw the logical trend curve based on the principles of air classification. The plotted curves are by no means a design correlation.

We hope to perform exclusive performance tests on this air classifier and every effort will be made to collect data that will show the fractional component correlations.

To Professor A. Buekens

I agree with Prof. Buekens' comment. Com­mercialization of the pyrolysis technique to

455

process MSW has a definite future. The principles of the pyrolysis process of MSW have been de­monstrated in the bench scale study, pilot plant work and in the demonstration type projects by various industries in this country and abroad.

However, the mechanical and process tech­nology related to the specific pyrolysis process has yet to be developed to a point where a munici­pality can adopt the method of processing MSW for harnessing the valuable energy.

Only continued efforts by the industries and government can make this pyrolysis process a success. Occidental, in their demonstration plant at San Diego, has proven the concept of the flash pyrolysis process. The process has produced an organic liquid that is combustible. The process technology hardware design has not, however, been perfected to a point where continued opera-· tion of the plant could be maintained.