DESIGN AND OPERATION OF A SUSPENSION

FIRED INDUSTRIAL SOLID WASTE DISPOSAL

SYSTEM FOR KODAK PARK

ROBERT L. MERLE, P.E. MELVIN C. YOUNG

GLEN R. LOVE

Eastman Kodak

INTRODUCTION

Kodak Park is an industrial complex in Rochester, New York where the center of photo· graphic technology is located. It is a 2000 acre complex with more than 200 buildings where 30,000 people are employed. This great concentra­tion of people and facilities has all the problems of a city including the problem of solid waste disposal.

A study of waste disposal problems was begun in 1964 and after consideration of various schemes it was decided that a suspension fired system would best meet the needs for burning general plant wastes and industrial waste treatment plant sludge. Some chemical wastes are disposed of in this facil­ity. All waste fuels are prepared and then convey­ed into the boiler furnace combustion chamber.

When this system concept was installed, it was new and untried, as a result there was a consider­able amount of debugging required. The major problems occurred in the material handling areas with storage bins and conveyors. Some problems have resulted because of limited area. There have been boiler problems but only of a minor nature.

This facility was a new system at a new location (see Figure 1) and as a result it was necessary for us to hire new men to develop a training program to instruct the men.

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DESIGN

BACKGROUND

Normally, Kodak performs engineering and design on most of its facilities but on this project we decided to retain an outside engineering firm, Metcalf and Eddy Engineers-of Boston. Our Engineering Division was overloaded during this period and we believed that the experience of an outside firm with a background in solid waste would be valuable. Much of the work was done in collaboration between Kodak and M&E Engineers. Consulting work was also performed by Arthur D. Little Inc. of Cambridge, Mass. and later Combus­tion Engineering assisted in completing the modi­fications.

The site selected for the new solid waste dispos­al system was in Kodak Park West near the geo­graphical center of the Kodak Park manufacturing operation. This area was also a desirable location because in the immediate vicinity we have an exist­ing incinerator, an ash silo, a steam distribution system and a 360 f1. (110 M) chimney.

We decided that the solid waste disposal system would be sized for 314 T.PD (285 metric tons/day) of general plant refuse and industrial waste water treatment plant sludge. The general refuse portion of the system was sized for 180 TPD (163 metric

152

tons/day) of paper, wood, plastics, rags, garbage, etc. with an assumed heat value of 7300 Btu/lb (1.697 X 107 j/Kg). The ultimate analysis is as shown in Table 1. The sludge portion of the system was sized for 134 TPD (122 metric tons/day) of 30 percent solids sludge or 114 TPD (103 metric tons/day) of 20 percent solids sludge. Sludge characteristics are as shown in Table 2.

REFUSE ULTIMATE

C

H

°

CI

S

Ash

H20

TABLE 1

CHARACTER ISTICS ANAL YSIS

40.0%

5.9%

34.2%

1.5%

0.5%

6.7%

11.2%

100.0%

Btu/lb 7,300 (1.697 X 107 j/Kg)

TABLE 2

DRY INDUSTRIAL WASTE TREATMENT PLANT SLUDGE

Moisture

Volatile Matter

Fixed Carbon

Ash

15%

49.50%

3.88%

31.62%

100.0%

Btu/lb 4,170 (9.24 X 107 j/Kg)

DISPOSAL SYSTEM

The solid waste disposal system selected was a suspension fired water wall boiler. This system was selected because Kodak Park has its own steam distribution and power producing facilities and as a result we can justify heat recovery. We believed that much better combustion would be attained with shredded refuse, 'and that silver recovery from the dry ash was desirable because it had to be shipped out. Use of an electrostatio precipitator was required to meet air pollution regulations and to get a dry flyash. The system would be required to dispose of both sludge and general plant refuse and we were not satisfied with the systems in common use.

There are two types of material delivered to the disposal system. These materials are:

a) Industrial waste water treatment plant sludge b) General plant refuse - mainly dry paper,

cardboard, plastic, sweeping and miscellan­eous production waste

SLUDGE

The sludge is delivered to a sludge storage bin by loadlugger bucket, (see Figure 2). A variable speed screw conveyor below the vibratory hopper controls the sludge feed rate. The hopper is sized to hold 1350 cu. ft. (38 Cu M) of sludge, which is a 7 to 8 hour supply. The sludge is delivered by conveyors to a flash drying system at a rate up to 5 TPH (4..5 metric tons/hr) (see Table 4). In the mixer sludge is conditioned with previously dried sludge to a mixture which is about 50 percent moisture. From the mixer the sludge drops into the cage mill where the flash drying occurs. The cage mill is similar to a fan, except that the spider has bars and paddles welded perpendicularly to it and does not have blades. Flue gases at 1000°F (538°C) are intimately mixed with the conditioned sludge. The water is flashed"off as vapor and is conveyed into the cyclone separator where solids are separated from the flue gas and vapor. The dried sludge has about 15 percent moisture. The sludge leaves the cyclone through a rotary air lock. As the sludge leaves the air lock, the stream is split recycling approximately 90 percent back for con­ditioning and 10 percent to be burned. Each sludge stream for burning goes through a rotary air lock into a tee injector where an air stream from a positive displacement blower picks it up and pneumatically conveys it to two diagd'nally oppo­site corners of the boiler for burning (see Table 7). At present we are supplementing the belt conveyor system with a moyno pumping system. The belt conveyors will be retained as a back-up system.

REFUSE

The general plant refuse (see Figure 2) is dump­ed into the storage pit by packer truck, loadlugger bucket or other collection vehicles. In front of the pit there is a 10 ft. (3.05 M) wide vestibule which the trucks back into, so that paper will be prevent­ed from blowing into the street. At each dumping point there is a down blast unit heater. The vesti­bule and pit area are completely sprinkler protect­ed. There are sprays both in the front and rear wall of the pit to suppress dust clouds that occasionally rise when a load is dumped. The pit is capable of

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COMBUSTION ENGINEERING ST,EAM GENERATOR TYPE VU-40

holding approximately 390 tons (345 metric tons) of Kodak refuse. The refuse is picked out of the pit by a bridge crane with a 5 cy (3.8 Cu. M) buck-

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et which is capable of feeding the shredder up to 20 TPH (18 metric tons/hr). The crane delivers the refuse to an infeed system which feeds the material to the final sizing shredder.

The crane is a two girder single trolley, 8� ton (8 metric tons), traveling grapple type. It operates over a refuse bin approximately 32 ft. (10 M) wide by 100 ft. (30 M) long by 17 ft. (5 M) deep. The crane rails are located about 32 ft. (10 M) above the top of the bin.

Control of the crane and grapple is from an air-conditioned pulpit located in and projecting from the side wall near the shredder. The shredder is located at one end of the runway. The crane is designed to perform at least 40 cycles per hour with an allowance of 20 percent of the hour for.re­handling and operators relief. The operator sits in an armchair with control levers conveniently located within his reach.

The full load speeds, horsepower, and motor RPMs of the units are as follows:

FPM(M/M) HP(MPH) RPM Holding Hoist 260(79) 125(127) 900

Closing Hoist 260(79) 125(127) 900

Trolley Travel 150(46) 15 ( 15) 1200

Bridge Travel 25 0(76) 40( 41) 1200

The control is a saturable reactor type which provides cushioned starting and acceleration. This reduces maintenance and provides for .slow soft speed spotting regardless of the load.

Protective zones are provided preventing the operator from drawing the grapple into the wall, pulpit, etc.

The system is designed to permit future auto­matic control.

The refuse shredder is designed to give a product 2 in. x 2 in. x 2� in. (5 CM x 5 CM x 6 CM), at a rate of 35 TPH (32 metric tons/hr). We are using an Eidal Shredder (see Table 11) which is a vertical shafted ring hammer type shredder driven by two 400 Hp (406 MPH) motors. At the entrance to the shredder an infeed unit puts in a constant feed. At the shredder bottom there are blades which sweep the material out the discharge. Directly coupled to the shredder discharge is an air classifier that separates the light and heavy fractions. The light fraction is pneumatically con­veyed to the cyclone separator (see Table 10). In

the cyclone air and material are separated, dropping the material into the surge bin. The air goes thru a wet scrubber before discharge to the atmosphere .

TABLE 3

Boiler

Combustion Engi·neering VU40 Boiler 400 Psig 550° F (2.81 X 105 Kgs/sq. m 288°C) .Expansion 2'/16" down (5.1 em)

Capacity 180 TPH (163 metric tons/hr) Refuse 134 TPH (122 metric tons/hr) Sludge 77 ,000 Ib/hr (34,900 Kg/hr) Steam on Refuse and Sludge 135,000 Ib/hr (61,300 Kg/hr) Steam on Refuse, Sludge

and Oil 150,000 Ib/hr (68,100 Kg/hr) Steam on No. 6 Oil

Boiler Bank 66" (170 em) 10 Upper Drum 111," (3.8 em) Thick 42" (105 em) 10 Lower Drum 1" (2.54 em) Thick 456 2" (5 em) 00 Convection Tubes-6" (15 em) Spac·

ing. 19 Rows Wide 24 Rows Deep

Furnace

7000 cf (198 em) 44 211," (6.2 em) 00 62 ft. (18.7 m) Length Each Side 39 - 211," (6.2 em) 00 60 ft. (18 m) Length Front Wall 39 - 211," (6.2 em) 00 43 ft. (13 m) Length Rear Wall 8'/." (21.8 em) Upper Header 10%" (27.3 em) Lower Rind Header 2 - 12" (30.5 em) Down Commers 2170 sq. ft. (201.5 sq. m) Radiant Surface

530 sq. ft. ( 49.2 sq. m) Convection Surface

Economizer

2030 sq. ft. (189 sq. m) Economizer Surface 2" (5 em) 00 Tubes

Air Heater

8750 sq. ft. (8.2 sq. m) Tubular Air Heater

Superheater '9 Platen Units Pendant Type Not Drainable 2'/." (5.2 em) 00 Tubes

Soot Blowers 4 Diamond Power Retractible Model IK Blowers 4 - Diamond Power IR Blowers

TABLE 4

Flash Drying Systems

Raymond Division of Combustion Engineering Capacity 114 TPD (104 MTPD) at 80% H20

134 TPD (122 MTPD) at 70% H20 #375-30 Cage Mill 30 Hp (30.4 MHP) 14' ( 4.2 m) Diameter Cyclone - Gunite Lined 16" (40 em) Rotary Air Lock on Bottom of Cyclone 22" (56 em) Double Paddle Mixer - 20 Hp (20.2 MHP) #37 Series 106 American Standard Vapor Fan 150 Hp

(152 MHP)

156

TABLE 5

Forced Draft Fan

Clarage #3089 Type A F Arr. 1 SWSl 81,800 Ib/hr (37,100 Kg/he) EV<lporation 25,500 cfm (722 cm m) at 80° F (27° C) 10.9" (27 cm) W.G. A Outlet 72.5 BHP (73.5 MBHP) at 1775 RPM 200 Hp (202.8 MHP)

TABLE 6

Induced Draft Fan

Clarage #5098 Type DN Arr. 36-2 DWD I 81,800 Ib/hr (37,100 Kg/he) Evaporation 63,00 cfm (1784 cm m) at 550°F (288°C) 3.2" (8.1 ern) W.G. At Inlet

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90.0 BHP (91.2 MBHP) at 875 RPM 250 Hp (253.5 MHP) Motor

TABLE 7

Boiler Pneumatic Feed Systems

Sludge

Rader Pneumatics 2 Systems 6 psi (4218 Kgs/sq. m) Sutrobilt Blowers - 2DHP

(20.3 MHP) 14 X 18 E F Feeders - 2 Hp (2 MHP) 5" (12.7 cm) Conveying Line

Refuse Rader Pneumatics 4 Systems 6 psi (4218 Kgs/sq. m) Sutrobilt Blowers - 2DHP

(20.3 MHP) 14 X 18 E F Feeders - 2 Hp (2 MHP) 5" (12.7 cm) Conveying Line

Worth ington

TABLE 8 Boiler Feed Pumps

3 - Pumps Model 2WTF-86 6 Stages 2 Motor Driven 125 Hp (126.7 MHP) 2 - Turbine Driven - Terry 2-1 Single Stage 3500 RPM 106,000 Ib/hr (1494 Kg/hr) 222°F (106°C) 517 psig (3.63 X 10' Kg/sq. m) 25 psig Inlet Pressure (1.75 X 10' Kg/sq. m)

TABLE 9

Electrostatic Precipitator

Wheelab·rator Corp. 101,500 ACFM (2874 cm/m) at 625°F (329°C) 99% Efficient 24 Plates 21 Electroces 288" (731 cm) Star Shape 2 - Series Sections 25,950 sq. ft. (2410 sq. m) Collecting Surfaces 24,150 Lf (7360 m) Electrodes 45 KV D.C. 24 Plate Hammers 23 Electrode Hamrrers Heated Insulator Compartments 2 - Silicon Full Wave Rectifiers 700 MA and 1000 MA at 45 V

Rader Pneumatics

TABLE 10

Pneumatic System

350 Hp (355 MHP) N.Y. Blower Series 40 Size 491 51,200 cfm (1449 cm/m) at 32" (81 cm) Static Pressure Arrangement 8 300 L F (90 m) of 38" (97 cm) Diam. Conveying Pipe 140 L F (42 m) of 44" (112 cm) Diam. Clean Air Pipe

. American Air Filter Type R Roto-Clone Size 12 and Type 48 Settling Tank

168" (427 cm) Diam. Cyclone 60" X 60" (152 cm X 152 cm) Rotary Air Lock with

25 HP (25 MHP) Motor Gama-O-Switch Plug Detector Air Density Separator Heavies Removal System

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TABLE 11

Refuse Shredder

Pangborn ( Formerly Eidal Int.! Model 800 Modified 2 - 400 Hp (406 MHP) 480/3/60 Motors 1250 RPM 35 TPH (32 MTPA) 1 - 75 Hp (76 MHP)

TABLE 12

Surge Bin

Sprout Waldron, Inc. Live Center Bin 4 - Horizontal Outfeed Screws Variable Pitch from 4"

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157

(10 cm) to 14" (45 cm), 18' (5.2 m) long, Driven by 7.5 Hp (7.5 MHP) Motor

14 - Vertical Screws Fixed Pitch 18" (48 cm) OD., 40' (12 m) Long, Each Driven by a 7.5 HP (7.5 MHP) Motor

The ·surge bin has a volume of about 81S cu. yd. (623 Cu. M) (see Table 12). This sytem consists of 14 vertical - 18 in. (46 em) 00, fixed pitch screws, 40 feet (12.2 M) in length, and four horizontal 18 in. (46 cm) 00, variable pitch, out feed screws. The vertical screws are designed to maintain a live center by raising the material up off the bottom outfeed screws. This reduces the bridging effect by removing one whole side of the bin. The outfeed screws load up with material dropping off the bot­tom and convey it out of storage to the boiler feed system.

The refuse is fed through four rotary air locks into a pneumatic feed system (see Table 7). The refuse drops into a pneumatic boiler feed system

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"T" injector where air supplied by a positive dis-placement blower, picks up the material. Refuse is air conveyed at velocities of 100 to 120 FPS (30 to 37 M/S) into the boiler for combustion. The refuse is fed to four corners of the boiler.

The heart of the system is a Combustion Engineering VU40 corner fired boiler (see Figure 3 and Table 3). Flash dried sludge is pneu­matically fed to two corners and shredded refuse is pneumatically fed to four corners of the boiler. In addition, waste solvents are being burned through one of the spare burners. The other spare opening will be used for burning another waste. The source of ignition is #2 oil. The boiler is fired with #6 oil as a supple-

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men tal fuel when refuse is fired and as full fuel . .

when only sludge is fired. The design capacity of the boiler on #6 oil is

l S0,000 lbs/hr (68,100 Kg/hr). Steam is generated at 400 psig (28.12 Kg/Sq. cm), SSO°F (288°C) and then reduced to 260 psig (18.28 Kgs/Sq. cm) as it enters the plant distribution system.

A portion of the .combusion occurs in suspen­sion. Material not burned in suspension falls to the dump grate where combustion is completed. The ashes on the grate are dumped into the ash pit twice a trick. The boiler is top supported and expansion is down. The ash hopper is separated from the boiler and is base mounted. A water seal on the top of the ash hopper seals the boiler and ash pit so that flue gases do not pass into the boil­er room.

The flue gases are about 2S00°F (1371 0c), and ISOO°F (816°C) at the boiler bank, (816°C) and 1000°F (S38°C) leaving. The 1000°F (S38°C) flue gas is taken off after the boiler bank and sent to the flash drying system. The flash drying system gases are sent back into the boiler at 2S0°F (I 21 °

C). This takes place in an area where the boiler tubes have been bent to allow cooled flue gas to enter for deodorization. Balance of gas continues through the boiler economizer and air heater leav­ing at about, SSO°F (288°C). The boiler bank has 2 in. (S.06 CM) tubes on 6 in. ( lS.24 CM) centers. The upper drum is 66 in. (167.6 CM) diameter and the lower drum is 42 in. (I06.6 CM) diameter. Originally a superheater was not supplied in this unit, but was later added because of turbine ero­sion in an adjacent building. The boiler is a balanc­ed draft unit with both a forced draft and induced draft fan (see Table S and 6). The furnace is run with a slightly negative pressure.

The boiler bank, air heater, and'economizer were shipped completely assembled to cut down on erection costs. The convection bank alone weighed 40 tons (36 metric tons). The furnace side walls were shipped in eight sections.

The heating surfaces in the boiler bank are cleaned by Diamond Power Model IK retractable soot blowers. IR type soot blowers have been install­ed for side wall deslagging. 260 psig (18.28 Kg/Sq. cm) steam is used for the cleaning medium.

The surfaces of the economizer and air heater are cleaned by a Diamond Power shot cleaning system which' dribbles steel shot down over the tubes.

Combustion air enters the boiler at three levels. About 40 percent enters through three levels of overflfe air nozzles (4 per level), SO percent enters with the fuel at the burners and 10 percent enters below the grate as underfire air.

The boiler has four burners, one on each boiler corner. The fuels and air are introduced tangential­ly into the furnace through the burners. Each burn­er has a wind box divided into four compartments. Three of the compartments introduce air with the fuels, the fourth compartment introduces only auxiliary air. In the oil burner compartment there is a #6 oil gun and a #2 oil Eddy plate ignitor. The burners are monitored by ultraviolet flame scanners.

IS8

The flue gas is cleaned by a Wheelabrator Electrostatic Precipitator before being vented to the atmosphere through a 360 ft. (109.7 M) chim­ney. The precipitator is rated 90 percent efficient at 101 ,SOO ACFM (2874 A CM/Min), at 62SoF (329.4°C).

Gas velocities through the precipitator will vary from approximately 2.24 ft./sec, (.68 M/sec.), at 77 ,000 lbs/hr (34,927 Kg/M) to 3.42 ft/sec (1,04/ sec), at 13S,OOO lbs/hr (61,236 Kg/M)(see Table

9). The precipitator consists of two series sections, each with 24 vertical plates (see Table 9).

The boiler feed water is supplied from an existing plant condensate system. The condensate forward­ing system provides pumping capacity to the new feedwater system. The condensate is passed through a cation exchange unit and then through a deaera­tor to a feedwater storage tanle Feedwater is pump­ed to the boiler by three Worthington Model 2WTF-86 boiler feed pumps (see Table 8) rated at 106,00 Ib/hr (48,082 Kg/M) roughly two thirds boiler capacity, and 517 psig. Two pumps are motor driven and the other is driven by a 260 to 5 psig (18.28 to .35 Kg/Sq. cm) steam turbine.

The control system for the Solid Waste Disposal system has been designed to burn all fuels with proper excess air. Because the refuse and sludge Btu value varies widely, it is necessary to determine the . air required for waste fuel burning by measuring the total Btu input by means of steam flow and subtracting the No. 6 fuel oil Btu input. Air is then distributed in proper proportion to the oil and waste fuel burners, with the final fuel air ratio adjusted from the flue gas O2 content. Any fuel

,rate increase will immediately increase the furnace air and any fuel rate decrease will reduce the furnace air on a delayed basis, insuring sufficient excess air during transient conditions. Smoke den­sity is monitored after the precipitator. Critical temperatures and pressures are monitored through­out the system.

The boiler bottom ash and the electrostatic precipitator flyash are removed by a United Con­veyor steam exhauster pneumatic system. The bottom ash is dumped manually and the flyash is automatically removed by a sequential system. Ash is removed from the silo and loaded into railroad cars. The ash is shipped to a smelter for silver recovery.

Since this waste disposal method was new, it was necessary to conduct some test work before proceeding with the concept. Tests were conducted on application of shredding, sludge storage, refuse storage, conveying and electrostatic precipitation. In addition visitations were made to various instal­lations before selecting a system.

OPERATION

On a new system such as this, things do not always operate the way you would like them to and it has been necessary to alter procedures and to revise equipment. The following section describ-

159

es some of our experiences and some things which we did to make corrections.

BOILER OPERATION

The boiler is equipped with combustion control equipment normally associated with a power boil­er in addition to boiler permissives required for firing waste fuels. Boiler start-up is accomplished with No. 2 oil ignitors and No. 6 main oil burners as prescribed by manufacturers' warm-up require­ments. When the boiler load is above oil fire ball, shredded refuse may be fired into the boiler. Nor­mally the refuse is started on one refuse burner at a time rod the oil flow to the boiler reduced to maintain approximately the same load. Prior to burning sewage sludge, the boiler exit temperature must be above 900°F (482°C) in order to have sufficient hot flue gas to dry the sludge in the flash drying system.

The sludge burning requirement is such that the sludge drying system must be operated on a con­tinuous basis. When sufficient refuse is not avail­able to maintain the boiler, main oil is fired in conjunction with sludge. Prior to refuse firing on a continuous basis, the boiler was operated on main oil and sludge in conjunction with the sludge flash drying system. During approximately nine months of operation in this manner, it was found the boil­er could operate from 70,000 lbs/hr (31,752 Kg/hr) to 15 0,000 lbs/hr (67,890 Kg/hr) of ste'am load and still maintain the boiler exit temperature near 1000°F (5 38°C) to operate the sludge drying system. This is accomplished by selected use of four soot blowers in the boiler bank area for cleaning the boiler tubes. Operation in this manner allowed the boiler to be used to fire waste fuels in addition to using it as a power boiler to meet the plant steam load demanded.

Startup of the boiler and operation in fuing waste fuels pointed out several problems and operating criteria not originally anticipated. Coordi­nation with the manufacturers resolved the main problem within a short period.

The vapor return plenum chamber refractory, located on the back of the boiler just above the burner level, was not installed with sufficient heat resistivity and was replaced with a castable insulat­ing refractory.

The economizer and air heater is equipped with a shot cleaning system to clean the gas side of the tubular surfaces. Shot carry-over problems were experienced in the breaching leading to the preci-

pitator. This problem was resolved by installing false tubes and an egg crate type baffle below the air heater to reduce the shot fall velocity, thus preventing carry-over.

Inspection of the boiler, air heater, economizer, and precipitator after operation on waste fuels indicated no signs of deterioration or corrosion due to the firing of waste fuels.

SLUDGE D RYING SYSTEM

The basic design, operation and capacity of the sludge drying system was covered under the design section. During startup of the system, it was found necessary to maintain a reliable, controlled wet sludge feed rate for correct heat and moisture balance in the flash drying system.

The sludge is put into a 25 cy (19 Cu. M) stor· age bin. This unit was a live bottom vibrating bin designed to discharge sludge onto a belt conveyor. This sludge metering method from storage was not successful. Furthermore, unit maintenance was excessive during the first six months. A remote controlled variable speed screw conveyor was installed to meter the wet sludge feeding the system. This along with a slide gate at the bin bottom has proved adequate for controlling the system feed rate.

The operators must understand and interpret the dried sludge characteristics; particularly the density, moisture, and heat value and adjust the system operation accordingly. The sludge char­acteristics vary greatly due to changes in makeup. Wet sludge is a variable mixture of primary and

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secondary sludge from the Kodak Park's industrial waste treatment plant.

A small air flow back through the rotary air 'lock can cause suspension of a dried low density sludge in the cyclone. Increasing dried sludge moisture content will increase the density and pre­vent cyclone plugging problems. The vapor fan suction and cyclone draft may be reduced to pre­vent cyclone plugging, but this reduces the drying capacity of the system.

A low moisture content in the dried sludge may cause the vapor fan to carry sludge particles in the gas stream leaving the cyclone. When this was experienced, this increased the combustibles in the precipitator and caused burning of the flyash in the precipitator storage hoppers. Increasing the dried sludge moisture content to excessive levels will cause unburned sludge to pile-up on the boiler grates and to be removed with the bottom ash.

Generally, a .dried sludge moisture level of 15 per­cent while firing oil and 15 to 25 percent while firing refuse is acceptable for complete combus­tion on the grates and preventing carry-over of unburned sludge to the precipitator.

During de-bugging of the sludge drying system, minor dust explosions were observed in the cage mill and adjacent ducts. This safety hazard was due to dry dust particles coming in contact with the hot metal surfaces during startup and shutdown of the system. To prevent this, a 10 psi (0.70 Kgs/Sq. cm) steam inerting system was installed at the cage mill and cyclone separator to be used on system startup and shutdown.

REFUSE PREPARATION SYSTEM

This system includes a pit, infeed unit, shredder, air classifier, dense fraction removal, pneumatic conveying system, air scrubber, and silo surge bin.

The original refuse preparation system suffered from numerous problems. The shredder, shredder infeed, belt conveyors, and storage silo only work­ed partially.

The shredder infeed would bridge over prevent­ing material from entering the shredder. The shred­der had two major bearing failures and material would wrap around the top shaft causing overheat­ing of the top bearing.

160

The shredded refuse was about Ilb/cf (16 Kg/CuM) density and dusty. This dust would accumulate in the belt conveyors causing a major housekeeping problem. The shredder would work metal to the pOint that the hot chunks would cause smoldering fires in the dust. The conveyors were designed for a density of 5 lb/cf (80 Kgs/ CuM), with the lighter density the system capacity could not be met.

The storage silo had a vibratory bottom design­ed to induce material flow to the boiler feed system. Only the vibration tended to densify and compact the shredded material. Consequently material bridges occurred across the silos 26 ft (7.8 M) diameter. At this point the silo was bypass­ed and a direct feed from the shredder to the boil­er via the conveyors was established.

At this point a major study was launched on the material handling system. Out of this study a complete change took place, in the Material Han­dling System.

The shredder was completely rebuilt. Major changes were made in the base and the bearing arrangement. The most significant change made

was moving the bottom bearing from above to below the bull gear with accessability from a bot­tom sump. The original bearing had an expected life of 2000 hours, the new bearing has an expected life of 35 ,000 hours. Adjustable choker bars were installed for grind size control and the discharge was rotated 90° CCW so as to close couple the air classifier.

After shredding the material is discharged direct­ly into an air classifier. The light fraction is convey­ed away and the heavy fraction drops and is con­veyed to a bucket elevator that discharges to a load lugger. This is presently landfilled. We are working on further separation of this material. The light fraction is Gonveyed about 150 ft (46 M) horizon­tally and 160 ft (49 M) vertically through a 38 in. (97 CM) diameter line to a 168 in. (427 CM) diam­eter cyclone. Here the material and air is separated. The air goes through a 40 in. (102 CM) American Air Filter wet scrubber and 350 HP NY Blower, venting to the atmosphere. The material ,in the cyclone drops down through a 60 in. x 60 in. (152 CM x 15 2 CM) rotary air lock, then into the surge silo. We are still experiencing minor carry over through the cyclone which causes plugging o

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the scrubber. Also the scrubber is plagued with dust plugging the spray nozzles. We are to solve these problems in the near future.

The storage silo was redesigned using a live cen­ter concept. The cone shaped bin bottom was re­moved and replaced with a wedge shaped bottom; it accommodates four horizontal outfeed screws. Fourteen vertical screws, 40 ft (12 M) long, 1.5 ft

(.45 M) diameter, fixed pitch; lift the material up­ward to drop freely into the outfeed screws. The four outfeed screws, 18 ft (5.3 M) long, 1.5 ft

(.45 M) diameter, variable pitch 4 in to 14 in (10 CM to 35 CM), convey material out to the boiler refuse feed system.

This silo surge bin partially worked, the outfeed screws continuously jambed against the bin side. The supplier Sprout Waldron Inc., was contacted for help. Actual field tests indicated that the screw jambing was caused by vertical and angular loads acting on the screw. A shroud was installed partial­ly covering the horizontal screw and transmitting the load into the vertical screws. This solved the pro-

,

blem and mixed the refuse much more thoroughly. The four silo outfeeds drop into separate

furnace feed systems, consisting of a 25 in. x

30 in. (63 CM x 77 CM) rotary air lock. The material is air conveyed into the four cdrners of

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the waste heat boiler.

161

The rotary air locks are susceptible to jambing caused by material wedging between the rotor and housing. We are presently investigating alternate means of feeding the boiler. This would mean eliminating the rotary air locks.

ASH HANDLING

The bottom ash is removed from the boiler by the use of air cylinder operated dump grates to ash hoppers. Ash is dumped manually. There are pro­visions for future installation of clinker grinders and automatic removal to the ash conveying line. The ash is pneumatically conveyed to the ash stor­age silo.

As stated earlier, sludge and oil firing resulted in clinker formation on the boiler walls. Large clink­ers falling caused the grates to bend and proved difficult in getting clinkers through and into the hoppers. A large amount of labor was required in reducing the clinkers down to a size for conveying. Since the bottom ash was very abrasive, it has been fOl,lnd necessary to replace wear backs in the ash conveying line elbows on six month intervals.

Some problems were also caused from the ash conveying system pulling flue gas into the convey­ing line, resulting in vapor condensation and line plugging. Other flyash problems encountered in the precipitator hoppers, during removal were, burning and clinker-like ash formations. A new ash grate with tight shutoff was installed to prevent air infiltration. More frequent ash removal and better combustion have helped to reduce this problem.

OPERATOR TRAINING

Since the solid waste disposal system was a new concept with very little knowledge and experience available from our operational aspect, a complete training program was formalized. Each operator was given a two month, on-the-job training period on boiler operation and feedwater testing in Kodak Park's power plant prior to startup of the solid waste disposal boiler. Approximately 25 hours of classroom instruction was presented to each operator along with a training manual containing the operating principles of all systems and equip­ment, operator maintenance, operating procedure, and startup and shutdown procedures. In addition, a great deal of training and supervision was required during the initial startup and operation of each system. Operators are also required to attend class-

es and obtain a Stationary Engineers License from the City of Rochester iri order to operate a high pressure boiler.

problems in the original design were associated ,

.

with the materials handling system. Since the redesign, the system is working extremely well.

CONCLUSION

Our experience to date indicates that we can burn refuse and sludge in suspension. The main

Our experience and research has shown us that technological development of refuse handling needs a great deal of work and that particular attention must be paid to details in designing a material han­dling system.

Key Words

Waste Disposal

Industrial Waste Disposal

Heat Recovery

Incineration

Solid Waste

Shredded Refuse

Suspension Firing

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