Report of Investigations 9476 

Facility for Melting Residues From Municipal 

Waste Combustion: Design Criteria and 

Description of Equipment 

By Alan D. Hartman, Laurance L. Oden, and Jack C. White 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Bruce Babbitt, Secretary 

BUREAU OF MINES 
CONTENTS 

Abstract ........................................................................... 1 

Introduction ........................................................................ 2 

Designcriteria ...................................................................... 2 

Description of equipment .............................................................. 3 

Feedhandling ..................................................................... 3 

Melter ........................................................................... 3 

Electric arc melting furnace ........................................................ 3 

Furnace refractories .............................................................. 5 

Furnacecooling ................................................................. 5 

Power supply, control, and monitoring ................................................ 6 

Slag tapping and granulation .......................................................... 7 

Fume-offgas handling ............................................................... 8 

Ducting, heat exchanger. baghouse, and thermal oxidizer ................................... 8 

Nitrogen inerting system ........................................................... 8 

Summary ................................................................... 10 

References ......................................................................... 10 

ILLUSTRATIONS 

Process system flow diagram ........................................................ Floor-level view of feed-handling system ................................................ Electric arc melting furnace showing fume settling chamber above metal taphole .................. Electric arc melting furnace cross-sectional schematic ...................................... Top view of furnace and roof ........................................................ Refractory placement in furnace shell and roof ........................................... Furnace and transformer cooling-water circuit diagram ..................................... Electric arc melting furnace power system electrical circuit .................................. Slaggranulator .................................................................. Fume-offgas handling system consisting of a double-pipe hairpin heat exchanger, baghouse, and thermal 

oxidizer ....................................................................... Oxygen. temperature. and pressure display board ......................................... 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

A ampere Ib pound 

"C degree Celsius Ib/ft3 pound per cubic foot 

c fm cubic foot per minute Ib/h pound per hour 

OF degree Fahrenheit mA milliampere 

it foot MHz megahertz 

ft3 cubic foot Pm micrometer 

gal gallon MMBtu/h million British thermal unit per hour 

gPm gallon per minute n ohm 

hp horsepower Pet percent 

Hz hertz psi pound per square inch 

in inch ~sig pound per square inch gauge 

kHz kilohertz s second 

kV kilovolt scfm standard cubic foot per minute 

kV*A kilovoltampere st short ton 

kW kilowatt V volt 

kW* h/st kilowatt hour per short ton V ac volt, alternating current 
FACILITY FOR MELTING RESIDUES FROM MUNICIPAL 

WASTE COMBUSTION: DESIGN CRITERIA 

AND DESCRIPTION OF EQUIPMENT 

By Alan D. ~artrnan,' Laurance L. 0den,* and Jack C. white3 

ABSTRACT 

The U.S. Bureau of Mines, under a Memorandum of Agreement with the American Society of 

Mechanical Engineers (ASME), established design criteria for a facility to fielt residues from municipal 

waste combustion. This facility, which is available to potential users on a cost-sharing basis, is also 

applicable to a variety of inorganic waste materials from smelting or melting operations. The design 

consists of a mechanical feed handling system, electric arc melting furnace, fume-offgas handling system, 

and thermal oxidizer for final offgas treatment. Screw conveyors and a bucket elevator deliver up to 

2,000 Ib/h of minus I-in material to a three-phase electric arc melting furnace. This unique 800-kVe A 

furnace has a water-cooled shell and roof to minimize interaction of the melt with the refracto~y lining. 

The volume of the hearth below the slag taphole is approximately 1.2 st of steel. The furnace is sealed, 

allowing atmosphere control within the furnace and fume duct by nitrogen or inert gas injection. A jetpulsed baghouse removes particulate from the offgas and serves as an acid gas scrubber. The clean 

offgas is heated to 1,800' F for 1 s in a propane-fired thermal oxidizer before being vented to the 

atmosphere. 

'chemical engineer. 

'~esearch chemist. 

'~etallur~ist. 

Albany Research Center, U.S. Bureau of Mines, Albany, OR 
INTRODUCTION 

The most widely applied method for the disposal of 

waste materials, including sludges,.dusts, scales, leachable 

slags from smelting or melting operations, and residues 

from the combustion of organic materials including municipal wastes, is to inter the materials in an appropriate 

landfill. Small quantities of some wastes are encapsulated 

within Portland cement or sulfur, and then consigned to a 

landfdl. However, landfill disposal of wastes is at best a 

short-term solution, because landfills are nearing capacity 

and new landfills are difficult to establish. A promising 

and technically viable permanent solution to the problem 

is to melt the waste materials to produce inherently nonpolluting amorphous or crystalline mixtures of inorganic 

oxide products, similar to slags produced by various metal 

industries (l-4).4 These products may be useful as aggregate for bituminous or Portland cement concrete, for grit 

blasting, as road building and construction ballast, and 

in the manufacture of mineral wool instead of landfill 

disposal. 

In 1984, the ASME Research Committee on Industrial 

and Municipal Waste asked the U.S. Bureau of Mines 

about the feasibility of melting (vitrifying) ash residues 

produced by the combustion of municipal wastes. A demonstration melting test of dry combined bottom ash and fly 

ash from a waste-to-energy (WTE) facility in Chicago, IL, 

was conducted by the Rolla Research Center (RORC) 

of the USBM in Rolla, MO, in 1984.5 This proof-ofconcept trial provided slag and metal phases that were 

environmentally benign, had a mean density three times 

greater than the parent residue, and had the potential for 

several beneficial uses. Similar results were observed in a 

1986 full-scale 1-st electric arc furnace test at the Albany 

Research Center (ALRC) of the USBM in Albany, OR. 

An agreement was signed by the ASME and the USBM 

in September 1990 to conduct scaled-up melting tests in a 

nominal 1-st electric arc furnace at the USBM ALRC. 

These melting tests were completed in July 1992 on five 

combustion residues. The residues consisted of combined 

dry bottom ash and fly ash from three state-of-the-art 

mass-burning WTE plants in the northeastern United 

States, dry combined ash from a multiple hearth (waste 

water treatment) sludge incinerator, and fly ash from a 

WTE plant burning refuse-derived fuel (RDF). 

The melting program required the design and construction of an electric arc melting furnace having watercooled shell and roof to cope with the corrosive slags; 

modification of an existing power supply designed for 

melting steel to accommodate the higher resistance of the 

slags; and construction of continuous feeding and fumeoffgas handling systems. A summary of the design criteria 

for the feed system, furnace, and fume-offgas handling 

system and a description of each follows. 

DESIGN CRITERIA 

The design criteria for the equipment that make up the 

furnace system consist of the following specifications. 

Feed system: 

1. Continuous feed rate of 2,000 Ib/h for municipal 

waste combustion residue with a bulk density of 80 Ib/ft3. 

2. Capability to convey material passing a 1-in screen. 

Furnace and power supply: 

1. Electrical voltage measured phase-to-phase at the 

furnace electrodes in the range of 240 to 350 V and full 

load amperage of 2,000 to 2,500 A. 

2. Melt rate up to approximately 2,000 Ib/h of material 

having an enthalpy requirement of 800 kW h/st. 

3. Open-arc, submerged-arc, or intermediate modes of 

operation. 

4. Hearth volume below the slag taphole of approximately 5 ft3, 

41talic numbers in parentheses refer to items in the list of references 

at the end of this repon. 

5. Option to tap the furnace slag taphole intermittently 

or continuously. 

6. Intermittent tapping of metal and the ability to 

empty the Furnace through the bottom of the hearth. 

7. Capability to granulate up to 500-lb batches of slag 

product with a high-pressure water jet unit. 

8. Capability to operate under ambient air or inert gas 

(N,) atmosphere. Nitrogen delivery rate up to 150 scfm. 

Fume-offgas handling system: 

1. Monitors in the fume duct to indicate 0, concen- . 

tration and temperature of gas entering the baghouse. 

2. Capability to maintain the 0, concentration in the 

fume duct below 6 pct, i.e., below the flammability range 

for CO by adding N,. 

3. Capability to add or remove heat from the fumeoffgas to maintain the temperature above the dew point, 

but below the destruction temperature of the baghouse. 

4. Baghouse capacity to remove 99 pct of particulate 

greater than 1 pm at a total flow rate of 150 scfm. 

'~esulu of RORC and ALRC tests are available. from Paul C. 

Turner, Bureau of Mines. Albany. OR 
5. Acid gas absorption provided by injecting up to 6. Omgas incineration beforc exhausting 10 the atmos100 Ib/h hydrated lime with the carrier gas, N,, into the phere to provide 1 s residence timc at 1,800" F for flow 

baghouse. rates up to 250 scrm. 

DESCRIPTION OF EQUIPMENT 

A flow diagram for the feed handling, melting, and 

fume-offgas handling systems is shown in figure 1. 

automatic or manual. Figure 2 is a floor-level view of thc 

feed-handling system, designed by Thomas R. Miles, Consulting Design Engineers, Portland, OR (5). 

FEED HANDLING 

MELTER 

Feed material is transferred by overhead crane, 

equipped with a crane scale, into a 60-ft3 receiving bin, 

which uses twin counter-rotating 12-in-diameter screws 

to feed a bucket elevator. The bucket elevator lifts the 

feed material 17 ft to a 10-ft3 meter bin, which discharges 

via twin counter-rotating 6-in-diame.ter screws to a 6-indiameter splitter screw. The splitter screw then feeds two 

6-in-diameter delivery screws. Each delivery screw then 

discharges into the furnace through a pneumatically activated splitter gate that divides and routes the feed to two 

separate ports in the Furnace roof. Feed is thereby uniformly admitted into the furnace through four ports in 

the roof. The feed system can deliver up to 2,000 Ib/h 

to the furnace of material with bulk density of 80 to 

100 Ib/ft3. Control of the feed system can be either 

Electric Arc Melting Furnace 

An existing tilting Lectromelt6 size ST (nominal capacity 

1 st of steel) refractory-lined furnace shell and roof were 

replaced by a stationary furnace having a water-cooled 

shell, water-cooled roof, and air-cooled bottom (fig. 3). 

The existing electrode arms and roof supports were unchanged. Figure 4 is a vertical section of the furnace shell 

and roof showing upper and lower water trough placement, air plenum for bottom cooling, taphole locations, 

slag launder, and placement of the furnace with respect to 

- - 

6~eference to specific products does not imply endorsement by the 

U.S. Bureau of Mines. 

Figure 1.-Process system flow diagram. 
noor level. Three carbon slccl ground straps (2 in wide by grounded on the outside with 00 size copper wire. A conapproximately 1/16 in thick) wcrc wclded Lo the inside crete pedestal supports the furnace between two rectabottom of the shell in a triangular array prior to placing gular pits each 3 ft 6 in deep by 5 ft 10 in wide by 7 ft 

the refractory lining in the shell. These straps were long. 

worked between the bricks during construction of the Figure 5 is a top view of the furnace and domed carbon 

hearth to provide a circuit-to-ground path between each steel roof identifying the numerous ports and water 

pair of electrodes. The furnace shell then was securely passages in the roof. The complex roof is designed with 

a circular water passage near the outer edge to protect the 

Figure 2.-Floor-level view of feed-handling system. 

Figure 3.-Electric arc melting furnace showing fume settling 

chamber above metal taphole. 

roof-to-shell seal, which consists of two annul& channels 

in the shell and two knife edges in the roof. The inner 

channel contains fine sand, and the outer channel contains 

a silicone elastomer. About 70 pct of the exterior surface 

Knife-edge roof seals 

Silicone elastomer 

Sand 

Refractory lining 

Water distribution 

trough Water-cooled 

Metal 

... dlf~ir plenum Water collectlon trough 

Figure 4.-Electric arc melting furnace cross-sectional schematic. 

Furnace roof 

water jackets 

I Electrode rports West wail of pit 

Holddown bolts for 

electrode seals 

TO woter / TO woter 

distribution trough V~ooiing woter collection trough 

inlets ~ ~ 

Figure 5.-Top view of furnace and roof. 
of the roof encompassing the electrode, feed, and exhaust 

ports is effectively water cooled by two water jackets, 

as shown in the figure. The roof is lined with 4 in of 

NARPHOS 85P plastic refractory (85 pct alumina) manufactured by North American Refractories Co., Cleveland, 

OH. This material was selected for ease of placement 

(owing to the complexity of the roof) and for its ability to 

withstand the high temperatures anticipated during openarc operation and the corrosive nature of the condensable 

fume within the furnace. 

The three central ports in the roof accommodate 4-indiameter graphite electrodes manufactured by Union 

Carbide (UCAR) Carbon Co. Inc, Cleveland, OH. The 

ports are 8-1/4 in diameter, extend about 2 in above the 

dome, and occupy the apexes of an equilateral triangle 

with 11-114411 sides. The roof refractory was not extended 

into the vertical extensions of the electrode ports; instead, 

two-part ceramic ring seals cast from Cast-0-Last G AdTech from Harbison-Walker Refractories, Pittsburgh, PA 

were fitted into the annular space between electrode and 

roof port to minimize gas leakage around the electrodes. 

A completed electrode seal consists of a ceramic-fiber gasket between a shelf on the bottom seal and the top of the 

roof port, and ceramic-fiber packing within the annular 

space between the bottom and top parts of the seal. The 

upper part of the seal was clamped to the roof to compress the ceramic packing around the electrode (fig. 4). 

The four charging ports in the roof are arranged in a 

rectangular array to distribute the feed uniformly to the 

furnace. Each charging port is 10-114 in. in diameter. 

The roof refractory does not extend into the vertical extensions of the charging ports. Ceramic seals, similar to the 

electrode seals, also are installed in the charging ports. 

Fume and offgas exit the furnace through the circular 

exhaust port in the roof. The roof refractory extends into 

the 10-in-diameter exhaust port to decrease the inside 

diameter to 6 in. A 10-in-square inspection port is fitted 

with a door that can be opened to provide access to the 

furnace. The roof refractory also extends into the inspection port to provide a square opening with 4-in sides. 

Furnace Refractories 

The carbon steel furnace shell is 65 in high and tapers 

from 60-in ID (inside diameter) at the bottom to 56-in ID 

at the top. Refractory placement within the shell and roof 

is indicated in figure 6. The bottom of the shell is lined 

with 5 in (two courses) of chromic-oxide-alumina-bonded 

90-pct alumina super-duty firebrick (Ruby) straight bricks 

from Harbison-Walker Refractories. Five courses of Ruby 

key bricks shape the hearth and form the sidewall up to 

the steel shelf 28 in above the bottom, which is approximately 7 in above the slag taphole. One inch of dry 

phosphate-bonded silicon carbide (Sic) ramming mix from 

Charge pwt 

! /- Electrode port 

85 pct alumina 

plastic refractory 

70 pct alumina 

firebrick, orch brick 

Mulllte flber insulation 

Dry silicon corbi 

Metal laphole 

Chromlc oxide-alumlno Y bonded 90 pct alumina 

super-duty firebrick i vl- Dry silicon carbide ramming mix 

Figure 6.-Refractory placement In furnace shell and roof. 

the Norton Co., Worcester, IvL4 was placed between the 

steel bottom and the fust course of Ruby straight bricks to 

improve heat transfer to the bottom. This ramming mix, 

about 1 in thick, also was placed between the Ruby key 

bricks and the sidewall for the same reason. The upper 

sidewall is lined with 4-112-in GM 70 DE (70-pct alumina) 

insulating arch firebrick from North American Refractories 

Co. One-inch Fiberfrax batting from the Carborundum 

Co., Niagara Falls, NY was placed between the. sidewall 

and the arch brick for additional insulation. At midheight 

the finished inside diameter of the furnace is about 46 in. 

The hearth is rammed to a depth of 6 in at the center with 

Permanente 165 AF (95-pct MgO) ramming mix from 

National Refractories, Oakland, CA. 

The furnace is tapped for metal and drained through 

the 1-1/2-in-diameter hole that was built into the furnace 

lining in the bottom center of the hearth during construction. The slag taphole, termed the cinder monkey, is 

grouted in place with the MgO ramming mix. The cinder 

monkey is a welded, water-jacketed copper structure 6 in 

diameter by 10 in long with a 1-in central hole designed to 

tap slag continuously at rates up to 2,000 Ib/h. The design 

capacity of the hearth, which finished to 48 in diameter by 

9 in. deep at the center, is approximately 5 ft3 and will 

accommodate about 2,600 Ib of steel or 800 to 1,000 Ib of 

slag. 

Furnace Cooling 

The base of the furnace is cooled by air flowing at 

approximately 1,300 cfm through a plenum formed by six 

4-in-high I-beams upon which the furnace rests. The 

furnace shell, roof, cinder monkey, slag launder, metal 

taphole collar, and power supply transformer, as well as 

the electrode arms, cables, and clamps, are,water cooled. 
Cooling water is pumped to the furnace from a 1,500-gal water if furnace power also is stopped. A flowmeter in 

cool water sump by a 15-hp centrifugal pump. The fur- the water circuit to the cinder monkey de-energizes and 

nace shell is cooled by a curtain of water (50 gpm) that opens the automatic valve in the city water line if the flow 

cascades down the wall from an annular distribution rate From the cooling tower decreases below 20 gprn in 

trough near the top of the shell. All cooling water is col- that circuit. 

lected at the base'of the furnace in a trough and is returned by gravity to a 1,500-gal warm water sump through 

a 6-in polyvinyl chloride (PVC) line. Water is pumped 

from the warm water sump to a Marley Model NC-111 

cooling tower of crossflow, induced draft design (6). The 

cooling tower supplies up to 150 gprn of water at 75" F 

with 142" F maximum return temperature and 70" F wet 

bulb temperature. Figure 7 is a circuit diagram for cooling 

water indicating maximum anticipated flow rates. 

City water is available for emergency cooling in case of 

general power failure or malfunction of the circulating 

pumps. The most critical application of cooling water is 

the copper cinder monkey, which is in direct contact with 

molten slag while the furnace is operating. All other 

applications likely will not be damaged by stoppage of 

Power Supply, Control, and Monitoring 

An existing three-phase power supply designed for melting steel was altered to provide an increase in voltage. 

This alteration provided a higher power input without 

requiring an increase in the depth of the electrodes into 

the melt. Alteration consisted of the addition of three 

single-phase 250 kV*A transformers configured with the 

primary circuit of each 250-kV*A transformer in parallel 

with the appropriate phase of the 800-kV* A transformer. 

The secondary circuit of each 250-kV* A transformer was 

connected in series with the appropriate phase of the secondary circuit of the 800-kV-A traxisformer (fig. 8) (7). 

Nameplate specifications for the 800-kV*A and 250-kV* A 

transformers are as follows: 

Transformer 

1' 25 gpm 

2' Tower water 1' 25 gpm Roof sad cooling Water Mow 

condult and half dlstributlon 1' 

150 gpm. 50 pal of roof cdlng trough - 

70 OF 

Water 

cdlection 

trough 

3/4' 10 gpm Electrode 1 

1' 25 gprn Half of roof 

coding 

I 

Electrode arms. 

cables. dam~s I 

6" drah I 

to warm .water 

sump 

Figure 7.-Furnace and transformer cooling-water circuit dlagram. 
Ill /// Fused disconnect 

I ) ) I) Circuit breaker 

Ill 

transformer 

(reactance 5 to 

3-250 kV.A 

single-phase 

transformers 

85- to 215-V 

secondory 

3 104- to 120-V 

secondaries 

electrodes 

Figure 8.-Electric arc melting furnace power system electrical 

circuit. 

Pennsylvania three-phase frtmace transformer specification 

8662: 

Voltage rating 11,500 - 215 V ac, 

Capacity rating 800 kVmA at 55" C rise, 

Class OW,' 

Frequency 60 Hz, 

Secondary current rated at 2,150 A at 215 V, 

Reactance of transformer at 215 V full capacity = 5 pct, 

Reactance of reactor at full capacity current = 30 pct, 

Reactance of transformer and reactor at 215 V full 

capacity = 35 pct. 

General Electric SPIRAKORE 250-kV* A single-phase transformer nameplate specification: 

Voltage rating 14,400 - 120/240 V ac, 

Capacity rating 250 kV- A at 55" C rise, 

Class OA,8 

Type HS,9 

Frequency 60 Hz, 

Secondary current rated at 2,080 A at 120 V, 

'~anufacturer's specification-not defined. 

'see footnote 7. 

'lbidern. 

Reactance of transformer at 120 V = 6.1 pct, 

lmpcdance at rated volts = 0.1 pct. 

The 12,500-V primary connections were used on the 

800-kV A transformer, and the 14,400-V primary connection was used on the three 250-kV-A transformers. 

The 800-kV*A transformer was configured internally to 

provide the following output voltages and impedance: 

Tap A - 182 V at 112 total reactance, R, 

Tap B - 137 V at 112 R, 

Tap C - 124 V at 1/6 R, 

Tap D - 95 V at 116 R. 

These settings resulted in the average secondary opencircuit voltages shown below, as measured at the electrodes in volts (8): 

TapA ..... 352 192 

TapB ..... 304 168 

TapC ..... 256 145 . TapD ..... 239 134 

Real-time electrical current and voltage referenced to 

ground are recorded for the three phases during ,furnace 

operation to compare real-time electrical parameters with 

the analog instruments on the control panel and to provide 

information for future analysis of arc stability. The voltage 

signals are obtained from the bus bars leading to the electrodes by using divide-by-40 voltage dividers. Currents are 

obtained from 0.00005-a shunts on the bus bars. All signals are transmitted to waveform recording equipment by 

Dyrnec 1-MHz analog fiberoptic links to achieve electrical 

isolation (9). A LeCroy 6810 digitizing system records 

electrical waveforms from the primary and secondary sides 

of the transformers (10). Data acquisition rates can be 

varied at 50,100, and 500 kHz. Data are to be transferred 

to a personal computer for analysis and graphing. 

SLAG TAPPING AND GRANULATION 

Slag is tapped continuously from the water-cooled copper taphole (cinder monkey) into 1,000-lb-capacity conical 

cast iron molds. The slag pit accommodates two molds, 

and the slag stream can be routed to either mold by moving the slag launder. Molds are moved by an overhead 

crane equipped with a crane scale. Slag to be granulated 

is tapped into a preheated, refractory-lined ladle and transferred to the granulator. 

The granulator consists of a refractory channel that 

directs a small stream of molten slag from the ladle into 

a jet of water moving within an 8-ft-long by 1-ft-high by 

112-ft-wide 18-gauge stainless steel trough. Water is supplied from a pump by a 1-1/2411 pipe entering a variable 

flow nozzle. The water and granulated slag exit the trough 

into a holding and settling tank (fig. 9). 
Figure 9.-Slag granulator. 

FUME-OFFGAS HANDLING propane rated at 2.2 MMBtu/h before exhausting to the 

atmosphere. The thermal oxidizer is designed to provide 

Ducting, Heat Exchanger, Baghouse, 1 s residence time at 1,800' F for gas flow rates in the 

and Thermal Oxidizer range 125 to 250 scfm (fig. 10) (11, pp. 1-3). 

Fumes and gases exit the roof of the furnace via a 6-indiameter duct into a 14-in-diameter settling chamber to 

capture large particulate material. A hydraulic ram with 

circular scraper blade, fastened at the top of the nearvertical duct section nearest the roof, is used to clear 

accumulations of particulate or condensate within the duct. 

After an approximate 204 run from the settling chamber, 

the offgas enters a water-jacketed double-pipe heat exchanger that either heats the cool gas during startup to 

prevent condensation, or cools the hot gas during continuous operation to deliver gas in the temperature range of 

2.50" to 400" F to the baghouse. Hot or cold water for the 

heat exchanger is provided by a SuperTrol temperature 

control unit manufactured by Enercon Systems Inc., Elyria, 

OH (11). The SuperTrol, which is rated at 36 kW, provides 120 gpm water at 180" to 250" F to the heat exchanger for heating or cooling. 

The offgas then enters a spark trap to capture incandescent particles and proceeds from the spark trap to a 

baghouse containing 21 4-in-diameter by 10-ft-long Gortex 

membrane-Teflon fluorocarbon polymer B, fiberglass 

fabric bags. The full complement of bags in the baghouse 

is 49, but only 21 bags were required for the listed design 

criteria (12). The bags are cleaned with a back pulse of 

100 psig N, at field selectable time intervals. Up to 

100 Ib/h hydrated lime can bc injectcd into thc baghouse 

with thc carrier gas, N,, for acid gas control. A 5-hp 

variable-specd furnc fan, located in-linc aftcr !hc baghousc, 

discharges the offgas into a thcrrnal oxitlizcr fuclctl by 

Nitrogen lnerting System 

The furnace and fume handling system are operated 

under an N,-enriched atmosphere. Liquid N, is vaporized 

and supplied to the following locations at the approximate 

rates indicated: 

Furnace interior - 5 cfm, 

Feed system splitter screw - 5 cfm, 

Exhaust duct settling chamber - 110 cfm, 

Duct between heat exchanger and baghouse - as 

needed to maintain 0, <6 pct and temperature <400° F, 

Baghouse pulsing unit - as needed, 

Fume fan bearings - 5 cfm, and 

Lime injector - 10 cfm. 

The rate of N, injection through two 4- to 20-mA 

controlled ball valves into the fume duct immediately after 

the fume cooler is automatically controlled by an 0, sensor and a temperature sensor (13-14). Nitrogen is injected, when needed, to maintain 0, below 6 pct and the 

temperature below 400" F. Limiting the 0, concentration 

in the offgas is essential to prevent combustion of CO in 

the fume duct, and the temperature upper limit prcvcnts 

overheating or burning of the baghousc bags. Additional 

tempcrature and prcssurc sensors are located througho~~t 

thc system, and thcir outputs arc displayed in a singlc 

location for rcady rcfcrcncc, as shown in figurc 11. 
Figure 10.-Fume-offgas handling system consisting of a double-pipe hairpin 

heat exchanger, baghouse, and thermal oxidizer. 

Figure I1 .--Oxygen, temperature, and pressure display board. 
SUMMARY 

Design criteria and a description are provided for a feeder, an 800-kV*A three-phase electric arc melting furmelting facility to convert waste materials such as sludges, nace having water-cooled sheU and roof, gas-cooling and 

dusts, ashes, scales, and leachable slags from smelting or cleaning apparatus, and thermal oxidizer for final offgas 

melting operations into nonleachable amorphous or crys- treatment. This unique facility is available to potential 

talline products. The facility comprises a mechanical users, both public and private, on a cost-sharing basis. 

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