Technologies for Centralized Resource Recovery

Chapter 15

Technologies for Centralized

Resource Recovery

Page

h@wh@iwandIssue sAd dressed . . . . . 95~WusOfth8Techno}o@es . . . . . . . . . . . . 96

Inventory of Centralized ResourceReoovery Facilities in the United~tates. . . . . . . . . . . . . . . . . . . . . . . . . . 96

Comparative Performance of Various“f’Qcllrlologies * . ● ● ., ● ,., , ● . . ,6 ● ● ● ● 9 7DagreeofProven Commercialization 97Waste Reduction Efficiencies . . . . . . 99Material Recovery Efficiencies. . . . . 99Ilnergy Recovery Efficiencies .. ....100

PotentiaMlnergy Savings FromCentralkmdR esourceRecovery .. ...101

Resource Recovery Experience inWes te rn Europe . . . . . . . . . . . . . . . . . . . 101

Environmental and Workplace Healthand Safety. . . . . . . . . . . . . . . . . . . . . . . . IOZ. Environmental Factors . . . . . . . . . . . . .103

Air Emissions. . . . . . . . . . . . . . . . . . .103Li dM$skns . .* . . .* . .* . IM. *.lMas Residuals..•• , ● ., * ● . ● ● ● * ● ● ,105

occupational klealth and SafetyFactors ● *99* **** **** **. *.. ***. *O 105

IWtiae ● Q , ● . ● ● . ● ● . . . ● ,. .., ● . ● ● ● , 105Fathogans ,, + . ● ● ● , ● . . ● . . ● . . ● ● . ● .105Dusts snd~oxic Substances . ......106lixpl~ions and Fires . . . . . . . . . . . . .106Mechanical and Ektrical Hazards. 107

Cm@ueions ● , ● , ● . ● ● . s . ● ● . . ● . ● ,.. ● , 107Mant W#3and System Design: The

~ Q f * @ ~ e * • • ● ● b ● ● * ● ● ● ● ● 9 ● o ● ● ~~Overview ● , a ● ● ● ● ● ● ● ● ., ● . . . ● ● * * * * ● 106MMcl@gProducers With Consumers .108

“l%18r@%l@lners ● c ● c * ● ● ● ● ● ● ● Q * ● 108Wt@O-PrOducers. . . . . . . . . . . ● . . . . 109

AdvamWges arid Disa*antages of@@l& Large Plants.. . . . . . . . . . . 110

Research and ~~lq~~~t in Resourceh“ovwy: The Federal Role.. . ........111

Page

Background * * ● ● 6 ● . ● ● ● ● . s ● ● ● o ● ● ● ● ● 111R&Dhleeds. . . . . . . . . . . . . . . . . . . . . .. 111

Findings on Technologies for CentralizedResource Recovery . . . . . . . . . . . . . . . . .112

References. . . . . . . . . . . . . . . . . . . . , ... , 115

Table No, Page

28. Municipal Solid Waste Energy andMaterials Recovery Systems, . . . . . . . 95

29. Resource Recovery Facilities in theUnited States. ... , . . . . . . . . . . . . . ., 97

30. Degree of Proven Commercialization ofEnergy Recovery Technologies . . . . . . 98

31. Degree of Proven Commercialization ofMateridsRecoveryT echnologies. . . . 98

32. Estimated Waste Reduction Efficienciesof Resource Recovery Technologies . . 99

33. Materials Recovery Efficiencies. .. ..10034. Energy Recovery Efficiencies of

Resource Recovery Processes. ... ...10035. Potential Amual Energy Savings From

Recovery and Recycling of 100 Percentof Various Materials From MSW .. ..101

36. Waste-to-Energy Systems in WesternEurope . . . . . . . . . . . . . . . . . . . . . . . . .102

37. Distribution of Waste-to-EnergyFurnaces, by Capacity and Country inWestern Europe. . . . . . , . . . . . . . . . , .103

38. U.S. City Size, Population, and WasteProduction in 1975*•• . ● . ● ,,, ● ,0 ● ● ● 109

39. U.S. Standard Metropolitan StatisticalAreas (SMSAs)Size, Population,and Waste production in 1975 .. ....110

40. Selected Research, JMvelopmenL and~em@Wr@ionNeeds for ResourceRecovery Technologies .. .....,.,., 112

CHAPTER 5

Technologies for Centralized

Resource Recovery

Introduction and Issues Addressed

c entralized resource recovery includesany process that can recover energy

and/or recyclable materials from collected,mixed municipal solid waste (MSW). Theseprocesses are listed in table 28. In complexitythey range from simple recovery of ferrousmaterials using magnets to complex systemsthat include the production of liquid orgaseous fuels by pyrolysis and the recovery offerrous metals, aluminum, glass, and other

Table 28.—Municipal Solid Waste Energy andMaterials Recovery Systems

. — — ———Energy recovery systems

Mass combustion of raw MSWWaterwall incinerationSmall-scale modular incineration with heat

recovery

Refuse derived fuel (RDF)Dry processes

Fluff RDFDust or powdered RDFDensified RDF

Wet processes

Pyrolysis systemsLow Btu gasMedium Btu gasLiquid fuel

Biological systemsLandfill methane recoveryAnaerobic digestionHydrolysis

Materials recovery systemsComportingFerrous metalsAluminumGlassFiber

Wet separationDry separation

Nonferrous metals

SOURCE Off Ice of Tecnology Assessment

nonferrous metals. While centralized re-source recovery is sometimes viewed as beingin the class of high-technology aerospacespinoffs, it includes small-scale modular in-cineration, simple mechanical processes suchas shredding, and such biological processesas comporting and anaerobic digestion.

In this chapter the following questions andissues are addressed:

●

●

●

●

●

What centralized resource recoverytechnologies are available?What is the status of these technologiesand how well do they perform the tasksof waste disposal and resource re-covery?What environmental, health, and safetyproblems may exist or emerge with cen-tralized resource recovery?H OW does the question of plant size or ,scale affect decisions about centralizedresource recovery systems?What should be the Federal role inmeeting research, development, anddemonstration needs?

In this chapter, the status of the technol-ogies and their effectiveness in resourcerecovery and waste reduction are examined.Issues related to environmental and work-place health and safety, the question of scalein resource recovery systems, and the Fed-eral role in research, development, and dem-onstration are addressed. Other issue-ori-ented questions regarding markets, eco-nomics, institutional problems, and selectionof overall waste managementdiscussed in other chapters.

The technologies listed indescribed briefly in appendix

strategies are

table 28 areC. More tech-

95

96 ● Materials and Energy From Municipal Waste

nical detail is available in the additionalreadings listed at the end of appendix C.

The problem of technology selection andsystem design to serve a particular communi-ty is a difficult one, It requires considerationindepth of local conditions and of technologi-cal capabilities. The purpose of this report isnot to provide sufficient detail to make suchlocal decisions but only to assist in making thepolicy decisions associated with resource re-covery programs.

Status of the Technologies

T his section includes an inventory ofresource recovery facilities in the United

States. The various technologies are thencompared in terms of (i) degree of provencommercialization, (ii) waste reduction effi-ciency, (iii) material recovery efficiency, and(iv) energy recovery efficiency. Estimates arepresented of the maximum potential energysavings from the recovery of energy andmaterials from MSW. Finally, information onthe status of European systems is reviewed.

Inventory of Centralized ResourceRecovery Facilities in the United States

Table 29, which lists centralized resourcerecovery facilities now operating or underconstruction in the United States based on arecent Environmental Protection Agency(EPA) publication,(l) is an update of anearlier table published by EPA in 1976 in itsFourth Report to Congress.(2) It lists 17 plantsin operation (down from 21 in 1976) with atotal capacity of 6,730 tons per day (tpd)(down from 9,880 in 1976). The main differ-ences between table 29 and the earlier EPAtable are the addition of Baltimore andBaltimore County, Md., and Milwaukee, Wis.,to the operational list; the deletion of ex-perimental facilities in St. Louis, Me., andWashington, D, C.; and the deletion of fivewaste incinerators in Chicago, Ill., (twoplants), Harrisburg, Pa., Merrick, N. Y., andMiami, Fla.

Table 29 also lists 12 facilities in startup orunder construction (up from 10 in 1976] witha total capacity of 11,860 tpd (down from12,560 in 1976). The major differences in thiscategory include shifting Baltimore, Bal-timore County, and Milwaukee to the oper-ational list; adding Akron, Ohio,; Bridgeport,Corm.; Lane County, Oreg.: Monroe Countyand Niagara Falls, N. Y.; and North LittleRock, Ark.; and deleting the 6,000-tpd pro-posal for St. Louis.

In the Fourth Report to Congress,(2) EPAlisted a number of communities engaged invarious stages of planning for centralizedresource recovery. Since 1976, neither EPAnor OTA has updated this list. Subsequentevents suggest that it is not a reliable guide tothe current situation nationwide.

In October 1978, the Department of Energy(DOE) announced that 20 communities wouldreceive grants to conduct studies for demon-strating the feasibility of recovering energyfrom waste.(3) None of these grants is to beused for construction purposes.

It is difficult to classify the operationalstatus of the facilities in table 29 becausemany of them are experimental or demonstra-tion facilities whose status can change quick-ly. The term “operational” does not nec-essarily mean “commercial. ” Several of thefacilities in the operational phase have beenbased on significant public or private sub-sidy. Others are similarly subsidized demon-stration plants. The San Diego County py-rolysis facility is shut down for major modifi-cation.(4)

Table 29 shows a trend toward large-scaleplants among those under construction or instartup. Over half have a capacity of 1,000tpd or more. A possible shift away from thisearly trend toward building large plants isdiscussed in this chapter. The table alsoshows that the most popular systems arewaterwall incineration and refuse-derivedfuel (RDF), but that there is interest in smallmodular combustion units such as those in

Ch. 5— Technologies /or Centralized Resource Recovery ● 97

Table 29.– Resource Recovery Facilities in the United States

Location

In operation:Altoona, Pa. . . . . . . . . . . . . . . . . . . . . .Ames, lowa. . . . . . . . . . . .Baltimore, Md. (D) . . . . . . . . . . . . . . . .Baltimore County, Md. (D). . . . . . . . . .Blytheville, Ark. ... . . . . . . . . . . . .Braintree, Mass.. . .E. Bridgewater, Mass. (D) . . . . . . . .Franklin, Ohio (D). . . . . . . . . . . . . . . . .Groveton, N.H. ., . . ... . . . . . . . . . .Milwaukee, Was. . . . . . . .Nashville, Term. . . . . . . . . . . . . . . . . .Norfolk. Va. . . . . . . . . . . . .Oceanside. N.Y. . . . . . . . . . . . . . . .Pales Verdes, Cal if. . . . . . . . ... . . . .Saugus. Mass. . . . . . . . . . . . . . . . . .Siloam Springs, Ark. . . . . . . . . . . . . . .South Charleston, W. Va.(D) . . . . . . .

Under construction; startup:Akron, Ohio . . . . . . .Bridgeport.Corm. . . ., ., . . . . . .Chicago, ill. . .Hempstead, N.Y. . . . . . . . . . . . . . . .LaneCounty, Ore. ..., . . . . . . . . . . . .Monroe County, N.Y., . . . . . . . . . . . . .Mountain View.Calif (D). . . . . . . . . . .NewOrleans, La.(D) . . . . . . . . . . . . . . .Niagara Falls, N.Y... . . . . . . . . . . . .North Little Rock, Ark.,. . . . . . . . . . . . .Portsmouth, Va.. . .San Deigo, Calif (D).... . . . . . . . . . .

Type’

CompostRDFPyrolysisRDFMCUWWCRDFWet pulpMCURDFWWCWWCRWI/WWCMethane recoveryWWCMCUPyrolysis

RDF/WWCRDFRDFWet pulp/WWCRDF/WWCRDFMethane recoveryMaterialsRDF/WWCMCUWWCPyrolysis

Capacity(tons/day)

200400700550

5024016015030

1,000720360750

1,20020

200

1,0001.8001,0002,000

7502.000

6502,200

100160200

a-RDF= refuse derived fuel WWC= waterfall combustion, RWl= refractory wall incineratorRDF/WWC= Waterfall combustion using processed waste D= Pilot demonstration facility

SOURCE H Freeman of EPA(l)

Products/markets

HumusRDF-utility, Fe,AlSteam heating&cooling. FeRDF,Fe,ALglassSteam processSteam processRDF-utilityFiber, Fe. glass, AlSteam processRDF-utility, paper Fe, AlSteam heating & coolingSteam (Navy base)SteamGas-utility & FeSteam processSteam processGas. Fe

Steam heating & coolingRDF utility. Fe, Al, glassRDF-utility, FeElectricity, Fe. Al, glassRDF-institution, FeRDF-utility. Fe, Al, glassGas/utilityNonferrous, Fe, glass, paperSteam industry, FeSteam processSteam loopLiquid fuel/utility, Fe, Al, glass

Startupdate

196319751975197619751971197419711975197719741967

1965/741975197619751974

19781978197619781978197819771976

—197719761977

with waste heat boiler MCU = modular combustion unit

operation at Blytheville, Ark,; Groveton, N. H.;and Siloam Springs, Ark. Industrial and insti-tutional interest in these same small wasteheat recovery incinerators appears to bestrong and growing. A late-1976 survey iden-tified 1 municipal, I school, 19 hospital, and22 industrial incinerators not listed in table29.(5)

Comparative Performance ofVarious Technologies

In order to gain some insight into how wellthese systems work, they are compared herein terms of four performance measures: (i)degree of proven commercialization, ( i i )waste reduction efficiency, ( i i i ) materialrecovery efficiency, and (iv) energy recoveryefficiency. It should be noted at the outset

that in many instances because of the emerg-ing nature or proprietary status of these tech-nologies, it is difficult to obtain adequate datafor these comparisons.

DEGREE OF PROVEN COMMERCIALIZATION

EPA has assessed the “degree of provencommercialization” of each of the materialsand energy recovery technologies.(6) Suchclassification is necessarily judgmental andis useful only as a general guide to commer-cialization status. Their classification schemeis augmented here with an additional cate-gory, “Research Technologies, ” which in-cludes processes that have not yet reachedthe pilot plant or demonstration stage, EPA’sassessments have been reevaluated by 0TAand a few differences have emerged. Thefour categories are defined as follows:


●

●

●

●

Commercially Operational Technol-ogies.—Existing full-scale commercialplants that operate continuously. Conse-quently, there are some operating dataavailable from communities and engi-neers already involved in the use of theprocess. Although such systems are be-ing commercially utilized, they may betechnically complex. To operate proper-ly, they will require maximum use ofavailable information leading to carefuldesign and operation by knowledgeableprofessionals. There may be only limitedoperating experience with some parts ofthese plants. Thus, technological uncer-tainties may still exist.Developmental Technologies.—Theseare technologies that have been provenin pilot operations or in related but dif-ferent applications (for example, usingraw materials other than mixed MSW).There is sufficient experience to predictfull-scale system performance, but suchperformance has not been confirmed.System design requires considerable en-gineering judgment about scale-up pa-rameters and performance projections;consequently, the level of technical andeconomic uncertainty is generallygreater than with commercially opera-tional technologies.Experimental Technologies.—These in-clude new technologies still being testedin laboratories and pilot plants. Becausethere is not sufficient information to pre-dict technical or economic feasibility,such technologies should not be consid-ered by cities contemplating immediateconstruction.Research Technologies.—These tech-nologies, which are only in the labora-tory testing stages with no pilot plant ac-tivity underway, are most technologi-cally and commercially uncertain.

Tables 30 and 31 show OTA’S version ofthe EPA assessment of the degree of provencommercialization for energy and materialrecovery technologies. The only commerciallyproven technologies for energy recovery arewaterwall combustion, modular incineration

Table 30.—Degree of Proven Commercialization ofEnergy Recovery Technologies

Commercially operational technologiesWaterwall combustionSmall-scale modular incineration with heat

recoverySolid fuel RDF (wet and dry processes)

Developmental technologiesLow Btu gas pyrolysisMedium Btu gas pyrolysisLiquid pyrolysisBiological landfill conversion

Experimental technologiesBiological anaerobic digestionWaste-fired gas turbine

Research technologiesHydrolysis systems

SOURCE Office of Technology Assessment -- —

Table 31 .— Degree of Proven Commercialization ofMaterials Recovery Technologies

Commercially Operational TechnologiesComportingMagnet ic recovery of ferrous metalsFiber recovery by wet separation

Developmental technologiesAluminum recoveryGlass recovery

Experiment/ technologiesNonferrous recoveryPaper recovery by dry processes

SOURCE Off Ice of Technology Assessment—— —

with heat recovery, and solid fuel RDF (wetand dry processes). Table 30 includes thewaste-fired gas turbine concept. Consider-able Federal research funds have been ex-pended on this system which uses waste com-bustion gases to drive a gas turbine. It has notbeen included in this assessment because ofserious corrosion and other problems.(6)

The only commercially proven materialrecovery technologies are humus productionby comporting, magnetic recovery of ferrousmetals, and low-grade fiber recovery by wetpulping. Other approaches have yet to beproven in an operational, economically soundproject.

Aluminum recovery is classed as develop-mental because no plants are currently pro-ducing a steady stream of recovered alu-

Ch. 5— Technologies for Centralized Resource Recovery . 99

minum. The New Orleans facility recoveredits first aluminum cans in March 1978.Samples were sent to Reynolds Metals Cor-poration for testing. Additional tests will benecessary before large quantities of alu-minum can be recovered.(4) The Ames, Iowa,aluminum magnet was damaged in a winterfreeze and only returned to operationalstatus in mid-April 1978. The plant manage-ment had not yet (spring 1978) concluded thepurchase agreement because the system hadnot been accepted from its manufacturer asoperating satisfactorily. The Baltimore Coun-ty facility aluminum magnet does not run on acontinuous basis, but only when smallamounts of RDF are being produced for anEPA contract calling for 3,000 tons for ex-perimental cement kiln firing. Normally theshredded waste is used for landfill after therecovery of ferrous material, and aluminumis not recovered when the plant is running inthis configuration. The Americology plant inMilwaukee, after correcting several prob-lems, is in roughly the same situation as theNew Orleans plant. Thus, none of theseplants has yet demonstrated the sustainedrecovery of aluminum that is necessarybefore such recovery can be considered acommercially operational technology.

The status of glass recovery technology issimilar to that of aluminum. It is, therefore,also considered to be in the developmentalstage.

WASTE REDUCTION EFFICIENCIES

Reducing the amount of waste that must belandfilled is a major concern of municipaldecisionmakers. Table 32 shows literatureestimates of the residual fraction of MSWthat must be disposed of by landfill or othermeans following resource recovery by thevarious technologies. As can be seen fromthis table, all of the systems reduce the land-fill burden. Recovering both materials andenergy helps reduce the disposal load. It isgenerally believed that residues that havebeen subjected to high temperatures in in-cineration or pyrolysis will be less hazardousin landfill because most pathogens cannot

Table 32.—Estimated Waste Reduction Efficienciesof Resource Recovery Technologies

— —Residue as percent

of input waste

Weight VolumeTechnology percent percent

Refer-ence

—.Waterwall combusion . . . . . 25-30a 10 (6)

20-35a 5-15 (7)25-30a — (8)

Small-scale incineration . . . 30a 10 (9)Dry fluff RDF. . . . . . . . . . . . l0-15 b — (8)

20C — (lo)Low Btu pyrolysis . . . . . . . . 15-20a 3-5 (lo)Medium Btu pyrolysis . . . . . 17C 2 (lo)Liquid pyrolysis . . . . . . . . . . 27b — (lo)

7b, d 1-2 (11)Anaerobic digestion . . . . . . 17b — (11)

awith metals not recoveredb with metal recoverycWith ferrous recoverydAssumes the char would have economic value and would not be Iandfilled

survive the high temperature and becausecinerator residue should be less subject

in-to

subsidence. However, the products of com-bustion and pyrolysis must be examined todetermine whether they create new kinds oftoxic landfill effluents.

MATERIAL RECOVERY EFFICIENCIES

Table 33 shows the materials recovery effi-ciencies of various processes based on datafrom the literature. The National Center forResource Recovery [NCRR) reports efficien-cies of up to 99 percent when the aluminummagnet is run at extremely slow (not commer-cially feasible) speeds. Product contami-nation is a problem with aluminum recovery.To reduce contamination an “air knife” canbe installed following the aluminum separa-tor. As mentioned earlier, the quality ofpaper fiber and glass recovered by the tech-nologies listed in table 33 is low. Ferrousrecovery is the most commercially feasible ofall the systems reviewed here. [Additional at-tention is given to the quality of recoveredmaterials in chapter 3.] Other dry paper re-covery processes such as the Flakt processare being explored in Europe where woodstock for paper is not as abundant as in theUni ted Sta tes .


Table 33.—Materials Recovery Efficiencies——

Percent of thewaste stream

content of eachmaterial

Technology recovered Reference— —Ferrous-magnetic . . . . . . . . 90-97 (6)Paper fiber—drya. . . . . . . . . 23 (6)Paper fiber—wet . . . . . . . . . 50 (12)Aluminum magnetb . . . . . . . 65 (15)Glass-froth flotation . . . . . . 65-70 (11)Glass-optical sorting. . . . . . 50 (12)

aCECCHINl Process in Italybshredded cans at a 1 ton per hour feedstock rate

ENERGY RECOVERY EFFICIENCIES

There is currently no standard acceptedway to evaluate the energy recovery efficien-cy of resource recovery systems. This prob-lem is illustrated by one study that cites sevendifferent efficiency figures from the litera-ture, ranging from 29 to 49 percent, for theOccidental liquid pyrolysis process. Dif-ferent efficiencies result from alternativeways of treating energy used by the processitself, from the choice of system boundariesfor which the calculation is made, from thechoice of higher or lower heating value of thewaste, and from including or excluding theenergy content of nonfuel materials. As thesituation presently stands, it is possible toproduce energy recovery efficiency figures toeither enhance or detract from the apparentattractiveness of a particular system. TheAmerican Society for Testing and Materials(ASTM) Committee E-38 on Resource Recov-ery is examining energy efficiency calcula-tions, but because of more pressing matters ithas a low priority according to the committeechairman.(17)

Table 34 shows system energy efficienciesin terms of the energy content of the fuel pro-duced, and in terms of the output energyavailable as steam. While comparison on thebasis of available steam makes thermody-namic sense in terms of standard systemboundaries, it ignores such important eco-nomic characteristics of the various waste-

Table 34.—Energy Recovery Efficiencies ofResource Recovery Processes

Efficiency basis

Energy in Energyfuel available

Process produceda as steamb

Fluff RDF. . . . . . . . . . . . . . . . . . . . . . . . 70C 49CDust RDF. . . . . . . . . . . . . . . . . . . . . . . . 80 63Wet RDF . . . . . . . . . . . . . . . . . . . . . . . . 76 48Waterwall combustion furnace. . . . . . — 59Modular incinerators. . . . . . . . . . . . . . — 25-50Purox gasifier. . . . . . . . . . . . . . . . . . . . 64 58Monsanto gasifier . . . . . . . . . . . . . . . . 78 42Torrax gasifier ., . . . . . . . . . . . . . . . . . 84c 58 c

Occidental Petroleum Co. pyrolysis. . 26 23Biological gasification. . . . . . . . . . . . 33c 29c

. — . — — . — —a Higher heating value of the fuel product, less the heating value of the energy

used to operate the system expressed as a percent of the heating value of theinput solid waste It was assumed that electricity IS produced onsite using thesystem’s fuel product

bin order t. compare all the processes on an equivalent thermodynamic basis,

the energy available as steam was calculated using an appropriate boiler effi-ciency for each fuel product

corrected figures are based on communications with EPA and an EPA contrac-tor (18,23).

dincludes energy recovered from sewage sludge which also goes into thedigester. This calculation also assumes that the filter cake residue from thedigester IS burned to recover heat

SOURCE EPA Fourth Report to Congress, p 59, with corrections by OTA asnoted All calculations are based on higher heating value ofInput solid waste of 5,000 Btu per pound, with some i-n.organic materials removed

derived fuels as the quality of the fuel prod-uct and its transportability. The temperatureof the steam produced by various technol-ogies may differ considerably.

The basis for table 34 is a similar table inEPA’s Fourth Report to Congress. However,several typographical errors in EPA’s reporthave been corrected. In addition, data forsmall-scale incinerators have been addedbased on conversations with an EPA contrac-tor, The energy savings from materialsrecovery have not been included. EPA’s useof the term “net energy” in their version oftable 34 differs from best practice in suchcalculations because of arbitrary limits onthe system boundary.

The energy efficiency figures in table 34are not based on tests from actual workingsystems. Rather, they were calculated fromdata available in the literature and from con-tacts with vendors. Therefore, care should beexercised in drawing inferences from thistable, particularly where efficiency differ-ences are relatively small.

Ch. 5— Technologies for Centralized Resource Recovery ● 101

Potential Energy Savings FromCentralized Resource Recovery

Resource recovery can save energy in twoways: by substituting fuels or heat recoveredfrom waste for nonrenewable energysources: and by substituting recovered mate-rials for their counterpart virgin materials.

Less energy is required to produce most in-dustrial materials from scrap than fromvirgin sources. Therefore, recovering mate-rials from MSW for recycling represents anenergy savings. Using data from the litera-ture(19,20,21 ,22) the potential energy savingswere calculated assuming that in 1975 all theiron and steel, aluminum, copper, and glasswere recovered from the MSW stream. Theresults of this calculation are summarized intable 35. Complete recovery of these materi-als would have saved 0.3 x 10’5 Btu or 0.3Quad. * This is equivalent to about 0,4 per-cent of the Nation’s energy use in 1975.

To calculate the amount of nonrenewableenergy that could be saved by recovery of fuelor energy from MSW it was assumed: (i) that100 percent of the combustible waste (includ-ing paper) could either be recovered as fuelor burned, (ii) that the substitution would beon a Btu for Btu basis, and (iii) that raw MSWhas an energy content as fuel of 5,000 Btu perpound. Thus, for the base year selected,1975, the energy content of the 136.1 milliontons of MSW generated would have been 1.36x 10’5 Btu or 1.36 Quads. This is equivalentto about 1.9 percent of the Nation’s energyuse in that year.

Thus, the maximum energy that could havebeen saved by centralized recovery of bothenergy and materials in 1975 is 1.66 x 1015

Btu or 2,3 percent of the energy used by theNation in that year. In actual practice, how-ever, the maximum amount of energy savedwould be considerably less than calculated inthese estimates. Technical, economic, and in-stitutional barriers would act to limit the con-tribution of resources recoverable fromMSW to the Nation’s energy pool,

Table 35.—Potential Annual Energy Savings FromRecovery and Recycling of 100 Percent of Various

Materials From MSW

Mater ia l - Energy savings(1015 Btu/year)

Iron and steel ... ... . . . . . . . . . . . . . . . 0.08Aluminum. ... ... . . . . . . . . . . . . . . . . 0.19Copper . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01Glass. . . . . . . . . . . . . ... ... ... . . . . 0.02

Total . . . . . . . . . . . . . . . . . . . . . . . . . 0.30

SOURCE - Off Ice of Technology Assessment

Resource Recovery Experience inWestern Europe

R esource recovery, especially for energyproduction, is more widespread in West-

ern Europe than in the United States. A re-cent study for DOE of 14 countries identified181 plants containing 243 separate units. The181 plants include a total of 413 fur-naces.** Most of these units recoversteam in waterwall or fire-tube boilers.Typical applications are electricity genera-tion, steam for district heating and industrialuse, and sewage sludge drying. Severalplants preshred the refuse and recover fer-rous metals before burning, and many havepollution control devices. Tables 36 and 37show the geographic distribution of units,both furnaces and plants. (Furnace sizes aregiven in metric tons, which are equivalent to2,205 pounds. The U.S. short ton is 2,000pounds.)

In comparison with Western Europe, EPAidentified seven waterwall combustion plantsand three small-scale modular combustionunits for MSW completed and operational inthe United States in 1976. Not all of theseseven large waterwall systems were able tomarket their steam. Thus, in terms of num-bers of units, Western Europe is considerablyahead of the United States.

Individual furnaces in Europe are smallerthan the large-sized units being installed inthe United States. Thirty-four percent of theEuropean furnaces are smaller than 5 metric

*One Quad = 1O15 Btu = 1.055 exajoule.**EPA is currently examining European systems in a

detailed study.


Table 36.— Waste-to-Energy Systemsin Western Europe

—Number Number

Country of unitsa of plantsb

Austria. . . . . . . . . . . . . . . = . . . . . . ‘- 2 2Belgium . . . . . . . . . . . . . . . . . . . . . . 3 3Denmark . . . . . . . . . . . . . . . . . . . . . 45 31Finland. . . . . . . . . . . . . . . . . . . . . . . 2 2France . . . . . . . . . . . . . . . . . . . . . . . 29 20Italy . . . . . . . . . . . . . . . . . . . . . . . . . 16 14Luxembourg . . . . . . . . . . . . . . . . . . 1 1Netherlands. . . . . . . . . . . . . . . . . . . 7 6Norway. . . . . . . . . . . . . . . . . . . . . . . 13 8Spain . . . . . . . . . . . . . . . . . . . . . . . . 3 2Sweden . . . . . . . . . . . . . . . . . . . . . . 22 16Switzerland . . . . . . . . . . . . . . . . . . . 33 29United Kingdom . . . . . . . . . . . . . . . 9 9WestGermany. . . . . . . . . . . . . . . . . 58 38

Total . . . . . . . . . . . . . . . . . . . 2 4 3- - ‘ - ” 1 8 1

aAUnit os a facility built at one time in a single locatonbA plant is bui lding which one or more waste-to-engery units is instal led

SOURCE (24)

tons per hour, and 60 percent are smallerthan 10 metric per hour. In contrast, forexample, the Resco plant at Saugus, Mass.,uses two waterwall combustion furnaces,each rated at682 metric tpd or 28 metrictonsper hour. The only units larger than theseoperating in Western Europe are two 50-metric-ton per hour furnaces in the Paris,France IVRYII plant and a few 40-metric-tonper hour furnaces installed in West Ger-many.*

With the exception of the large furnaces inFrance and West Germany, other Europeanplants use a modular approach to achievelarge plant capacity. The French plant atLyon Zeme achieves a daily capacityof 960metric tons with four, l0-ton per hour fur-naces. The Sorain Cecchini plant in Rome,Italy reaches 576 metric tpd with six, 4-tonperhourunits.

Most of the incineration units in Europeare in large cities that often have more thanone facility. However, several small towns inDenmark have small units with capacities

*One DOE official believes that the French will notagain build and try to operate systems with large fur-nace units but would achieve large scale by using amodular approach with several smaller furnaceunits,(25)

less than 5 metric tons per hour. Almost allthese plants are used for hot water and dis-trict heating. In Switzerland, centrally lo-cated facilities serve rural areas. The plantat Monthey, for example, generates electrici-ty from the solid waste of 57 villages.

There are institutional differences be-tween European and U.S. society that affectresource recovery systems. Denmark has alaw requiring source separation that removesa large portion of the organic combustiblesfrom MSW and thus discourages certainkinds of centralized waste-to-energy systems.Comporting is successful in the Netherlands,whereas it usually fails in the United States.The Netherlands subsidizes comporting oper-ations. Markets for the composted product,humus, are good in the flower and bulb in-dustries.

Some of the factors that might explainEuropean adoption of energy recovery in-cinerators are: (i) relatively high populationdensities with less land available for dump-ing, (ii) high fossil-fuel prices, (iii) coldclimates in which district heating systemshave long flourished, (iv) strong manufactur-ing firms including several furnace gratemanufacturers, and (v) localized electricityproduction, which makes the sale of electrici-ty easier (except in France and Italy, whichhave state monopolies) .(24)

Environmental and WorkplaceHealth and Safety

T his section examines the environmentaland workplace health and safety aspects

of resource recovery systems in order todetermine whether problems exist that mightrequire attention by Congress, the regulatoryagencies, or the R&D community. The topicsaddressed include air, liquid, and solid emis-sions from resource recovery facilities, andworkplace conditions such as noise, patho-gens, dust, toxic substances, explosion andfire hazards, and the safety of mechanicaland electrical equipment. Few, if any, of theproblems discussed appear to be insoluble,

Ch. 5—Technologies for Centralized Resource Recovery ● 103

but they could add to the cost of building andoperating resource recovery plants and con-strain the range of practical technologies.

Environmental Factors

Questions have been raised about potentialair and water pollution from resource re-covery plants. Emission standards exist forsuch air emissions as particulate matter,sulfur dioxide, nitrous oxides, carbon monox-ide, and hydrocarbons. Because MSW con-tains larger concentrations of some heavymetals and other hazardous substances thancoal and oil, there is increasing interest inassessing the potential health and environ-mental hazards of these substances. How-ever, very little good data are available forthis purpose. A report by the Midwest Re-search Institute (MRI) for EPA lists 84 sub-stances known to be in MSW; many of whichare known to be hazardous. Research iscited which indicates that a number of haz-ardous inorganic substances are found inhigher concentrations in RDF than in coal.

EPA has recently initiated research tobuild a data base on the environmental as-pects of resource recovery systems. This

should enable development of control technol-ogy, if necessary. The consequences ofhazardous substances in resource recoverysystems are currently not understood andthere are no regulatory standards applicableto their emission into the air or water, or assolid waste. EPA has proposed an ambient airquality standard for lead and is consideringregulation of other hazardous materials.

AIR EMISSIONS

Some data exist on emissions of the five“criteria pollutants” (particulate, sulfur ox-ides, nitrogen dioxide, carbon monoxide, andphotochemical oxidants) from incinerationand from combined RDF/coal-fired systems.Little data on the emission of these pollutantsfrom pyrolysis or biological systems are avail-able. Air emissions from pyrolysis plants cancontain particulate matter as well as hydro-carbons and such gases as hydrogen chlor-ide, hydrogen sulfide, and nitrous oxides. Airpollution from biological systems can resultfrom the incineration of digester filter cakeresidues. Other air emissions can result fromcleaning methane digester gas. The charac-teristics of these potential pollutants areunknown.

104 Materials and Energy from Municipal Waste

Air pollution control equipment is nec-essary for incineration systems. * Averageuncontrolled particulate emissions from amodern waterwall incinerator were found tobe 1.24 grains per standard cubic foot (SCF)(2.84 grams per standard cubic meter, g perSCM) compared to the EPA standard of 0.08grains per SCF (O. 18 g per SCM).(7) However,air pollution control technology, when proper-ly selected, installed, and operated appearsto bring particulate emissions within EPAstandards.(7) Since waste has a higher ashcontent than fossil fuels, burning RDF withcoal may increase the load on air pollutioncontrol equipment. The efficiency of elec-trostatic precipitators may be reduced whenMSW is burned with coal at high boilerutilization rates.(10)

Research indicates that sulfur dioxide, ox-ides of nitrogen, carbon monoxide, and hydro-carbons are not likely to cause problemswhen MSW is burned. Since MSW has amuch lower sulfur content than most coals,cofiring RDF and coal could reduce sulfurdioxide emissions per unit of electric energyproduced. In cofiring RDF and coal, for whichthere are more data than for waterwall in-cineration, there is evidence of increased airemissions of such heavy metals as beryllium,copper, lead, cadmium, and mercury.Based on very limited tests, researchers atIowa State University reported increases incopper and lead air emissions from the pow-erplant at Ames when RDF was added to thec o a l . * *

*Incinerators of less than so tpd are excluded fromFederal air quality standards.(28) There is great vari-ability among States and between State and Federalstandards for incinerators. For example, in theBaltimore and Washington metropolitan areas ofMaryland, single-stage incinerators with a capacity ofless than 5 tons per hour are prohibited. (29l) It is notclear whether this ban would apply to small, two-stageincinerators of the kind under discussion here.

**A furor was caused in the fall of 1977 when re-searchers erroneously reported very high concentra-tions of toxic substances in the RDF from the Ames,Iowa RDF plant. The error was subsequently cor-r e c t e d .

Hydrogen chloride gas produced by burn-ing plastics in MSW can combine with waterto form hydrochloric acid and may createpotential health and corrosion problems. Hy-drochloric acid, if it is found to be a signifi-cant health problem, should not be difficult tocontrol with scrubber technology.

Little is known about air pollution from co-firing liquid pyrolysis fuel with oil, since theOccidental pyrolysis plant in California is notin operation.

Dry process refuse-derived-fuel plants mayemit dust, odor, and noise to the plant en-vironment, but these can be confined to theplantsite with proper design. (See the follow-ing section for a discussion of these sub-stances in the workplace environment. )

LIQUID EMISSIONS

Important characteristics of waste waterfrom resource recovery systems, some ofwhich could require control, are: hightemperature, dissolved oxygen (DO), biochem-ical oxygen demand (BOD), chemical oxygendemand (COD), hydrogen ion concentration(pH), alkalinity, hardness, total solids, totaldissolved solids, suspended solids, settleablesolids, phosphates, nitrates, chlorides,fluorides, heavy metals, odor, and color.(8)

Not much is known about the characteris-tics of water pollutants from incinerationprocesses, in which one potential source ofwaste water is from ash slurrying. Studies atthe St. Louis RDF/coal-fired plant indicate in-creased levels of BOD, COD, and total dis-solved solids. Characteristics of wastewater from pyrolysis plants are not wellknown, but it may be high in BOD, COD,alcohols, phenols, and other organic com-pounds. Biological systems present wastewater pollution problems because the proc-ess requires large quantities of water in thedigesters, part of which is recycled, but partof which must be discharged. Little informa-tion is available on these emissions since thedemonstration plant at Pompano Beach is stillunder construction.


SOLID RESIDUALS

Solid wastes from resource recoveryplants include combustion ash, pyrolysisresidues, and particulate matter recoveredby air pollution control devices, all of whichcan produce undesirable leachates whenused as landfill. Although data are scarce, flyash particulate from waste incineration maycontain trace elements such as cadmium,lead, beryllium, and mercury (30)) The solidsludge from biological processes may containbacteria that could create leachate problemsif landfill is chosen for its disposal.

Occupational Health and Safety Factors

Persons working in and around resourcerecovery plants may be subjected to potentialhealth and safety hazards such as bacterio-logical and virological pathogens, dust, toxicsubstances, noise, explosions and fires, andmechanical and electrical equipment. Sincethese systems are new, little is known aboutthe characteristics of the hazards they pose,This section describes these hazards and re-views some of the ongoing research and reg-ulatory activity associated with them.

NOISE

Resource recovery processes such asshredders, air classif iers, trommels, andcyclones can produce noise in excess of pres-ent Occupational Safety and Health Adminis-tration (OSHA) standards. A study of a small,3-ton per hour resource recovery system re-ported noise levels in excess of 90 dBA* nearthese devices. Control of noise in suchequipment by engineering design will prob-ably be costly. Consequently, administrativecontrols (limiting the time exposure of em-ployees in high noise areas) and personal pro-tective equipment may be needed to controlexposure. Noise levels in larger commercial-ized shredders will undoubtedly exacerbatethe problem. Current OSHA regulatory activi-

*Ninety decibels on the A scale (90 dBA) is the max-imum noise level permitted for an 8-hour day by presentOSHA standards. This level is thought to be too high bysome organizations who prefer an 85 dBA standard.

ty should be adequate to control noise ex-posure unless the plant is operated by amunicipality in a State in which municipalemployees are not covered by OSHA.

PATHOGENS

As MSW is shredded, air-classified, andtransported within resource recovery facil-ities, workers are exposed to bacterial,fungal, and virological pathogens containedin the waste stream. Air sampling indicatesthat total bacterial counts in the Ames plantare around 100 times greater than in normalnonplant environments.(34) MSW containshuman and animal fecal matter due, for ex-ample, to the use of disposable diapers andthe disposal of animal litter. Fecal coliformsand fecal staphylococci at the Ames facilityare about 5 percent of total bacteria. Gooddata on the impact of these pathogens on thehealth of workers are not available. No stand-ards exist for microbiological contaminantsin the workplace except for hospital oper-ating rooms—a standard not applicable to re-source recovery plants.

The data base for viral contaminants inresource recovery plants is even less ade-quate. Even though viruses would be ex-pected in such plants, air sampling studiesdone by MRI for EPA have not detected any.The sampling method may be inadequate, andfurther tests are underway at Ames .(34)

Epidemiological studies of persons withlong-term exposures to environments typicalof resource recovery plants do not exist. Onestudy of New York City uniformed sanitation-men found no evidence of an increasedamount of chronic pulmonary disease whencompared to other job titles in the depart-ment.(35) The same author reported thatthese sanitationmen have a rate of coronaryheart disease almost twice that of othergroups of males in similar age categories. Heis unable to explain this finding, and urgesthat epidemiological studies are needed toidentify causes.

Some research is underway on pathogensin resource recovery plants. EPA is funding a


study in this area by MRI. The National In-stitute of Occupational Safety and Health(NIOSH) is presently funding research at theStanford Research Institute on occupationalhealth and safety (emphasis on health) inemerging energy industries. One of the tasksbeing carried out is an assessment of healthand safety problems in resource recovery fa-cilities. This limited preliminary study is ex-pected to produce a qualitative assessment ofpotential problems with pathogens and tosuggest what needs to be done. Related workis being done at the Ames Laboratories ofDOE. ASTM has formed a subcommittee onhealth and safety of its Committee E-38 on Re-source Recovery. One of this subcommittee’stasks is to develop standardized methods forsampling microbiological aerosols. Someresearchers in this field indicate that if in-formation on bacteriological and virologicalexperiments done by the military could bedeclassified, research on resource recoveryplants might be expedited.

DUSTS AND TOXIC SUBSTANCES

Processing MSW produces considerabledust—another potential health hazard.OSHA standards for dust specify maximumpermissible concentrations of dirt or nuis-ance dust. However, because of the variety ofmaterials in MSW there is additional concernabout specific substances such as asbestos,metal dusts, and other toxic substances. Inone test at a resource recovery plant asbestosfibers were not found in the air, and a singletest for aluminum and cadmium dust gavenegative results. Roughly half the dust ona particle count basis at the Ames plant iscomposed of particles less than 4 microns indiameter . S imi lar resu l t s a re repor tedelsewhere.(33) Retention of dust in the lungsis highest for particles of about 2 microns,so it appears that MSW dust retention maypresent a problem. The National Center forResource Recovery reports that an average ofdust samples in their experimental test facili-ty showed only 12 percent of the dust to be inthe respirable range.(37) Their dust measure-ments were made on a weight basis, ratherthan the particle count basis used at Ames.

Dust particles too large to enter the lungs canbe captured in mucous membranes and ulti-mately carried into the digestive tract. This isanother source of infectious potential of un-known significance.

Obviously, dust control measures and per-sonal protective equipment for workers inresource recovery plants need considerableattention on the part of workers, managers,and regulators. In the long term more workneeds to be done to characterize the nature ofdust in resource recovery plants and toassess the health effects of long-term ex-posure to this kind of dust.

EXPLOSIONS AND FIRES

MSW occasionally contains dynamite; gun-powder; flammable liquids and gases; aerosolcans; propane, butane, and gasoline fuel con-tainers; and other explosive substances.When such substances are shredded an ex-plosion can occur. A 1976 study of explosionhazards in refuse shredders reported 95 ex-plosions in the 45 MSW-shredding plants in-cluded in the survey. Thirty-four of theshredding operations had experienced atleast one explosion. Injuries were reported inonly three incidents. No fatalities occurred.Only five of the explosions produced morethan $25,000 property damage or put theshredder out of operation for more than 1week. Because shredders are designed towithstand mild explosions, shredder explo-sions usually damage peripheral equipmentsuch as ducts and conveyors.

Protection from shredder explosions canbe achieved by manual or automated surveil-lance of input material, explosion venting, ex-plosion suppression/extinguishing systems,water spray, or equipment isolation. Manualscreening to remove explosive material isalready being practiced, but cannot be ex-pected to remove all explosive substances.The feasibility of automatic detection of suchmaterials is questionable. Shredders can bedesigned with hinged walls and tops to allowrapid venting of exploding gases. This methodcan minimize shredder damage, but requires

Ch. 5—Technoligies for Centralized Resource Recovery ● 107

careful attention to the protection of person-nel and adjacent equipment. Explosion extin-guishing systems detect the pressure in-crease at the beginning of an explosion andtrigger the release of chemical explosion-suppressing agents into the shredder. Whenoperating properly these devices can controlshredder explosions and extinguish flames.However, such devices cannot control explo-sions of self-oxidizing explosives such as ord-nance. Continuous water sprays in the shred-ding operation can reduce explosion and firehazard, but water in the shredded refuse re-duces its heating value, reduces the efficien-cy of ferrous separation, and can causeshredder corrosion. Finally, personal injuryfrom shredder explosions can be controlledby isolating the shredder and keeping em-ployees away from it while in operation.

It appears possible to reduce the incidenceof shredder explosions by substituting a ro-tary drum air classifier for the shredder asthe first step in waste processing. Using thisapproach, only the light fraction of the wasteis shredded while most of the potentially ex-plosive components become part of the heavyfraction, which is not shredded. Such a sys-tem has been tested at the waste shreddingfacility in New Castle, Del.

Dust from MSW shredding does not appearto be a great explosion hazard. However,mixtures of combustible dust and flammablegas or vapor may explode even thoughneither the dust nor the gas by itself is in anexplosive concentration range. In addition,dust can be a contributing factor in firescaused by explosions.

Dust explosions may be more likely wherefine powder RDF is produced. An explosionwith a fatality occurred at the ECOFUEL II”plant in East Bridgewater, Mass., in the fallof 1977. According to the plant owners, Com-bustion Equipment Associates (CEA), thecause of this explosion is still undetermined.(39) CEA claims that their powdered RDF isless explosive than grain or starch dust orpulverized coal.

MECHANICAL AND ELECTRICAL HAZARDS

Resource recovery systems contain an ar-ray of mechanical and electrical devicesranging from equipment for handling mate-rials (front-end loaders, cranes, and con-veyors) to the separation and combustionprocesses discussed earlier. This environ-ment exposes employees to a variety of poten-tial accidents. However, most of these de-vices fall under existing OSHA safety regula-tions. Assuming that these regulations are en-forced and that workers are covered, controlof these hazards maybe adequate.

Conclusions

Several potential environmental and oc-cupational health and safety problem areasin resource recovery need further investiga-tion. Many questions about the environmentalimpacts of waste-to-energy systems remainunanswered. EPA is now monitoring andstudying control of pollution from resourcerecovery facilities as they come online. If con-struction of resource recovery facilities con-tinues, this activity may need to be accel-erated to ensure against the emergence of en-vironmental problems in the future. Explo-ration of control technologies for heavymetals in air emissions and for toxic leach-ates from solid residuals of resource recoveryin landfill, is particularly important.

Some of the occupational health and safetyproblems such as noise and mechanical andelectrical hazards can probably be controlledby OSHA’S existing regulatory apparatus.However, work on pathogens as health haz-ards should be accelerated. NIOSH has re-cently announced an interest in developing acriteria document on occupational safety andh e a l t h s t a n d a r d s f o r i n c i n e r a t i o n s y s -tems. Under this procedure, 1982 is theearliest date for promulgation of a health andsafety standard for incinerators. NIOSHshould consider issuing a criteria documentfor all the resource recovery technologies, notjust incineration, on an accelerated timeschedule. Finally, relevant military researchon pathogenic agents should be made avail-able.


Plant Size and System Design:The Question of Scale

Overview

M ost of the resource recovery technol-ogies in the United States examined in

this chapter are currently being designed andbuilt as large-scale plants, with capacities inthe 1,000- to 3,000-tpd range. The exceptionsare small-scale modular incinerators and bio-logical conversion processes. Such largeplants are attractive because they promisesignificant economies of scale in processing(average costs decline as plant size grows—see chapter 6) and because they can includeeconomical systems for the recovery of mate-rials as well as energy.

Recently, however, strong interest hasemerged in small-scale, modular incineratorswith heat recovery. This interest is stim-ulated by the realization that the institu-tional, financial, and technological barriersto large-scale systems discussed in chapters 6and 7 are real, especially in view of the un-certainty about the capability and reliabilityof available technologies.

Interest in small-scale systems has alsoparalleled the attention being given to theconcepts of “decentralized,” “appropriate,”or “soft” technology. These concepts arebeing examined for many technologies suchas energy supply, sewage treatment, and pro-vision of government services. For resourcerecovery systems these concepts suggest thatthe scale of a technology should match thescale of its users.

In the remainder of this section, the im-plications of scale matching are explored forresource recovery system design. The sizes ofpotential producers and consumers of re-covered energy are examined, and some ofthe advantages and disadvantages of small-and large-scale systems are addressed.

Matching producers With Consumers

ENERGY CUSTOMERS

Resource recovery plants can be viewed asfactories that produce energy from a raw ma-terial—MSW. The larger such a plant, themore waste it can process from more people,and the larger the energy customer it re-quires. For example, a plant with 1,000-tpdaverage capacity can process the waste ofapproximately 570,000 people. The energycontent of that waste as fuel is about 9 billionBtu per day, or the equivalent of the energyrequired to support a 37-megawatt electric(MWe) powerplant. * Such a powerplantwould, in turn, serve about 3 percent of theelectric power needs of the 570,000 people;who would use a total of about 1,200 MWe.

Electric powerplants are often consid-erably larger than 37 MWe; in fact, plants of1,000 MWe are not unusual. Because electricpowerplants are large consumers of fuel,they have been suggested as major potentialcustomers for the fuel or energy output of re-source recovery projects. However, to dateutilities have been reluctant to use fuel fromthese sources, in part for the financial and in-stitutional reasons discussed in chapter 7. Inaddition, however, utilities may be less thanenthusiastic because solid waste as a fuelsource is just too small. The potential finan-cial, regulatory, technical, and political prob-lems of burning solid waste may not be worththe effort for only 3 percent of a utility’s fuelneeds.

On the other hand, the energy output froma l,000-tpd” plant is much too large for mostalternative customers for energy as steam orhot water. For example, the space heatingand cooling energy demand of office buildingsis estimated to be on the order of 850 Btu perft2 per day.(42) Thus, a 1,000-tpd plant might

*This calculation is based on an MSW heating valueof 9 million Btu per ton, a per capita waste generationrate of 3.5 pounds per day, and an electrical generationefficiency of one-third.

Ch. 5— Technologies for Centralized Resource Recovery ● 109

serve up to 5 million ft2, * an area correspon-ding to a very large office building or multi-building complex, such as the Pentagon,which has 6.55 million ft2 of space. (43) Onealternative is for a large, centrally locatedfacility to serve a number of surrounding cus-tomers, This approach has been taken inNashville, Term., and in a plant under con-struction in Akron, Ohio.

Another alternative is to build a number ofsmall resource recovery plants that producesteam or hot water. These modular combus-tion units (MCUS) would serve such cus-tomers as small- to medium-sized manufac-turing plants and office buildings, and largeinstitutions. The number of such potentialcustomers greatly exceeds the number ofpotential industrial customers for the outputof the larger 1,000- to 3,000-tpd plants.

The large number of potential industrial,institutional, and commercial users of heatfrom MCUS is suggested by the following in-formation from DOEO(44) Several institutionsare already using MCUS to recover energyfrom their own wastes, and in 1972, about25,000 small boilers comparable in size toMCUS were producing heat for industrialprocesses. This indicates considerable poten-tial industrial interest in MCU heat, especial-ly as energy costs rise. There are also some7,200 hospitals, 3,026 public and private col-leges and universities, and 108,676 publicand pr iva te elementary and secondaryschools, Although many of these institutionsare too small to use the entire output of even asmall MCU, only 2 percent of them would be2,400 potential users. For commercial build-ings, Friedricks(43) thinks there might be a“realistic potential” for 1,000 to 2,000 MCUS.The possibility of matching the output ofsmall-scale modular incinerators for MSW tothe many potential users of heat warrantsmore extensive examination.

WASTE PRODUCERS

Experience to date suggests that in theUnited States resource recovery plants can

*Assumes roduction of 4 million Btu of steam or hotwater energy per ton of MSW.

be implemented more easily to serve a singlecommunity, or part of a community, than toserve a multicommunity region. As noted inchapter 7, the institutional, political, andeconomic barriers to multicommunity proj-ects are difficult to overcome.

The potential market for resource recoveryplants of various sizes can be estimated byconsidering the size distribution either of in-dividual communities or of Standard Metro-politan Statistical Areas (SMSAS). A biggermarket is predicted for small plants when thefirst approach is used and for large plantsusing the second approach.

Table 38 shows the size distribution ofAmerican cities along with estimated wastegeneration rates, neglecting any change inper capita waste generation with a change incity size. Only 23 cities are large enough tosupport a 1,000 + tpd plant on their own.Another 34 cities fall in the 500- to 1,000-tpdrange. On the other hand, over 800 citiesmight use resource recovery plants in the 50-to 500-tpd range, and an additional 1,200cities are in the 15- to 50-tpd group. Thesenumbers suggest that there may be a largepotential m a r k e t f o r “small” resourcerecovery plants.

A somewhat different view of the potentialfor large plants is suggested by table 39,which shows the distribution of U.S. popula-tion in the SMSAS. These areas typically in-

Table 38.—U.S. City Size, Population, andWaste Production in 1975

— -— .Average –

Average municipalCity Number Popula- population solid waste

size range of lation a per city per city(thousands) cities a (million) (thousands) (tons/day)b

5-10 . . . .: . ; ‘1,463 10.3 – -7.1 1210-20 .., . . . . . 977 13.8 14.1 2520-25 . . . . . . . . . 238 5.3 22.0 3925-50 . . . . . . . . . 514 17.9 34.9 6150-100 . . . . . . . . 230 16.1 70.0 122

100-250 . . . . . . . . 105 14.9 142,0 248250-500 . . . . . . . . 34 11.8 348.0 609500-1,000 . . . . . . 17 11.3 664.0 1,160over 1,000. . . . 6 17.8 2,970.0 5,200

—a SOURCE (45)

bEstimated by OTA based on 3.5 pounds, of MSW per capita Per day


Table 39.—U.S. Standard MetropolitanStatistical Areas (SMSAS) Size, Population, and

Waste Production in 1975———— —

AverageAverage municipal

SMSA size Number Popula- population solid waste(thousands) of SMSAS’ tiona per SMSA per SMSAb

(m!llion) (thousands) (tOns/rjay)

un-der-l OO .-. . – 27 – - 2.5 92 1 6 0 –

100-250 . . . . . 97 16.6 171 300250-500 . . . . . 63 22.7 361 630500-1,000. . . . 37 27.1 733 1,2801,000 -2 ,000. . 20 28.3 1,417 2,4802,000-3,000. . 8 19.0 2,373 4,150over 3,000 . . . 7 40.0 5,693 9,960

aSORCE (46).bEstimated by OTA based on 3.5 pounds of MSW per capita Per day

elude several cities and contiguous unin-corporated areas. Table 39 shows that sevenSMSAS produce around 10,000 tpd of MSW,28 more are in the 3,000-tpd range, andanother 37 are in the 1,200-tpd” range.

Advantages and Disadvantages ofSmall and Large Plants

Large resource recovery plants canachieve significant economies of scale andcan include economical systems for recoveryof both materials and energy. They representlarge financial investments and may thusserve as a dramatic focus for the attention ofcitizens, industry, and government officials.

The disadvantages of large plants include:(i) their high first cost; (ii) the inflexibility theycreate by their requirements for future utili-zation in order to meet debt obligations, (iii)the difficulty of identifying a suitable energycustomer; (iv) the problems of regionalization;(v) their vulnerability to strikes, sabotage,and mechanical failure; and (vi) the logisticsand cost of delivering such large amounts ofwaste to a single site.

The advantages of small-scale systems in-clude: (i) the fact that a large community orregion can start small and add units or facil-ities incrementally; (ii) their compatibilitywith smaller waste producers and energyconsumers; (iii) the system reliability inherentin operating several dispersed units; (iv) thefact that they can help avoid the political

problems of regionalization; (v) their potentialfor reducing siting problems by locating themon customer property; and (vi) the fact thatthey can be produced in relatively largenumbers with factory technology accordingto standard plans and installed relativelyquickly with greater use of local skills.

The disadvantages of small-scale systemsinclude: (i) potentially higher direct costs perunit of waste processed, (ii) the need to con-trol a large number of relatively small airpollution sources, (iii) the requirements ofsmall waste incinerators for auxiliary oil orgas fuel, and (iv) the fact that materials re-covery in small-scale systems may be un-economic since shredding and classifyingwould be very expensive at small scale. How-ever, little or no thought has been given tosmall-scale materials recovery systems, orfor that matter to small-scale cogeneration ofelectric power from MSW.

In comparing the advantages and disad-vantages of small and large resource re-covery plants, two characteristics warrantfurther elaboration: reliability and redun-dancy considerations, and implications fortechnological innovation.

The consequences of system failure arepotentially more serious with one large plantthan with several small plants. This factcreates the need in large plants to build incostly storage space, backup landfill, orequipment redundancy. To illustrate, con-sider two alternative ways of providing forresource recovery in a given city: one 1,000-tpd facility without storage or landfill, or fivedispersed 200-tpd plants. If the waste thatgoes to any one of the 200-tpd plants could betemporarily redistributed to the others in theevent of failure in any one plant, then thesystem of five plants possesses a kind of built-in redundancy. It can be shown with reliabili-ty theory that the reliability [probability ofsuccessful operation) of a single 1,000-tpdplant would have to be 0.9997’ to equal thereliability of the five plant system if thereliability of the individual 200-tpd” plantswere only 0.80.


Factory production of a larger number ofsmaller incinerators may also have implica-tions for incremental technological innova-tion and for system performance standards,both of which relate to aspects of potentialFederal involvement. With several producersof small systems competing for sales to nu-merous municipalities and other buyers,market forces might stimulate technologicalimprovements with minimal Federal involve-ment. In the case of construction of a smallernumber of large, custom-designed systems,however, which take a relatively long time toplan and construct, market forces may not beadequate to induce technological innovation,and there may thus be greater pressure forFederal assistance. But the presence of alarge number of competing systems may tendto complicate the technology/vendor selectionprocess for local officials. Under these condi-tions, Federal technical assistance to localgovernments might be as important as iflarger systems were involved.

Research and Development inResource Recovery:

The Federal Role

Background

T he Federal Government has sponsoredresearch, development, and demonstra-

tion programs in resource recovery for thelast 15 years; first in the Public Health Serv-ice and later in EPA, in the Energy Researchand Development Administration (ERDA)(now DOE), in the National Bureau of Stand-ards, in the Bureau of Mines, and in the Na-tional Science Foundation. A good part of thefunds has been spent on several large-scaledemonstration plants. Other work has beendone on innovative separation technologies,environmental impacts of resource recovery,and characterization of recovered resources.The Federal Government has also funded avariety of economic evaluations and state-of-the-art review studies.

Federally funded demonstrations havelimited usefulness as a means for promotingthe diffusion of technology. A recent study byOTA on the role of demonstrations in FederalR&D policy(47) found that only a low rate ofsuccess can be expected. Furthermore, theevaluation of the success or failure of ademonstration will be difficult and subjec-tive. In part, this is because there is frequentconfusion over the goals of a demonstrationproject, and in part because the informationreceived from a project is likely to be unclearand imperfect.

In the last decade there have been severalvigorous private sector R&D programs, dem-onstrations, and commercial ventures, some-times jointly with Federal agencies. A pri-vately funded R&D center has been in oper-ation at the National Center for ResourceRecovery, which has also received Federalgrant and contract funds.

The following discussion of Federal R&Dneeds for resource recovery is set within thiscontext of vigorous private sector activityand an important but limited Federal role intechnology demonstration.

R&D Needs

The technical problems that have occurredat many of the operational or demonstrationplants are sufficient evidence that more R&Dis needed to make the technologies work re-liably and economically. Much of this workmight be accomplished most effectively byprivate firms in the normal process of com-mercial development. In view of the con-siderable existing private activity, the needfor a Federal role to further support pilotplant and large-scale demonstration activityis limited.

However, Federal R&D programs con-cerned with potential environmental and oc-cupational problems of resource recovery areneeded because the private sector usuallyunderinvests in such research, and because itis unlikely to be done by State and localgovernments or labor organizations. Suchresearch should be focused on identifying

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and clarifying hazards to health, and ondeveloping methods for their control. At thesame time, a vigorous program to enforcehealth, safety, and environmental standardswould help to stimulate this kind of R&D inthe private sector. A Federal R&D programfor occupational and environmental problemsis also needed in order to develop and main-tain a reservoir of knowledgeable govern-ment personnel who can participate in theregulatory process.

R&D needs and problem areas in resourcerecovery technology have been presented inthe literature. (10,48) The list in table 40 illus-trates their range. It is beyond the scope ofthis assessment either to develop a compre-hensive list or to set priorities.

Many of the problems listed in table 40could be dealt with best in the process of com-

Table 40.—Selected Research, Development,and Demonstration Needs for Resource

Recovery Technologies——.—.—————

HanLing and storage of RDF; fluff, densified, anD pow-dered.

—Material handling processes to cope with the abrasive,corrosive, and mixed nature of MSW.

—Ferrous, aluminum, nonferrous (nonaluminum), and glassrecovery improvement and optilmization.

—Shredder optimization.—Air classifier optimization.— Resource recovery with mixed wastes such as: MSW with

sewage, commercial waste, industrial waste, agricul-tural waste, forestry waste, etc.

—Fundamental parameters in MSW pyrolysis processes.— Fundamental combustion parameters in firing all classes

of RDF and raw MSW with traditional fuels.— Fundamental MSW bioconversion parameters.—Fundamental hydrolysis processes for MSW.—CofiMing of MSW with sewage sludge.—Corrosion in the combustion of MSW.—New uses for glass aggregate, pyrolysis char, etc.—Upgrading of fiber recovered from MSW.—Improved recovery of materials from incinerated waste.—Use of magnetic fraction from MSW in foundries.—Systems optimization problems such as cost effective-

ness of trammeling prior to shredding, particle size in-teraction with grate and boiler design, etc.

—Resource recovery processes in synergy with other non-waste developments such as biomass energy conver-sion, cogeneration, industrial hydrolysis, etc.

—Small-scale materials recovery processes.—Small-scale cogenerat ion.—Small-scale combustion processes.— Markets for small-scale energy output.

SOURCE - Office of Technology-Assessment -

mercial development by private firms. How-ever, there may be a tendency to neglect themore fundamental research questions, suchas: (i) materials characterization; (ii) proc-esses of size reduction, separation, combus-tion, and chemical reaction; and (iii) explora-tory design work on innovative systems forpurifying and utilizing recovered materials,and for utilizing energy products, particular-ly at small scale. Consequently, there mayalso be a useful Federal role in dealing withthese problems.

Findings on Technologies forCentralized Resource Recovery

w idespread interest in the systematicrecovery of materials and energy from

MSW in the United States is just a decadeold. The construction of centralized facilitiesfor separating MSW into useful componentshas only recently been considered as onepotentially important approach to the prob-lems of waste management. The rationale forcent ra l ized resource recovery has beenthreefold: (i) effective and safe disposal ofsolid waste, (ii) recovery of materials forrecycling, and (iii) production of energy fromthe combustible portion of the waste. Theseare also the major components of the poten-tial revenues from resource recovery.

A number of technologies for burning thecombustible portion of MSW or for convert-ing it to solid, liquid, or gaseous fuels are atvarious stages of development. Techniqueshave also been developed, with differing suc-cess, for recovery of ferrous metals, alumi-num, glass, nonferrous metals, and paperfiber. Waterwall combustion and small-scalemodular incineration to produce steam, andthe production of refuse-derived fuel (RDF) bywet and dry processes are currently the onlycommercially operational methods for recov-ering energy. The only commercially opera-tional technologies for recovering materialsfrom mixed MSW are the magnetic recoveryof ferrous metals, the recovery of low-gradefiber by wet separation, and the production

Ch. 5— Technologies for Centralized Resource Recovery 113

of compost by natural processes. Aluminumand glass recovery are being actively ex-p l o r e d a s i s e n e r g y r e c o v e r y b y b o t hanaerobic digestion and pyrolysis.

Energy can be recovered by centralizedresource recovery either as fuel or as heat,and also as the savings that accrue fromrecycling materials. As an upper limit, the

total recovery of all energy in MSW couldsupply about 1.9 percent of the Nation’s cur-rent annual energy consumption. Recyclingall of the iron and steel, aluminum, copper,and glass could save about 0.4 percent morefor a total savings of 2.3 percent of currentenergy use, or the equivalent of about800,000 barrels of oil or 200,000 tons of coalper day, Thus, centralized resource recoverymight play a small, but not insignificant rolein conserving energy. Technical, economic,and institutional factors, however, will keepthe energy saved by resource recovery in theforeseeab le fu ture to a f rac t ion o f i t spotential.

Relatively little is known about the ef-fluents from operating centralized resourcerecovery plants or about the nature anddegree of workplace hazards they may pre-sent. This is largely because there has beenlittle opportunity to gather data and becausethere is considerable variability in and ig-norance about the composition of both MSWand the recovered products. A number ofstudies currently underway should producesome information and data about air andwater emissions, bacteria and viruses in theplant environment, and toxic substances inall media including solid residuals. Authorityexists for regulating these workplace and en-vironmental problems, if needed. Should ac-tivity in centralized resource recovery ac-celerate, i t will be desirable to step upresearch and to promulgate regulations tocontrol any potentially harmful side effects.

Over the past 15 years, there have been anumber of federally funded research, devel-opment, and demonstration projects con-cerned with centralized resource recovery,There has also been vigorous activity in theprivate sector. The Federal R&D presence

would be most effective in identifying, eval-uating, and controlling environmental and oc-cupational problems: in characterizing mate-rials; in basic studies of processes for sizereduction, materials separation, combustion,and chemical reaction: and in exploratory de-signing—particularly of small-scale systemsfor processing and using recovered materialsand energy, The remaining technical prob-lems would probably be best solved in thecourse of commercial development by privatefirms.

Recently, there has been a substantial shiftfrom materials recovery to energy productionas a more significant driving force. This shift,which has taken place because energy priceshave risen more rapidly and steadily thanscrap materials prices over the last severalyears, may have important implications forresource recovery system planning, design,and operation:

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It creates the need to consider morecarefully matching resource recoveryplants with the potential customers forthe energy produced.Attention to such matching may induce ashift from large, centralized to small,dispersed resource recovery plants.With smaller plants there may be lessneed to consider regionalization of solidwaste disposal, with its attendant prob-lems,There may be increased attention todirect incineration and to cofiring ofwaste with coal, as opposed to more ex-otic approaches.There may be less recovery of materialsfrom waste than had been envisionedearlier since materials recovery may beless feasible in small plants.There may be an increased urgency toassess, regulate, and control potentialenvironmental and workplace problems.There may be less concern that bev-erage container deposit legislation mightimpair resource recovery development,if material revenues become relativelyless important.

114 . Materials and Energy From Municipal Waste

● There may be increased flexibility fordesigning resource recovery systemsthat include source separation activities,and that can respond more readily tochanging patterns of waste generationin the future.

Only electric powerplants, large factories,or large complexes of office buildings canconsume all the energy output of a 1,000-tpdresource recovery facility. These kinds ofpotential customers have proven to be dif-ficult for proposed resource recovery proj-ects to reach. Electric utilities have been lessthan enthusiastic because it presents tech-nical difficulties and because they have es-sentially no incentive to use refuse-derivedenergy and, if they do, face many problems.In a given service area, MSW can provideonly a few percent of the fuel needs of anelectric utility. Thus, a’ utility must contendwith numerous difficulties to obtain just aminor part of its total fuel supply.

On the other hand, for smaller quantities ofrefuse-derived energy there are a large num-ber of potential customers such as office

buildings, institutions, and smaller factories.Smaller resource recovery plants, say in the25- to 200-tpd range, might adequately servetheir energy needs. These would help to avoidsome of the problems that arise when severalcommunities attempt to regionalize in orderto build large plants. Smaller resource re-covery plants, which are more common inEurope, may feature direct incineration toproduce steam or hot water and may foregomaterials recovery altogether. They may alsoallow for a more flexible approach in a com-munity or region by making it possible toadopt resource recovery gradually ratherthan all at once.

However, a few cautionary words aboutsmaller energy recovery systems are in order.Not enough is known about their reliability,or about the environmental and workplacehealth implications of operating a network ofdispersed, small plants. Also, more needs tobe known about the energy demand charac-teristics of the small customers mentionedabove, in order to learn whether they can in-deed become consumers of energy fromwaste.

Ch. 5— Technologies for Centralized Resource Recovery . 115

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