tdf-047 - the use of scrap tyres in the us cement industry[1]

8/2/2019 TDF-047 - The Use of Scrap Tyres in the US Cement Industry[1]

1/6

The use of scrap tyres inthe US cement industryMichael Blumenthal discusses the main issuesthat have limited the use of scrap tyres incement kilns and examines the advantages ofadapting to this alternative fuel source;concluding that production rates can beincreased and fuel costs lowered.

REPRINTED FROMWORLDCEMENTDECEMBER 1992


2/6

The use ofscrap tyres inthe US cementindustryMichael Blumenthal*discusses the main issuesthat have limited the useof scrap tyres in cement killand examities theadvantages of adaptingto this alternative fuelsource; concluding thatproduction rates can beincreased andfuel costs lowered.

Theissueof usinoscrao vresas asuoolementfuelin rotarv organization. The Council's primary goal is the expansion ofcementkilnshas6eenraiiedanddiscksed before. i t shouldbe recognized that scrap tyres, although aspecial waste ma-terial, are an excellent source of energy. Yet, even thoughscraptyrescanbeobtained nabundantsupply,theiruseasasupplement fuel has not been anovernight success.In order to oain a historical oenoective of this situation.we will begin wih aauickreview'of solid wastedisposal man-aaement in the United States. It was not so long ago thatscrap tyres were simply landfilled, ike most other waste rna-terials. They were not perceived as a disposal problem noravailable in a quantity attractive to the kiln operator.Two maior factors have chanaed that situation. The lirst

e&ironrnentally sound and ewnomi&lly viable markets forscrap tyres. One of the lirst tasks undertaken by the Counciwas the determination ol existing and potential markets lorscrap tyres. That initial market study identified the cementindustry as a major potential user of scrap tyres.Armed with the knowledge that kilns could use a signili-cant number of scrap tyres, {he Council set out to determinethe information necessary to persuade hecement ndustry tomake use of this energy-source. Basically. there were fourissues that needed to be addressed: potential impacts onemissions; consistent supply; the effects on clinker; and theeffects to the kiln. As the use of scrap tyres has increased.major fact& was diminishing laKdfill capacity. With fewer several other issues have been raised, most noticeably thelandfills available, scrap tyres, which do not decompose or reaction of the public to the use of scrap tyres as a supple-compact easily, have been phased out as an acceptable ment fuel. The purpose of this article is to address some ofmaterial. In certain cases this was a decision by the landfill the issues regarding the effects and considerations whenoperator, in other cases, a decision due t o legislative using whole orprocessed yrederived fuel (TDF) as it relatesmandate. to the operation of the k~lnnd the production of clinker.Secondly, scrap lyres were no longer considered as part The use of scrap tyres as a supplement fuel in Unitedof the municipal solid waste stream, and therefore not col- States'cement kilns has increaseddramaticallyoverthelast

lectedordisposedofby the municipality. This, in um, caused two years. Since the founding of the Council, the number oftheaeneratorsof scraptvresto use the sewicesof scrap tyre cement kilns using TDF in the US has increased from two totransporters, commonly elerred to as "lyre ockeys". Theseentrepreneurs typically lound nexpensive ways todispose oftheir cargo; usually by stock piling the tyres in some remotelocation. Until 1985, this form of disposal was very muchaccepted practice.Thewmbinedeffectsofthesedevelopmentshas resultedin an inventory of some two to three billion scrap tyres in theUnited States. With heightened environmental awareness.the addition of the 242 million scraotvres annuallv. and leois-lationlregulations n virtually eveb state, scraptyres havebecome a sianiflcant environmental ssue.The scrap Tire Management Council was established in1990 by North American tyre manufacturers as an advocacy

14. There are an additional 24 facilities currently planning oconduct testing programmes using TDF, or that have con-cluded their testing procedures and are awaiting permissionto begin use of TDF (refer to Tables 1 and 2). The Councioredicts hat bvl997,some 55-60millionscra~tvreswuldeked ,which wou~dinoeed akethecementiridustryasignif icant market for scrap tyres in the United States.Characteristics of TDFCarbon and oxygen amounts to 88% of a tyre, which ac-counts for its rapid combustion and relatively high heatingvalue. Tyres contain approximately 15 000 British thermalunits (Btus) per pound. This c.o,mpares favourably to coal

'Execu l~ve freclor,Scrap 7 i e Managem enlCouncd. Washmglon. DC


3/6

Arizona Portland CementAsh Gmve Cement WestCalaveras CementEssroc MaterialsHawaiian CementHolnam Inc.Holnam Inc.Lehigh CementLone StaxIndustriesMedusa CementMonalrhCementNational Cement~oulhdownnc.Scuthdown Inc.

Rillito, ArizonaDurkee, OregonReddinkCaliforniaFrederick, MarylandOahu,HawaiiSeattle, WashingtonMorgan, UtahLeeds, AlabamaCape Gi rd ea u, MissouriClinchfield GeorgiaHumboldt, KansasRaglin, AlabamaLyons, ColoradoVictorville,California

TDFWhole t y mWhole t y mWhole t y mTDFTDFTDFWhole tyresTDFWhole tyresTDFTDFWhole lyresWhole t y m

which. on the averaqe, contains some12 000 Btus per pound. Subsequently,when substitutinq TDF for coal, a kilnoperatorcan ed& wa lby 1.25poundsfor every pound of TDF used.An additional advantage of TDF useis its steel portion. Each passenger cartyre contains2% lb ol high grade steel.The steel can substitute, in part, for theiron requirement n he raw meal recipe.Another point of nterest s thattyrestend to have a lower percentage ofsul-phur than most coals. Sulphur in tyresaverages 1.3% by weight. Sulphur incoal ranges from 1.lo 2.3% or higher,depending on the coalquality. Emissiondata from a variety of kilns has clearlydemonstrated a wnsistent reduction insulphurandotheremissionswiththeuseof TDF fFiaure 1-4).~ in&&thewmponentsof thetyresare either destroved, combined into theclinker or captuied in the air pollutioncontrol device. there is no ash or otherresidue that must bedisposed Finally,the components of the scrap tyre, oncechernicallywmbinedintotheclinker, arenot capableof eaching out. This iscom-parable o silica not leaching romglass.In short. the cement kilns use 100% ofthe scrap tyre in a completely environ-mentally sound manner.Destructionof TDFTyrederived fuel can be wmpletely de-stroyed in cement kilns for a variety oftechnical reasons. The combination ofextremely high temperatures (2650 to2750F), a positive oxygen atmosphereand a relatively long gas residence time14 to 12 seconds at the elevated tem-beratures) assures the complete com-bustion of the scrap We. The complete~m b u s t i o n ~ r e c l u d e ~ ~ r o d u c t s o f i i w m -plete combust;on (PICs), black smokebrodours beino released rom the stack.

lble2 US -nt kilns planning, permiMingw waiting to use scrap lyresAllentown Cement . .Blue Circle CementBoxCmw CementRorida Crushed StoneGifford HillHoln am Inc.

Halnam, Inc.Illinois CementW r g e orp.IafargeCorp.IafargeCorp.Lehigh CementLehigh CementLonestarlndustriesMedusa CementRinker MaterialsRiverside CementRMC LonestarSouthdown Inc.Southdown Inc.Southdown lnc.Southdown Inc.Tarmac CementTexas Lehigh Cement

Blandon, PennsylvaniaS.CamlinaHarleyvilleMidlothian,TexasBmoksville, FloridaMidlothian, TexasMidlothian,Texas

Aida. OklahomaLaSalle, IllinoisNew Braunkls, TexasDavenpo h IowaWhitehall, PennsylvaniaCementon, New YorkMitchell, IndianaOgtesby,IllinoisChartevoil; MichiganMiami, RoridaRiveraide, CaliforniaDavenp olt CaliforniaBmakville, FloridaFalrborn, OhioKosmosdale. KentuckyPittsburgh PennsylvaniaMiami, FloridaBuda, Texas

Whole t y mWhole ty m

Whole t y mWhole lyresWhole lyresWhole t y m

Whole or TDFWhole tymWhole tyresWhole t y mWhole t y mTDFWhole tyresTDFWhole t y mWhole tyresTDFWhole t y mWhole tyresWhole t y mWhole tyresWhole tyresWhole tyresWhole t y m


4/6

This is the main reason the use of scrap tyresdoes not mpactthe stack opacity.Feeding TDF into kilnsConventional kilns may use either whole tyres or shreddedtyres as a supplement fuel. Shredded tyres can be fed intothe kiln by insufflation, that is, blowing shreds into the dis-charge end of the kiln. Due o the short residence ime (threeto five minutes) within the kiln, the shreds should be2 n. x 2in., or smaller, which assuresthe complete combustion of theTDF prior to falling nto the clinkercooler.Whole or sectioned tvres can be introduced throuah amid-section eeding syst& of the straight kiln. in he ~s -andCanada there are two methods that allow for the feeding ofwholetyres nto the kiln's calcining zone. Thesetechnologiescould allow for an extended service life of this arouo of kilns.whose high fuel costs can make these faci~ities-rnai~inalro:ducers of cement.Preheater and precalciner kilns can use shredded and/orwhole tyres. Two-inch chips may be fed with coal in aprecalciner. Whole or shredded tyres can be fed as wellbetween the fourth staae and the kiln at the riser duct to thefourth stage preheater;essel. Tyrescan be introduced at theriser duct to the fourth staae preheater vessel through a dou-.ble tipping valve.Product ion of cementProduction rates mav be increased in oreheater kilns whileburningwholetyres. hisispossible by birtueoftheprehealercalcination rate increasina in the oreheater second and thirdstages when burning tyr& cornpired to the normal calcina-tion rate while burnino coal onlv. Calcinina rates have beenincreased from 45% 6urning coal only to56% when burningwhole tvres. Use of tvres has decreased the carbon dioxidetranspdrted by the kiin which, in turn, allows room for addi-tional oxygen to be used in he kiln. The extraoxygen allowsfor the burning ol additional clinker. All of the above kilnsrequire clinker cooler capacity to receive the burned cementclinker and cool it. The clinker cooler also serves to preheatthe primary, secondary and tertiary air flows which are usedto b;rn the clinker, d j he coal, and to help calcine the rawmeal.

Figure1.Analysis tor metals using EPA Method12during slacktestinglor Holnam Incorporated ndustries. Arsenicwasbelowdetectionlimits.

METAL

Cost considerationsAnother ootential advantaae to using whole tvres is loweroperating costs, when compared to using 100%coal. Wholescrap tyres in the United States can currently be obtained byan operating facility at a positive cost. That is, a fee can beassessed by the kiln operator to scrap lyre transporters inexchange for the right to deliver scrap tyres to the cementcompany. Theuseof scraDtvres reducesthetonnageof coalused, and consequently lowers the cost associated with theacquisition of coal. Finally, as indicated in the precedingsection. the steel component of a tyre can substitute for ironwhich reduces the cost of ironacquisition. The use of shred-ded scrap tyres, while not as cost effective as whole tyres.typically can be obtained or less han the cost of most coals.Since the use of TDF requires no new pollution controldevices, the only capital expenses required are atrailerstor-age area and a feeding system. As has been demonstratedby several of the kilns, the costs related to the use of TDFaresimilar to anv imorovement oroiect in a cement olant. Thepayback forthecapitai imbrovements i~~ehera~~yessthan 18months. deoendina uoon he oercentaae and cost ofthe TDF used. he actuai &pita1 &sts to co>slruct a lyrefeedino svstem will vary. deoendina on the ki ln wnfiaurationand teihio logy used a id he com$exity of the syste% itself.In general. ca~ it alosts have ranaed between $200 000 and$560000.' ' -Maintenance costs are likelv to increase slightly. Thereshould be a lower coal mill maintenance due tothereducedcoal through-put, however, here will bemaintenance requiredon the TDF feedinglweighingsystem that may offset this re-duction. Theonly otherinitialexpenseencounteredhas beenthe cost to train plant personnei with the new feeding equip-ment and the expense of additional fire fighting equipmentnear the TDF conveying feeding system. The plant's firefighting plan should be modified to reflect the additional fireprotection systems installed for the TDFsystem.Cement qualityThe quality of the cement, whether using whole or shreddedtvres and reaardless of the ooint of entrv, is as aood or betterthan when &ing only coal. case in point is ~h n a m ' sdealSeatlle (Washington) ong straight kilns. which have provided

Figure2.GaseoussulphuremissIonslromnpriI,1991 OhioCamplianceslacktest at Southwestern PortlandCement Company. 'Highermetalsinput rale; "lower metals input rate


5/6

bener quality cement using TDF than 2 in. lyre shreds at 2.5 tph.with their basic fuel of a coal and Holnam introduces the TDF viapetroleum coke mixture. Holnam uses insufflation and estimates that the

~ure3.Gaseousca~onemissionsfromApril.991OhioCompliancestacktestatSouthwestenlrtland Cement Company. 'Higher metals input rate; "lower metals input rate.r

Figure4. GaseousnitrogenemissionsfromApril. 1991OhioCompliancestacktestalSouthwesern PorilandCementCompany. 'Higher metals input rate; "lower metalsinput rate.

NOx

shreds are lifted 25 to 30 ft into the kiln.They have never had evidence of lyresteel in the cooler. The clinkering zonewasshortenedand alitesizewas smallerand the clinker crystal definition was im-proved. This improvement was prob-ably caused by the stabilization oi freelime in the kiln. Prior to the use of tyre-derived fuel. free lime jumped aroundconsiderably. This stopped with theburning ofscraptyresdue, itisbel~evedto a shorter clinkering zone brought onby the high vo la ti li ~a nd igh energycontent of the TDF.The cement quality has also im-proved in pre-heater kilns when usingTDF. Thisis broughtabout becausetheraw meal calcining in the preheater isincreased by 22 to 25%. depending onthe tyre burn rate. The increased cal-cining rate, in turn, makes the kilns op-erate more smoothly which makes formore consistent quality. Clinker crystalstructure and clinker appearance alsotend to improve. Furthermore, clinkersize is reduced. The combination oftnese improvements has been dernon-strated a t one plant in a two-daygrindability test on Type Icement. Theground cement's Wagner increased to2140, as compared to the precedingmonth's 2000 Wagner average. TheBlaine was 3860 compared to 3640 av-erage for the preceding month's aver-age Blaine. The percent passing 325mesh increased from 94.6% averageoverthepreceding30daysto96.9%forthe twodav test arind.From fk ld exierience, it is reportedthat there is no discernable cement col-ourchange. AlSouthdown'sViclorville,Californiaplant, cement aualitv was asgood or better than base linestudies.Microscopy studies revealed more dis-creet crystal structure. There was alsono reported build-up of rubber in thef ou r t hs~a~e~rehea te rvesse l .owever.there was reported additional build-upof calcinedraw mealscale n theareaofthe feed shelf, which was easily man-aged. The kiln operation presented noother problems.Kiln production rates~he~roductionatesinlong straight kilnsand preheater-precalcinerkilns, at leastaccordingtotheoperatorswe havespo-ken with, were unchanged. Productionratesinpreheaterkilnsmaywellincreaseby virtue of calcining completed in thepreheater from 20% to 25%. Increasedproduction ates may be realized f hereis fan capacity lor additional oxygen,cooler capacity for additional clinker, orfeed and grind capacity for additionalraw meal. This really should not besur-prising sinceit is the same principlelhatpreheater-precalciner kilns use to in-crease pro'duction over preheater unitsof like size.Plant operationsThere is an additional point to considerwhen first burnina TDF. Kiln operatorsfrequentiy tend 6 over fire when firstusinq the process. This rnav be due to


6/6

tile greater Btullb of tyres to coal (20% + higher). The belite C O ~ C ~ U S ~ O ~ Scrystal shape will be a first indicator of a reducing atmOS- This report has reviewedsome of the key and more commonphere, or that good oxidizing conditions exist. The impor- internal ssues raised when afacil ity first considers the use oftance in this rests on the fact that regulators frequently use TDF. FromfieldexperienceitcanbecuncludedthattyrescanCO as the ultimate measuring stick as to the ability to cum- be used successfully in cement kilns,and that good qualitypletely burn TDF. It is important to watch carefully for over cement can be made from the clinker generated while usingfiring during the initial days as a reducing atmosphere will scraptyres. Furthermore, production ratescan be increasedyield highCO readings. and fuel costs lowered. Environmental quality can also bemaintained. Finally, the useof scraptyresincementki lns saviable energy recovery programme that can maintain theenvironmental quality of the kiln.

The Scrap T ir e Management Council is committed todeveloping the awareness ofscrop ryresoso valuableresource and to promoting rheir disposal in anenvironmenrally an d economically sound manner.Its primary g o d is to reduce the amount ofscrap ryresnow being IandfiNed o r stockpiled by more rhan 50 %by 1995.

tdf-047 - the use of scrap tyres in the us cement industry[1]

Documents