外文翻译(英文)能源审计和干法水泥回转窑系统

1、EnergyConversionandManagement46(2005)551EnergyauditingandrecoveryfordrytypecementrotarykilnsystemsAcasestudyTahsinEngin*,VedatAriDepartmentofMechanicalEngineering,UniversityofSakarya,EsentepeCampus,54187Sakarya,TurkeyReceived30January2004;accepted29April2004Availableonline2July2004AbstractCementprod

2、uctionhasbeenoneofthemostenergyintensiveindustriesintheworld.Inordertoproduceclinker,rotarykilnsarewidelyusedincementplants.ThispaperdealswiththeenergyauditanalysisofadrytyperotarykilnsystemworkinginacementplantinTurkey.Thekilnhasacapacityof600ton-clinkerperday.Itwasfoundthatabout40%ofthetotalinpute

3、nergywasbeinglostthroughhotuegas(19.15%),coolerstack(5.61%)andkilnshell(15.11%convectionplusradiation).Somepossiblewaystorecovertheheatlossesarealsointroducedanddiscussed.Findingsshowedthatapproximately15.6%ofthetotalinputenergy(4MW)couldberecovered.Ó2004ElsevierLtd.Allrightsreserved.Keywords:C

4、ementplant;Rotarykiln;Energyaudit;Heatbalance;Heatrecovery1.IntroductionCementproductionisanenergyintensiveprocess,consumingabout4GJpertonofcementproduct.Theoretically,producingonetonofclinkerrequiresaminimum1.6GJheat1.How-ever,infact,theaveragespecicenergyconsumptionisabout2.95GJpertonofcementprodu

5、cedforwell-equippedadvancedkilns,whileinsomecountries,theconsumptionexceeds5GJ/ton.Forexample,Chinesekeyplantsproduceclinkeratanaverageenergyconsumptionof5.4GJ/ton2.Theenergyaudithasemergedasoneofthemosteectiveproceduresforasuccessfulenergymanagementprogram3.Themainaimofenergyauditsistoprovideanaccu

6、rateaccountofenergyconsumptionandenergyuseanalysisofdierentcomponentsandtorevealthedetailed*Correspondingauthor.Tel.:+90-264-346-0353;fax:+90-264-346-0351.E-mailaddresses:.tr,tahsinengin(T.Engin).0196-8904/$-seefrontmatterÓ2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.enconma

7、n.2004.04.007552T.Engin,V.Ari/EnergyConversionandManagement46(2005)551562informationneededfordeterminingthepossibleopportunitiesforenergyconservation.Wasteheatrecoveryfromhotgases4andhotkilnsurfaces5inakilnsystemareknownaspotentialwaystoimproveoverallkilneciency.However,itisstillfairlydiculttondadet

8、ailedthermalanalysisofrotarykilnsystemsintheopenliterature.Thispaperfocusesontheenergyauditofahorizontalrotarykilnsystem,whichhasbeenusingintheVanCementPlantinTurkey.Ade-tailedthermodynamicanalysisofthekilnsystemisrstgiven,andthen,possibleapproachesofheatrecoveryfromsomemajorheatlosssourcesarediscus

9、sed.2.ProcessdescriptionanddatagatheringRotarykilnsarerefractorylinedtubeswithadiameterupto6m.Theyaregenerallyinclinedatanangleof33.5°,andtheirrotationalspeedsliewithin12rpm.Cyclonetypepre-heatersarewidelyusedtopre-heattherawmaterialbeforeitentersthekilnintake.Inatypicaldryrotarykilnsystem,pre-

10、calcinationgetsstartedinthepre-heaters,andapproximatelyonethirdoftherawmaterialwouldbepre-calcinedattheendofpre-heating.Thetemperatureofthepre-heatedmaterialwouldbeoftheorderof850°C.Therawmaterialpassesthroughtherotarykilntowardstheame.Inthecalcinationzone(700900°C),calcinations,aswellasan

11、initialcombinationofalumina,ferricoxideandsilicawithlime,takeplace.Between900and1200°C,theclinkercomponent,2CaOÆSiO2,forms.Then,theothercomponent,3CaOÆSiO2,formsinasubsequentzoneinwhichthetemperaturerisesto1250°C.Duringthecoolingstage,themoltenphase,3CaOÆAl2O3,forms,andifthe

12、coolingisslow,alitemaydissolvebackintotheliquidphaseandappearassecondarybelite6.Fastcoolingoftheproduct(clinker)enablesheatrecoveryfromtheclinkerandimprovestheproductquality.ThedatatakenfromtheVanCementPlanthavebeencollectedoveralongperiodoftimewhentherstauthorwasaprocessengineerinthatplant.Theplant

13、usesadryprocesswithaseriesofcyclonetypepre-heatersandanincline-kiln.Thekilnis3.60mindiameterand50mlong.Theaveragedailyproductioncapacityis600tonofclinker,andthespecicenergyconsumptionhasbeenestimatedtobe3.68GJ/ton-clinker.Alargenumberofmeasurementshavebeentakenduring2yr,andaveragedvaluesareemployedi

14、nthispaper.TherawmaterialandclinkercompositionsaregiveninTable1.TherotarykilnsystemconsideredfortheenergyauditisschematicallyshowninFig.1.Thecontrolvolumeforthesystemincludesthepre-heatersgroup,rotarykilnandcooler.Thestreamstoandfromthecontrolvolumeandallmeasurementsareindicatedinthesamegure.3.Energ

15、yauditingandheatrecovery3.1.MassbalanceTheaveragecompositionsfordriedcoalandpre-heaterexhaustgasareshowninFig.2.Basedonthecoalcomposition,thenetheatvaluehasbeenfoundtobe30,600kJ/kg-coal.Itisusuallymoreconvenienttodenemass/energydataperkgclinkerproducedperunittime.Themassbalanceofthekilnsystemissumma

16、rizedinFig.3.Allgasstreamsareassumedtobeidealgasesatthegiventemperatures.T.Engin,V.Ari/EnergyConversionandManagement46(2005)551562Table1RawmaterialandclinkercomponentsandtheirpercentagesComponentSiO2Al2O2Fe2O3CaOMgOSO3K2ONa2OH2OOrganicsIgnitionlossTotalRawmaterial(%)13.554.102.6040.742.070.560.300.0

17、80.50.934.6100Clinker(%)20.555.984.0864.582.811.300.500.201005533.2.EnergybalanceInordertoanalyzethekilnsystemthermodynamically,thefollowingassumptionsaremade:1.Steadystateworkingconditions.2.Thechangeintheambienttemperatureisneglected.3.Coldairleakageintothesystemisnegligible.554T.Engin,V.Ari/Energ

18、yConversionandManagement46(2005)5515624.Rawmaterialandcoalcompositionsdonotchange.5.Averagedkilnsurfacetemperaturesdonotchange.Basedonthecollecteddata,anenergybalanceisappliedtothekilnsystem.ThephysicalpropertiesandequationscanbefoundinPerayshandbook7.Thereferenceenthalpyiscon-sideredtobezeroat0

19、6;Cforthecalculations.ThecompleteenergybalanceforthesystemisshowninTable2.ItisclearfromTable2thatthetotalenergyusedintheprocessis3686kJ/kg-clinker,andthemainheatsourceisthecoal,givingatotalheatof3519kJ/kg-clinker(95.47%).Also,theenergybalancegiveninTable2indicatesrelativelygoodconsistencybetweenthet

20、otalheatinputandtotalheatoutput.Sincemostoftheheatlosssourceshavebeenconsidered,thereisonlya273kJ/kg-clinkerofenergydierencefromtheinputheat.Thisdierenceisnearly7%ofthetotalinputenergyandcanbeattributedtotheassumptionsandnatureofdata.Thedistri-butionofheatlossestotheindividualcomponentsexhibitsreaso

21、nablygoodagreementwithsomeotherkeyplantsreportedintheliterature2,5,7.3.3.HeatrecoveryfromthekilnsystemTheoverallsystemeciencycanbedenedbyg¼Q6=Qtotalinput¼1795=3686¼0:487or48.7%,whichcanberegardedasrelativelylow.Somekilnsystemsoperatingatfullcapacitywoulddeclareaneciencyof55%basedonthe

22、currentdryprocessmethodology.Theoveralleciencyofthekilnsystemcanbeimprovedbyrecoveringsomeoftheheatlosses.Therecoveredheatenergycanthenbeusedforseveralpurposes,suchaselectricitygenerationandpreparationT.Engin,V.Ari/EnergyConversionandManagement46(2005)551562557ofhotwater.Thereareafewmajorheatlosssou

23、rcesthatwouldbeconsideredforheatrecovery.Theseareheatlossesby:(1)kilnexhaustgas(19.15%),(2)hotairfromcoolerstack(5.61%)and(3)radiationfromkilnsurfaces(10.47%).Inthefollowingsection,wediscusssomepossiblewaysforrecoveringthiswastedheatenergy.3.3.1.Theuseofwasteheatrecoverysteamgenerator(WHRSG)Thereare

24、opportunitiesthatexistwithintheplanttocapturetheheatthatwouldotherwisebewastedtotheenvironmentandutilizethisheattogenerateelectricity.Themostaccessibleand,inturn,themostcosteectivewasteheatlossesavailablearetheclinkercoolerdischargeandthekilnexhaustgas.Theexhaustgasfromthekilnsis,onaverage,315°

25、C,andthetemperatureoftheairdischargedfromthecoolerstackis215°C.Bothstreamswouldbedirectedthroughawasteheatrecoverysteamgenerator(WHRSG),andtheavailableenergyistransferredtowaterviatheWHRSG.TheschematicofatypicalWHRSGcycleisshowninFig.4.Theavailablewasteenergyissuchthatsteamwouldbegenerated.This

26、steamwouldthenbeusedtopowerasteamturbinedrivenelectricalgenerator.Theelectricitygeneratedwouldosetaportionofthepurchasedelectricity,therebyreducingtheelectricaldemand.Inordertodeterminethesizeofthegenerator,theavailableenergyfromthegasstreamsmustbefound.Oncethisisdetermined,anapproximationofthesteam

27、ingrateforaspeciedpressurecanbefound.Thesteamingrateandpressurewilldeterminethesizeofthegenerator.Thefol-lowingcalculationswereusedtondthesizeofthegenerator.QWHRSG¼QavailablegwheregistheWHRSGeciency.Becauseofvariouslossesandinecienciesinherentinthetransferofenergyfromthegasstreamtothewatercircu

28、latingwithintheWHRSG,notallofthe558T.Engin,V.Ari/EnergyConversionandManagement46(2005)551562availableenergywillbetransferred.AreasonableestimateontheeciencyoftheWHSRGmustbemade.Weassumeanoveralleciencyof85%forthesteamgenerator.AsthegaspassesthroughtheWHRSG,energywillbetransferredandthegastemperature

29、willdrop.Targetingapressureof8barsattheturbineinlet,theminimumstreamtemperatureattheWHRSGsexitwouldbehigherthanthecorrespondingsaturationtemperature,whichisroughly170°C.Asalimitingcase,weassumetheexittemperaturestobe170°C.AfterexitingtheWHRSG,theenergyofthosestreamscanberecoveredbyusingaco

30、mpactheatexchanger.Hence,thenaltemper-aturecanbereducedaslowaspossible,whichmightbelimitedbytheaciddewpointtemperatureofthestream.Accordingtothenaltemperaturesofbothstreams,thenalenthalpieshavebeencalculatedtobehair¼173kJ/kg,andheg¼175kJ/kg.Therefore,theavailableheatenergywouldbe:Qavailabl

31、e¼½megðheg1Àheg2Þþmairðhair1Àhair2Þ󰀉ÂmcliQavailable¼½2:094Âð337À175Þþ0:94Âð220À173Þ󰀉Â6:944%2662kWTherefore,theenergythatwouldbetransferredthroughtheWHSRGisQWHSRG¼0:85

32、94;2662¼2263kWThenextstepistondasteamturbinegeneratorsetthatcanutilizethisenergy.Sinceasteamturbineisarotatingpieceofmachinery,ifproperlymaintainedandsuppliedwithacleansupplyofdrysteam,theturbineshouldlastforasignicantperiodoftime.Consideringaturbinepressureof8barsandacondenserpressureof10kPa,i

33、tcanbeshownthatthenetpower,whichwouldbeobtainedfromtheturbine,isalmost1000kW.Ifweassumethattheusefulpowergeneratedis1000kW,thentheanticipatedsavingswillbebasedontheloadreductionof1000kW.Assuming8000hofusage,wendEnergysaved¼ðPowergeneratedÞÂðhoursofusageÞEnergysaved¼

34、;ð1000kWÞÂð8000h=yrÞ¼8Â106kWh=yrTheaverageunitpriceofelectricitycanbetakenas0.07USD/kWh,andtherefore,theantici-patedcostsavingswouldbeCostsavings¼0:07Â8Â106¼560;000USD=yrIfweassumethatlaborandmaintenancecostsaveragedoutto20,000USDannually,thesav

35、ingsbecomes540,000USD/year.Thecostassociatedwithimplementationofthisadditionalsystemwouldbethepurchasepriceofthenecessaryequipmentanditsinstallation.Anadditionalcostwillbetherequiredmainte-nanceofthepowergenerationunit.ForthewholesystemshowninFig.4,basedonourcalcu-lations,wewereabletodetermineabudge

36、testimationbetween700,000and750,000USD,includingshippingandinstallation.Hence,wecanmakearoughestimateforasimplepaybackperiod:Simplepaybackperiod¼ðImplementationcostÞ=ðAnnualcostsavingsÞ750;000USD¼1:38yr%17monthsSimplepaybackperiod¼540;000USD=yrT.Engin,V.Ari/EnergyC

37、onversionandManagement46(2005)551562559TheenergysavingsbyusingaWHSRGsystemwouldalsoresultinanimprovementintheoverallsystemeciency.Itshouldbenotedthatthesecalculationsreectaroughestimationandmayvarydependinguponplantconditionsandothereconomicfactors.3.3.2.Useofwasteheattopre-heattherawmaterialOneofth

38、emosteectivemethodsofrecoveringwasteheatincementplantswouldbetopre-heattherawmaterialbeforetheclinkeringprocess.Directinggasstreamsintotherawmaterialjustbeforethegrindingmillgenerallydoesthis.Thiswouldleadtoamoreecientgrindingoftherawmaterialinadditiontoincreasingitstemperature.However,inmostplants,

39、thefreshrawmaterialtakenfromthemillisnotdirectlysenttothekiln,andtherefore,thetemperatureincreaseoftherawmaterialdoesnotgenerallymakesensebecauseitwillbestoredinsilosforawhilebeforeenteringtheclinkeringprocess.Ontheotherhand,someplantsmayhaveonlykilnsystemsratherthangrindingsystems.Insuchcases,thism

40、aynotbepossibleunlesssomeadditionalmodicationsaremadeintheplant.Thereisagrindingmillintheplantconsideredinthisstudy,andthefollowingcalculationsaremadetoshowhowmuchenergycouldbesavedthroughpre-heatingtherawmaterial.Themainadvantageofthepre-heatingofrawmaterialinthemillistodrythematerial,sinceitisheav

41、ilymoistinnature.Fortheplantconsidered,themoisturecontentoftherawmaterialwasabout6.78%,whichindicatesamassowrateofwaterof0.7845kg/s(0.113kg/kg-clinker)comingintothemill.Mixingthetwomainhotgasstreamswouldleadtoasinglegasowatabout280°C,asshowninFig.5.Applyingtheconservationofmassprincipleandconse

42、rvationoftotalenergylawforthemill(ignoringheatlosses)resultsinanincreaseoftemperatureoftherawmaterialby85°C,whilethegasstreamcoolsdownto150°C.Itisclearthatthemajorityoftheusefulenergymustbeusedtoheatthewaterfrom15to100°C,andtovaporizeitatthistemperaturecom-pletely.Abasicenergybalancef

43、orthemillsystemwouldgiveQgasflow;inþQmoistrawmaterial¼QwaterþQgas;outþQdryrawmaterialTherelatedenthalpiesareshowninFig.5.Therefore,wecanwrite6:944Âð3:034Â300þ1:780Â12ÞÀ0:7845Âð419À63þ2257ÞÀ6:944Â1:667Â88&#

44、188;Qgas;outQgas;out%3400kW;hgas;out%156kJ=kg;Tgas;out%150°C:560T.Engin,V.Ari/EnergyConversionandManagement46(2005)5515623.3.3.HeatrecoveryfromkilnsurfaceThehotkilnsurfaceisanothersignicantheatlosssource,andtheheatlossthroughconvectionandradiationdictatesawasteenergyof15.11%oftheinputenergy.Ont

45、heotherhand,theuseofasecondaryshellonthekilnsurfacecansignicantlyreducethisheatloss.Sincethekilnsurfaceneedstobefrequentlyobservedbytheoperatorsoastoseeanylocalburningonthesurfaceduetolossofrefractoryinsidethekiln,wewouldnotconsiderinsulatingthekilnsurface.Thebasicprincipleofthesecondaryshellisshown

46、inFig.6.Forthecurrentrotarykiln,Rkiln¼3:6m,andaradiusofRshell¼4mcanbeconsidered.Sincethedistancebetweenthetwosurfacesisrelativelysmall(40cm),arealisticestimationforthetemperatureofthesecondaryshellcanbemade.WeassumeT2¼290°C¼563K.Wewouldconsiderstainlesssteelforthematerialoft

47、hesecondaryshellsinceithasrelativelylowsurfaceemissivityandthermalconductivity.Theheattransferratebyradiationisthencalculatedusingthefollowingequation8:AkilnrðT14ÀT24ÞQr¼R1Àeþe2Rshelle1wherer¼5:67Â10À8W/m2K4,T1¼Ts¼581K,e1¼0:78(foroxidizedki

48、lnsurface)ande2¼0:35(lightlyoxidizedstainlesssteel).Qr%147kWThisheatlossistobetransferredthroughtheinsulationonthesecondaryshell.Therefore,assumingareasonabletemperaturefortheoutersurfaceoftheinsulation,wecandeterminetherequiredthicknessofinsulation.Forglasswoolinsulation,thethermalconductivity

49、istakenas0.05W/mK.Therefore,theresistanceoftheinsulationlayerwouldbe󰀁󰀂ÀRÁRinslnshellln4¼Resistanceofinsulation¼15:7082kinspLkilnT.Engin,V.Ari/EnergyConversionandManagement46(2005)551562561AssumingatemperaturedierenceofDTins¼250°C(whichmeansanoutersurface

50、temperatureof58°C),Rinscanbedetermined:DTins¼QÂðresistanceofinsulationÞ250°C¼147;000ÂWefoundRinslnðRins=4Þ15:708¼4:108m,andthethicknessofinsulationwouldbee¼RinsÀRshell¼0:108m%11cmItshouldbenotedthatwhenthesecondaryshellisaddedonto

51、thekilnsurface,theconvectiveheattransferwouldpresumablybecomeinsignicant.Thisisbecauseofthefactthatthetem-peraturegradientinthegapwouldberelativelyverylow,e.g.,0.45°C/cm.Therefore,thetotalenergysavingsduetothesecondaryshellwouldbeð386kJ=kg-clinkerÞÂð6:944kg-clinker=sÞ&#

52、192;147¼2533kWfromtheradiationheattransferandð171kJ=kg-clinkerÞÂð6:944kg-clinker=sÞ¼1187kWfromtheconvectiveheattransfer.Therefore,wecansafelyconcludethattheuseofasecondaryshellonthecurrentkilnsurfacewouldsaveatleast3MW,whichis11.7%ofthetotalinputenergy.Thisenergysa

53、vingwouldresultinaconsiderablereductionoffuelconsumption(almost12%)ofthekilnsystem,andtheoverallsystemeciencywouldincreasebyapproximately56%.4.ConclusionsAdetailedenergyauditanalysis,whichcanbedirectlyappliedtoanydrykilnsystem,hasbeenmadeforaspecickeycementplant.Thedistributionoftheinputheatenergytothesystemcomponentsshowedgoodagreementbetweenthetotalinputandoutputenergyandgavesig-nicantinsightsaboutthereasonsforthelowoverallsystemeciency.Ac