an estimation of a billet temperature during reheating furnace.pdf
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an estimation of a billet temperature during reheating furnace.pdf
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InternationalJournalofControl,Automation,andSystems,vol.5,no.1,pp.43-50,February200743AnEstimationofaBilletTemperatureduringReheatingFurnaceOperationYuJinJangandSangWooKimAbstract:
Reheatingfurnaceisanessentialfacilityofarodmillplantwhereabilletisheatedtotherequiredrollingtemperaturesothatitcanbemilledtoproducewire.Althoughitisveryimportanttoobtaininformationonbillettemperatures,itisnotfeasibleduringfurnaceoperation.Consequently,abillettemperatureprofileshouldbeestimated.Moreover,thisestimationshouldbedonewithinanappropriatetimeintervalforanon-lineapplication.Inthispaper,abilletheattransfermodelbasedon2DFEM(FiniteElementMethod)withspatiallydistributedemissionfactorsisproposedforanon-linebillettemperatureestimationandalsoameasurementiscarriedoutfortwoextremelydifferentfurnaceoperationpatterns.Finally,thedifferencebetweenthemodeloutputsandthemeasurementsisminimizedbyusinganewoptimizationalgorithmnameduDEAS(UnivariateDynamicEncodingAlgorithmforSearches)withmulti-steptuningstrategy.Theobtainedemissionfactorsareappliedtoasimulationforthedatawhicharenotusedinthemodeltuningforvalidation.Keywords:
Billettemperatureestimation,emissionfactors,FEM,reheatingfurnace,uDEAS.1.INTRODUCTIONWireisproducedbysendingabillettoarollingmachineatrodmilplant.Inthisprocess,thebilletisheatedinareheatingfurnace,whichshouldbeheatedascloselyaspossibletotherequiredrollingtemperaturetobemilledwithoutanydamagetotheroller.Typicalreheatingfurnacehasthreezones(i.e.,preheating,heating,andsoakingzones)1-4,10andsomenewreheatingfurnaceshaveonemoresoakingzone.Afterabilletischargedintoareheatingfurnace,thebilletgoesthroughthesezonesfrominlettooutletandfinallyitreachesatargettemperature.Althoughitisafundamentalobjectiveofthereheatingfurnacetoheatupthebillettothetargettemperature,sometimes,inadditiontothatobjective,itisalsonecessarytocontrolatransientbillettemperaturepatternaccordingtothematerialcharacteristicstopreventawirefrombreaking.Forexample,asteelcord,whichisusedasatirereinforcementmaterial,ismadeofverythinhighcarbonsteelwire.Ingeneral,abilletwithahighcarboncontenthascarbonsegregationatcentersideowingtothedifferenceofcoolingspeedbetweentheManuscriptreceivedApril28,2006;acceptedAugust26,2006.RecommendedbyEditorJaeWeonChoi.YuJinJangiswiththeFacultyofDepartmentofInformation&CommunicationEngineering,DonggukUniversity,Sukjang-dong,Kyungju780-714,Korea(e-mail:
seasondongguk.ac.kr).SangWooKimiswiththeFacultyofElectricalandComputerEngineeringDivision,POSTECH,Pohang790-784,Korea(e-mail:
swkimpostech.ac.kr).billetsurfaceandcenteraftercasting.Thiscarbonsegregationisoneofthemajorcauseofwire-breakinginwireproductionprocess.Fortunately,theeffectofthecarbonsegregationcanbeminimizedbycontrollingthebillettemperatureaccordingtothepredefinedspecialbillettemperaturepatterninthefurnace.Therefore,itisveryimportanttoobtainacorrectinformationofbillettemperatures.However,itisnotfeasibletoobtainaninformationofabillettemperatureduringreheatingfurnaceoperation.Consequently,abillettemperatureprofileshouldbeestimated.Ingeneral,sinceacombustioncontrolofareheatingfurnaceisdoneatevery2minutesand90billetscanbeheatedatthesametimeinthefurnace,thebillettemperatureestimationshouldbedoneasfastaspossible.Sincea3DFEMmodelisinappropriateforbilletheattransfermodelduetoitsheavycomputationtime,a2DFEMmodelisadoptedinthispaper.Temperaturesofabilletandambientfurnacegasaremeasuredfortwoextremelydifferentfurnaceoperationpatterns.A2DFEMheattransfermodelofthebilletwithtemperature-dependentspecificheatandthermalconductivityisconstructed.Inthis2DFEMmodel,aboundaryconditionisconsideredasaformofradiativeheattransferusinganemissionfactor.Althoughonlyaradiativeheattransfertermwithanemissionfactorisconsideredattheboundaryofthebillet,theeffectofconvectiveheattransferbetweenthebilletanditsambientgasandconductiveheattransferbetweenthebilletandskidbuttonaretakenintoaccountbycontrollingtheemissionfactor.Hence,theemissionfactorusedin44YuJinJangandSangWooKimPreheatingZoneHeatingZoneSoaking:
SoakingZone111Zone2.(a)Furnacestructure.ChargingDataCollectionDeviceC=:
!
n-DataCollectionDeviceTestBIiietrackBDischarging(b)Experimentsetting.Fig.1.Furnacestructureandexperimentsetting.thispaperisnotatrueemissionfactorbutjustatuningparameter.Thisemissionfactor(i.e.,tuningparameter)isdifferentaccordingtothegeometrybetweenbilletsurfaceandfurnacewall.Hence,thisparameterisdifferentaccordingtothebilletpositioninthefurnace.Moreover,itisalsowellknownthattheemissionfactorisdifferentaccordingtothebilletsurfacecondition.Thistuningparameterisalsoaffectedbytheflowoffurnacegaswhichflowsfromthesoakingzonetothepreheatingzoneowingtothepressuredifference.Inthispaper,itisassumedthatthistuningparametercanberepresentedbytheconstantbetweenshortintervalsalongthebilletmovingpath.Bythisassumption,thefurnaceisdividedinto10partsalongthebilletmovingpathanddifferentemissionfactorsareappliedontop,bottomandleft/rightsidesofthebilletateachpart.Subsequently,thedifferencebetweenthemeasuredbillettemperaturesandtheestimatedbillettemperaturesobtainedfromtheFEMmodelisminimizedbytuningtheaboveemissionfactorsusinganoptimizationalgorithm.Atthistuningprocess,uDEAS,whichisaneffectiveandeasilyapplicableoptimizationalgorithm,isappliedwithdifferentcostfunctionstoobtaintheoptimalemissionfactors.2.REHEATINGFURNACEANDBILLETTEMPERATUREMEASUREMENTThereheatingfurnaceatrodmillplantofPOSCO(PohangIron&SteelCo.,Ltd.)consistsoffourzones(i.e.,preheating,heatingandsoakingzone1and2)andithastwotracks(i.e.,billet-movingpaths)asshowninFig.l(a).Thebilletsmovealongthetrackslowly.Also16,14,9,and6billetsarecontainedinpreheating,heating,soakingzone1and2,respectively,oneachtrack.Therefore,thereare90billetsinthefurnace.Thisfurnaceisdividedintofourzones;moreclearlythantheconventionalfurnace.Also,theexhaustgasisdischargedthroughtheoppositeburnerby80%,owingtotheoperatingmechanismoftheregenerativeburner.Hence,theinterferencebetweenneighboringzonesisreducedsignificantlycomparedtotheconventionalfurnace.BillettemperaturesaremeasuredbyusingadatacollectiondevicemountedonabilletasshowninFig.l(b).Totalof20pointsareselectedformeasurementbyusingTC(thermocouples)asshowninFig.2.Thedatacollectiondeviceisputintoawaterjacketfilledwithwater.Thiswaterjacketiscoveredwithheatprotectivematerialtominimizeexposuretoheatradiation.Whenthetestbilletisdischargedfromthefurnace,thedatacollectiondeviceisremovedandthestoreddataaretransferredtoaPCusingaserialcable.Thismeasurementiscarriedoutforthefollowingtwoextremelydifferentfurnaceoperationpatterns:
1)CCR(ColdChargeRolling)pattern:
Anoperationpatternwhenthebilletwithanormaltemperatureischarged.2)WCR(WarmChargeRolling)pattern:
Anoperationpatternwhenthebilletwithhighinitialtemperatureischarged.Ingeneral,thefurnacetemperaturesetvalueofsoakingzonesisfixedtosatisfytherequiredrollingtemperatureofthebillet.Therefore,thebillettemperaturecanbecontrolledbycontrollingthetemperaturesetvalueofpreheatingzoneandheatingzone.Sincethedischargingbillettemperatureissensitivetothevariationoffurnacetemperaturesetvalueofheatingzone,thevariationrangeoftheAnEstimationofaBilletTemperatureduringReheatingFurnaceOperation45X:
MeasurementPoints1-20:
TCnumberDeptholellmeasurementpointsIntheblllet:
200mm.,.43e.,.615.,.115.115.115H615M115.,.115SkidButtonKJX11x185-10BIiietBottomSide(a)MeasurementpositionsforCCRpattern.438.,.115.X3SkkfButton.,.615.,.615M115-IHI.,.65.,11510.X11Xx13,c15x17X12x1816Xx13x19lnSetDlrectknX14(b)MeasurementpositionsforWCRpattern.Fig.2.Measurementpositions.furnacetemperatureofheatingzoneissmallerthanthatofthepreheatingzone.Inpractice,thebillettemperaturepatterniscontrolledbycontrollingthefurnacetemperatureofpreheatingzone.ThedifferentfurnacetemperaturesetvalueofpreheatingzoneisthemaindifferenceoftheaboveCCRandWCRpattern.Itisobservedthatthemeasuredtemperatureshaveseveralcharacteristicsasfollows:
1.Theambienttemperatureofthebillettopsidealongthetrackisnotuniformatthesamezone(TC11)-2.Theambienttemperatureofthebilletatafurnacecentersideishigherthantheambienttemperatureatfurnacewallsides.(TC1,3,ll,18,and20).3.Theambienttemperatureofthebilletrightside(TC16)ishigherthanthetemperatureofthebilletleftside(TC19).Thetemperaturedifferencebetweenthemdecreasesasthebilletistransportedthroughthefurnace.Finally,TC11,16,and19havesimilarvaluesatthesoakingzones.4.Also,thebilletcoretemperature(i.e.,TC2,4,6,8,13,15,and17)atthefurnacecentersideishigherthanthatofthethecoretemperatureatthefurnacewallside.Forexample,(TC2-TC17)isabout60Cwhenthebilletisdischarged.Sincethepartofthebilletwhichisontheskidbuttoniscalledtheskidpart,measurementpointswithinthebilletcanbeclassifiedintoskidandnon-skidparts.Thetemperaturesoftheskidandnon-skidpartsaremeasuredbyusingTCinstalled
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