AuthorBiography
IanCameron istheprincipalmetallurgist,ferrousinthePyrometallurgysectorpracticeat HatchLtd.,Ontario,Canada.Hedevelopsclient-focusedsolutionstoproduceironandsteel startingfromthebasicrawmaterials.Ianhas extensiveinternationalexperienceinprocess technology,plantoperations,technologytransfer,commissioningandtrainingwithironand steelclientsandresourcecompanies.Hisexperienceincludescokeplant,pelletplantand blastfurnacedesignandoperations,assessing steelworksenergybalances,andtheimplementation/impactoffutureironandcokemakingtechnologies.Ianholdsbachelorand master’sdegreesinmetallurgicalengineering fromMcGillUniversity,Montre ´ al,Quebec, Canadaandisalicensedprofessionalengineer inOntario,Canada.Hehas38+yearsofexperienceincluding23+yearsasaconsulting engineerforHatchandpreviouslyCorus ConsultingandHoogovensTechnicalServices. CameronisalifememberoftheAssociation forIronandSteelTechnology(AIST)andtwo timewinnerofAIST’sJosephS.Kapitanaward forbesttechnicalpaperintheironmaking division.
MitrenSukhram isaseniorprocessengineer inthePyrometallurgysectorpracticeatHatch Ltd.,Ontario,Canada.Heworksonallaspects ofblastfurnaceironmakingincludingreline planning,techno-economicassessments,campaignlifeassessment/extension,andoperationalsupportforblastfurnaceslocated aroundtheworld.
Morerecently,Mitrenhasfocusedondevelopinginnovativetechnologiestoimproveblast furnaceproductivityandreducegreenhousegas emissions.Mitrenisagraduateofthe UniversityofToronto,Toronto,Canadawhere hecompletedbachelor,master’s,andPhD degreesinmaterialsscienceandengineering. Hisareasofexpertiseincludethermodynamics, heat,mass,andmomentumtransferinpyrometallurgicalprocesses.MitrenisalicensedprofessionalengineerinOntario,Canadawith5+ yearsexperienceasaconsultingprocess metallurgist.
KyleLefebvre isaprocessengineerinthe PyrometallurgysectorpracticeatHatchLtd., Ontario,Canada.Hehasworkedextensively onmass,energy,andlogisticsmodelsto designandimprovetheperformanceof numerousironandsteelproductionfacilities. Kylehasworkedacrosstheglobeintheiron andsteelindustrywithexperienceinthe designandoptimizationofbothintegrated andelectricarcfurnacebasedsteelplants. Kyleholdsabachelor’sdegreeinchemical engineeringandbiosciences,andamaster’s degreeinappliedsciencefromMcMaster UniversityinHamilton,Ontario,Canada.Kyle isalicensedprofessionalengineerinOntario, Canadawith4+yearsofexperienceinthefield ofprocessengineering.
EmeritusProfessorWilliamGeorge Davenport isagraduateoftheUniversityof BritishColumbia,CanadaandImperial College,UniversityofLondon,UK.Priortohis
academiccareer,heworkedoniron-andsteelmakingtechnologieswiththeLindeDivisionof UnionCarbideinTonawanda,NewYork,USA. Hespentacombined43yearsofteachingat McGillUniversity,Montre ´ al,Quebec,Canada andtheUniversityofArizona,USA.Hewas alsoavisitingprofessoratTohokuUniversity, Sendai,JapanandvisitoratCambridge University,UK.
ProfessorDavenportspentmuchofhis careervisitingindustrialplantsaroundthe world.Thishasresultedinhisco-authoringof thefollowingbooks:
ExtractiveMetallurgyofCopper
IronBlastFurnace
FlashSmelting
ExtractiveMetallurgyofNickel,Cobaltand PlatinumGroupMetals SulfuricAcidManufacture and: RareEarths,Science,Technology, ProductionandUse.
ProfessorDavenportisafellowandlife memberoftheCanadianInstituteofMining, MetallurgyandPetroleumanda25-yearmemberofthe(U.S.)SocietyofMining,Metallurgy, andExploration.HeisarecipientoftheCIM AlcanAward,theTMSExtractiveMetallurgy LectureAward,theAus.IMMSirGeorge FisherAward,theAIMEMineralIndustry EducationAward,theAmericanMiningHall ofFameMedalofMerit,andtheSMEMiltonE. Wadsworthaward.
Preface
TheideaforthisbookarosefollowinganironmakinglecturebyIanCameronatthe2014 ConferenceofMetallurgists,Vancouver, Canada.Hislectureentitled, TheIronBlast Furnace;TheoryandPractice-35YearsLater,discussedhowthefundamentalapproachprovided inthe1979bookbyJohnPeaceyandBill Davenporthadappliedtoensuingindustry improvements.BillDavenportattendedthelectureandafterwardaskedIanifhewouldliketo writeanewbookontheironblastfurnace.In 1979,IanhadbeenastudentinBill’sironmaking/steelmakingclassatMcGillUniversity, Montre ´ al,Quebec,Canada.Later,IanwasfortunatetoworkwithJohnPeaceyaspartofthe NorandagroupandatHatch.
Ianagreed,andwritingbegan.Theseauthors weresoonjoinedbyMitrenSukhramandKyle Lefebvre,co-authors,whoworkwithIanat HatchLtd.,Mississauga,Canada.AnqiCai joinedin2018andmadeastrongcontribution duringthelast8monthswhenthebookwas finalized.
Wewereveryfortunatetoworkwithfive younguniversityinterns,allfromMcGill University,duringourwriting,namely;
• AnqiCai,
• SabrinaLao,
• DenzelGuye,
• Max(Shuhong)Shen,and
• WilliamDixon.
Theyproofreadourmanuscripts,didthe end-of-chapterexercises,andshowedusolder folkswhatengineeringstudentsin2015 18 alreadyknewanddidn’tknow.Theywereall
proficientinmatrixalgebra,ExcelGoalSeek, ExcelSolver,andOptimization.Wethankthem profuselyfortheirhelpandwishthemthebest ofluckwiththeirstudiesandfuturecareers.
Theobjectivesofourbookaretodescribe blastfurnaceironmakingasitistodayandto suggesthowitwillbeinthenearanddistant future.Toachievetheseobjectives,wevisited andworkedatmanyblastfurnacesaroundthe worldwhilewewerewriting.Theprinciple visitswereto:
• AKSteel,Dearborn,BlastFurnaceC,United States
• AlgomaSteel,BlastFurnace7,Canada
• ArcelorMittalDofascoBlastFurnaces2and 4,Canada
• ArcelorMittal,Fos-sur-Mer,BlastFurnaces1 and2,France
• ArcelorMittalMonlevadeBlastFurnaceA, Brazil
• ArcelorMittalIndianaHarbor,BlastFurnace 7,UnitedStates
• ArcelorMittal,TubaraoBlastFurnace1and 3,Brazil
• BlueScopeSteel,PortKembla,BlastFurnace 5,Australia
• EVRAZNTMKBlastFurnace5and6, RussianFederation
• JFEFukuyamaWorks,BlastFurnace5,Japan
• HebeiIron&Steel,HandanWorks,P.R. China
• NLMK,BlastFurnaces3 7,Russian Federation
• NipponSteel,NagoyaWorks,BlastFurnace 1,Japan
• NipponSteel,OitaWorks,BlastFurnace2, Japan
• Gerdau,Acominas,BlastFurnaces1and2, Brazil
• StelcoLakeErieWorks,BlastFurnace1, Canada
• TataSteelEurope,BlastFurnaces6and7, TheNetherlands
• TerniumCSA,BlastFurnaces1and2,Brazil
• TerniumSiderar,BlastFurnace2,Argentina
• U.S.SteelGreatLakesWorks,Blast FurnacesB2andD4,UnitedStates
• U.S.SteelGaryWorks,BlastFurnaces4 and14,UnitedStates
Wethankthepersonnelatthesefacilitiesfor theirkindnessinshowingusaroundtheir plantsandforansweringallourquestions.
Ourbookconsistsofthreemainsections:
1. Threeintroductorychaptersdescribingthe blastfurnacefromtheoutsideandthenthe inside.Thisisfollowedbyabriefdescription ofhowtheblastfurnace’smolteniron productisusedformakingsteel.
2. Anarithmeticalsectionthatdevelopsa thermochemicalmodeloftheblastfurnace processfromfirstprinciplesand culminatingwithseveralchapterson controlandoptimization.
3. Athoroughexaminationofmodern industrialblastfurnacepracticearoundthe worldbasedonpriorknowledgeandour plantvisits.
Abriefnoteaboutunits.WehaveusedSI unitsthroughoutexcept Cfortemperature andpascalsandbar(1 3 105 Pa)forpressure. Wealsousetheunitnormalcubicmeter(Nm3) whichisam3 ofgasat0 Cand1barpressure. ANm3 contains0.0440kgmolofidealgas.
Oneoftheauthorswouldliketothankhis wifeMargaretDavenportforreadingportions ofthemanuscriptandhissonGeorge Davenportforhisassistancewithmanycalculations.TheauthorsthankHatchLtd.,especiallyMr.TedLyon,ManagingDirector,Bulk Metals,forthecontinuingsupportwereceived aswecompletedthebookovera5-yearperiod.
Preparingthebookprovidedagreateducationaswediscussedanddebatedthebestway topresentblastfurnacepracticetoyou,thatis, ourreaders.Ourapproachwillhelpyoubuild knowledge/toolstounderstandandcontrol thecomplexblastfurnaceoperation-oneof mankind’smostimportantindustrialfurnaces.
IanCameron,MitrenSukhram, KyleLefebvreandWilliamDavenport September2019.
Acknowledgments
ANQICAI,McGILLUNIVERSITY
Ms.AnqiCaiplayedakeyroleinwriting thisbook.Shewasespeciallyhelpfulto ProfessorDavenport.Theyspokeeveryday forabout3monthseventhoughshewasin Mississauga,OntarioandhewasinTucson, Arizona.Shewasespeciallyhelpfulinthethermodynamicaspectsofthebook,writingequations,challengingothersandproviding documentationtoproveeverypoint.Vigorous argumentsoftenensued.
Anqialsomadecriticalcontributionstothe book’smatrices,makingsurethatthevariables wereproperlyidentifiedandunchanged throughoutthebook,thattheequationswere properlynumberedandthateverycellhadits propervalue.Herconsistentequationnumberingwasespeciallycritical.
Finally,Anqicompletedallthebook’safterchapterexercisesandmadesurethattheexerciseswereappropriateandclearlyworded. Studentscompletingtheexerciseswillhave hertothankfortheirclarity.
TEDLYON,MANAGING DIRECTOR—BULKMETALS, HATCHLTD.
Mr.TedLyonprovidedimportantsponsorshipoftheHatchteamduringtheauthoringof thebook.Hewasalwaysencouragingand supportedthecompletionofthebook,understandingitsimportancetotheironmaking
communityandasatooltotrainprocess engineers.
CONTRIBUTINGAUTHORS
Dr.AfshinSadri,Mr.ManuelHuerta,andMr. LukeBoivinallofHatchLtd. tookonthechallengeofprovidingimportantcontenttoseveralchaptersinthebook.Theirdedicationto providehigh-qualitymaterialsisappreciated bytheauthors.
SUSANNECRAGO,CHAMELEON GRAPHICS
Susannecreatedtheexcellentgraphicsin thebook.Sheperseveredthroughthemany changesrequestedbytheauthors.Weappreciateherskillsasagraphicsartistandpatience togetthebestpossibleimages.
WILLIAMDIXON,DENZELGUYE, SABRINALAO,ANDMAX (SHUHONG)SHEN,ALLFROM McGILLUNIVERSITY
InadditiontoMs.AnqiCai,thesestudents reviewedpartsofthebookastheauthorswere preparingthemanuscript.Theirinputonthe contentandapproacharegreatlyappreciated bytheauthors.Knowingthatthebooks’ contentappealedtoeachofthesestudents reinforcedourapproachanddirection.
Thestudentsalsohelpedwithmoreroutine aspectsthateveryauthorappreciateswhen preparingamanuscript.
OTHERCONTRIBUTORS
Theauthorswouldliketothankand acknowledgemanyotherswhocontributedto thebook.Oursupportersarelistedbelowand reflecttheglobalnatureoftheironmaking community.
MichaelGrantAirLiquide,Germany
PeterHamerlinckArcelorMittalDofasco,Canada
AdelmoMonacoArcelorMittalDofasco,Canada
DouglasRuyArcelorMittalTubarao,Brazil
KenLandauAssociationofIronandSteel Technology(AIST),UnitedStates
DarryleLathleanBlueScopeSteel,Australia
FangYuanQing (Tracy)
LiZhiyou (William)
CISDIInternationalEngineering& Consulting,P.R.China
CISDIInternationalEngineering& Consulting,P.R.China
PeterMcCallumCRH,Canada
JohnBusserHatchLtd.,Canada
Anneliese Dalmoro HatchLtd.,Canada
BarryHydeHatchLtd.,Canada
AnneKirkpatrickHatchLtd.,Canada
KiyoshiFukudaJFE,Fukushima,Japan
Hedetoshi Matsuno JFE,Fukushima,Japan
KentaroNozawaKobeSteel,Kakogawa,Japan
ProfessorHiro Fukunaka KyotoUniversity,Japan
ChrisRavenscroftMidrexCorporation,UnitedStates
KCWoodyMidrexCorporation,UnitedStates
ProfessorIvan Kurunov NLMKLipetsk,Russia
TadashiImaiNipponSteel,Nagoya,Japan
TakayukiNishiNipponSteel,Nagoya,Japan
JumpeiKonishiNipponSteel,Oita,Japan
LaurenceKaylPaulWurthS.A.,Luxembourg
RobertNeuholdPrimetalsTechnologies,Austria
ProfessorChenn QuiZhou PurdueUniversity,UnitedStates
Dr.Jens Kempken SMSGroup,Germany
JohnD’AlessioStelcoHoldingsInc.,Canada
ScottDedrickStelcoHoldingsInc.,Canada
Dr.JohnQuanciSunCokeEnergy,UnitedStates
GerardTijhuisTataSteelEurope,TheNetherlands GeraldToopTeckResources,Trail,Canada
Frederico GodinhoCunha TerniumCSA,Brazil
OscarLingiardiTerniumSiderar,Argentina MattKraeuterThyssenkruppIndustrialSolutions, UnitedStates
Claude, Bodeving TMT TappingMeasuring Technology,Luxembourg
ProfessorToru Okabe TokyoUniversity,Japan
RalphAlbaneseUnitedStatesSteelCorporation, UnitedStates
DevbratDuttaUnitedStatesSteelCorporation, UnitedStates
JasonEntwistleUnitedStatesSteelCorporation, UnitedStates
MichaelJ.McCoyUnitedStatesSteelCorporation, UnitedStates
Professor EvgueniJak UniversityofQueensland,Australia
TheIronBlastFurnaceProcess
OUTLINE
1.1IntroductiontotheBlastFurnace Process1
1.2BlastFurnaceRawMaterials2
1.2.1Top-ChargedMaterials4
1.2.2ChargingMethods6
1.2.3Tuyere-InjectedMaterials7
1.3ProductsFromtheBlastFurnace7
1.3.1MoltenIron7
1.3.2MoltenSlag8
1.3.3TopGas9
1.4BlastFurnaceOperations10
1.4.1Pressure10
1.4.2PrincipleChemicalReactions11
1.4.3MainThermalProcesses11
1.4.4BlastFurnaceInformation11
1.1INTRODUCTIONTOTHE BLASTFURNACEPROCESS
Theironblastfurnaceisatallverticalshaft furnace, Fig.1.1.Itsprincipleobjectiveisto producemoltenironfromironoresforsubsequentandimmediateproductionofmolten/
1.4.5ProductionStatistics11 1.4.6CampaignLife11 1.5Costs15 1.5.1Investment(Capital)Costs15 1.5.2OperatingCosts15 1.5.3MaintenanceandReliningCosts16 1.6Safety16 1.7Environment16 1.8Summary17 Exercises18 References18 SuggestedReading18
liquidsteel.Aphotographofablastfurnace plantisshownin Fig.1.2.
SolidFeoxideore(hematite,Fe2O3),coke (87 91%carbon),andfluxesarechargedto thetopoftheblastfurnace.Amolteniron alloy,1500 C,94.5%Fe,4.5%C,and1%[Si 1 Mn], iscastfromthehearthalongwithmoltenand
FIGURE1.1 Cutawaydrawingofanironblastfurnace. Itisatallcylindricalfurnace B40mhighand10 15min diameter.
impurity-richoxideslag.Hot,highpressure airisblownintotheblastfurnacethroughthe tuyeres,burningcoke,andinjectedfueltocreatetheheatneededtosmelttheironoresand fluxes.Theresultinggasrisesquicklyup throughthefurnacechargematerialsalso knownasburden.Theburdenisheated,Fe oxidesarereducedtoFe,andsolidmaterials aremeltedandcollectedinthehearth.Molten ironproductionistypically4,000 12,000tonne perblastfurnaceperday.Theprocessiscontinuousandoperateswithveryhighavailability, typicallyover95%oftheavailabletime.
In2016,94%oftheworld’sironorereductionwasdoneinblastfurnaces.Theremainder wasdonebysolidstatereductionknownas DirectReductionIronmaking.TheblastfurnaceemployscarbonincoketoreduceFe oxidepellets,sinter,andcrushedoreto
metalliciron. Inthisbook,reductionmeans removalofoxygen(O)fromironoxides. Theblast furnaceproducesamoltenironalloyat1500 C:
• 94.5mass%Fe;
• 4.5mass%C;
• 0.6mass%Si;
• 0.4mass%Mn;and
• minoramountsofS,P,andTi.
Virtuallyallthemoltenironalloy,commonlyreferredtoashotmetalorrawiron,is immediatelyrefinedintolowercarbonmolten steelatotherfurnaceswithinthesteelplant.
TheFeoxidesandcokearechargedtothe topoftheblastfurnaceatfurnacepressure andinseparatelayers.Themoltenironis tappedfromthebottomofthefurnaceinto ladlesknownastorpedoladles.Itisimmediatelysentmoltentothesteelmakingshop.Byproductmoltenandimpurity-richoxideslagis tappedwiththemolteniron,separatedimmediatelyoutsideoftheblastfurnace,solidified, andsoldasroadaggregateorforusein cementproduction.Theslagismadeupof;
1. impurityoxides,mostlySiO2 andAl2O3 presentinoregangueandcokeash,plus 2. fluxoxides,mostlyCaOandMgO.
Ironorepelletsandmetallurgicalcokecan beseenin Figs.1.3and1.4.
Heatfortheprocessiscreatedbyburning thecokewithhot B1200 Chighpressureair injectedthroughtuyereslocatednearthebottomofthefurnace.Theairisblownthroughas fewas15toasmanyas45water-cooledcopper tuyereslocatedaroundthefurnacecircumferenceatthetopofthehearth, Figs.1.1and1.5
1.2BLASTFURNACERAW MATERIALS
Theblastfurnace’sprinciplerawmaterials are:
FIGURE1.2 TwoironblastfurnacesandsupportingequipmentatFormosaHaTinhinVietnamsuppliedbyChina’s CISDI.Conveyorbelts(fromrighttoleftintheupperpicture)transportironoxideores/sinter/pellets,coke,andfluxup tothetopofeachfurnace.Fourverticalblastheatersorstoves(lowerpicture)heattheblastairto B1200 C.Alargeflue, knownasthedowncomer,descendsfromthefurnacetopandremovestopgasfromtheblastfurnace.Theblastfurnace gasiscleanedandthestovesusethisasafuel. Source:PhotographscourtesyofCISDIInternationalEngineering&ConsultingCo.
FIGURE1.3 Firedhematite(Fe2O3)pelletsreadyfor chargingtoanironblastfurnace.Theyare8 16mmin diameterandcontain B64mass%Feascomparedto70 mass%FeinpureFe2O3. Source:Photographcourtesyof MidrexTechnologiesInc.
FIGURE1.4 Metallurgicalcoke,about70 100mm long.Cokeismadebyhigh-temperaturevaporizationof volatiles,(e.g.,CH4)fromcoalheatedintheabsenceofair, Chapter55,MetallurgicalCoke—AKeytoBlastFurnace Operations.“Met”cokecontains87 91%carbonand 9 13%oxideash;mostlysilicaandaluminafromtheoriginalcoal.Thecokeburnswithblastairnearthebottomof theblastfurnaceandinfrontofthetuyeresto(1)provide heatfortheironmakingprocess,and(2)carbonmonoxide forironoxidereduction. Source:Photographcourtesyof SunCokeEnergyInc.
1. top-chargesolids(Feoxide,coke,andflux), and
2. hotblastair B1200 C,whichisforcefully blownintothefurnacethroughtuyeresnear thebottomofthefurnace, Figs.1.1and1.5.
FIGURE1.5 Newtuyeresinarebuiltblastfurnace. Theyarewater-cooledcopperwithaprotectivemetalcoatingnearthetip.Tuyeresareabout0.15minsidediameter andpenetrateabout0.4mintothefurnace.Theyaresituatedabout3mabovetheblastfurnacetapholeandare about1.2mapartaroundtheblastfurnacecircumference. 1200 Cblastairentersthetuyeresat180 240m/sanda pressureof3.5 4.5bar(gauge). Source:Photographcourtesy ofStelcoHoldingsInc.
Pulverizedcoal,naturalgas,andother hydrocarbonsareinjectedinthroughthe tuyerestoreplacecoke.Oxygenandsteamare alsoaddedtotheblastair.
1.2.1Top-ChargedMaterials
Thetop-chargedrawmaterialsaretypically:
1. ironoxides:Overwhelminglyhematite, Fe2O3.Thisoxideisaddedas;
a. 8 16mmdiameterpellets(B64mass% Fe)producedbyheatingfinelyground andbeneficiatedore, Fig.1.6;
b. 10 45mmsinterpieces(57mass% Fe)producedbyheating nonbeneficiatedorefinesandother solids;and
c. naturalore,crushedto50mmpieces (62 67mass%Fe).
Allironoxidescontainsilica(SiO2)and otheroxideimpurities.
FIGURE1.6 Blastfurnaceinputandoutputmaterialflows.All%aremass%.Threeironoxidefeeds;pellets,sinter,andcrushedorearechargedwithcoke.Productsare moltenironandslag.Themoltenirongoesdirectlytosteelmaking,andmoltenslagissolidifiedandusedforroad aggregateorincementproduction.Reductantsforironmaking are(1)chargedtothetopofthefurnaceasmetallurgicalcoke,and(2)injectedwithhotblastairaspulverizedcoalandotherhydrocarbonfuels.Thetop-chargedcokeandiron oxidesareaddedinlayers;a B0.7mthickFeoxideorelayerthena0.4mthickcokelayer,thena0.7mthickorelayer,andsoon.Notshownistopgasleavingthefurnace;it leavesat100 200 Candissenttodedustinganddemistingbeforeitisusedasfuelforheatingblastairandforotherin-plantduties.
2. coke:87 91mass%C,9% 13%ash,bothon adrybasis,and1 5mass%H2O—addedas 50 60mmdiameterpieces.Thismaterial mustbe:
a. reactiveenoughtocombustrapidlyat elevatedtemperature,and b. strongenoughtoavoidbeingcrushedin theblastfurnace.
Cokeashconsistsofalumina(Al2O3)and silica(SiO2)andoftenalkaliimpurities(K2O andNa2O).Largeandstrongcokeis essentialintheblastfurnaceto:
a. preventthechargefromcollapsinginto thebottomofthefurnace;
b. permitupwardgasflowbetweenthe cokepieceswhereoreandfluxare reducedandmelted;and
c. allowdownwarddrippingofnewly formedmoltenironandslag.
3. fluxes:MostlyCaOandMgO.Theseoxides fluxthesilicaandaluminaimpuritiesinore andcoketomakeafluidmoltenslagwhich iscastortappedfromthefurnacetogether withtheproductmolteniron.Fluxesare addedas50mmdiameterlimestone (CaCO3)anddolomite(CaCO3:MgCO3) piecesorasCaOandMgOcontainedin pelletsandsinter.Thesefluxescausesulfur, andalkaliimpuritiestobeabsorbedin moltenslagratherthaninthemolteniron.
1.2.2ChargingMethods
Continuousblastfurnaceoperation demandsthattopchargingdoesnotinterfere withgasflowoutofthefurnace,whilethe chargeburdenmustbeaddedat1 3barfurnacepressure(gauge).Thisisachievedusing:
1. gasuptakeflueslocated awayfromthe centralsolidschargingequipment,and
2. twocentralsealedchargehoppers,one loadingatambientpressure,whiletheother
isdischargingintothefurnaceatfurnace pressure, Fig.1.7.
Thissystemallowstopgastoflowcontinuouslyoutofthefurnacewhilethefurnaceis beingchargedwithsolids.
FIGURE1.7 Bell-lesschargingsystemdevelopedby PaulWurthforchargingablastfurnaceunderpressure. Thetwoholdinghoppersarenotable.Theyarefilledcyclicallywhereonehopperisfillingatambientpressure, whiletheotherisemptyingatfurnacepressure.The chargeisdistributedacrosstheblastfurnacethroatareaby arotatingdistributionchute.Thefurnace’stopgasleaves theblastfurnacecontinuouslythroughfourgasuptakes locatedbelowthechargingsysteminthefurnacetopcone (betweenstocklineandfeederspout)—see Fig.1.8
FIGURE1.8 Threeoffourgasuptakesandthedowncomerpipeusedtocaptureandremovetopgasfromablastfurnace. Source:PhotographcourtesyofCISDIInternationalEngineering&ConsultingCo.
1.2.3Tuyere-InjectedMaterials
Rawmaterialsintroducedthroughthe tuyeres(Fig.1.5)are:
1. hotblastair:Heatedto B1200 Candoften enrichedwithpureoxygen.Theblastair burnsdescendingincandescentcoke . 1500 Cinfrontofthetuyerestoprovidea 2000 2200 Cflamethatishotenoughto:
a. heatandreduceironoxidesthroughout theblastfurnace,and
b. meltironandslag.
2. injectants:Mostoftenpulverizedcoalbut alsootherhydrocarbons(e.g.naturalgas) areinjectedandcombustedinfrontofthe tuyerestoprovideheatplusextraCO(g) andH2(g)reducinggases.
Pulverizedcoalischeaperthancokeperkg ofcontainedC.Pulverizedcoalinjectionlowerstheblastfurnacecokerequirementand totaloperatingcost.
1.3PRODUCTSFROM THEBLASTFURNACE
Theironblastfurnacemakesthree products:
1. moltenblastfurnaceiron,alsoknownashot metalorrawiron;
2. moltenoxideslag,knownasblastfurnace slag;and
3. blastfurnacetopgas,knownasBFG.
1.3.1MoltenIron
Themainproductoftheblastfurnaceis molteniron,castat1500 C.Itiscastthrougha pluggabletapholeinthefurnacehearthwall nearthebottomofthefurnace.Asmallblast furnaceisequippedwithonetaphole;alarge furnacewillneedthreeorfourtapholestocontinuouslydrainthefurnace.Largerfurnaces
alternatelyusetwotapholeswiththeothers beingrefurbishedoronstandby.
Themoltenironexitstheblastfurnacesaturatedwithcarbon.Theirontypicallycontains thefollowing:
1.3.2MoltenSlag
Asshownin Fig.1.9,moltenblastfurnace slagistappedfromtheblastfurnacetogether withthemolteniron.Slagisseparatedfrom ironbygravitythensolidifiedandsold.
Blastfurnaceslagisamoltenoxidesolution at1500 Cmadeupofthefollowing:
Thehotmetalisimmediatelysentmolten B1500 Ctothesteelmakingplantwhereitis sequentially:
1. desulfurizedinalargeladlebyinjectinga [CaO,CaC2,and/orMg] basedpowder intotheiron,therebyremovingthesulfur containedasamoltenCaO-,MgO-,S-rich slag1;
2. oxidizedwithvirtuallypureoxygenand fluxedwithCaOandMgOinabasic oxygenfurnacetoremovemostofthe impurities,thatis,Si,C,S,andP;
3. alloyedwithothermetals;forexample,Mn, Cr,Ni,V,andMo;
4. degassedtoremoveH2(g),N2(g)andlower carbontoverylowlevels[removingCas CO(g)];
5. continuouslycastintosteelslabs,billets, and/orblooms;and
6. finishedbyhotandcoldrolling, occasionallycoated,andthensold asdescribedinChapter3,MakingSteelFrom MoltenBlastFurnaceIron.
Fe(totalindropletsandions)0.2
Chemically,theslagisahightemperature solutionofcations(suchasCa11 andMg11) andanions(suchasO2 andSiO44 ).2 SlagcontainsverylittleFe-anindicationoftheblast furnace’sexcellentreductionefficiency.
Blastfurnaceslagcompositionischosento:
1. guaranteethattheslagismoltenandfluid; 2. removetheore’sganguemineralsandthe coke’sashfromthefurnaceburdenasa fluidslag;
3. absorbK2OandNa2O(alkalis),whichwill otherwisebuildupinthefurnace;and 4. absorbsulfurthatwillotherwiseenterthe productmolteniron.
Aslag“basicity”ratio,B4isdefinedas:
B4 5 Mass%CaO 1 Mass%MgO Mass%SiO2 1 Mass%Al2 O3
AB4valuebetween0.9and1.1bestmeets thesefourslagcompositionobjectives.
FIGURE1.9 Moltenironandslagbeingtappedfromablastfurnace.Theyareseparatedinthemaintroughbyallowingdensemolteniron(6.8t/m3)toflowunderarefractoryskimmingblockwhileforcingthelessdensemoltenslag (2.7t/m3)tocollectabovetheironandflowintoaslagrunner.Themoltenironflowscontinuouslyintoatorpedo-shaped railcarladleusedtotransportthehotmetaltosteelmaking.Themoltenslagflowstoagranulationmachineorissolidifiedinpits-thensold.Noticethehugebustlepipethatdistributesblastairtoindividualtuyeres. Source:Photographcourtesy ofTMT—TappingMeasuringTechnologyS.a`.r.l&G.m.b.H.
1.3.2.1SlagUses
Solidifiedblastfurnaceslagisusedforroad aggregateandincementproduction.Forroad aggregate,slagisaircooledinlargepitsthen crushed.Forcement,moltenslagiswater quenchedthenfinelyground.Thisfinelyground slagisaddedtoPortlandcement(30 70%blast furnaceslag,remainderPortlandcement).This mixtureisstrongerthanPortlandcementalone andmoreresistanttosulfateandchlorideattack. Slagcementisalsofireresistant.3
Successfulslaggranulationrequiresthat themoltenslagmustalwaysbehot,
1450 1500 C,sothatitflowssmoothlyinto thegranulator.
1.3.3TopGas
BFGleavesthefurnacethroughfourwidely spaceduptakeflueslocatedinthefurnacetop cone, Figs.1.1and1.8.Thegasisdedusted, demisted,andburntfor:
1. heatingblastairinregenerativestoves, Fig.1.2, 2. heatingotherfurnacesaroundthesteelplant,
3. producinglow-pressuresteamforthesteel plant,and
4. makingelectricity.
BFGistypicallycomposedofthefollowing:
BFG’sfuelvalueisabout10%thatofnaturalgas,thatis,BFGisa“weak”fuel.Despite beingaweakfuel,BFGhasmanyvaluableinplantuses;itisbyfarthelargeststreamof wasteenergyinanysteelworks.Themoist dustfromdedusting/demistingisagglomeratedbysinteringorbriquettingthenrecycled totheblastfurnacetorecoveritsFeandC.It accountsforabout5%oftheblastfurnace charge.
1.4BLASTFURNACEOPERATIONS
Theblastfurnaceoperationentails:
1. nearlycontinuouschargingofore,coke, andfluxthroughthetopofthefurnace;
2. continuousblowingofhotblastairand hydrocarboninjectantsthroughtheblast furnacetuyeres;and
3. continuous(onsmallerfurnaces intermittently)castingofmoltenironand slagthroughatapholenearthebottomof thehearth.
Mostoftheseoperationsarecontrolledby skilledoperatorsusingmultiplesensors aroundthefurnace.Continuouslymonitored processvariablesincludethefollowing:
Pt Rhthermocoupleinflowing-tapped moltenironstream.Itisinsidetheverticalrefractoryprobe (bottomendclosed)togiveacontinuousmeasureofhot metaltemperature. Source:PhotocourtesyofAlgomaInc.
temperatures: Hotblast,coolingwater, furnacewall,topgas; pressures: Blast,furnaceinterioratseveral points,top; flowrates: Blastair,tuyereinjectants,cooling water;and moisture: Ofchargematerialsaddedtothe furnace.
Inaddition,productironandslagtemperaturesaremeasuredcontinuouslyorintermittentlywithspecializedhigh-temperature Pt Rhthermocouples, Fig.1.10.4
Powerfuldrillingmachinesareusedto openthetaphole.Attheendofacast,amud gunisusedtoblockthetapholeandstopmoltenironandslagflow.
1.4.1Pressure
Mostblastfurnacesarepressurizedto 1 3bar(gauge)atthetopgasofftakesand 2.5 4.5bar(gauge)atthetuyeretips.These pressuresdensifythegas(n/V 5 P/RT),giving itanextendedresidence/reactiontimein thefurnace.
FIGURE1.10
1.4.2PrincipleChemicalReactions
Themainchemicalreactionsthatoccur insidetheblastfurnaceare:
1. stronglyexothermicoxidationofcarbonby air/oxygeninfrontofthetuyerestogive CO2(g)plusheat: CsðÞ 1 O2 g -CO2 g ΔH D 395MJ=kgmolofCsðÞ
2. endothermicreactionoftheCO2(g)with carbontoproduceCO(g),theprinciple reducinggasoftheblastfurnaceprocess:
CO2 g 1 CsðÞ-2COg ΔH D 1 165MJ=kgmolofCsðÞ (1.2)
3. slightlyexothermicreductionofhematiteto solidFe:
0 5Fe2 O3 s ðÞ 1 1 5COg -FesðÞ 1 1 5CO2 g ΔH D 20MJ=kgmolofFesðÞ (1.3) and
4. formationofmoltenironfromitssolid components: solidFe 1 solidC-moltenFe 1 Calloy(1.4) whichisslightlyexothermic.
1.4.3MainThermalProcesses
Theblastfurnaceisacountercurrentheat exchanger-tuyerestofurnacetop-inwhich:
1. hotgas(B2100 C)isproducedinfrontof thetuyeresbyburninghotcokewithhot blastairandaddedoxygen; 2. thesehotgasesascendthroughthefurnace, andsequentially:
a. heatandmeltironandslag, b. provideheattoreduceironoxidesto iron,
c. heatthedescendingsolidcharge,and
d. nearthetopoftheblastfurnace,remove moisturefromthechargeburden;
3. theascendinggasleavesthefurnaceat 100 200 C,abovethegasH2O(g)dew point.
Thiscountercurrentflowaspectisdiscussed throughoutthisbook.Itiskeytotheblastfurnace’soutstandingchemicalandthermal efficiency.
1.4.4BlastFurnaceInformation
Withitsdeephistoryandglobalfootprint, blastfurnacedesignandoperationvariesfrom regiontoregionandcompanytocompany. Blastfurnaceoperatorsworktoobtainthelowestoperatingcostandlongestcampaignlifeto maximizethevaluethatblastfurnaceironmakingprovides.Specificbasicdesignand importantinputandoutputinformationfor selectedindustrialblastfurnacesareprovided in Table1.1.
1.4.5ProductionStatistics
In2016,about1.2billiontonnesofmolten ironwereproducedfromblastfurnaces ranginginoutputfrom0.2to5.0Mt/year.5 Theexactnumberofblastfurnacesoperating ischallengingtoidentify;annualproduction wouldsuggestthat700 900blastfurnacesare inoperationglobally.Blastfurnacesoperateon everycontinentbutAntarctica, Table1.2.
Theglobaldistributionofblastfurnace capacityisillustratedfurtherin Fig.1.11.
1.4.6CampaignLife
Optimally,blastfurnaceironmakingnever stopsexceptforsafetyconcernsortoreplace thefurnacerefractoriesandcoolingsystem, knownasafurnacereline.Theblastfurnace operatescontinuouslyfor12 15years(occasionally20 1 years)beforethefurnace
TABLE1.2 BlastFurnaceMoltenIronProductionby Country,2016
Country
2016BlastFurnaceIron Production,Megatonnes(Mt)
Argentina2.1
Australia3.6
Austria5.6
Belgium4.9
Brazil26.0
Canada6.2
Chile0.7
China701
CzechRepublic4.2
Finland2.7
France9.7
Germany27.3
Hungary0.9
India63.0
Iran2.3
Italy6.0
Japan80.2
Kazakhstan3.3
Mexico4.5
Morocco0.8
TheNetherlands6.1
Poland4.7
Romania1.6
Russia51.8
Slovakia4.0
SouthKorea46.3
Spain4.1
SouthAfrica4.3
Sweden3.1
Taiwan,China14.9
TABLE1.2 (Continued)
Country
(Continued)
2016BlastFurnaceIron Production,Megatonnes(Mt)
Turkey10.3
Ukraine23.7
UnitedKingdom6.1
UnitedStates22.3
Othercountries4.6
Total1160
ChinaDominatesWithIndia,Japan,Russia,andSouthKoreaata Second,MarkedlyLowerLevels5.worldsteelAssociation.
becomesunsafeandirreparable—whereupon itisrelinedorrebuilt.Thisisreferredtoas theblastfurnacecampaignlife.Thecurrent recordholderisArcelorMittal,BlastFurnace #1,Tubara ˜ o,ES,Brazil.Thisblastfurnace operatedforover28yearsandproduced morethan90milliontonnesofhotmetal. DetailsoftheBlastFurnace#1campaignare providedin Fig.1.12.
Longcampaignsareobtainedbygoodblast furnacedesign,stableoperations,andquality burdenmaterialstoavoidrefractorythermal shock,abrasion,andslag/chemicalattack. Rebuildinghaltsironproduction,whichis expensive,solongcampaignsareeconomically veryadvantageous.
Majorimprovementscanbemadeoutside theblastfurnacewhilethefurnaceisoperating.Forexample,theblastfurnace’sentire controlsystemisoftenmodernizedduringa longcampaign.Itisunlikelythatthecontrol systemwouldhavesparepartsfor30years! Otherancillaryequipmentmayneedtobe replacedorupgraded.
Blastfurnaceutilizationcanbeashighas97% or98%overextendedperiods,withonlyshort 1-to2-daylongshutdownsformaintenance. World-classblastfurnaceswillonlyhavefour,
Capacityoftheworld’sironblastfurnaceplants. Mt/y,Megatonnesperyear.
ArcelorMittalTubaraoBlastFurnace#1-LongestCampaignc.2012. Source:PhotocourtesyofArcelorMittal Brazil.
FIGURE1.11
FIGURE1.12
1 2daymaintenancestopsperyear.Longer stoppages(i.e.,greaterthan1week)maybeneed forinterimrefractoryandcoolingsystemrepairs.
1.5COSTS
Blastfurnaceironmakingisthesinglemost expensiveoperationinanintegratedsteelworksfromanoperating,maintenance,and capitalcostperspective.Thecostofproducing moltenpigironisabout75%ofthecaststeel cost.Relinesandrebuildsareamongthemost expensivemaintenanceactivitiesthatasteelworksmustplanfor.Theinitialinvestmentfor anewblastfurnaceisoneofthecornerstone investmentsforanewsteelworks.
1.5.1Investment(Capital)Costs
Atthetimeofwriting,thecosttobuilda newblastfurnacecomplexwasestimatedto
be150USDperannualtonneofproduct molteniron.Thus,theinvestmentcostfora complexproducing4milliontonnesofmolten ironperyeariscalculatedbytheequation:
Blastfurnacecomplexcost
5
½Investmentcostperannualtonneofmolteniron
5
½Plantcapacity; tonnesofmoltenironperyear
½150USDperannualtonneofmolteniron
½Plantcapacity; 4 3 106 tonnesofmoltenironperyear
5 600millionUSD
Tothis,wemustaddabout10%forworkingcapitaltocovertheplant’sstart-upcosts.
1.5.2OperatingCosts
Table1.3 estimatesthecashcostsfor producingmoltenblastfurnaceiron.Thetotal 2017costis B274USD/t.About95%ofthiscost isforironoreandfuelinputs,sothattotalcostis controlledalmostcompletelybythepricesofiron
TABLE1.3 EstimatedCashCost(2017)ofProducingMoltenIronFroma70%Sinter,30%PelletBlastFurnace Charge
ItemUnitCostConsumption
CostofProducing1t ofMoltenIron,USD
Feoxidesinter$71/t1.1t78.1
Feoxidepellets$123/t0.5t61.5
Coke$250/t0.3t75.0
Injectedpulverizedcoal$115/t0.2t23.0
Flux:(CaCO3 MgCO3)$10/t0.03t0.3
Electricalenergy$0.1/kWh150kWh15.0
Labor$25perlabor-hour0.23labor-hour5.8
Repairs/Maintenance$6/tofproductmolteniron6.0
Refractories$1/kg1kg1.0
Total 274
TheLargestCostisFeSinter 1 PelletsFollowedbyCoke 1 CoalandElectricalEnergy.TogetherTheseAccountfor95%ofMoltenIron ProductionCost.
ore,metallurgicalcoal,andinjectedfuels,suchas pulverizedcoalandnaturalgas.
1.5.3MaintenanceandReliningCosts
Blastfurnacesmustbecompletelyrelined andrebuiltattheendofthecampaignlifewhich isusuallydeterminedbythehearthlife.Relines takeabout2yearstoplanandareanimportant opportunitytorenewnotonlytheblastfurnace properbutmanysupportingsystemsthatareat theendoftheirservicelife.Arelinewilllast 60 90days,andthecostwillbebetween150 and300MUSDdependingonthescopeofthe repairandsizeoftheblastfurnace.
Duetothesehighreliningcostsandrelated productionlosses,blastfurnaceoperatorswork tirelesslytoextendthecampaign.Thismay includeshorterstopsfrom5to20daystoreplace worncoolingstaves,sprayrefractorymaterials ontheshaftwalls,orrebuildthehearthwall andtapholes.Inaverylongcampaign,twoto threeshorterrepairsmaybecompletedduring thecampaign.Verycarefulinspectionand dataanalysisiscompletedinadvanceofthese repairstoidentifypartsoftheblastfurnace thatneedtobereplacedorremediated.
1.6SAFETY
Ofparamountconcernaroundtheblastfurnaceisworkersafety.Asafeworkingenvironmentisfosteredby:
1. settingsafetyasaprimarygoal;
2. closeattentiontosafetybymanagement;
3. thoroughworkersafetytraining;
4. thoroughmaintenanceandhazard identification/elimination;and
5. specialattentiontouniqueblastfurnace hazards:6
a. carbonmonoxidepoisoning,
b. molteniron/slagburns,
c. gaseoussulfurcompoundpoisoning,
d. water-molteniron/slagexplosions, e. hydrogenornaturalgasexplosions, f. waterleakageintothefurnace,and g. workerheatstress.
COpoisoningisbyfarthegreatestconcern because:
1. enormousamountsofCOarepresent aroundthefurnace,and
2. COhasarapid,potentiallyfataleffecton thehumanbodyduetoitsrapidabsorption intothebloodstreamandabilitytoblock oxygenuptakebythehumanbody.
PersonalCOmonitorsmustbeworninall areas,andasign-in,sign-outsystemisrigorouslyenforced.
1.7ENVIRONMENT
Blastfurnace basedsteelplantsarevery large,upto3 10km2 ofgroundarea.They typicallyhave:
• ocean-goingshipunloadingfacilities;
• marshalingyardsforfreighttrains;
• oreandcoalstockyards;
• cokeplantandrelatedfacilities;
• sinterand/orpelletplants;
• blastfurnaces;and
• slagsolidificationandcrushingplants whichimpactland,sea,andair.
Itisimperativethatcloseattentionbepaid tominimizingtheenvironmentalimpactofthe facility.Thisisbeingdoneinmodernblastfurnaceplantsby:
1. installingfilters,precipitationtanks,and watertreatmentonalldischargewater streams;
2. reusingwaterincriticalsystems;
3. biologicaltreatmentofcokeplantwaste watercontainingphenolsandthiocyanates;
4. installingcustomfittedhoodsinthe casthousetocollectfumes.Usingbagfilters
