外文翻译中英文冲天炉炼铁Word文件下载.docx
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冲天炉炼铁
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J.E.Rehder,President,MetkemProcessesLtd,Toronto,Canada
ITiswellknownthatironcanbemadebyheatingpelletsofmixedironoreandcarbon..Thereareconsiderableattractionstothisprocedureincludingtheuseoforefinesordusts,low-costreductioncarbonandpossibilityofoperatingeconomicallyatmoderateratesof50,000to300,000ton/year.Variousattemptshave,therefore,beenmadetofindacommerciallysuccessfulroute.Outlinedherearetheproblemandasolutionthatisworkingverywellatpilotplantscale.
Metallurgy
Thebasicprocedureistomakeacompactoffinelydividedironoxidewithenoughcarbontocompletelyreducetheoxidetometal,andthentoheatthiscompactuntilreactioniscomplete.Twocourseofaction,whichhavedifferentresults,arepossible.
Oneistoheattheore-carboncompactstosomewhatbelowtheirfusionpoint,tomakeaproductofsolidstatereducedironmixedwithgangueandcarbonash.Thiscanbedoneinarotarykiln,onatravelinggrateorinaverticalshaftfurnace,andconsiderabledevelopmentworkhasbeendoneonthefirsttwomethods.Theproductcanbeusedasblastfurnacefeedorcanbemeltedandrefinedtosteelinanarcfurnace.However,itisnowclearthatuseofreducedpelletsasblastfurnacefeeddoesnotgivethebesteconomics,andmeltingrefiningofsteelmustcontendwiththeaddedslagvolumeandsulfurbroughtinwiththereductioncarbon.
Theothercourseistoheatore-carbonpelletstoandthroughthefusionpointsofironandgangue,toproducehotmetalandmoltenslag.Thiscanandhasbeendoneinanarcfurnaceandinaninductionfurnace,butthemosteconomicalwayisinafuelfiredshaftfurnace.Thebestknownsuchfurnaceisacupola,suchasisusedinironfoundries.Whenore-carbonpelletsarechargedtoacupolathatisbeingoperatedundertherightconditions,hotmetalandslagarereadilyproducedandtappedwithexcellentrecovery.Thishasbeensuccessfullydoneduringadevelopmentprogram,andatonestagealeanorethatproduced2tonofslag/tonofhotmetalwas
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satisfactorilyhandled.Scrapironorsteelisreadilyincorporatedinthecharge.Thehotmetalproducedcanbeuseddirectlyinanironfoundryorconvertedtosteel.
Thecupola
Atthispointacleardistinctionmustbemadebetweenacupolaandablastfurnace.Oneisnotasmallorlargeversionoftheothersincethemodesofoperationandinternalconditionsarequitedifferent.Innormalpracticethecupolaisoperatedsolelyasaheatgeneratortomeltsolidchargematerial,whetheriron,bronzeorstone,anditdoesthiswiththehighestthermalefficiencyofanywidely-usedfuel-firedmeltingfurnace.Fuelcokeisburnedunderconditiontocreatethemaximumcarbondioxidecontentconsistentwithlowoxidationlossesofironandalloys.Thisisnormally11to13%andmeansthatmorethanintheblastfurnace.Thetopgasisleanbutisampleinheatcontenttorecuperativelyheatcombustionairtothemoderatedegreerequired.
Whenore-carbonpelletsarechargedtoacupola,aconsiderableamountsofcarbonmonoxideisgeneratedfromthereductionreactionsandenrichesthetopgas.Thetopgasalsoishigherinvolumeduetothecombustionoftheincreasedamountofcoketosupplylargeheatofreaction.Thenetresultis70,000to80,000cuftoftopgas/tonofhotmetalcontaining25to30%carbonmonoxide,whichgivesasurplusafterblastheatingofabout5MMBtu/tonofhotmetal.
Stockcolumnheightisrelativelylow,20to50ft,andresidencetimeis1.0to1.5hr.Blowingrateincfm/spftofshaftcrosssectionisaboutdoublethatintheblastfurnace,butpressureislowerduetotheshorterstockcolumnandahigherpermeability.Productionratesof4to5tonofhotmetal/sqft/dayappearpractical.Atthisstageitisnotknownhowlargethecupolacanbeeffectiveinthismanner.Thelargestexistingironmeltingcupolais12.5ftIDwhichcouldrepresent600tonofhotmetal/dayassmelter,butthereisevidenceofadead-manandsomequestionastowhetherthecupolamodeofcombustioncanbemaintainedinthisorlargercupolas.
Duetolowerblastpressurethecupolaoperatedasasmeltercanbetappedcontinuouslythroughasiphonifdesired.Thecupolaisalsoreadilyexternallywatercooledinthehightemperaturezone,andiseasilyshutdownforrepairaftera3to
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5-weekcampaign.Theseandotherfactorsindicatethatforexample,600tonofhotmetal/daywouldbemorepracticallyobtainedfromtwo8.8–ftdiacupolasthanfrom
oneof12.5ftdia.
Hotblastandoxygenenrichment
Useofhotblastsavescokeinlinearproportiontoairtemperatureandalsoincreasesproductionrate,butinironmeltingpracticeabout1200F(649C)isthemaximumused.Thisisprimarilyduetothecostofhighertemperatureairheatingequipment,butateveryhighairtemperaturethereisevidenceoflowercombustionefficiencytuyeres.Themaximumeconomicalairtemperatureforthesmeltingmodeofoperationisnotpresentlyknown.
Oxygenenrichmentofcombustionairiseffectiveindecreasingcokeconsumptioninironmeltingandinsmelting.Theeconomy,ofcourse,dependonlocalpricesofoxygenandofcoke.
Bothhotblastandoxygenenrichmentareeffectivethroughincreaseinflame(i.e,maximumbed)temperature,andthisissubjecttodifferentconstraintsinthecupolaandintheblastfurnace.Theproductionofincreasedreducinggasbyusingtuyereinjectedfuelisuselessinthecupola,sincetheobjectiveisacombinationofmaximumbedtemperaturewithmaximumheatproduction.
Agglomeration
Strengthrequirementofore-carboncompactsforacupolaaremuchlessseverethanforblastfurnacepellets,sincethestockcolumnisshorterandinmanycasesthecompactscanbemadeatthecupolasitesothathandlingisminimal.
Pelletizing,extrusionandbriquettinghaveallbeenused,andbindersarecarbonates,silicatesorasphalt.Theprincipallimitationisthatthecompacts,ofcourse,cannotbeheatedforhardeningabovetheignitiontemperatureofthecontainedcarbon,unlessautoclaved.Thereareseveralsystemsavailableandthesewillnotbereviewedhere.
Economicsanduses
Thereisnoquestionthatsmeltingofore-carboncompactsinacupolaisnotexpectedtobeeconomicallycompetitivewiththeblastfurnace,ortooperateinor
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nearitsproductionratesandsizeranges.However,theredoesseemtobeaplaceformoderatetonnagesinsuitablesupplysituations.
Ore-supply
Supplyofironorefinescanbeaneconomicproblemsincetheironoreindustryisorganizedtoprovidepelletsorlumporeinlargequantity,andobtaining150,000ton/yearofcleanconcentrateforexamplecouldencounterhighfreightcosts.Millwastes,suchasblastfurnacedustandmillscale,can,however,bereadilyhandledandareinreasonablequantity.Thereisbasisforthinkingthatsuchwastescanbeturnedintohotmetalatlowercapitalandoperatingcostinthecupola,thanbyprocessingoverasinterstrandandthroughablastfurnace.Anaddedfactorhereisthatvolatileelements,suchaszinc,shouldbemorereadilyhandledinthecupolathanintheblastfurnace.
Coke
Itisessentialtotheeconomyofcupolaoperationtousecokeofreasonablelargelumpsize,thisbeingoneofseveraldifferencesfromblastfurnaceoperation.Ifacupolaisusedtosmeltmillwastesinornearasteelplant,theeconomiccourseistousetheoversizecokefromthecokeplantprimaryscreenorgrizzly,sincethisavoidsthecostofcrushingtoblastfurnacesize,andtheproductionofhotmetal/tonofcokeishigherthanfromablastfurnace.
Ifthecupolaisusedseparatelyfromasteelplantandsuchcokeisnotavailable,foundrycokemustbeusedbutatconsiderablyhigherprice.Lumpanthracitecanbeusedtoreplaceaportionofthecokecharge,andbriquettedcalcinedpetroleumcokeisanexcellentcupolafuel.
Reductioncarbon
Thedesirablepropertiesofthecarbontobemixedwiththeorearehighfixedcarboncontent,goodreactivity,andlowsulfurashandvolatilemattercontents.Thesecanbemetbyaconsiderablevarietyofrelativelylowcostcarbons,andthisisaprinciplereasonforgoodeconomicsinsmeltingore-carboncompactsinthecupola.Thetotalfixedcarbonrequired/tonofhotmetalwillbeintheorderof1250to15001b,but40to45%ofthisdoesnotrequiretobecokedorcokeable.
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Uses
Therearethreeareaswherecupolamodesmeltingcanbeeconomicallyinteresting.Thesearetreatingmilloxidewastes,providinghotmetalfordirectuseinironfoundriesandforministeelmillsbasedonsmalloxygenvessels.
Processingofmillwastesisimmediatelyinterestingbecauseofthereadysupplyofrawmaterials,thereisactivityinmorethanonelocationindevelopingthisroute.Thecostadvantagewill,ofcourse,varywithlocalconditions,suchaswhetheranexistingsinterplantisoverloaded,wornoutorrequiringextensivenewairpollutioncontrol.
Hotmetalformediumsizeandlargeironfoundriescanshoweverygoodeconomicsfromironore,themainuncertainlyatthepresenttimebeingtheavailabilityandcostofironorefines.Thisdependsonlocationandontheinterestofironoresuppliersinsuchamarket.Therewouldappeartobeopportunityforaconsiderableindependentbusinessinthemanufactureandsaleofore-carbonpelletsorcompacts.
Operationofaministeelmilloranoxygenvesselsuppliedbyhotmetalfromacupolacanbeeconomicdependingonlocalprices.Afeasibilitystudyona300,000ton/yearmillusinga35-tonves