RHvacuumdegasseractingasoneofthemost importantsecondaryrefiningprocesseshasreceived considerableattentionintheproductionofhigh qualitysteel.ThemainfunctionsofRHvacuumde gassingprocessaredegassinganddecarburization duringrecirculationofmoltensteelbetweenanevac uatedvesselandtheladle.Soitisimportanttoun derstandthepatternsoffluidflowandthemecha nismofdecarburizationtomakethedecarburization ratehigheranddevelopnewrefiningtechnology.In thepastdecades,variousmodelswerepresentedto describetheflowanddecarburizationintheprocess RHtreatment<1-6>.However,thesimulationofthe flowwasonlyconfinedtotheladleandtheeffectof argonblowinginup legwasnottakenintoac count<1,2>.Althoughmuchprogresshasbeenmade onthestudyofdecarburizationmechanism,thede carburizationwasnotsimulatedpreciselybecausean idealflowpatternwasassumed.Actually,thede carburizationislinkedtotheturbulentflowofmol tensteelinRHdegasser.Inthepresentstudy,a mathematicalmodeltodescribetheactualflowpat ternanddecarburizationinRHdegasserwaspresen ted,andtheeffectsofliftinggasflow,thediameter ofup legandthetopoxygenblowingontheprocess wereinvestigated. 1MathematicalModel 1.1Controlequation ThefluidflowinRHdegassercanbedescribed bycontinuityequation,Navier Stokesequationsand turbulentmodel,asfollows:Continuityequation ·(ρu )=0(1) Navier Stokesequation ·(ρu u )=- p+ ·(μeff u )+F (2) whereF meansbodyforce,i.e.αρlgincaseofgas blowingintheup leg;αisvolumefractionofgasin plumezone;ρlisdensityofmoltensteel;gisgravi tationalacceleration;ρisdensityoffluid;u isveloc ityvector;pispressure;μeffiseffectiveviscosity andcanbedeterminedbyκ εtwo equationmodel<7>; isdivergence.SincetherecirculatingflowinRH degasserisdrivenbythebuoyancyofbubbles,the gasfractionisaveryimportantparameter.Thear gongasisinjectedhorizontallyintoRHdegasser throughthenozzlesplacedaroundtheup leg.Be causetheargonflowratethrougheachnozzleisnot largeandmostbubblesaremovingalongthewallof up legasobservedinwatermodeling,eachplumeof bubblescanbetreatedasbottomblowninthepres entmodel.Anexperimentalcorrelationshownby Eqn.(3)proposedbyCastillejosandBrimacombe canbeemployedtodeterminethegasfraction<8>: ααmax=exp-0.7rrα,max/22.4(3) where αmax=293.77gd50(ρl-ρg0)Q20ρg00.269zd00.993-1,N>4 αmax=100gd50(ρl-ρg0)Q20ρg00.269zd00.993-0.22,N≤4 γα,max/2gQ201/5=0.243gd50(ρl-ρg0)Q20ρg00.184zd00.48N=gd50(ρl-ρg0)Q20ρg00.269zd00.993 αmaxisvolumefractionofgasatplumecenterline;r, rα,max/2areradialcoordinateandradiusatαmax/2ofthe plume;Q0andρg0aregasflowrateanddensityat blowingpoint,respectively,whichcanbedeter minedbythefollowingequation: Q0=PaQaPs+ρlgH,ρg0=Ps+ρlgHPa·ρga(4) Pa,Qaarepressureandflowrateatnormaltempera tureandpressure,respectively;Psispressureabove theliquidsurfaceinthevacuumvessel;andHis distancebetweenthegasblowingpointandthesur faceofliquidinthevessel. 1.2Decarburization AccordingtoMTakahashietal<9>,thedecar burizationcanbeassumedinvacuumvesselmainly, andthevariationofcarbonconcentrationduringRH operationcanbedescribedbythefollowingequa tion: ·(ρω
)+ ·(ρu ω)= ·(Γeff ω)+SC (5) whereSCissourcetermandcanberepresentedas -ρKCω;KCisrateconstantofdecarburization. Whenωishigh,thedecarburizationreactionis mainlycontrolledbythemasstransferofoxygenin themoltensteel,andthemasstransferofcarbon becomesthecontrollerwhenωislessthan 0.02%,therefore,followingequationsrepresentthe fullrangeofdecarburization: Forthereactioncontrolledbyoxygendiffusion KC=1216·ωω·1W<1/QL+1/(akOρ)>(6) Forthereactioncontrolledbycarbondiffusion KC=1W<1/QL+1/(akCρ)>(7) whereakisvolumetricmasstransfercoefficient, (m3·min-1),relatedtothesurfaceareaoftheves selandtherecirculatingflowrateofmoltensteelQL anddeterminedbytheexpressionofKYamaguchiet al<6>;Wismassofmoltensteelintheladle. 1.3Boundaryconditions Atthewalls,symmetricplaneandfreesurface, thevelocitiesandturbulentpropertiesweresetin standardmannerdescribedelsewhere<10>,andthe normalgradientofcarbonconcentrationwassetto zero. 1.4Numericalsolutionprocedure Fornumericalsolution,thedifferenc
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