88-paper-Discrete Particle Simulation Applied to B

1DiscreteParticleSimulationAppliedtoBlastFurnaceModellingA.B.Yu1),Z.Y.Zhou1),P.Zulli2)1).CenterforSimulationandModellingofParticulateSystemsandSchoolofMaterialsScienceandEngineering,UniversityofNewSouthWales,Sydney,NSW2052,Australia2).BluescopeSteelResearch,P.O.Box202,PortKembla,NSW2505,AustraliaAbstract:Thepaperpresentsabriefreviewoftherecentstudiesofparticleandparticle-fluidflowinanironmakingblastfurnace(BF)bymeansofdiscreteparticlesimulationcoupledwiththeconventionalcomputationalfluiddynamics.Thekeyfeaturesofthismethodaredescribedfirst.ThentheresultsarediscussedwithreferencetofourresearchareasinBFmodelling:burdendistributionatthetop,gas-solidflowintheshaft,gas-solidflowintheraceway,andsolidflowinthehearth.ItisshownthatthisapproachdoescapturethemainfeaturesofthecomplexBFflowandisaneffectivewaytogenerateparticlescaleinformationforbetterfundamentalunderstanding.Keywords:discreteparticlesimulation,blastfurnace,solidflow,particle-fluidflow1INTRODUCTIONBlastfurnace(BF)ironmakingisanimportanttechnologybywhichironisefficientlyreducedfromiron-bearingparticles.Thisisaverycomplicatedchemicalprocessinwhichthelayeredcokeandoreparticlesarechargedfrombellorbell-lesstop,thendescendalongtheBFshaftduetogravity.Duringthedescent,oreisreduced,becomesliquid(slagandiron)inthecohesivezoneandthenflowsintothehearth.Thecokeispartiallygasifiedbeforeflowingintotheraceway,whereitcombustswithhotblast(naturally-humidified,oxygen-enrichedair)toformreducinggasandheat.Thesereducinggasesrisethroughtheparticlebedandescapefromthetop.Therefore,amodernBFisahightemperaturereactorinvolvingcomplexgas-liquid-powder-solidfour-fluidflow.Understandingandmodellingthiscomplexmulti-phaseflowsystemhasbeenafocusofresearchinthepastdecades(see[1,2]forexample).Ofparticularinteresthereistheflowofsolids,whichiscloselyrelatedtothepermeabilitycontroland,toalargedegree,governstheflowofotherphases.Physicalmodellinghasbeenusedforyears(see[3-5]forexample).Recentresearcheffortsaremainlymadeonmathematicalmodellingwhichcanbegenerallyclassifiedintotwocategories:thecontinuumapproachatamacroscopiclevelandthediscreteapproachatamicroscopiclevel[6].Thecontinuumapproach,basedonlocalaverageprinciples,ispreferredinprocessmodellingandappliedresearch.However,itseffectiveuseheavilydependsonconstitutiveorclosurerelations.Indeed,variousempiricalorarbitrarytreatmentshavetobeemployedtodescribethesolidflowinaBF[7-9].Thediscreteapproachcanovercomethisproblemproducinginformationthatcanleadtobetterunderstandingofthefundamentalsinvolved.IthasbeenheavilyusedinrecentstudiesofvariousflowphenomenainaBFbydifferentresearchgroups.Thispaperreviewsbrieflyourworkinthisarea[10-19].2MODELDESCRIPTIONAparticlecanhavetwotypesofmotion:translationalandrotational,determinedbyNewton’ssecondlawofmotion.Duringitsmovement,theparticlemaycollidewithitsneighborparticlesorwallatthecontactpointsandinteractwiththesurroundingfluid,throughwhichthemomentumandenergyareexchanged.Atanytimet,theequationsgoverningthetranslationalandrotationalmotionsofparticleiare∑=+++=ikjd,ijc,ijipf,iiimdtdm1)ff(gf/v(1)2Figure1(a)PaulWurthtestrig;(b)asnapshotofparticleflowfrombell-lesstop;(c)comparisonofthemeasuredandsimulatedtrajectoriesofcokeparticles.(a)(b)(c)∑=+=ikjijrijciidtdI1,,)(/TTω(2)wheremi,Ii,viandωiare,respectively,themass,momentofinertia,translationalandrotationalvelocitiesofparticlei.Theforcesinvolvedare:theparticle-fluidinteractionforce,fpf,i,whichismainlythedragforceforgas-solidflowsystems,gravitationalforce,mig,andinterparticleforcesbetweenparticlesiandj.ThetorquesincludetheinterparticletorqueTc,ijandrollingfrictiontorqueTr,ij.Formultipleinteractions,theinterparticleforcesandtorquesaresummedforkiparticlesinteractingwithparticlei.Equationstocalculatetheinteractionforcesbetweenparticlesandbetweenparticleandfluidcanbefoundelsewhere[6,10,11].ThecontinuumfluidfieldiscalculatedfromthecontinuityandtheNavier-Stokesequationsbasedonthelocalmeanvariablesoveracomputationalcell,whicharegivenby0)(/=⋅∇+∂∂guggtεε(3)g)τ(/)f()uu(/)u(,ggkiipfgggggggm∆Vptcεεερερ+⋅∇+−−∇=⋅∇+∂∂∑=1(4)whereuandpare,respectively,thefluidvelocityandpressure;τ,εand∆Varethefluidviscousstresstensor,porosityandvolumeofacomputationalcell.Themodellingofthesolidflowbydiscreteparticlesimulation(DPS)isattheindividualparticlelevel,whilstthefluidflowbycomputationalfluiddynamics(CFD)isatthecomputationalcelllevel.Theircouplingisnumericallyachievedasfollows.Ateachtimestep,DPSwillgiveinformation,suchasthepositionsandvelocitiesofindividualparticles,fortheevaluationofporosityandfluiddragforceinacomputationalcell.CFDwillthenusethesedatatodeterminethegasflowfieldwhichthenyieldsthefluiddragforcesactingonindividualparticles.IncorporationoftheresultingforcesintoDPSwillproduceinformationaboutthemotionofindividualparticlesforthenexttimestep.Ifthemotionoffluid(mainlygasinthiswork)orsolidphasecanbeignored,theaboveDPS-CFDapproachwillbereducedtotheDPSorCFDapproach.3RESULTSANDDISCUSSION3.1Bell-lessandbelltypeatthetopDPSmodellinghasbeenusedtostudythesolidflowinaBFtop.Figure1(a)showsabell-lessPaulW