操作温度对褶皱型不锈钢编织型过滤器阻力特性的影响_英文_ 6页

SEPARATIONSCIENCEANDENGINEERINGChineseJournalofChemicalEngineering,17(6)949—954(2009)EffectofWorkingTemperatureontheResistanceCharacteristicofa*PleatedStainlessSteelWovenFilterLIJuan(李娟)**,SHIYumei(石玉美)andWANGRongshun(汪荣顺)InstituteofRefrigerationandCryogenics,ShanghaiJiaoTongUniversity,Shanghai200240,ChinaAbstractEffectofworkingtemperatureontheresistancecharacteristicincludingthepermeabilitycoefficientandthepressuredropevolutionofapleatedstainlesssteelwovenfilterwithanominalporesizeof0.5µmhasbeenstudied.ThepermeabilitycoefficientwasobtainedbasedonthepressuredropdataandtheDarcy’slaw.Inthreefil-trationexperiments,purecarbondioxideat283K,nitrogenat85Kandliquidheliumat18Kareadopted,respec-tively.Itisfoundthatthepermeabilitycoefficientdecreasesattheworkingtemperatureduetothecoldshrinkofthefilterelementatcryogenictemperature.Then,twokindsoffeedslurries,mixtureofliquidnitrogenandsolidcarbondioxideat85K,andmixtureofliquidheliumandsolidnitrogenat18K,flowintothefiltercell.Thesolidparticlesaredepositedonthefiltersurfacetoformafiltercakeandthepurifiedliquidflowsthroughthefilter.Itisfoundthatthepressuredropevolutionshowsthesametrendonthesetwotemperatures,whichcanbedividedintothreestageswithhighfiltrationefficiency,indicatingthefeasibilityofthefilterforcryogenicapplication.However,variantcakeresistancesareobtained,whichisresultedfromthedifferentinteractionsbetweensolidparticlesinthefeedslurryatlowerworkingtemperature.Keywordsresistancecharacteristic,permeabilitycoefficient,pressuredrop,wovenfilter,workingtemperature1INTRODUCTIONcoefficient,whichisaninherentpropertyofthefiltermedium,andmainlydependsonthephysicalstructureofthefiltersuchasporosity,poresizeandporenum-Pleatedstainlesssteelwovenfilterwithfineporebersperfiltrationarea[13].However,someexternalsizeofseveralmicronsisoneofthemostpreferred,factorsincludingworkingtemperaturemayhavesomeeffectiveandeconomicmediaforsolid-liquidsepara-impactonthecoefficient[14].tion.Pleatedstructure,comparedwithnormalflatInthispaper,aseriesofexperimentsareconductedconfiguration,isbeneficialtomoderatetheincreasingtoinvestigatetheeffectofworkingtemperatureontheratioofpressuredropduetoitslargerfiltrationareapermeabilitycoefficientandpressuredropevolution[1].Stainlesssteelownsfavorableductilitysothatitofapleatedstainlesssteelwovenfilterwithanem-doesnoteasilyfractureundermechanicalandthermalphasisontheconditionsatcryogenictemperatures.shocks[2].Wovenmedium,knownas“surface”and“cleanable”,ownsmoderateporosity,permeability,pressuredropandseparationefficiencyincomparison2EXPERIMENTALtofleeceandgranularones[3].Asaresultoftheadvantagesabove,thepleatedstainlesssteelwovenfiltermediumcanbereusedTheexperimentalsetup(Fig.1)iscomposedofmanytimeswithconsistentfiltrationperformance.thefollowingsixparts:(1)liquiddeliverysystem;(2)Comparedwithsinteredglassfrit,compactedmeansgasfillingsystem;(3)amixingchamber,inwhichgasofironoxideparticles,nylonmeshandsinteredce-issolidifiedintosolidparticlesattheliquidtempera-ramic[4-7]usedforfiltrationproceduresatcryogenicture,andmixeswiththeliquidthoroughlyanduni-temperature,stainlesssteelisamuchmoreexcellentformlytoformthefeedslurry;(4)filtercellincludingmaterialduetoitsfavorableresistancetopreventbrit-thefilterelementandahousing;(5)cryogenicvacuumtlefracture.Manystudieshavebeendedicatedtothesystemandsafetysystemincludingavacuumgauge,amechanismsandapplicationsofthisfiltermediuminburstdiscandasafetyvalve,whichcanmonitortheindustrialprocessesatroomandespeciallyhightem-vacuumstateintheinterlayeroftheexperimentalde-perature[8-10],butvirtuallyfewliteraturesareavail-war,decreasetheevaporationofcryogenicliquidandableconcerningtheirbehaviorsatlowtemperature[11].guaranteethesafetyofthesystem;(6)measuringsys-Thefiltrationprocessofthepleatedstainlesstemincludingtwogasflowrategauges(typeofsteelwovenfiltermediumbelongstothecakefiltra-M-100SLPM-D/5M,accuracyof1%),twopressuretion.Cakefiltrationisfrequentlyusedfortheremovalgauges(typeofMPM4730,accuracyof0.1%),atem-ofparticulatesolidsfromfluidsinindustrialprocesses.peraturedevice(typeofAMACsilicondiode,accu-Thebuild-upofafiltercakeisusuallyaccompaniedracyof0.003%)tomonitorthefluidstate,andagasbyanincreasedpressuredropoverthefiltermediumconcentrationdetector(typeofF2000-CO2,accuracy[12].Permeabilityischaracterizedbythefiltrationof2%).Received2008-09-05,accepted2009-04-10.*SupportedbytheShanghaiCommitteeofScienceandTechnology,China(03DZ14014).**Towhomcorrespondenceshouldbeaddressed.E-mail:lijuan_54@sjtu.edu.cn 950Chin.J.Chem.Eng.,Vol.17,No.6,December2009Figure1SchematicdepictingtheexperimentalsetupFigure2Structuralsketchofthepleated316Lwovenfilter(Unit:mm)1—cap;2—boss;3—perforatedtube;4—filterelementPressures,temperatureandgasconcentrationareTable1Specificationsofthepleatedstainlesssteelregulated,monitoredandrecordedcontinuouslythrough-wovenfilterouttheexperiments.SincetheflowrategaugescanSpecificationsParametersonlybeusedattemperatureoftheenteringfluidhigherthan10°C,anairheatexchangerisadoptedtodesigncodeASMECodeVIIIDiv.1vaporizethefilteredliquidmedium.Whatneedstobedegreeoffiltration8-10µm100%,0.5µmnominalexplainedisthat,forpurecryogenicliquid,theread-2－2filtrationsurface/m6.4×10ingsoftheflowrategaugeintheoutletisexactlythegasstateflowrateoftheliquid,andcanbetrans-teststobecarriedoutbubblepointtest,glassbeadstestformedtobetheliquidflowratebasedonthedensitymaximumallowablepressure0.1ofthetwophases.However,asforthepurificationloss/MPaexperiments,sincethevolumeratioofthefillinggasandtheliquidisverysmall,andthefilteristestedtoTable2Fourpartsofthepleatedstainlesssteelwovenfilterbeahighefficientone,thenthereadingsoftheoutletflowrategaugearedeemedasthatofthefillingliquid,PartDescriptionDimensions/mmMaterialandtheresultederrorcanbeignored.Theparticlesize1capφ22/19×3AISI316LofCO2andN2solidsareassumedapproximatelytobe2bossφ36.6/21.5×3.6×42AISI316Lintherangeof0.05-2mmbasedontherelatedtheo-3perforatedtubeφ22×208×1AISI316Lreticalandcomputationalstudy[15-18].Thefilterisapleatedstainlesssteelwovenmedium4filterelementφ35×214AISI316L Chin.J.Chem.Eng.,Vol.17,No.6,December2009951withanouterdiameterof35mmandalengthof214Duringfiltration,solidsaredepositedonthefiltermm,andismadeupoftwolayersofmeshsinteredsurfaceandpurefiltrateflowsdownstream.Pressuretogethertoformanintegratedporouselement.Thedropevolutionsaremonitoredandrecorded,andthemeshisofveryfinegaugeanddeterminesthefiltra-filtrationefficienciesarecalculatedasfollows:tionefficiency.ItisoverlaidwithacoarsesupportNdownmeshlayerwithbiggerporediameterof3mm.TheE=−1(6)structuresketchofthefilterisshowninFig.2.Speci-NupficationandfourpartsofthefilteraresummarizedinwhereEisthefiltrationefficiency,NdownandNupareTables1and2,respectively.thevolumeratiosofsolidinthefiltrateandinthefeedTwogroupsofexperimentsarecarriedout:slurry,respectively.(1)Threekindsofpurefluidsincludingcarbondioxideat283K,nitrogenat85Kandheliumat18K,flowthroughthefilter,tomeasurethepermeability3RESULTSANDDISCUSSIONcoefficientofthefilterandexaminetheinfluenceof3.1Firstgroupexperiments:permeabilitycoeffi-workingtemperature.cientmeasurementAsshowninFig.1,pressuregaugesarelocatedattheflowingpipelines,notexactlyattheinletandoutletofthefiltercell.Therefore,BernoulliequationTable3showsthreedifferentconditionsinclud-isadoptedtocalculatetheexactpressuredropgener-ingtheworkingtemperatureandcorrespondingfluidatedbythefilter[19]:viscosity,flowrate,pressuredrop,andthecalculated22permeabilitycoefficientsbasedonEqs.(1)-(5).pV11pV22Itisfoundthat,ingeneral,thepermeabilitycoef-z12w++=+++zh(1)rg22rgficientdecreaseswiththeworkingtemperature.Therelationbetweenpermeabilityandworkingtempera-hhhpwfjf=++∆ilter(2)tureisnotlinear,andthepermeabilityatroomtem-peratureistwotothreeordersofmagnitudehigher32µVlh=(3)thanthatatcryogenicconditions.Thiscanbeex-f2ρgdplainedbythecoldshrink[20]ofthewovenfilterelementatlowtemperature,whichchangestheflow2Vpathstructureandresultsinthereductionofthepo-hj=×ξ(4)2grosityandthepermeability.Thisresultiscoincidentwiththatintheliterature[8],inwhichitwasindicatedwherezisthehorizontalheight,pistheabsolutethatthewovenmetalbagshowedadistinctdepend-pressure,risthegravityofunitfluidmass,Vistheenceoftemperature,andfiltrationatelevatedtem-fluidvelocity,gisthegravityacceleration,hwistheperaturecausedpenetrationofacertainamountoftotalresistanceloss,hfistheon-wayresistance,hjisdustintothefilterdepthduetothethermalexpansionthelocalresistance,∆pfilteristhepressurelossgener-ofthefiltermedium.atedbythefiltercore,µisthefluidviscosity,listheTheuncertaintyinthissetofexperimentscomespathlength,ρisthefluiddensity,disthepipeinnerfromthegaugesofthetemperature,thegasflowratediameter,andζisthelocalresistancecoefficient.andthepressure.AccordingtothetypeBuncertaintyPermeabilitycoefficientiscalculatedbaseontheDarcy’slaw,whichisappliedforlaminarflow:evaluationandtherectangulardistributioninwhichµLtheconfidencecoefficientis3,theuncertaintyfor∆=×pQfilter×(5)eachgaugebasedonthegaugeaccuracyisequaltoKA0.002%,0.577%and0.058%,respectively.Then,thewhereKisthepermeabilitycoefficient,Qisthefluidoveralluncertaintyiscalculatedtobe0.58%.volumeflow,Listhefiltrationdepth,Aisthefiltrationarea.3.2Secondgroupexperiments:purificationof(2)Twokindsoffeedslurries,mixtureofnitrogencryogenicliquidsandcarbondioxideat85K,andmixtureofheliumandnitrogenat18K,flowintothefiltercell,respectively.FlowrateoftwocryogenicliquidsandvolumeratioofThepurificationisconductedunderaconstantsolidsaremaintainedconstantinthesetwomixtures.fluidvelocity,i.e.,theflowratesoffillinggasandTable3Threeexperimentalconditions3－12FluidWorkingtemperature/KViscosity/Pa·sFlowrate/m·sPressuredrop/PaPermeability/m－6－5－12carbondioxide28314.15×108.33×101001.33×10－6－6－14nitrogen85121.11×102.17×1014001.47×10－6－4－15helium183.369×104.97×10255003.09×10 952Chin.J.Chem.Eng.,Vol.17,No.6,December2009liquidaremaintainedstableduringafiltrationprocess.beclearlyidentified:Theoretically,thetotalpressuredrop∆pmcomprises(1)Duringthefirststage,thepressuredropin-twopartsasexpressedinEq.(7)[21].∆pmisresultedcreasesveryslowlyandcanevenbedeemedasstable.fromthefiltermedium,whichcanbecalculatedbytheSolidparticlesaremostlycollectedontheexteriorofDarcy’slaw(5)[22]andisaffectedbythepermeabil-thewovenfilterandasmallamountmaydepositinityconstant.∆pcisgeneratedbytheevenlythickenedthebottomspaceofthefilterhousing.Nocompletefiltercake,whichisexpressedinEq.(8).Asforcon-filtercakeisformed.Inthiscase,thepressuredropisstant-velocityfiltrationwithanincompressiblefilteronlymainlygeneratedbythefilterelementandisaf-cake,thepressuredropwillincreaseduetothesecondfectedbythepermeabilityconstant.Thisstagelastspartwhichwillincreasethetotalresistance.about35min.(2)Pressuredropshowsasharpriseatabout40∆=∆+∆pppmc(7)min,andthentheintermediatestagebegins.Inthisµcα2stage,theplotappearsalinearandstableincreasing∆=pQc2t(8)trend,whichisthesignificantcharacteristicofsurfaceAfiltrationasshowninEq.(9).Asforthefirstitemin3wherecisthesolidmassinunitcakevolume,kg·m;Eq.(9),thepressuredropgeneratedbythefilterre-－1αisthespecificcakeresistance,m·kg;Qisthefluidmainsunchangedunderastableflowrate.However,3－1flow,m·s;tisthefiltrationtime,s.Therefore,theasfortheseconditem,thepressuredropresultedfromtotalpressuredropcanbeexpressedasfollows:thefiltercakewillincreaseovertimeduetothecakeµLcµα2growth.Therefore,thecompletefiltercakeisformed∆=××+pQ××Qt(9)atthesharprisepointofabout40min,whichresultsKAA2inabreakontheplot.Thisstagelastsabout120min.Comparingthefirstandsecondstage,another3.2.1FeedslurrycomprisingliquidnitrogenandimportantconclusioncanbebroughtoutthatthecarbondioxidesolidspressuredropgeneratedbycakeismuchhigherthanFigures3and4depictdataforthepressuredropthatbythefilteritself.Thismeansthatforthiskindofandfiltrationefficiencyasafunctionoffiltrationtime－1pleatedstainlesssteelwovenfilter,ittakesthemainunderthenitrogenflowrateof20L·min(readingoffunctionoffiltrationandthefiltermediumonlyplaysthegasflowrategaugeintheoutletofthesystem)and－1aroleofsupportingafteracompletedcakeisformed.thecarbondioxideflowrateof2L·min,respectively.Thisisanothercharacteristicofsurfacefiltration.Thetemperatureismaintainedat85K.(3)Asecondsharpincreaseofpressuredropisobservedinthebeginningofthethirdstage.Thiscanprobablybeattributedtothehighpressuredifferenceexertedonthefiltercake,whichleadsthecaketobealittlecompressibletosomeextentandultimatelyraisesthespecificcakeresistance.Thisstageonlylastslessthan10minuntilthepressuredropreachesitsmaximumallowablevalueof100kPa.Thesethreestagesaredifferentfromthatinthedepthfiltration,asdepictedintheRef.[12],inwhichthefiltrationprocedureisdividedinto5stagesforsolidandliquidaerosolmixture.Firstly,thepressuredropincreasesslowlyduetothattheparticlesarede-Figure3Pressuredropevolutionpositedpreferentiallyonthosealreadypresentedonthefibrestoformaggregates.Then,thepressuredroprisessharply,whichisresultedfromtheliquidbridgesandfilmsdevelopedatthefibreintersections.Thethirdstageischaracterizedbytheformationofafiltercake.Then,asharpincreaseisobservedduetothehigherenergyneededfortheliquidtopercolatethroughthecakeandthefilter.Thelaststageisthedrainage.Thesedifferencesareresultedfromthedi-versestructureofthefiltermedium.FiltrationefficiencyiscalculatedaccordingtoEq.(6).ItcanbeobservedinFig.4thattheefficiencyinthewholepurificationprocedureishigherthan90%,Figure4Filtrationefficiencycurveindicatingthatthispleatedstainlesssteelwovenfilterisakindofhighefficientmediumforcryogenicap-ItisobservedinFig.3thatthepressuredropin-plication.However,efficiencyduringthefirststageiscreasesovertime,whichisconsistentwithclassiclowercomparedwiththatinthesecondandthirdfiltrationtheories.Moreover,threedifferentstagescanstages,whichfurtherapprovesthatthecompletecake Chin.J.Chem.Eng.,Vol.17,No.6,December2009953takesthefunctionofpurificationandseemstobeaffectsthepressuredropandfiltrationefficiency.moreefficient.3.2.2Feedslurrycomprisingliquidheliumandni-4CONCLUSIONStrogensolidsDuringthiswholepurificationprocess,thetem-Filtrationtestsareconductedwithapleatedperatureiscontrolledatabout18K.Tomaintainthisstainlesssteelwovenfiltertoresearchitspermeabilitylowtemperature,heliumflowrate(readingofthegasconstantandpressuredropevolutionatdifferentflowrategaugeintheoutletofthesystem)shouldbeworkingtemperature.Thefilterisapprovedtobea－1kepthigherthan100L·min.Figs.5and6depictpreferredmediumforcryogenicapplicationwiththedataforthepressuredropandfiltrationefficiencyasafiltrationefficiencyofhigherthan90%.functionoffiltrationtimeundertheheliumflowratePermeabilityconstantsaremeasuredbasedonthe－1of100L·minandthenitrogengasflowrateof10pressuredropdataandtheDarcy’slawat283K,85K－1L·min,respectively.and18K.Itisfoundthatthepermeabilityconstantsdecreasewithtemperatureduetothecoldshrinkofthewovenfilteratlowtemperature,whichchangestheflowpathstructureandresultsinthereductionofporosity.Purificationproceduresareexecutedat85Kand18K.Threedifferentstagescouldbeidentifiedforthesetwoproceduresandthepressuredropgeneratedbyfiltercakeismuchhigherthanthatbythefilterelementitself,whicharethetwosignificantcharac-teristicsofsurfacefiltration.Pressuredropevolutionsappearthesametrendsonthesetwotemperatures,indicatingthattheover-allwovenstructureofthefil-Figure5Pressuredropevolutionterremainsunchanged.However,theinteractionsbe-tweensolidparticlesmayappeardifferenttosomedegree,whichcanresultinavariantcakeproperty,andultimatelyaffectthefilterperformance.Thisneedsseriousattentionandfurtherinvestigation.REFERENCES1Ning,Z.,Zi,X.Y.,ZhangC.R.,Liu,J.H.,Kuang,C.J.,“Preliminarystudyonthecharacteristicsofmetalmeshfilterandthereversecleansingtechnology”,Chin.J.Mech.Eng.,39,123-127(2003)2Wang,R.Z.,Wang,R.S.,CryogenicEngineering,ShanghaiJiaoTongUniversityPress,Shanghai(2000).(inChinese)Figure6Filtrationefficiencycurve3Yin,F.J.,Fang,Y.C.,Chen,X.,Zhan,D.Q.,Cu,L.,Xiao,Z.X.,“Rigidcombinedsinteringmetalwiremeshmicro-porositymaterialandgassolidfilteringseparationtechnique”,Petro-Chem.Equip.ItisobservedinFigs.5and6thattheplotsofTechnol.,19(4),25-29(1998).(inChinese)pressuredropandfiltrationefficiencyappearthesame4Carl,W.S.,“Methodforisolatingnitrogentri-fluoridefromnitroustrendswiththoseinFigs.3and4,andtherearealsooxideandtetra-fluorohydrazine”,U.S.Pat.,3181305(1965).threestages.Theseresultsindicatethattheover-all5James,E.,“Heliumrefiningbysuperfluidity”,U.S.Pat.,3192730pleatedwovenstructureofthefilterelementremains(1965).unchangeduponthecryogenictemperatureof18K6John,S.,David,E.C.,Howard,D.B.,“Sterilizationofcryogenicliq-andapprovestobeafavorablemediumforcryogenicuidsbyultra-filtration”,U.S.Pat.,4759848(1988).application.7Richard,A.S.,“ApparatusandmethodforproducingandinjectingThefiltrationprocedurelastsamuchshortertime,sterilecryogenicliquids”,U.S.Pat.,5749232(1998).about55min,andthetotalpressuredropincreases8Wolfgang,P.,“Hightemperaturefiltrationintheprocessindustry”,Filtr.Separat.,6,461-464(1998).morerapidlycomparedwiththelastliquidnitrogen9Wu,X.F.,Song,Y.Q.,Shen,L.H.,“Studyofgascleaningwithasin-andcarbondioxidesolidsfiltration.Therearemainlyteredmetalmeshfilter”,BoilerTechnol.,36(2),9-12(2005).(intworeasons.OneisthattheliquidflowrateandsolidChinese)massare10timeshigher,whichinducesahigherpres-10Normanda,L.F.,Jose,A.S.G.,Murilo,D.M.I.,Jose,R.C.,“Devel-suredropgeneratedbythefilterelementandafastopmentofadouble-layerceramicfilterforaerosolfiltrationatgrowthvelocityofthefiltercake.Theotheristhatthehigh-temperatures:Thefiltercollectionefficiency”,J.Hazard.Ma-interactionsbetweensolidparticlesmaybedifferentter.,B136,747-756(2006).tosomedegreeatamuchlowertemperature,which11Li,J.,Wang,R.S.,Shi,Y.M.,Gu,J.M.,“Studyonheliumpurificationresultsinavariantpropertyoffiltercake,andultimatelytechnologyappliedinAMScryogenicgroundequipmentsystem”, 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