布袋除尘英文文献pdf.docx

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布袋除尘英文文献pdf

布袋除尘英文文献.pdf

LT

94M.Saleem,G.Krammer/PowderTechnology173（2007）93–106

directionblowthecakeoffthebagsurface,whichiscollectedinthedusthopperlocatedatthebottomofthefilterhousing.Assoonasthecakeisremoved,thePisreducedandfiltrationcontinuesforanotherfiltrationcycle.

TheJPcleaningprocessmaybedividedintothreephases:

（a）accelerationofthefiltermediumtowardsoutside,（b）decelerationofthefiltermediumonceitreachesacircularshapeand（c）accelerationofthefiltermediuminwardstowardsthecageaftercompletionofthecleaningcycleandafterthedecayofthecleaningpulseinthebaginterior.Thedustcakeonthesurfaceofthebagisbrokenbytheinflationofthefilterelement.Theaccelerationfromaconcavetoaconvexshapewithsuddenimpactmechanicallyejectsthedusttogetherwithparticlesthathavepenetratedthefelt.Theflowingairfollowingthepressurepulseflushesoutthedustassistingcakeremoval[1].Thereverseflow,inadditiontoacceleration,isreportednecessaryforcakedetachmentin[2].Thecakeremovalisimprovedathighercakeloadinaccelerationtests[3].Inpracticeafractionoffiltrationareaisexposedtojetpulsesandpossiblyonlyafractionofthecakeisremovedfromthejetpulsedarea[4]resultinginanon-uniformcakedistributioncalledpatchycleaning.Non-uniformfiltercakedistributiononthebagsurfaceisanaturaloutcomeofpatchycleaningandpossessesmanyconsequenceslikedifferentresidencetimesofthecakesonthebagsurface[5],distributionofgasvelocitiesacrossthefiltersurfaceasaresultofthecakeheightdistribution[6],differentcakecharacteristicsdependingondifferentformationconditions[7],andasaconsequencemorefrequentbagcleaningisrequired.

VarioustheoreticalandexperimentalstudiesarereportedinliteraturetoprovideunderstandingofunderlyingprocessofcakeformationanddetachmentwhichaffecttheP.ThePisrelatedtotheoperatingparametersusingregressionanalysis[1]

inoneapproach.Mostly,the

Pwithinthefiltermedia（Pm）

andthePwithinthecake（

Pc）,aretakenadditivebasedon

theassumptionthattheresistancescontributedbythefiltermediaandthecakeactinseriesasreportedin[1,5]forexample.Filtrationprocessissimulatedusingonedimensionalmodelin[8]fromitsstart-up,whereauniformcakeisassumedtoformonacleanfiltermedium.Attheend,JPremovesapartofthecakeleavingathindustlayerbehindonthefiltersurface.Thesecondcyclestartswithtwomodelareas,onewiththecakeandoneregeneratedandcontainingathindustlayer.ADarcyequationrepresentseachmodelareabutpressuredropisthesameacrossbothareas.Thefactthatonlyafractionoftotalareamaybesubjectedtojetpulsesisnotconsideredby[8].Therefore,thecharacteristicpropertyofcakedetachment,afractionofcakeofcertainthicknessremovedonjetpulsing,isnotdetermined.Themodelpresentedin[9]dealswiththecaseoffiltrationatconstantpressuredrop.Italsodoesnotdistinguishbetweenthefractionsofthefilterareathatissubjectedtojetpulses.Amodelconsideringthefractionalareasubjectedtojetpulsesisusedforpredictingoperatingpointsfromspecificcakedetachmentexperiments[10].Themodelparametersareestimatedfromthelinearpartofthepressuredropcurveignoringthesteepriseofthepressuredropcurve.Thecakeformationonnon-uniformlycoveredfiltersmay

influencethecakedetachmentduetohighlynonuniformgasvelocities,thoughtheoverallgasflowremainsconstant.Thereforeignoringthecakeformationmayleadtoerroneousresults.Othermodelsdescribingfiltercakeadditionallyconsidercohesivestressesbetweensinglepatchesoffiltercakes.However,thethreedimensionalstructuralinformationofthefiltercakeneededbythesesophisticatedapproachesisnoteasilyavailable[11,12].Thesizeandthicknessofsinglepatchinconjunctionwiththelengthofboundarytotheneighbouringpatchesaredecisiveforplausibilityoftheassumptionofrectilinear,parallelgasflow.Thequestionwhethertheactualsizeofpatchesobservedinfilterexperimentsallowstheassumptionofrectilinearflowisnotyetsettled,althoughthisassumptionisoftenusedforthereasonsofsimplicity.Transientgrowthofthefiltercakeissimulatedusingtwo-dimensionalmodelin[13].Resultsrevealedthatthepressuredropafteracleaningpulsewithconstantcakemassremovedishigherorlowerdependingonwhethertheremovedpatchesarelargerorsmallerrespectively.Inthefringezonebetweenthickandthincakes,gasenterssidewaysincreasingthepermeabilityofthefiltercake.However,discrepanciesinthepressuredropcurvesaresmallandrestrictedtothefirst10%ofthefiltercycleonly.TheDarcy'slawwithconsta