MembraneFiltrationHndbk

MembraneFiltrationHandbookPracticalTipsandHintsbyJørgenWagner,B.Sc.Chem.EngSecondEdition,revision2June2000PublishedbyOsmonics,Inc3IntroductionThisisthesecondeditionoftheMembraneFiltrationHandbook.InanefforttoimprovetheHandbook,ithasbeenenlargedtoincludethedescriptionofpretreatment,automaticcontrolsandpumps.ThisHandbookistheproductofmanyyearsofexperienceinthefieldofmembranefiltration,anditisintendedtobeamixedbagofinformation.TheHandbook’sgoalistoprovideinformationaboutmanycommonproblems,andhelpanswerquestionsthatnewcomerstomembranefiltrationoftenface.Thebookalsoprovidesinformationhelpfultotheengineerwhodesignsandbuildsmembraneequipment,orworkswithexistingplants.StudentsmayalsofindtheHandbookhelpfulinunderstandingbasicmembraneplantdesignandoperation.Theinformationisbasedonpracticalexperienceratherthantheoreticalcalculationsandspeculations.Consequently,itisnotatraditionaltextbookcommonlyfoundattechnicaluniversities.AlthoughtherearevirtuallynomathematicalcalculationsintheHandbook,itwillstillproveusefultobothindustryanduniversitiesbecauseitcontainsotherpiecesofinformationthatareobvioustothe“oldhand”inmembranefiltrationbutwhich,tothebestofmyknowledge,haveneverbeenpresentedinaprintedformat.ThisHandbookisnotintendedforusebytheabsolutenovicetomembranetechnology.Althoughitdoesdescribeandexplainmembranesandmembranetechnologyinquiteabitofdetail,somefundamentalknowledgeofmembranesandchemistryisassumed.Mostoftheinformationisbasedonexperiencewithflatsheetmembranes(theDDSplate-and-framesystem)andspiralwoundelements(DESAL).Spiralwoundelementsaccountforthevastmajorityofmembraneareasoldworldwide,whilethemarketshareoffibersystems,ceramicsystemsandtubularsystemsisrelativelysmall.Althoughtheyhavetheirplaceinthemembraneworld,thechancesoffiber,ceramicandtubularsystemsbecomingmajorplayersbeforetheyear2000arerelativelysmall.Therefore,littleinformationregardingthesesystemshasbeenincludedintheHandbook.Membranesarebeingputtohardworktoday,buttheyarerelativelyunknowntoconsumerssincetheyareusuallyhiddenwithinindustrialprocesses.Someindustriesdependonmembranesforthemanufacturingofbasicproducts,othersneedmembranestosolvecomplexseparationprocesses,whileothersagainusemembranestomeetenvironmentalstandards.Membranesaresomewhatlikecomputers:fewunderstandthem,onlysomelikethem,butwearealldependentuponthem.Evenifwedonotlikethem,weknowthattheyarenecessarytomakelifeeasierandmorecomfortable.Ithastaken35yearstodevelopsufficientlygoodandinexpensivemembranestotreatavarietyofliquids,includingwastewater.However,thereisstillalongwaytogobeforeitisgenerallyknownhowtoengineerandoperatemembraneplants.ItismyhopethatthisHandbookwillhelpavoidsomemistakeswhichcertainlyhavebeenmadebefore.IwanttospeciallythankBjarneNicolaisenforverythoroughtechnicalandlinguisticadvice,andmywifeforbeinganexcellentpartnerdiscussingtechnicaldetails.SeveralotherindividualshavecontributedtotheHandbookinvariousways,too.JorgenWagner5Pressure,averageAveragepressure,(Pfeed+Pconc)/2.Pressure,averageNDPTheaverageNetDrivingPressureisthepressureavailabletodriveliquidthroughamembrane.(Pfeed+Pconc)/2-Pperm-((conc-(perm.)Pressure,dropThelossofpressurebetweeninletandoutletofamembranesystem,ahousing(pressurevessel)oramembraneelement.Pressure,feedEitherthepressurefromthefeedpump(standardmeaning),orthepressureattheinlettoamembranestageinarecirculationsystem.Pressure,osmoticAtheoreticalvaluewhichhighlyimpactsreality.TheosmoticpressureisafunctionofthecontentofsaltandotherlowMWsolutes.HighMWsolutescantheoreticallynotcontributetoosmoticpressure,butinrealityaphenomenaisexperiencedwhichresemblesosmoticpressure.TheosmoticpressureofelectrolytesandlowMWsolutescanbecalculatedwithsomeaccuracy,buttheosmoticpressureofhighMWsolutescanonlybedeterminedbyexperimentation.TheosmoticpressureisusuallywrittenasPIorA,whereA=i*n*R*TPressure,unitPsi(poundspersquareinch):14.5PSI=1bar.Bar:1bar=0.1mPa=100kPaPS(PSO)Poly-sulfone(eitherpoly-ether-sulfoneorpoly-aryl-ether-sulfone).PVDFPoly-vinylidene-di-fluoride.RetentateAnothertermforconcentrate.SDSIindexStiffandDavissaturationindex.ItissimilartotheLangelierindex,butcanbeusedinhighsalinitywater.SeeLangelierindex.TFC,TFMAcronymsforthinfilmcompositemembranes.THMTrihalogenatedMethaneprecursors.Thesearechemicalcompoundsofunspecifiedchemicalnaturewhichresultfromthereactionofhalogenslikechlorinewithorganicsubstanceslikehumicacid.Theyareconsideredacarcinogen.TMPTransmembranepressure.SeePressure,average.TSTDSTotalsolids;thetotalofdissolvedandsuspendedsolids.Totaldissolvedsolids.Bothvaluesaremostlyexpressedasmg/l,ppmor%.6TheFourMembraneProcessesReverseOsmosis(RO)isthetightestpossiblemembraneprocessinliquid/liquidseparation.Waterisinprincipletheonlymaterialpassingthroughthemembrane;essentiallyalldissolvedandsuspendedmaterialisrejected.ThemoreopentypesofROmembranesaresometimesconfusedwithnanofiltration(NF).TrueNFrejectsonlyionswithmorethanonenegativecharge,suchassulfateorphosphate,whilepassingsinglechargedions.NFalsorejectsuncharged,dissolvedmaterialsandpositivelychargedionsaccordingtothesizean