安全阀计算手册[1]

ReliefValveSizing(SinglePhase)Calculation安全阀（单相泄放）计算手册Page1of12DESCRIPTIONThisdocumentbrieflydescribestheonephasereliefvalvecalculationspreadsheet,whichwillbethestandardreliefvalvecalculationtoolofLGN.ThecalculationmethodusedinthisspreadsheetisbasedoncalculationmethodsasgiveninAPI520part1(7thed.,2000,page41-56).Itisstronglyrecommendedtoreadthesepagesbeforeonestartswiththecalculations.AllcalculationsaredoneinSIunits.FORMULASGASANDVAPORFLOWFlowthroughthereliefvalveiscalledcriticalif112iikkibkPPwhere:PbMaximumbackpressurekPaaPUpstreamrelievingpressure.Thisisthesetpressureplustheallowableoverpressureplusatmosphericpressure.kPaakiIdealgasheatcapacityratioorCp,ig/Cv,ig-Cp,igIdealgasheatcapacityatconstantpressurekJ/kg.KCv,igIdealgasheatcapacityatconstantvolumekJ/kg.KAlthoughthisequationisonlyvalidforidealgases,itmaybeusedtocalculatecriticalpressureratio.kicanbeobtainedfromtable7inAPI520part1.Otherwise,thefollowingformulacanbeused:RMWcMWckigpigpi,,where:kiIdealgasheatcapacityratio-Cp,igIdealgasheatcapacityatconstantpressurekJ/kg.KMWMolecularweight-RGasconstantKJ/kmol.KIftheidealgasheatcapacityisnotknown,usetheactualheatcapacityinthesameequation.Errorsarefoundtobeonlysmall.ReliefValveSizing(SinglePhase)Calculation安全阀（单相泄放）计算手册Page2of12CriticalFlow(GasorVapor):Thefollowingequationcanbeusedtosizeapressurereliefdeviceingasorvaporservicethatoperatesatcriticalflowconditions.MWZTKKPKCWAcbd160,13where:ARequireddischargearea(forstandardtypesseetable1)mm2WRequiredmassflowthroughthedevice.kg/hrCCoefficientdeterminedfromanexpressionoftheratioofthespecificheats(k=Cp/Cv)ofthegasorvaporatinletrelievingconditions.Thiscanbeobtainedfromfigure32inAPI520orwiththefollowingformulae:1112520kkkkChrlbRlblbfmolemCpHeatcapacityatconstantpressureatrelievingconditionskJ/kg.KCvHeatcapacityatconstantvolumeatrelievingconditionskJ/kg.KKdEffectivecoefficientofdischarge.Forpreliminarysizing,usethefollowingvalues:Forreliefvalvewithorwithoutrupturedisk:0.975Forinstallationofrupturediskonly:0.62-PUpstreamrelievingpressure.Thisisthesetpressureplustheallowableoverpressureplusatmosphericpressure.kPaaKbCapacitycorrectionfactorduetobackpressure,tobeappliedforbalancedtypereliefvalvesonly;Forpreliminarysizing,thiscanbeestimatedfromfigure30inAPI520(seealsotable2).ForconventionalandpilotedoperatedvalvesKb=1-KcCombinationcorrectionfactorforinstallationswitharupturediskupstreamofthePSV.Kc=1.0whenarupturediskisnotinstalledKc=0.9whenarupturediskisinstalledupstreamthePSVanddoesnothaveapublishedvalue-TRelievingtemperatureatinletofthereliefvalve.KZCompressibilityfactoratinletrelievingconditions-MWMolecularweightKg/kmolTheaboveequationshouldalsotobeusedtosizebalancedpressurereliefvalvesinsubcriticalflow(inthiscaseKbshouldbeobtainedfromthemanufacturer).ReliefValveSizing(SinglePhase)Calculation安全阀（单相泄放）计算手册Page3of12SubcriticalFlow:RequiredreliefvalveareaforconventionalandpilotoperatedreliefvalvesbcdPPPMWTZKKFWA29.17where:ARequireddischargearea(forstandardtypesseetable1)mm2WRequiredmassflowthroughthedevice.kg/hrF2Coefficientofsubcriticalflow,seefigure34inAPI520orusethefollowingequation:rrrkkFkkk111122-kRatioofspecificheats,Cp/Cv-rRatioofbackpressuretoupstreamrelievingpressure,Pb/P-CpHeatcapacityatconstantkJ/kg.KCvHeatcapacityatconstantvolumekJ/kg.KKdEffectivecoefficientofdischarge.Forpreliminarysizing,usethefollowingvalues:Forreliefvalvewithorwithoutrupture:0.975Forinstallationofrupturediskonly:0.62-KcCombinationcorrectionfactorforinstallationswitharupturediskupstreamofthePSV.Kc=1.0whenarupturediskisnotinstalledKc=0.9whenarupturediskisinstalledupstreamthePSVanddoesnothaveapublishedvalue-ZCompressibilityfactoratinletrelievingconditions-TRelievingtemperatureatinletofthereliefvalveKMWMolecularweightKg/kmolPUpstreamrelievingpressure.Thisisthesetpressureplustheallowableoverpressureplusatmosphericpressure.kPaaPbMaximumbackpressurekPaaReliefValveSizing(SinglePhase)Calculation安全阀（单相泄放）计算手册Page4of12STEAMRELIEFSHNcbdKKKKKPWA4.190where:ARequireddischargearea(forstandardtypesseetable1)mm2WRequiredmassflowthroughthedevice.kg/hrPUpstreamrelievingpressure.Thisisthesetpressureplustheallowableoverpressureplusatmosphericpressure.kPaaKdEffectivecoefficientofdischarge.Forpreliminarysizing,usethefollowingvalues:Forreliefvalvewithorwithoutrupture:0.975Forinstallationofrupturediskonly:0.62-KbCapacitycorrectionfactorduetobackpressure.Thiscanbeobtainedfromthemanufacturer’sliteratureorestimatedfromfigure30ofAPI520(seealsotable2).Thebackpressurecorrectionfactorappliestobalancedbellowsvalvesonly.ForconventionalandpilotedoperatedvalvesKb=1-KcCombinationcorrectionfactorforinstallationswitharupturediskupstreamofthePSV.Kc=1.0whenarupturediskisnotinstalledKc=0.9whenarupturediskisinstalledupstreamthePSVanddoesnothaveapublishedvalue-KNCorrectionfactorforNapierequation.ForP10,339kPaaKN=1ForP10,339andP22,057kPaa106103324.0100002764.0PPKN-KSHSuperheatsteamcorrectionfactor.Thiscanbeobtainedfromtable3(equival