II pressure relief system flow-P90.pdf

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1、PreviousPageweatherprotectionanddrainsasneededtailpipesystemventlinevalvesafetyheadassemblyinletpiping(a).RuptureDiskSystem(b).PressureReliefValveSystemFIGUREII-5.Typicalpressurereliefsystemconfigurations.tationalconvenience,theflashcanbecarriedoutatconstantenthal

2、py(thatispotentialandkineticenergytermsareneglected).Vapor-liquidequilibriummodelsandflashroutinesareoutlinedinAppendixU-B.3-6.ApplicationtoPressureReliefSystemElementsTheapplicationoftheabovetechnologybasetoparticulartypesofreliefdevicesandinstallationsisoutlined

3、inthefollowingparagraphs.Elementsconsideredarereclosingvalve-typedevices,rupturedisks,andtheassociatedpiping.ExampleassembliesareshownschematicallyonFiguresII-5aandb.3-6-1.PressureReliefValveSystemsSeeFigureII-5bforatypicalpressurereliefvalveinstallation.3-6-1-1.V

4、alveCapacity.Pressurereliefvalvesrequiresomeelevationofpressureabovethesetpressure(overpressure)toreachthefull-opencapacity.Certifiedvalves[6]areopenwithin10%ofthesetpressureforserviceunderSectionVIIIofReference[4].ThecorrespondingoverpressureforSectionIvalves[4]i

5、s3%.Certifiedflowsare90%oftheobservedflowwhenoperatingat10%(SectionVIII)or3%(SectionI)overpressure.springforcebodyoutletforcefromflowareapressureinbodyprimarysecondaryflowareaannularareaFIGUREII-6.Flowpaththroughtypicalpressurereliefvalve.Associatedpipingshouldbes

6、izedatthebestestimatecapacityofthevalve,ratherthanatthecertifiedcapacity.ThecomplexitiesoftheflowpaththroughatypicalpressurereliefvalveareshownonFigureII-6.Uncertaintyremainsastotheproperflowmodeltouseforflashingflowinthisgeometry.AccordingtothecriteriaofSection3-

7、2-3-2,equilibrium-flowmodelswouldbeexpectedtoapplyfornozzleslongerthan100mm.Thenozzlelengthinstandardpressurereliefvalveorificesisusuallyslightlylongerthanthislimit.However,thereisnoassur-ancethattheorificeisalwaystheflow-controllingsection.ManyDIERStestsshowflows

8、inexcessofpredictedequilibriumvalues[12,13,31,32],Itcannotbedeterminedwhetherthishighflowistheresultofnonequilibriumbehaviorortheresultofsomeslightsubco