Rev2.1 ‐1‐ January9,2018

SimpleDewPointControl–HYSYSv10StepstosetupasimulationinHYSYSv10tomodelasimpledewpointcontrolsystemconsistingof:

Gaschiller Flashseparator Liquidstabilizerwithgasrecycle&compression Productgascompression Simplepropanerefrigerationloop

WhenthesimulationissetuptheoverallPFDshouldlooklikethefollowingfigure.

BasisAgasplantisprocessing100MMscfd(drybasis)toproduceaspecpipelinegasaswellasapipelinerawmixliquidproduct(YGrade).Thefollowingareknownconditionsforthefeedstockandspecificationsfortheproducts:

Thecompositionofthefeedgasisshowninthefollowingtable.

Thegasenterstheplantat400psia&120°F. Thegasisnearlysaturatedwithwaterattheinlet

conditions,48lbwaterperMMscfdrygas. Theproducedpipelinegasshouldhaveagrossheating

valuebetween905to1050Btu/scf1&ahydrocarbondewpointnohigherthan15°F.

Theproducedpipelinegasshouldbedeliveredtothepipelineat1000psiaandnohigherthan120°F.

Theproducedliquidsshallbeexportedviapipeline&stabilizedtohaveaTVP(truevaporpressure)@100°Fnogreaterthan103psia.

Component Mol%N2 0.357CO2 0.194C1 80.980C2 13.238C3 3.438i‐C4 0.431n‐C4 0.742i‐C5 0.199n‐C5 0.156n‐C6 0.163n‐C7 0.065n‐C8 0.026n‐C9 0.010

1Ifthegrossheatingvaluespeccannotbeachievedsetthechilledseparatortothelowestreasonabletemperaturewhenusingasimplepropanechillingloop,‐30°F.

Rev2.1 ‐2‐ January9,2018

Apropanerefrigerationloopwillbeusedtoprovidethechillingduty.Thecondenserwill

operateat120°F.Theminimumapproachtemperaturewithinthechillerwillbe10°F. Aircoolerswillbeusedtocoolgases&liquidsto120°F.

CreatenewsimulationfileStartHYSYS.OnewaytodothisfromWindows10istopressStart,godownthealphabeticallisttoAspenHYSYS,thenAspenHYSYSV10.WhentheprogramopenschoosetheNewbutton.DefinetheComponents&thePropertyModelsSpecifycomponents,fluidpropertypackages,&crudeoilassays

Thefirststepistoaddasetofpurechemicalspeciestorepresentthegas&waterphases.WithComponentListshighlightedclickontheAddbutton.Fromthelistofpurecomponentspick:H2O,Nitrogen,CO2,Methane,Ethane,Propane,i‐Butane,n‐Butane,i‐Pentane,n‐Pentane,n‐Hexane,n‐Heptane,n‐Octane,&n‐Nonane.

Rev2.1 ‐3‐ January9,2018

Thenextstepistopickafluidpropertypackage.FromtheFluidPackagesscreenclicktheAddbutton.ChoosethePeng‐RobinsonoptionandmakesureitisassociatedwithComponentList–1.

Itwouldbeagoodideatosavethisfile.ClicktheFiletab&selectSaveAs.Chooseanappropriatename&location.Setup&SolvetheFlowsheetGasChilling&SeparationWhenyouactivatetheSimulation&you’llseeablankflowsheet.Wewillwanttocreateadryfeedstream,addtheappropriateamountofwater,&attachthe“wet”feedtoanLNGExchanger.Theoutletwillbeattachedtoaflashseparator.

Rev2.1 ‐4‐ January9,2018

EnsurethatthemodelPaletteisvisible.Ifitisnot,presstheViewtab&clickModelPalette.Placethefollowingitemsontheflowsheet:

AMaterialStream,DryFeed AMaterialStream,FeedWater AMixer,Combine AnLNGExchanger,Chiller A3‐PhaseSeparator,DPCSeparator.

Double‐clickontheDryFeedstreamtoopenuptheentryformsforthisstream.Enterthetemperature&pressure.Enterthe100MMscfdflowrateintheMolarFlowbox.Notethatdependinguponyourdefaultsetofunitsthevaluesenteredmaychange.Thefigureontherightshowspressureinpsig(eventhoughwe’dreallylikepsia)&molarflowinlbmole/hr(thoughwe’dreallylikeMMscf/day).We’lllookathowtochangetheseaftersettingupthisinitialpartoftheprocess.Nowweneedtospecifythecomposition.SelectCompositionunderWorksheetintheleft‐handcolumn.ClicktheEdit…buttontobringupaformtoenterthecompositionofthisstream.EnterthevaluesfromthetableintheBasissectionasMoleFractions.Notethattheseadduptoapproximately100,not1.SelecttheNormalizebutton.ClickOK.Nowyoushouldseethattheformassociatedwiththestreamisingreen,meaningthatallvaluesforthestreamhavebeencalculated.

Rev2.1 ‐5‐ January9,2018

WewanttodothesamethingforthewaterportionofthefeedrepresentedbythestreamFeedWater.Double‐clickontheFeedWaterstreamtoopenuptheentryformsforthisstream.Enter4,800lb/dayintheMassFlowbox(torepresentthe48lb/MMscfwatercontent).Enterthepressurebutdonotenterthetemperature.NotethatforthesetofunitscurrentlyinuseHYSYSautomaticallyreplacesthemassratewiththeequivalentamountinlb/hr.

Rev2.1 ‐6‐ January9,2018

SelectCompositionunderWorksheetintheleft‐handcolumn.ClicktheEdit…buttontobringupaformtoenterthecompositionofthisstream.Entera1fortheH2Omolefraction.SelecttheNormalizebutton.ClickOK.Nowyoushouldseethattheformassociatedwiththestreamisstillyellowbecausethetemperaturehasnotbeenspecified.ThatisOK,we’regoingtoback‐calculatethefinalconditionsothatthetotalfeedgasis120°F.Formostoftheunitoperationswe’lldefineconnectionsandcreatenewstreamsusingtheoperations’Designforms.Double‐clickonMixer.Definethe2InletsasDryFeed&FeedWater(bypullingdownthestreamnamesfromthelists).DefineanewOutletstreamasTotalFeedbytypinginthenewname.SelecttheWorksheettab.Notethattheflowrate&pressureoftheTotalFeedstreamarecalculated.ButwestillhavetospecifysometypeofconditionstofullycalculateTotalFeed.Specifythetemperatureas120°F.NotethatnotonlyhaveallpropertiesbeencalculatedforTotalFeedbutalsothefinalconditionsforFeedWaterhavebeendetermined1.

1AMixerisanisenthalpicoperation,sotheenthalpyforFeedWater(andhenceitstemperature&quality)becamespecifiedoncewefullyspecifiedTotalFeed.

Rev2.1 ‐7‐ January9,2018

WenowwanttomodelthegassideoftheChiller.WecoulduseaCooleroperation,butsincewe’llultimatelywanttocalculateapproachtemperaturesbetweenthegas&thepropaneinthechillingloopanLNGExchangerismoreappropriate.Double‐clickonChiller.Specifythe1stInletStreamasthepreviouslydefinedTotalFeed&definetheOutletStreamasanewstreamChilledGas.FornowspecifythePressureDropas0.MakesurethatspecificationforHot/ColdisHot.Wenowwanttospecifythecoldseparator&determinethepropertiesoftheproducedgas.Double‐clickonDPCSeparator.SpecifytheInletastheexistingstreamChilledGas.Createnewstreams,ColdVapor,ColdLiquid,&ColdWaterastheVapour,LightLiquid,&HeavyLiquid,respectively.

Rev2.1 ‐8‐ January9,2018

Let’sestimatetheneededtemperatureforthecoldseparator.ClickontheWorksheettab&specify15°FforthetemperatureofChilledGas.NoticethatallvaluesarecalculatedforChilledGas,ColdLiquid,&ColdVaporat15°F.Thismeansthatthevaporoutoftheseparatorisatitsdewpointat15°F.Thismakesthepipeline’sdewpointspec,right?No,notreally.Buthowwouldweknowthis?WecanlookatthephaseenvelopeforColdVaportodetermineifthevaporwillhaveaminimumdewpointtemperatureatallpressuresitislikelytoexperienceinthepipeline.We’lldothisusingaStreamAnalysis.UpintheribbonundertheHometab,clickonStreamAnalysis&chooseEnvelope.Inthepop‐upformchooseColdVaporastheObject&clickOK.TheresultsintheDesigntabshowthattheCricondenthermis20°F,warmerthanthetemperatureneededtomeetthe15°Fpipelinedewpointspec.Atwhatpressuredoesthisoccur?WecanviewthePTdiagrambyselectingthePerformancetab&thePlotsoption;nowwecanseethatthemaximumtemperatureforthephaseenvelopeisat600psig,verymuchinthepossiblerangeofpipelineoperatingpressures.Sincethegasinthepipelinewillexperiencepressureslowerthantheinlet’s1000psia,itismoreappropriatetousethecricondenthermasthecontrollingvalueforthisspec.Andsincethetemperatureis20°F,thisgasdoesnotmakethisspec.

Rev2.1 ‐9‐ January9,2018

Fornowwe’llusetrial‐and‐errortodetermineanappropriatetemperatureforthecoldseparator.NotethatifwespecifythetemperatureofChilledGasas9.5°FwegetacricondenthermofColdVaporofjustover15°F.

Rev2.1 ‐10‐ January9,2018

Nowthatwe’vemetthedewpointspecwecandetermineifwe’vemettheheatingvaluespec.WecandeterminethisfromadditionalpropertiescalculatedforColdVapor.Double‐clickonColdVapor&selectPropertiesundertheWorksheetintheleft‐handcolumn.NoticethatanHHVhasbeencalculatedas446.000Btu/lb.mole.Isthiswithintheacceptablerange?Sincetheunitsaredifferentthanthoseinthespec(950–1050Btu/scf)wehavetodoaunitconversion.Instead,let’sresettheunitsusedforreportingtheresults&comebacktothis.SettingtheUnitsUsedbyHYSYSThepreferenceforthisexampleistouseU.S.Customaryunitstypicallyusedinthegasprocessingindustry:temperaturein°F,pressureinpsia,molarflowinMMscf/day,heatingvaluesinBtu/scf,liquidflowingal/min,&massflowinlb/hr.Thedefaultthatwasinplacewhenthissimulationwasstartedwasprettyclose.Butlet’sdobetter.UndertheHometabthereisasectionforUnitsthatshowthecurrentsetbeingused&abuttontochangeoptionswithinaunitset.ForthisproblemthedefaultisasetcalledRefining‐US1(fornewfilesthestartingsetisdependentonwhatwaspreviouslyusedontheparticularcomputerbeingused).Tocontroltheactualsetbeingusedlet’screateanewonewhichwewillcallGas

Rev2.1 ‐11‐ January9,2018

Processing‐US.ClickontheUnitSetsbuttontobringuptheformtoexaminetheavailableunitsets&change(ifdesired).Inthelowersectionlet’sstartwiththeFieldunitset.SelectField&pressCopy.Anewunitsetwillbecreated(herecalledNewUser).Doubleclickonthisname&enterGasProcessing‐US.

Intheuppersectionwecansettheunitsusedforvariouspropertiesinthesimulation.Wecanseethatmostunitsusedareveryreasonable.Forexample,temperatureisin°F,actualliquidvolumeflowasUSGPM,&pressureisinpsia.(Great!Wedon’thavetodoanythingforthis.).

Rev2.1 ‐12‐ January9,2018

Let’schangetheunitsformolarflow&heatingvaluetomeetoutpurposes.GototheDisplayUnitslist&changetheseunitstoMMSCFD&Btu/SCF,respectively.NowwecanclosethisformbyclickingOK.

Nowthatwe’vechangedtheunitsonheatingvaluewecangobacktothepropertiesforColdVaportoseeifwe’vemadetheHHV(higherheatingvalue)spec.Nowthevalueisclearlyreportedas1175Btu/scf&weseethatitistoohigh.Thiswillrequiremoreheavyhydrocarbonsberemoved.Butbeforewefocusonthislet’saddadditionalprocessingtostabilizetheliquidformed(sincethiswillinvolverecyclingbacksomeevolvedgas).LiquidStabilizationBeforechangeconditionstoleanoutthegaslet’sdetermineiftheproducedliquidwillmaketheTVPspecof103psia.Double‐clickonColdLiquid&selectPropertiesundertheWorksheetheadingintheleft‐handcolumn.AtthebottomofthelistthereisanitemforTrueVPat37.8C[psia].Thevalueis654.9psia,muchhigherthanourspec.Wecanlookatthecompositiontoseetheproblem–ithas16%methane.ThisismuchtoohightotrytohaveinarawNGLmix.

Rev2.1 ‐13‐ January9,2018

Wecanprocessthehigh‐pressureliquidinalowerpressurestrippingcolumntoremovetheselightends.Let’saddtwomoreunits:

AControlValve,VLV‐001 AReboiledAbsorber,Stabilizer.

Rev2.1 ‐14‐ January9,2018

Double‐clickonVLV‐100.SpecifytheInletasColdLiquidanddefineanewstreamFlashedLiquidastheOutlet.Thereisamessagethatthepressredropacrossvalveisunknown,butthatisOK,we’llsetthatinabit.Let’sdefinethestabilizingcolumnasa10‐stagecolumnwithakettlereboiler.Double‐clickontheReboiledAbsorber.RenameitStabilizer.SettheTopStageInletfeedasFlashedLiquid.DefinenewstreamsRecoveredGasfortheOvhdVapourOutletandStabilizedLiquidfortheBottomsLiquidOutlet.DefinethestreamQ‐ReboilerfortheReboilerEnergyStream.Setthe#Stagesas10.PresstheNext>buttontocontinuethedefinitionforthistower.AcceptthedefaultOnce‐Throughreboilerconfiguration.Thiswillmodelakettlereboiler.PresstheNext>buttontocontinuethetower’sdefinition.

Rev2.1 ‐15‐ January9,2018

Let’slookrunningthetowerat200psia.Specify200forbothTopStagePressure&theReboilerPressure.PresstheNext>buttontocontinuethetower’sdefinition.We’reabletospecifytemperaturesonthisnextform.Ultimatelywewillwanttorunthereboilerinsuchawayastoproducealiquidwitha103psiavaporpressureat100°F.Ifwewererunningthetowerat103psiathenwecouldsetthereboilertemperatureas100°F.However,sincewe’rerunningthetoweratahigherpressurethereboilertemperatureshouldbehigher;fornowlet’ssetanestimateof200°F.PresstheNext>buttontocontinuethetower’sdefinition.Wewillnothavetospecifyaboil‐upratiosincewe’regoingtouseaTVPspeconthereboiler.Leavethisblank&pressDone…

Rev2.1 ‐16‐ January9,2018

Thetowerdoesnotrunautomaticallybecausethespecificationshavenotbeenfullydefined.SelectSpecsSummaryitemintheleft‐handcolumn.Noticethatthedefaultspeconthecolumnistoproduceanoverheadproductrate(whosevaluehasnotbeenspecified).Butthisisnothowwewanttorunthiscolumn.BeforeweenterthetruespecclickontheActiveboxforOvhdProdRatetoturnitoff.Let’saddthereboilertemperatureastheoperatingspec.SelectSpecsitemintheleft‐handcolumn.PresstheAddbuttonforcolumnspecifications.OnthelistselectColumnTemperature&pressAddSpec(s)…SelectReboilerastheStage&enter200fortheSpecValue.Closethisform.

Rev2.1 ‐17‐ January9,2018

EventhoughwehavefullyspecifiedthetowerthefeedcomingfromVLV‐100hasnotbeenfullyspecified,sothetowerwillnotrun.GototheWorksheettabandenter200forthepressureofFlashedLiquid.Nowthatthisfeedisfullyspecifiedthetowerwillquicklycalculate&converge.HowclosearewetocreatingastabilizedliquidwiththecorrectTVP?Let’screateanewspecforthisbutdon’tmakeitactive;wecanthenseehowcloseweare.SelecttheDesigntabandthentheSpecsitemintheleft‐handcolumn.PresstheAddbuttonforcolumnspecifications.OnthelistselectColumnStreamPropertySpecnearthebottomofthelist&pressAddSpec(s)…SelecttheStabilizedLiquid@COL1.You’llhavetogotoanotherformtoactuallypickthetypeofstreamproperty.ClicktheSelectPropertybutton.OnthenextformselectthetreestructureunderStandard&chooseTrueVP@37.8C;pressSelect.Enterthevalue103.Closethisform.

Rev2.1 ‐18‐ January9,2018

Nowlet’sgobacktotheDesigntab&Specsselection.HighlighttheStreamPropertySpec&youcanseethatthecalculatedTVPisactually67.71psia,lowerthanthedesired103psia.Wecandecreasethereboilertemperaturetoallowthevaporpressuretoincrease.SelecttheActivecheckbox;nowthetowerbecomesunconverged(becausewehaveoverspecifiedtheunitwithboththeTVPspec&thereboilertemperaturespec).SelecttheTemperaturecolumnspecification&uncheckitsActivecheckbox.Nowthetowerwillreconverge;thecalculatedreboilertemperatureis166.9°F.

Rev2.1 ‐19‐ January9,2018

Whatdoesthestabilizedliquidlooklike?Double‐clickonStabilizedLiquid&selectCompositionundertheWorksheettab.Notethatthereisessentiallynomethane&verylittleethane–allofthismaterialhasbeenstrippedoutintotheoverheadvaporstream.Justenoughisallowedtoremain(bychangingthereboilertemperature)tohavethedesiredvaporpressure.Let’slookathowmuchGashasbeenstrippedout.Double‐clickonRecoveredGas.SelectCompositionundertheWorksheettab.Noticethatthisgashasveryhighconcentrationsofmethane&ethane.Butcouldthisbedirectlyproducedaspipelinegas?SelectProperties.NotethattheHHVistoohigh,1449Btu/scf.Morethanlikelyitwon’tmakethedewpointspeceither.RecycleofRecoveredGasOnemightaskwhywedidn’tincludeacondenseronthestabilizercolumn.Acondenserwouldallowustowashthepropane&heavier(C3+)backdownthecolumn&outwiththeStabilizedLiquid.WecaneffectivelygetthiseffectbyreconfiguringtheprocesstorecycletherecoveredgasfromthestabilizingcolumnupstreamofChiller.However,sincetherecoveredgasisproducedatalowerpressure,itmustbecompressedtoahigherpressureconsistentwiththeoriginalfeedgas.

Rev2.1 ‐20‐ January9,2018

Let’saddthreeunits:

ACompressor,RecycleGasCompressor AMixer,RecycleMixer. ARecycle,RCY‐1.

NotethatsomeoftheitemshavebeenflippedonthePFDshownabove.ThiswasdonebyselectingtheitemontheFlowsheet,selectingFlowsheet/Modifyintheribbon,&thenselectingFlipHorizontal.Double‐clickRecycleGasCompressor.SettheInletastheRecoveredGasstream.CreateanOutletstreamHPRecycleGas&aworkEnergystreamW‐RecycleCompressor.SelecttheWorksheettab.SettheoutletpressureoftheHPRecycleGasto400psia.Notethecalculationsarecompletedusingthedefaultadiabaticefficiency,75%,andgivesanoutlettemperatureof112.7°F.

Rev2.1 ‐21‐ January9,2018

Double‐clickonRCY‐1.SelectHPRecycleGasastheInlet.CreateastreamRecycledGasastheOutlet.Nowlet’scombinetheHPRecycleGaswiththeTotalFeed&introduceitintotheChiller.Double‐clickonChiller&deleteTotalFeedasanInletStream.Instead,createanewstream,ProcessFeed,astheInletStream.Double‐clickontheMixerRecycleMixer.SelectProcessFeedastheOutlet.Fornow,onlyselectTotalFeedastheInlet.AtthispointthesimulationhasconvergedbutwithouttheRecycledGasbeingmixedwiththefreshfeed.Butthestreamhasbeeninitializedandtherecyclecalculationcanproceed.Now,double‐clickonRecycleMixer&addRecycledGasasthesecondInletstream.Nowthesimulationshouldconvergeincludingthisrecyclebacktothefreshfeed.

Rev2.1 ‐22‐ January9,2018

Howhasaddingtherecyclegasaffectedthefinalresults?ThereisnotagreatdealofRecycledGasbeingmixedwiththefreshfeedsothecompositionoftheColdVapordoesnotchangebymuch.Thecricondenthermincreasesonlyslightlyto15.07°F.Theproducedgasalsostillhasahigherheatingvaluethatistoohigh,1176Btu/scf.WecantrytodecreasetheHHVbyreducingthetemperatureoftheChilledGas.Let’slowerthistemperaturetothelowestlimitreasonableforasimplepropanechillingloop,‐30°F.Reducingthistemperaturedoesshiftmoreoftheheavyendsoutoftheproducedgas&theHHVislower.However,theHHVofChilledGasisstilltoohigh,1145Btu/scf.Unfortunatelythisisprettymuchthebestwecandowhenusingachilledsingle‐stageflashseparationunit.PreventionofFreezinginDPCSeparatorTheinletfeedgasisnearlywatersaturatedattheentrytotheprocess.WhenthewaterdropsoutofthegasphasewhenitiscooledthereisapotentialfreezingintheChiller&DPCSeparator.Atypicaltechniquetopreventiceorhydrateformationistoinjectethyleneglycol(EG)upstreamoftheChiller.AnaqueoussolutionofEGhastheabilitytosuppresstheformationofice.Init’spurestateEGhasafreezingpointof8°F,butaqueoussolutionshavefreezingpointsthatarelower.Noticefromthechartontheright1onemaygetfreezingprotectionto‐30°ForlowerbymaintainingaEGconcentrationinwaterof85wt%to50wt%.Whataretheappropriateconcentrationstoconsiderforourprocess?

Wewouldliketomakesurethatthereisfreezingprotectionfortheentireconcentrationrangebefore&afterthewaterisabsorbed.

Wewantprotectionnotonlyattheprocesstemperaturebutalsothecoldesttemperatureatthetubewall.Thismeanswehavetoprotectbelowthe‐30°Fprocesstemperaturebuttothecoolanttemperatureof‐40°Forlower.

BasedontheseconsiderationswewillwantaconcentratedEGsolutionof83wt%(protectionto‐40°F,thecoldesttubetemperatureexpectedinChiller).Thisshouldbeinjectedatasufficientratesothatitwillbedilutedtonolowerthan80wt%(protectionto‐50°F)2.

1EngineeringandOperatingGuideforDOWTHERMSR‐1andDOWTHERM4000InhibitedEthyleneGlycol‐basedHeatTransferFluids,DowChemicaltechnicalpublication,http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_010e/0901b8038010e413.pdf?filepath=/heattrans/pdfs/noreg/180‐01190.pdf&fromPage=GetDoc2Notethateventhoughwecouldtrytooperateintheregionoflowerglycolconcentrations(60wt%dilutedto55wt%)thenormalpracticeistooperateinthehigherconcentrationrange;ifexcesswatercomesinwiththegasthenthehigherconcentrationsactuallygetbetterfreezeprotection,notworse.

Rev2.1 ‐23‐ January9,2018

TobeabletoaddanEGsolutionwemustaddethyleneglycoltothecomponentlist.ReturntothePropertiessection.SelectComponentList‐1toviewtheactivecomponentlist.HighlightH2Ointheselectedcomponents.Usethesearchterm“egly”.SelectEGlycolfromthedatabanklist&pressAdd.ThecomponentEGlycolwillbeplacedrightafterH2O,secondinthelist.ReturntotheSimulationsection.Let’saddastreamfortheethyleneglycol,EG,intotheRecycleMixer.

Rev2.1 ‐24‐ January9,2018

Double‐clickonthestreamEG.SelectComposition&setitto83wt%ethyleneglycol&17wt%water.SelectConditions;setthepressureto400psia&itstemperatureto60°F(typicalforundergroundstorage;we’llfindoutamorereasonabletemperaturelater).Fornowsetthemassflowrateto5,333lb/hr(thisshouldmaketheColdWaterstreamabout80wt%glycol).

PropaneRefrigerationLoopThenextdetailwecanisarefrigerationlooptobeabletocoolthefeed&recyclegasestoDPCSeparator.Addthefollowingequipmenttotheflowsheet:

ACompressor,C3Compressor ACooler,C3Condenser. AControlValve,C3Valve.

Let’screatethestreamsfortherefrigerationloopstartingattheChiller.Double‐clickonChiller.Createnewinlet&outletstreamsRefrigLiquid&RefrigVapor,respectively.MakesurethatthesestreamsareassociatedwiththeColdside.Specifyazeropressuredrop.UndertheWorksheettabspecifytheconditionsfortheoutletstreamRefrigVapor(1vaporfraction&‐40°F).

Rev2.1 ‐25‐ January9,2018

Nextlet’sconnectthecoldliquidtothelet‐downvalve.Double‐clickonC3Valve.SettheOutletasRefrigLiquid.CreateanewstreamCondensedLiquidastheInlet.SelecttheWorksheettab;setthetemperatureofCondensedLiquidto120°F&theVapour/PhaseFractionto0(i.e.,saturatedliquid).Donotspecifythepressuredropacrossthevalve–thiswillbedeterminedautomaticallywhenthehighpressure(forcondensation)andlowpressure(forvaporization)aredetermined.

Rev2.1 ‐26‐ January9,2018

Youcanspecifythecompositioninalmostanyofthestreamsinthisloop.Itismostconvenienttodosoatthestreamoutofthecondenser.(Maybenotforasinglestageofcompression,butdefinitelymostconvenientwhengoingtomultiplestages.)DoubleclickontheCondensedLiquidstream.SelecttheCompositionitem&presstheEdit…button.Entera1forPropane,pressNormalize,thenOK.Notethatthecalculationshavebeenperformedforthisstream,includingthedeterminationoftheflowrate(277,990lb/hr);thisflowratehasbeencalculatedtoensureanenergybalanceinChiller.

Double‐clickonC3Compressor.SelectRefrigVaporastheInlet&createHPVaporastheOutlet;createW‐C3CompressorastheEnergystream.Normallywewouldwanttospecifytheoutletpressure,butwe’regoingtoletHYSYSusethecondenser’spressureforthis.

Rev2.1 ‐27‐ January9,2018

Nowlet’scompletetherefrigerationloop.Double‐clickonC3Condenser.SelectHPVaporastheInlet&CondensedLiquidastheOutlet;createQ‐C3CondenserastheEnergystream.Atthispointthecondenserhasnotyetbeenfullydefined.UnderParameterssettheDeltaPas0.Nowthestatusisgreen&therefrigerationloopcalculationsarecompleted.ProductCompressionThefinalstepinthissimplesimulationistoaddcompressionforthefinalproductgas.Addtotheflowsheettheunit:

ACompressor,ProductGasCompressorDouble‐clickonProductGasCompressor.SelectColdVaporastheInlet&createHPProductGasastheOutlet;createW‐ProductCompressorastheEnergystream.SelecttheWorksheettab;settheoutletpressureas1000psia.Notethatoutlettemperatureis100.9°F(lessthanthespecof120°Fminimum),soafinalcoolerisnotneededtobeabletointroducethisgasintothepipeline.

Rev2.1 ‐28‐ January9,2018

AdditionaldetailtotheFlowsheetTheremanydetailsthatcanbeaddedtothisflowsheet.Whendonewiththeseadditionstheflowsheetwilllooklikethefollowing.

EthyleneGlycolRegenerationTheinitialflowsheetassumesthat83wt%ethyleneglycol(EG)canbemadeavailabletotheprocess.InanactualprocessthisEGisnotafreshfeed,butratheritisrecirculatedafterthewaterpickedupintheDPCSeparatorisstrippedout.WecanaddthefollowingmajoroperationstoregeneratetheEG:

astrippingcolumnwithareboiler&partialcondenser across‐exchangertorecoverheatfromthestrippedEG apumptobringtheleanEGuptotheinjectionpressure arecycleoperation.

Rev2.1 ‐29‐ January9,2018

Let’screatethestreamswhilecreatingtheunitoperations.CreatethestrippingcolumnusingtheDistillationColumnSub‐flowsheetmodulefromtheColumnstabofthemodelPalette.Doubleclickonthismodule;onthisfirstscreen:

NamethecolumnEGStripper.

Setthenumberofstagesto2 Setthecondensertypeto

FullRflx. CreatethestreamHotRich

EGastheInletStreamtostage2.

SettheOvhdVapourOutletasWaterVapor,theBottomsLiquidOutletasHotLeanEG,theCondenserEnergyStreamasQ‐EGCondenser,andtheReboilerEnergyStreamasQ‐EGReboiler.

WhenreadypresstheNext>key.We’lldefinethereboilerasakettlereboiler.KeepthedefaultoptionofOnce‐through&RegularHysysreboilerandpressNext>.

Rev2.1 ‐30‐ January9,2018

EGstrippersoperatenearatmosphericconditiontokeepthereboilertemperaturesaslowaspossible.We’llfirstassumeazeropressuredropacrossthecolumn.SettheCondenserPressureandtheReboilerPressureto1atm.(Notethatthepressurewillbeconvertedtounitsofpsia.)PressNext>.Theproductoffthetopofthecolumnshouldbeessentiallywatervaporat1atm,sowecansetatemperatureestimateforthisas212°F.PressNext>whendone.Fornowlet’sestimatetherefluxratioas0.15.PressDone…

Rev2.1 ‐31‐ January9,2018

Let’sdefinethecrossexchangerthatwillpreheatthecoldwater/EGfeedandrecoverheatfromthehotstripperbottoms.UsetheLNGExchangermoduletocreateEGCrossExchanger(youmaywanttofliptheexchangerhorizontallydependingonhowyouplaceitonyourflowsheet).SpecifyColdWaterasaninletstream&itsoutletasHotRichEG;specifythisasaColdstream.SpecifyHotLeanEGasaninletstream&createLPLeanEGasitsoutlet;specifythisasaHotstream.Setbothpressuredropsas0.We’dliketostartthecalculationswithoutcreatingaheat‐basedrecycleloop.So,let’sspecifytheoutlettemperatureinHotRichEGas200°F.Nowthehotsidestreamsshouldbecalculated.(Thetowerhasn’texecutedyetsothesestreamsarestillunavailable.)Let’sgoback&runthecolumn.DoubleclickonEGstripper.Wehavemadeaspecificationonthecondenserbutnotonthereboiler.SelecttheSpecsitem.ClicktheAdd…buttonforcolumnspecifications.SelectColumnComponentFraction&clickAddSpec(s)…NamethisspecBottomsMassFraction;settheMassFractionvalueto0.83forEGlycolfortheLiquidcomingfromtheReboiler.Closethiswindow.

Rev2.1 ‐32‐ January9,2018

SelectSpecsSummary.TheonlytwoactivespecsshouldbeRefluxRatio&BottomsMassFraction.SelectRun(youmaynotevenhavetopressthisbutton).Itshouldconvergeveryquickly.SelectthePerformancetab&theColumnProfilesitem.Youcanseethatourestimateforthetoptemperaturewasprettyclose.Thebottomstemperatureis261.1°F.

Rev2.1 ‐33‐ January9,2018

The214°Fcondensertemperaturehastheimplicationthatthereusafairamountofglycolintheoverheadvapor.Themoreglycolthatleaveswiththevapor,themoremakeupthatmustbeadded.Let’sminimizetheseglycollossesbysettingthetemperatureto212°F.Dothisbyaddingatemperaturespeconthecondenser(gototheDesigntab,selectSpecs,clickAdd…,selectitemColumnTemperature&clickAddSpec(s)…;thensetthespecvalueforCondenseras212F).Nowwhenyoumakethisactivethecolumnwillreconvergewiththisasthecondenser’stemperature.YoucanclickontheWorksheettab&seethatthereisonlyasmallamountofglycolbeinglostintheoverhead.

Rev2.1 ‐34‐ January9,2018

Wecangobacktotheflowsheet&seethatEGCrossExchangerhasalsoconverged.WecannowfinishupthereturnoftheleanEGstream.TheLPLeanEGstreamneedstobepumpeduptothedeliverypressure&tiedintotheEGfeedstream.AddapumpGlycolPump(youmaywanttofliphorizontaldependingonhowyouplaceitonyourflowsheet).SettheInletasLPLeanEG,createtheOutletasEGtoRecycle,andcreatetheEnergystreamasW‐EGPump.GototheWorksheettab&setthepressureforEGtoRecycleas400psia(tomatchtheEGstream).Noticethatthepumpoutletis30.1°F.Thisisnotablefortworeasons:

Thisislowerthantheinitialspecthattheethyleneglycolwouldbeenteringat60°F.TheEGCrossExchangeractuallyallowsustogetfairlycoldbyrecoveringrefrigerationintheColdWaterstream.

Infact,thistemperaturemayactuallybetoolow.Typicalreturntemperaturesshouldbe40to55°F.ThishighertemperaturecannotbedirectlyspecifiedinEGCrossExchanger;assoonasyouchangethespecfromoneontheoutletofthehotsidetooneonthecoldsideyousetuparecycleloopandthismodulecannotautomaticallysolvethis.ButyoucanmanuallyreducethetemperatureofHotRichEGuntilthetemperatureofLPLeanEGrisesabove40°F.Reducingthespecfrom200°Fto191°Fwilldothis.

Rev2.1 ‐35‐ January9,2018

Finally,let’scloseofftherecycle.Double‐clickonRCY‐2&settheInletasEGtoRecycle&theOutletasEG.Thecalculationwillquicklyconverge.OptimizingtheProcessThebasicprocesshasnowbeensetup.Notethattherearethreemajorpowerusers:

ProductGasCompressor–4,027hp RecycleGasCompressor–111hp RefrigerationCompressor–7,988hp

Inadditiontherearetwomajorheatusers:

Stabilizer’sreboiler–3.3MMBtu/hr EGstripper’sreboiler–0.5MMBtu/hr.

Aquestionforoptimization–cananyofthesestreamsbereducedtoreducetheoperatingexpensefortheprocess?Somethoughts:

MostofthesevaluesaredependentontheoperatingconditionsofDPCSeparator.Thissetstheamountofgasthatneedstoberecompressed,theamountoflightendstotheStabilizerthatneedtobestrippedoff,compressed,&recycledback,andtheamountofwaterabsorbed&regeneratedinEGStripper.

Thebigoperatingcostandonethatcanbeaddressedwithfurtherdesignisthepowerneededfortherefrigerationloop.Therearetwowaysthatthiscouldbedone:

o WecouldtrytorecovertherefrigerationfromthecoldstreamsfromtheDPCSeparator.Bydoingsotherewouldbelessrefrigerationdutyneeded,reducingthepowerrequirementfortheC3Compressor.Also,bywarmingtheColdLiquidbeforegoingtotheStabilizertheamountofreboilerdutywillalsobereduced.However,notethatbyincreasingthetemperatureofthegasbeforetheProductGasCompressortherequiredpowerinthiscompressorwillincrease,negatingthemajorityofthepowersavings.

o Wecouldincreasethenumberofrefrigerationstagesofcompressionwithassociaterecycleoftheintermediategasesfromtheintermediatestageeconomizers.Itistypicalthatatwo‐stagesystemcansaveabout20%ofthepowerrequiredbytherefrigerationsystem.