Crude Tower Simulation-AspenPlus v8.6

Rev0.0 1 November9,2014

CrudeTowerSimulationAspenPlusv8.6StepstosetupasimulationinAspenPlusv8.6tomodelacrudetowersystemconsistingof:

CrudeOilPreheatTrain AtmosphericCrudeTower VacuumCrudeTower DebutanizertostabilizetheoverheadnaphthastreamfromtheAtmosphericCrude

TowerThefeedstocktothecrudesystemwillbeanequalmixofLight,Medium,&HeavyCrudeoils.WhenthesimulationissetuptheoverallPFDshouldlooklikethefollowingfigure.

CreatenewsimulationfileStarttheprogramfromStart,AllPrograms,AspenTech,ProcessModelingV8.6,AspenPlus,AspenPlusV8.6.Whentheprogramopenschoosethenewbutton.thereareseveraltemplatesthatcanbechosen.SelecttheRefineryoptioninthelefthandcolumn&chosethePetroleumwithEnglishUnitstemplate.PressCreate.


SaveasyougoOneofthethingsyoullwanttodoistosaveyourfilesasyougo.ThefirsttimeyougototheSaveAsoptionyoullhaveseveralformatsfromwhichtochoose.ThereareadvantagestosaveastheAspenPlusBackup(BKP)formatthefilestendtobesmaller&lesslikelytobecomecorrupted.


DefinetheComponents&thePropertyModels Specifycomponents,fluidpropertypackages,&crudeoilassays

Thefirststepistoaddasetofpurechemicalspeciestorepresentthelightcomponentsofthecrudeoils.TheComponentSpecificationsformshouldbethedefault.(Ifnot,presstheSpecificationsitemunderComponentsinthelefthandcolumn.)Wwillwanttoaddthefollowingpurecomponents:water,methane,ethane,propane,ibutane,nbutane,ipentane,&npentane.OneofthedirectwaystodothisistopressFind&usethesearchformtofindthedesiredcomponents.ThefollowingformshowsasearchforH2O;keyphrasescanbeusedtowiththeEqualsorContainsoptionstofindallcomponents.Foreachsucceedingcompoundyouwillbeaskedtoreplaceoneofthecompoundsoraddtothelist;chooseaddtothelist.


AspenPluswillretrieveinformationabouteachcomponent&alsocreateaComponentIDforthissimulation.YouarefreetochangetheseIDstomatchyourpersonaldesires.Forexample,youchangetheIDforMETHA01toC1bydoublingclickingonthattextitem;afterchangingthetextvalue&pressingenterAspenPluswillverifythatyouwanttoRenamethecomponent&notchangeittosomethingelse.Thiscanbedoneforallofthecomponentstocreate(IMHO)morereasonableIDs.


AspenPluscanguideyouthroughtheprocessofdefiningyoursimulation.ThisisdonebypressingtheNextbutton( ,eitherintheribbonorinthequickaccessbar).DoingthisshowsthatthenextstepistopickafluidpropertypackageontheMethodsSpecificationsform.FromtheBaseMethodpulldownlistchoosePENGROB.


Clickthe button.ThenextformallowsustomodifyvaluesforthePengRobinsonbinaryinteractioncoefficients.Wewillnotchangeanyofthemfromthedefaults.

Wenowwanttoaddassaydataforthethreecrudeoils:LightCrude,MediumCrude,&HeavyCrude.ThedatatobeaddedisshowninthefollowingTables1to3.Clickthe button.But,sincewewanttoaddcrudeassaydata&thisisnotanoptiononthisform.PressCancel.


Table1.AssayDataforLightCrudeLightCrude

CumulativeYield

[wt%] Density API Sulfur LightEndsAnalysisIBP EP @IBP @Mid lb/ft3 Gravity wt% [wt%]WholeCrude 53.27 34.17 1.77 Ethane 0.00031 160 0 2.5 42.75 74.91 0.019 Propane 0.146160 236 5 7.5 45.40 62.90 0.031 iButane 0.127236 347 10 15 48.33 51.09 0.060 nButane 0.702347 446 20 25 50.46 43.38 0.379 iPentane 0.654446 545 30 35 52.38 36.97 1.064 nPentane 1.297545 649 40 45 54.18 31.37 1.698 649 758 50 55 56.04 25.96 2.159 758 876 60 65 57.92 20.86 2.554 876 1015 70 75 60.05 15.45 3.041 1015 1205 80 85 62.84 8.94 3.838 1205 1350 90 92.5 64.92 4.44 4.503 1350 FBP 95 97.5 70.64 6.57 6.382

Table2.AssayDataforMediumCrudeMediumCrude

CumulativeYield

[wt%] Density API Sulfur LightEndsAnalysisIBP EP @IBP @Mid lb/ft3 Gravity wt% [wt%]WholeCrude 55.00 28.97 2.83 Ethane 0.00088 180 0 2.5 43.47 71.51 0.022 Propane 0.030180 267 5 7.5 47.14 55.69 0.062 iButane 0.089267 395 10 15 49.42 47.08 0.297 nButane 0.216395 504 20 25 51.83 38.78 1.010 iPentane 0.403504 611 30 35 54.08 31.67 2.084 nPentane 0.876611 721 40 45 55.90 26.36 2.777 721 840 50 55 57.73 21.36 3.284 840 974 60 65 59.77 16.15 3.857 974 1131 70 75 62.30 10.15 4.706 1131 1328 80 85 65.74 2.74 5.967 1328 1461 90 92.5 68.08 1.87 6.865 1461 FBP 95 97.5 73.28 11.08 8.859


Table3.AssayDataforHeavyCrudeHeavyCrude

CumulativeYield

[wt%] Density API Sulfur LightEndsAnalysisIBP EP @IBP @Mid lb/ft3 Gravity wt% [wt%]WholeCrude 55.20 28.36 2.8 Ethane 0.03926.8 153.6 0 2.5 42.92 74.11 0.005 Propane 0.284153.6 255.1 5 7.5 45.75 61.40 0.041 iButane 0.216255.1 400.5 10 15 49.44 46.98 0.341 nButane 0.637400.5 523.4 20 25 52.23 37.47 1.076 iPentane 0.696523.4 645 30 35 54.49 30.47 1.898 nPentane 1.245645 769.6 40 45 56.62 24.36 2.557 769.6 901.9 50 55 58.77 18.65 3.185 901.9 1043.8 60 65 61.09 12.95 3.916 1043.8 1198.1 70 75 63.61 7.24 4.826 1198.1 1380.5 80 85 66.63 0.94 5.990 1380.5 1499.7 90 92.5 68.71 3.07 6.775 1499.7 FBP 95 97.5 73.10 10.78 8.432

ThefollowingstepsshowhowtoenterthedataforLightCrude.Similarstepsshouldbeusedfortheothercrudeoils.

SelectAssay/BlendunderComponentsinthelefthandcolumn.ClickontheNewbutton.


CallthenewcrudeassayLIGHT&chooseAssayfromtheSelectTypedropdownlist.PressOK.

MakesuretheDistCurvetabisactive.MaketheAPIgravityoptionactive&enterthe

valuefromTable1.IntheDistillationCurvetypedropdownlistmaketheTrueboilingpoint(weightbasis)optionactive.Inthetableenterthecumulativeyieldvaluesvs.associatedtemperatures.Notethattheyieldvaluesshouldbeenteredaspercentages,scaledfrom0to100.

Nowwelladdinthecompositionofthelightends.MaketheLightEndstabactive&

theformwillchangetoallowyoutoenterthecompositions.Selectthecomponentstobeusedtodefinethelightends(basedonthecomponentlistpreviouslyspecified).ChangetheFractiontypetoMass.EnterthevaluesfromTable1.Notethattheseareintermsofmassfraction,notpercent,andarescaledfrom0to1.


NowwelladdintheAPIGravitydata.MaketheGravity/UOPKtabactive.Makethe

APIgravityoptionactiveintheDatatypearea.AddthedatafromTable1.Notethattheyieldvaluesshouldbeenteredaspercentages,scaledfrom0to100.


Eventhoughwecannowcharacterizethepseudocomponentsfortheflashcalculationswestillneedtoaddthesulfurdistributionsothatthesulfurcontentcanbetracked.Firstwellhavetoneedtodefinesulfurasaproperty;thiswillonlyhavetobedoneonce,notforeverycrudeassay.SelectPropertySetsinthelefthandcolumn.NotethatthereareoveradozenpropertypredefinedbyourselectingthePetroleumtemplate.OntheformpressNewSettheIDasSULFUR.OnthenextformpulldownthePhysicalPropertieslist&selectSULFUR.

Nowwewilldefinethesulfurdistributioninthecrudeoilassay.CheckforLIGHTinthelefthandcolumnunderComponents&Assay/Blend.NoticethereisnowasubheadingforPropertyCurves;selectthis.OnthenextformpulldownthePropertyNamelistandselectSULFUR.EntertheBulkvalue(i.e.,thesulfurcontentofthewholecrude)andthenthedistribution.


AtthispointyoucouldpresstheRunbutton( ineithertheRibbonortheQuickAccesstoolbar).NowyoucanselectResultsandseemanyofthecalculatedvaluesformtheinputdata,suchastheconversionofthelightendsanalysistovol%&molefractionbases,breakdownofthedistillationcurveintonarrowboilingfractionpseudocomponents,etc.


RepeatthestepsfortheMedium&HeavyCrudes.Specifycrudeoilblend,&installintoflowsheetNowwellcreateablendofthethreecrudesandusethatasourfeedstockinthesimulation.SelectAssay/BlendunderComponentsinthetreestructureofthelefthandcolumn.PresstheNewbutton.CalltheblendMIXOIL&chooseBlendfromtheSelectTypedropdownlist.PressOK.


OntheSpecificationstabselecteachcrudeoilinthepulldownlistintheAssayIDcolumn.SettheStdvolFractionvalueforeachto0.3333.

YoucanpresstheRunbutton&viewtheResults.Onemorethingyoumaywanttocheck.SelectSpecificationsunderComponents.Notethatthecrudeoilassays&theblendarelistedassingleitems.Thepseudocomponentrepresentationsarenotshowninthiscomponentlist.


Setup&SolvetheFlowsheetCrudeOilFeed&PreheatWhenyouactivatetheSimulationyoullseeablankMainFlowsheet.Wecannowstartaddingstreams&unitstorepresentourprocess.

Thefollowingaretheconditionstobesetontheoperations.

CrudeOilFeed:100F,300psig,101,000bpd Preheat1outlet:260F,294psig Desalteroutlet:260F,294psig,500bpdofwater Preheat2outlet:450F,260psig

IntheModelPaletteclickontheMaterialstream.Click&drawastreamontheMainFlowsheet.Clicka2ndtimetofinishdrawingthestream.WhenpromptednamethestreamCRUDEOIL;clickOK.

Letsdefinethisfeedstream.EitherdoubleclickonthestreamintheflowsheetorchooseCRUDEOILinthelefthandcolumnunderStreams.Specifythetemperature&pressurefortheFlashType;specify500F,300psig,&101000bpdintheStatevariablessection.WewillusethemixedrepresentationoftheblendedcrudebyspecifyingtheStdvolFracofMIXOILas1.


Letsaddintheequipment&otherstreamsforthepreheattrainbeforewespecifyrates&operatingconditions.AddtwoHeatersandmaterial&heatstreamstogiveaconfigurationasshownatthebeginningofthistopic.WecanusetheNextbuttontostepusthroughwhatneedstobeaddedbeforewerunthesimulation.ThefirstthingweshoulddoisdefinethewatercarriedoverfromtheDesalter.Entertheinformationasshown.Notethatwedontreallyknowanappropriatetemperatureforthewaterbeforeitismixedwiththecrude,rather,thetemperatureafterthemixing.Fornowspecifythetemperatureas260F.


Thenextrecommendationistospecifytheoperatingconditionsforthe1stPreheater.Specifytheoutlettemperature&pressure.


Thenextrecommendationistospecifytheoperatingconditionsforthe2ndPreheater.Specifytheoutlettemperature&pressure.


PressingNextshowsthatalloftherequiredspecificationshavebeenmade.PressOKtorunthesimulation.AtabfortheControlPanelshouldopenup&indicatethatthesimulationhasrunsuccessfully.


Whataresomeoftheresults?Wecangetanoverviewbypostingsummaryconditionsontheflowsheet.ClickonStreamResultsintheModifytaboftheribbon.SelectTemperature,Pressure,Volumeflowrate,&Heat/Duty.PressOK.Nowthesenumbersarepostedontheflowsheet;notethatthevolumetricflowrateshownintheactualvolumetricflowrate(attheflowingtemperature&pressureconditions),notthestandardvolumetricflowrate(thatwehavebeenspecifying).

Wecanseemoredetailedresultsbyexaminingtheindividualstreams&units.Forexample,ifweselectResultsforWETCRUDE&usetheFormatPETRO_Ethenwecanseethe


calculatedtemperature(257.4F),thestandardliquidvolumeflowrateofthecomponents(includingthepseudocomponentsused).Atthebottomofthelistyoucanfindthetotalvolumetricflowanddistillationcurves(onadrybasis).Wecanseethesesameresults(andmore)byselectingtheStreamResultsforADDWATER.


Noticethatwewouldlikethetemperatureofthecrude/watermixturetobe260F,buttheresultofthemixingoperationisalittlebitlower,257F.Isthisasignificantdeviationfromthespecifications?Notforanythingdownstreamofthe2ndpreheater;thispreheatersets


theoveralltemperature&isnotdependentontheinletconditions.However,itwillcauseaslightdifferenceinthedutyinthe2ndpreheater;havingaslightlyhigherinlettemperaturewillreducethedutyrequiredtobringtheoutlettemperatureupto450F.Therearetworeasonablewaystodothis:

WecouldchangeADDWATRtoadummyHeater&setthetemperatureofthemixture.

WecouldadjustthetemperatureoftheWATERstreamsothatitgivestheproperoutlettemperature.Thisadjustmentcouldbedoneeithermanually(trial&error)orusingaDesignSpecblock.

Ifweadjusttheconditionsofthewaterstreamwefindoutthatthewaterhastobesetasasteam/liquidmixturetogettherightpropertiesofWETCRUDE.Sincewerenotreallyinterestedintheconditionsofthisaddedwater,letstakethedummyheaterapproach.HighlighttheMixerADDWATR&delete.LetsputaHeaterinitsplace;chooseablockforitsicon;calltheblockADDWATR.RightclickonWARMCRD1,selectReconnectDestination,&connecttoADDWATR.DothesameforWATER.RightclickonWETCRUDE,selectReconnectSource,&connecttoADDWATR.InthelefthandcolumnselectADWATRunderBlocks.Specifytheoutlettemperature&pressure.PressRun.NowwhenwelookattheStreamResultsforADDWATRweseethattheoutlettemperatureiscorrect.FromtheFlowsheetwecanseethat,indeed,thedutyonthe2ndpreheaterhasbeenreducedslightly,from150MMBtu/hrto148MMBtu/hr.


AtmosphericDistillationColumnThenextstepistosetuptheAtmosphericDistillationColumn.Table4containstheconditions&configurationforthiscolumn.


Table4.DefinitionsforAtmosphericDistillationColumnType OperatingParameterTrays&Efficiencies 50trays.Numberingfromtop:

Trays1to6:80%Trays7to10:50%Trays11to16:70%Trays17to30:50%Trays31to39:30%Tray40:100%Trays41to50:30%

CondenserType TotalCondenser;130F(approximate)Distillateproduct410FD86T95;30,200bpd(approximate)

ReboilerType None,DirectFiredHeaterPressures Condenser:4psig

TopTray:12psigBottomTray:22psig

Temperatures TopTray#1250F(estimate)BottomTray#50650F(estimate)

FeedLocations CrudeoiltoTray#40StrippingSteamatbottom(Tray#50)20,000lb/hr@500F,150psig

FeedHeater Outlet@25psig&635FDesireis2,500bpdoverflash(liquidratefromtrayabovefeed,Tray#39)

SideStrippers KeroseneStripper10trays@30%efficiencyKerosenedrawfromTray#10,vaporreturnedtoTray#6Strippingsteam@bottom(Tray#10)2500lb/hr@500F&150psigKeroseneproduct525FD86T95;8800bpdproduct(approximate)

DieselStripper10trays@30%efficiencyDieseldrawfromTray#20,vaporreturnedtoTray#16Strippingsteam@bottom(Tray#10)2500lb/hr@500F&150psigDieselproduct645FD86T95;10,240bpdproduct(approximate)

AGOStripper10trays@30%efficiencyAGOdrawfromTray#30,vaporreturnedtoTray#26Strippingsteam@bottom(Tray#10)2500lb/hr@500F&150psigAGOproduct750FD86T95;3835bpdproduct(approximate)

Pumparounds KerosenePumparoundDrawfromTray#10,returnedtoTray#725,000bpdflow,200Freturntemperature

DieselPumparoundDrawfromTray#20,returnedtoTray#1715,000bpdflow,250Freturntemperature

AGOPumparoundDrawfromTray#30,returnedtoTray#2710,000bpdflow,350Freturntemperature

AspenPlushasaspecificmoduleforefficientlysolvingcrudetowertypeproblems,thePetroFracmodel(notRadFrac).OntheColumnstabselectthelistarrowforPetroFrac.Now


wecanchooseaniconthatwillmostcloselyrepresentoutcolumn;chooseCDU10F,theonewithacondenser,firedheater,3pumparounds,&3sidestrippers.(Thischoiceonlychangestheicon,nottheabilitytospecifysideoperationsorthenumberofeach).Placeontheflowsheet&nameATMCOL.Highlighttheiconontheflowsheet&grabacornertoresize(makeitmuchbiggerthantheiconsrepresentingthepreheattrain).

Letsmakethestreamconnections.RightclickWARMCRD2,selectReconnectDestination,&connecttoATMCOL.Createthefollowingadditionalstreams&connecttoATMCOL:


MaterialstreamATMSTMtoMainColumnFeedconnections. MaterialstreamsKEROSTM,DIESSTM,&AGOSTMtoStripperSteamFeed

connections. MaterialproductstreamsNAPHTHAfromtheDistillateProductconnection,

ATMWTRfromtheCondenserWaterDecantconnection,&ATMRESIDfromtheBottomsProductconnection.

MaterialproductstreamsKERO,DIESEL,&AGOfromtheBottomsProductfromStripperconnection.

HeatstreamsQATMCfromtheCondenserHeatStreamconnection;QPA1,QPA2,&QPA3fromtheHeatStreamfromPumparoundconnection;

Yourflowsheetshouldhaveacolumnthatlookssomethingliketheimagebelow.Youcancleanuptheimagebyclickingthecolumnicon,grabbingthecoloredinletoroutletarrowsandmovingthearrowstomakeanoverallimagethatlooksmorereasonable;seethesecondimagebelow.Thenewimagedoesnotchangeanyconnectionsbutrathershowsamorelogicalflowpath.


ClickingtheNextarrowwillstepthroughrequiredstepstosetupthisdistillationcolumn.Thefirstthingrequiredwillbethesteamstreams:ATMSTM,KERSTM,DIESTM,&AGOSTM.Allstreamswillbe500F&150psig;eachhastobesetupwiththepropermassflowrate.

Oncepastthesteamstreamstheconfigurationforthecolumnitselfcomesup.TheConfigurationtaballowsyoutosetupthemostbasicinformationforthecolumn.NotethatAspenPluscountsthecondenserasastage,sothetotalnumberis51(1forthecondenser&50forthetrays).Onthisformentertheestimateforthedistillaterate(i.e.,theratefortheunstabilizednaphtha,NAPHTHA).


ClickNext.Nowwellsetuptheexternalfeedstothecolumn.Thecrudeoilwillgothroughthefurnacefirst(thefurnaceiscalculatedaspartofthecolumnalgorithm);rememberthatthecondenserisStage#1sowehavetoaddthistothetraynumberingforthefeedlocation.Thesteamifintroducedtothebottomstage;remembertomarkthisasOnStagesothatthereisvaportraffictothisstage.

ClickNext.Nowwewillenterthepressures.

ClickNext.Nowwewillenterthefurnaceinformation.SelectSinglestageflashsothatAspenPluswillperformaflashfortheoutlettemperatureofthefurnace.


ClickNext.Nowwearetoenterconfigurationinformationforthepumparounds.Butfirstletsrenamethepumparoundstomatchtheproductsections.SelectPumparoundsunderATMCOLinthelefthandcolumn.Selecteachrow&clickRename.ChangenamestoPAKERO,PADIESL,&PAAGO.

NowletsgetbacktothePumparoundconfigurationforms.SelectPAKEROinthelefthandcolumn.WhenspecifyingtheDrawstage&Returnstageremembertoadd1toaccountforthecondenserasStage1.DothesameforPADIESL&PAAGO.


ClickNext.Nowwearetoenterconfigurationinformationforthesidestrippers.Butfirstletsrenamethesidestripperstomatchtheproductsections.SelectStrippersunderATMCOLinthelefthandcolumn.Selecteachrow&clickRename.ChangenamestoSKERO,SDIESL,&SAGO.

Nowletsgetbacktothesidestripperconfigurationforms.SelectSKEROinthelefthandcolumn.WhenspecifyingtheDrawstage&Returnstageremembertoadd1toaccountforthecondenserasStage1.DothesameforSDIESL&SAGO.

ClickNext.Nowaformcomesuptoverifyconnectivity.Wevealreadyconnectedallofthematerialstreams,nowwehavetoconnecttheheatstreams.TheheatstreamisconnectedtothecondenserbyvirtueofhowtheywereoriginallyconnecttoATMCOL.Butwestillhavetodothepumparoundheatstreams.SelectPAKEROunderPumparoundsinthelefthandcolumn.NowselecttheHeatStreamtab;selectthepulldownlistforOutlet&selectoneoftheQPAstreams.DothesameforPADIESL&PAAGO.


ClickNext.Wehavenowenteredenoughinformationtorunthesimulations.HoweverwehavenotenteredthestageefficienciesnortheASTMD86specs.LetspressOKandrunthesimulationanyway.Itconvergesveryquickly,inabout4outerloopiterations.Whatdotheresultslooklike?WecanselecttheStreamResultstabtolookatflowrates&T95results.Notethefollowing:

Thestreamflowrateslisted(the2ndimage)arelowerthanthespecificationsmadeonthecolumn;thatisbecausethisshowstheflowrateonadrybasis(i.e.,withthewaterneglected)&thespecificationisonatotalbasis(withthewaterincluded).

TheT95resultsforthedistillationcurvesareclosebutnotwhatisdesired.WewillwanttoadjustthedrawratestogetthedesiredT95values.


WellnowsettheT95specifications.SelectDesignSpecificationsunderATMCOLinthelefthandcolumn.PressNewYoucannotnamethedesignspecs,onlynumberthem;acceptthenumberswhenpresentedintheCreateNewIDform;pressOK.LetsfirstspecifytheT95valueforthenaphtha.PulldowntheTypelistontheSpecificationstab;selectASTMD86temperature(dry,liquidvolumebasis).SettheTargetvalueas410F&theLiquid%as95.SelecttheFeed/ProductStreamstab;highlighttheNAPHTHAstream&press>tomove


ittotheSelectedStreamcolumn.SelecttheVarytab;pulldowntheTypelist&selectDistillateflowrate.


SpecifyingtheT95valuesforthekerosene,diesel,&AGOstreamsisdoneinasimilarmannerexceptwhenspecifyingwhattovary.ForthekerosenestreamselecttheVarytab;pulldowntheTypelist&selectBottomsflowrate&thenselectSKEROfromtheStrippernamelist.Dosimilarspecificationsforthediesel&AGOstreams.

Wenowhavereplacedthe4flowratespecificationswiththe4T95specifications.SelectRun.Itshouldagaintakeabout4outerloopiterationstosolvethecolumnequations.WecanagainlookattheproductstreamsbychoosingStreamResults.


Westillhaventaddedthestageefficienciestomodelactualtrays.ForthemaincolumnselectEfficienciesunderATMCOLinthelefthandcolumn.SelecttheMurphree/Vaporizationtab.Youdonothavetospecifytheefficienciesforeachindividualstagebutrathertheycan


begrouped.Remembertoadd1stagetoaccountforthecondenserbeingStage#1;theefficiencyofthecondenserwillbe100%.

Theefficienciesforthesidestrippersaredoneintheircorrespondingsection.ForthekerosenesidestripperselectEfficienciesunderSKEROinthelefthandcolumn.SelecttheMurphree/Vaporizationtab.Dosimilaroperationsforthediesel&AGOsidestrippers.

Wecannowrerunwillallspecifications.SelectRun.Itwilltakemoreiterationsbutshouldstillconvergeinlessthan25outerloopiterations.WecanagainlookattheproductstreamsbychoosingStreamResults.


DebutanizerColumnNext,letsdothesimplerofthetworemainingcolumns,theDebutanizerColumn(i.e.,theNaphthaStabilizer).WewillwanttooperatetheDebutanizeratahigherpressurethantheAtmosphericDistillationColumn,sowewillneedapumpfortheUnstabilizedNaptha.Wewillalsopreheatthefeedenteringthecolumn.Table5showstheoperatingconditionsforthecolumn&thefeedspump&preheater.

Table5.DefinitionsforDebutanizerColumnType OperatingParameterFeedPrep Increasepressureto250psig;usedefaultadiabaticefficiencyforpump(75%)

Preheatto250F;assumenegligiblepressuredropthroughexchangerTrays&Efficiencies 45trays.Numberfromtop.Alltrays80%efficiencyCondenserType Totalcondenser

1.5refluxratioReboilerType KettlereboilerPressures Condenser:150psig

TopTray:150psigBottomTray:160psigReboiler:160psig

Temperature NootherestimatesneededFeedLocations UnstabilizedNaphthatoTray#22Products OverheadLPGs,5,500bpd

StabilizednaphthafrombottomPlaceaPump&Heaterontheflowsheet&definetheconnectionsasshownontheflowsheet.ClickNext&weretofillinthefeedheaterinformation;setthevalueforPressureto0tosignifyazeropressuredrop.ClickNextagain&wellfillinthefeedpumpinformation;clickforDischargepressure&setthePumpefficiencyto0.75.


NowwecandefinetheDebutanizer.JustlikewiththeAtmosphericDistillationColumnwellpickanoptionfromPetroFrac.Choosetheicononthebottomrowwithjustareboiler&acondenser(FRACT).ConnectFEEDDEC4asafeed,createproductsstreamsLPGS&SNAP,overheadwaterDEC4WTR,&heatstreamsforthecondenser&reboiler.

ClickNexttostartfillingininformationforthisDebutanizer.Remembertoadd2totheNumberofstagestoaccountforthecondenser&thereboiler.AlsonotethatthefeedlocationchosenisAboveStage;thismeansthatliquidfromthefeedwillbeintroducedtothestagewhereasvaporwillbeputtothestageabove(justasifafeednozzleisputinto


thevaporspaceaboveatray).RemembertoaddonetothestagelocationtoaccountforthecondenserbeingStage#1.

Thesimulationberunbutweneedtoaddthestageefficienciesfirst.SelectEfficienciesunderDEC4inthelefthandcolumn.SelecttheMurphree/Vaporizationtab.Youdonothavetospecifytheefficienciesforeachindividualstagebutrathertheycanbegrouped.Remembertoadd1stagetoaccountforthecondenserbeingStage#1&1stageforthereboilerbeingStage#47;theefficienciesofthecondenser&reboilerwillbe100%.


NowwecanclickNexttorunthesimulation.Itshouldconvergeinlessthan10outerloopiterations.VacuumDistillationColumnThefinalstepistodefinethefeedheater&VacuumDistillationColumn.AdditionalsteamisinjectedintotheVacuumFeedHeatertoincreasevelocity&minimizecokeformationwithintheheater.EventhoughtheVacuumColumnispackeditwillbemodeledastrays,i.e.,sectionsofnonequilibriumstages.PlaceaMixerontheflowsheetdownstreamfromtheAtmosphericColumn.NextletsplacetheVacuumDistillationColumn.JustlikewiththeAtmosphericDistillationColumnwellpickanoptionfromPetroFrac.Choosetheiconwithjustafiredheater&twopumparounds(VACUUM1F).ConnecttheoutletfromtheMixer&asteamstreamtotheVACCOLasfeeds,createproductsstreamsLVGO,HVGO,&SLOPWAXasSideProductsfromMainColumn,overheadvaporVACOVHD,&heatstreamsforthetwopumparounds.


Table6.DefinitionsforVacuumDistillationColumn

Type OperatingParameterTrays&Efficiencies 14trays.Numberingfromtop:

Tray1:100%Trays2to11:50%Tray12:100%Trays13to14:30%

CondenserType Nocondenser,LVGOpumparoundliquidreturntotopstageReboilerType None,DirectFiredHeaterPressures TopTray:50mmHg

BottomTray:62mmHgTemperatures Top180F(controlledbytopLVGOpumparound)FeedLocations CrudeoiltoTray#12

StrippingSteamatbottom(Tray#14)20,000lb/hr@500F,150psigFeedHeater 20,000lb/hrsteaminjectedintoheatercoilswiththeAtmosphericResidfeedstock

(500F&150psig)Outlet@180mmHg&760F;wouldlike3,000bpdexcesswashliquid(liquidratefromtrayabovefeed,#11)

Pumparounds LVGOPumparoundDrawfromTray#4,returnedtoTray#122,300bpdflow,outlettemperatureadjustedtocontroltoptemperatureoftower;approximately85F,40MMBtu/hrcooling

HVGOPumparoundDrawfromTray#8,returnedtoTray#550,000bpdflow,150Fcoolingapproximately400F,40MMBtu/hrcooling

Products LVGOfromTray#4;915FD1160T95;5,000bpd(approximate)HVGOfromTray#8,1050FD1160T95;21,000bpd(approximate)SlopWaxfromTray#11,1,000bpdVacuumresidfrombottom

FirstdefinethesteamstreamgoingtotheVacuumHeaterCoils.SelectCOILSTMunderSTREAMSinthelefthandcolumn.DothesameforthesteamstreamgoingtothebottomoftheVacuumDistillationColumn,VACSTM


LetsconfiguretheVacuumDistillationColumnitself.SelectVACCOLunderBlocksinthelefthandcolumn.Eventhoughthecolumnwillbepackedwellmodelitwithasetofnonequilibriumstages.OntheConfigurationtabpicktheCondenseroptionNoneToppumparound.OntheStreamstabdenotethatVACFEEDgoesthroughafiredheaterbeforegoingtoStage#12&theVACSTMgoesdirectlyOnStageto#14.Setthetop&bottompressuresonthePressuretab.OntheFurnacetabspecifytheFurnacetypeasSinglestageflashwithliquidrunback&settheoutlettemperature&pressure.


Nowletssetupthepumparounds.ChangethenamestoPALVGO&PAHVGO.Setdrawrates&conditionsontheSpecificationstab.LetsapplytheapproximatespecsasHeatdutyspecs(sincethesearethemostlikelytoconverge).NotethattheHeatdutyvaluesarespecifiedasanegativenumberssincetheyrepresentcooling(i.e.,heatremoval).ConnecttheappropriateheatstreamontheHeatStreamstab.


Letsspecifythestageefficiencies.SelectEfficienciesunderVACCOLinthelefthandcolumn.SelecttheMurphree/Vaporizationtab.Youdonothavetospecifytheefficienciesforeachindividualstagebutrathertheycanbegrouped.


Toaidintheconvergenceofthecolumnletsaddacoupletemperatureestimates.ClickontheEstimatesiteminthelefthandcolumn.Specifyvaluesfortrays#1,#2,.

Letsapplythefirstdesignspecbeforetryingtorunthesimulation,theoneforthetoptemperature.Thisisachievedbyadjustingtheoperationofthetoppumparound,PALVGO.ClickonDesignSpecificationsinthelefthandcolumn,clickNew,andselectOKforthedefaultname1.ThespecTypeisStagetemperatureforStage1;wellVarythePumparounddutyforPALVGO(sincethisisthespecweappliedtothispumparound).


Runthesimulation.TheVacuumColumnshouldconvergeinabout10iterations.Wehavenotappliedallofthedesignspecs,butletsseehowclosewecometothedesiredperformance.WearemostinterestedintheD1160T95valuesfortheLVGO&HVGOaswellastherunbackliquidfromthesectionaboutthefeedtray(i.e.,theliquidratefromTray#11).NotethattheD1160values(correctedto1atm)above50%aretheTBPvalues.TheT95valuescanbefoundwhenselectedtheStreamResultsinthelefthandcolumn;theTBPvaluesare768.3FfortheLVGO&913.9FfortheHVGO.TheliquidrunbacktothefeedtraycanbecalculatedfromtheinformationintheProfilestable.NormallythenetflowofliquidfromonetraytotheonebelowwouldbetheamountintheLiquidflowcolumnminustheamountintheLiquidproductcolumn.However,forthefeedheaterchosen,allofthenetliquidisfedbacktothefrontoftheheater&isconsideredliquidproduct,too.So,thenetliquidisreallytheamountintheLiquidproductcolumnminustheSlopWaxrateproduced;herethisis186,800bpd.


ToincreasetheT95valueofasidedrawwewouldnormallyincreasethedrawrate.Wehavetobecareful,though,nottoexceedthevaluesgoingintoeachsection(andcausethatsectiontodryup).LetsaddresstheHVGOfirst.Createanewdesignspec&varytheHVGOdrawratetoachievethis.Rerunthesimulation;itshouldconvergeinlessthan20iterations.Nowwehavewithdrawn30,676bpdHVGOtomakethisT95spec.Theliquidrunbackhasreducedconsiderably,nowdownto3,050bpd.


NowletslookattheLVGOresults.For5,000bpdLVGOratetheD1160T95valueistoolow.SincetheT95valueistoolow,wewillhavetoincreasetheLVGOdrawratetotrytomeetthisspec.However,thereisonly3,518bpdrunbackabovethefeedtray,sowenormallythinkthatcantraisetherateabovethisamount.However,wecanactuallyraiseitconsiderably&notdryupthetopoftheVacuumColumn.NotethatifweraisetheLVGOspecto4,000bpdwecandothisandactuallyincreasetherunback.How?BecausetheHVGOratedecreasesbymorethan3,000bpdtokeepitsT95spec.SoletsapplytheLVGOT95spec;nowwevemadebothT95specswithoutdryingupthetopoftheVacuumColumn.Thefinalspecthatweneedtoachieveistheliquidratefromabovethefeedtray.Thecurrentrateis6,776bpd,higherthannecessary.Wecanreducethisratebyreducingthefeedheatersoutlettemperature(whichwillreducetheamountofthefeedvaporized).Wecanadjustthefeedheatertemperaturemanuallyto739.5Fandgetaliquidrunbackrateof2,990bpd(justalittlebittoolow).Canweadjustthisautomaticallytodeterminetheactualtemperature?WecouldaddadesignspectomodifythefurnacetemperaturemaketheliquidratefromTray#11;inpastexperiencethiswilltendtocrashtheprogram.Insteadwewillusethebuiltinfacilitytomodifythefurnacesoutletconditionsbyspecifyingthefractionaloverflashinthecolumn.Sincethetotalstandardflowtothecolumnis53,632bpdthen3,000bpdoverflashmeansafractionalvalueof0.05594.Makingthisspecificationwillgivethecorrectoverflashvalue&resultsinafurnaceoutlettemperatureof739.56F.


Theresultsofallofthesestepsaresummarizedinthefollowingtable.

VacuumColumnResultsWhenApplyingDifferentSpecsLVGORate[bbl/day]

LVGOD1160T95[F]

HVGORate[bbl/day]

HVGOD1160T95[F]

SlopWasRate[bbl/day]

RunbackfromTray#11[bbl/day]

1,000 768.4 21,000 924.4 1,000 186,8101,000 797.1 30,676 1050 1,000 3,0504,000 825.9 27,220 1050 1,000 3,56216,487 915 13,855 1050 1,000 6,77616,835 915 13,185 1050 1,000 2,99016,808 915 13,212 1050 1,000 3,000

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