Rev0.0 ‐1‐ January1,2015
SteamCycleSimulation–AspenPlusv8.6TheattachedgivesstepstosetupasimulationinAspenPlusv8.6tomodelasimpleRankinesteamcycleforelectricityproduction.Thesystemconsistingof:
Fuelsidewithnaturalgasfeed,airblower,combustionchamber,&fuelsideofthesteamboiler.
Steamsidewithsteamturbine,steamcondenser,condensatepump,&steamsideoftheboiler.
Thesimulationwillbesetupassumingisentropicstepsfortherotatingequipment.WhenthesimulationissetuptheoverallPFDshouldlooklikethefollowingfigure.
Createnewsimulationfile
StarttheprogramfromStart,AllPrograms,AspenTech,ProcessModelingV8.6,AspenPlus,AspenPlusV8.6.WhentheprogramopenschoosetheNewbutton.ChoosetheGasProcessingthentheGasProcessingwithMetricUnitstemplate.ClicktheCreatebutton.
Rev0.0 ‐2‐ January1,2015
DefinetheComponents&thePropertyModels
Specifycomponents,fluidpropertypackages,&crudeoilassays
Thefirststepistodefineasetofpurechemicalspeciestorepresent:
Steamasmodeledbypurewater&usingpropertycorrelationsconsistentwiththeASMESteamTables.
Thenaturalgasfuel,air,&combustionexhaustaspurelightcomponentsmodeledbythePeng‐Robinsonequationofstate(EOS).
Nowlet’saddcomponentstomodelthefuelsideofthesystem.GobacktotheComponentListsitem&clickontheAddbuttontocreateComponentList‐2.Weneedcomponentsforthefollowing:
Steam.Fornowwe’llmodelaspurewater. Naturalgas.Fornowlet’smodelthisasapossiblemixtureofmethane,ethane,&propane. Air.Fornowwe’llmodelthisasamixtureofoxygen&nitrogen. Combustiongases.Attheminimumwe’llalsoneedcarbondioxideandwater(whichwe
alsoneedformodelingthesteam).However,we’llalsowanttotakeintoaccountincompletecombustion(formingcarbonmonoxide)aswellasNOxformation(fornowjustasNO,NO2,&N2O).
ClicktheFindbuttontobringupthedatabanksearchform.Youcanentereithertheentireformula,partofaname,orseveralotherpossiblesearchitemstofindallofthedesiredchemicalspecies.Whenthepropercompoundisfound,selectitinthelist&clickAddselectedcompounds.ThefollowingfigureshowsasearchforH2O.Asyouareaddingcompoundsyoumaybeaskedwhethertoaddorreplacethecompoundalreadyinthelist;choosetheAddoption.
Rev0.0 ‐3‐ January1,2015
BelowisanexampleofcomponentsretrievedfromtheAspendatabanks.Therearetwoissueswithdefaultmannerinwhichthislistispresented.One,theComponentIDsarenotverydescriptiveofthecompound(especiallyascomparedtotheAliasvalues).Two,theorderdoesnotgroupthecompoundsinaconvenientmanner.Wecanaddressbothoftheseissuesbeforeproceedingmuchfurther.
Let’schangetheComponentIDvaluestomostlymatchtheAliasvalues.SelecttheComponentIDvalueeitherbydouble‐clickingonitorbyclicking&thenpressingtheF2key.Onceselected,typeinthenewID&presstheEnterkey.AspenPluswillaskwhatyoureallywanttodobymakingthischange;clicktheRenamebutton.ChangeallIDs.
Rev0.0 ‐4‐ January1,2015
NowpresstheReorderbutton.Aformpopsupthatwillallowyoutomoveselectedcompoundsupordownsothattheyinaconvenientorder.PressClosewhendone.
Rev0.0 ‐5‐ January1,2015
Thenextstepistoassurethatanappropriatefluidpropertypackagehasbeenchosenforthesecompounds.ClickonMethodsintheAllItemslistontheleft.FromhereweseethatthePeng‐RobinsonEOShasbeenspecifiedasthebasemethod(perthechoiceoftemplateoriginallychose).AlsotheASMEsteamtableoptionhasbeenspecifiedforcaseswhenonlywaterispresentinthestream.Thesearethedesiredoptionssowecancontinueon.
Nowisagoodtimetosavethefilebeforewestartsettinguptheprocesssimulation.ClicktheFiletab&thentheSaveAsitem.ChoosetheAspenPlusBackupoption.Setup&SolvetheFlowsheet
WorkingUnits
ActivatetheSimulationoption.Notethatyou’llseeablankflowsheet.WewouldliketoshowthecalculationswithamodifiedsetofSIunits,inparticular:
Temperatureas°C. Pressureasbar(absolute). Massflowaskg/sec. Molarflowaskg.mol/sec. HeatdutyaskJ/sec. PoweraskW.
Rev0.0 ‐6‐ January1,2015
UndertheHometabclicktheUnitSetsbutton.InthelistofunitsetsclickontherowforSI‐CBAR&pressEdit.Proceedingthroughthevarioustabsallowsyoutodeterminewhatwillbeusedforthedisplayoftheresultsaswellasthedefaultunitsfortheinput.Mostoftheunitsarewhatwedesire,butnotall.Forexample,youcanseethatMassFlowwillbereportedinkg/hr,notquitewhatwewant.
Let’spulldownthelistsassociatedfortheFlowrelatedvalues&pickoptionsthatareintermsofseconds,nothours.GointotheHeattab.ChangeHeatrelatedvaluesfromJtokJandpowerrelatedvaluesfromWtokW.
SteamCycle
WewillwanttocreateasimpleRankinecyclewiththefollowingprocessconditions: Saturatedsteamproductionat125bar. Finalcondensationto20°C. Steamturbineoperatingatidealreversibleconditions. Condensatepumpoperatingatidealreversibleconditions. Noextrapressuredropthroughheatexchangersorpiping.
Rev0.0 ‐7‐ January1,2015
Let’splacethefollowingunitsfromtheModelPalettetotheflowsheet1:2Heaters,aturbine(asPressureChangers,Compr,ICON3),&Pump.Ultimatelyitwillbedepictedasfollows(withrotationofthepumpicon).
Connecttheunitswiththefollowingstreams:
IntheModelPaletteclickontheMaterialstreambutton.Drawasfollows:o DrawastreamintotheredarrowofPUMP;callitCONDNSAT.o DrawastreamfromtheredarrowoutofPUMP&intotheredarrowofBOILER;callit
HP‐STEAM.o DrawastreamfromtheredarrowoutofBOILER&intotheredarrowofSTMTURBN;
callitAIR‐2.o DrawastreamfromtheREDarrowoutofSTMTURBN&intotheredarrowof
CONDNSR;callitEXHAUST.o DrawastreamfromtheredarrowoutofCONDNSR;callitCOND‐2.
IntheModelPaletteclickontheHeatstreambutton.Drawasfollows:o DrawastreamoutofthebluearrowofBOILER;callitQ‐BOILER.o DrawastreamoutofthebluearrowofCONDNSR;callitQ‐CONDSR.
IntheModelPaletteclickontheWorkstreambutton.Drawasfollows:o DrawastreamoutofthebluearrowofPUMP;callitW‐PUMP.o DrawastreamoutofthebluearrowofSTMTURBN;callitW‐TURBN.
Let’sstarttoinitializethewatercirculatingthroughthesteamloop.
1IftheModelPaletteisnotvisiblechoosetheViewtab&clickontheModelPalettebuttonorpresstheF10key.
Rev0.0 ‐8‐ January1,2015
Double‐clickontheCONDNSATstream.SelectTemperature&VaporFractionfortheFlashType.Enter20CfortheTemperature&0fortheVaporFraction(i.e.,asaturatedliquid).SpecifytheCompositionaspurewater;entera1forH2OinthelistwiththeMole‐Fracoption.Let’suseaflowbasisof1kg/s.
Nowlet’ssettheoperatingparametersforthevariousunits.DoubleclickonthePUMPicontoopentheinputsheet.MakesurethePumpoptionisspecifiedunderModel.SpecifytheDischargePressureas125bar.Finally,todefinethisasanidealpumpspecifya1forboththePump&DriverEfficiencies.
Nowlet’sdefinetheoperatingconditionsforthesteamsideoftheboiler.DoubleclickontheBOILERicontoopenitsinputform.Wewanttospecifytheoutletsteamassaturatedvapor.Wecouldspecifythevaporfraction.Insteadwe’lldefine0°Cofsuperheat.Wealsowanttospecifyazeropressuredrop.Wecandothisbyspecifyingazerovalueforthepressure.
Rev0.0 ‐9‐ January1,2015
Nowlet’sdefineoperatingconditionsfortheturbine.DoubleclickontheSTMTRBNicontoopentheinputsheet.MakesuretheTurbineoptionisspecifiedunderModel.Wewanttodefinethisasanidealturbinesospecifya1forboththeIsentropic&MechanicalEfficiencies.WeneedtospecifysomethingabouttheDischargePressureeventhoughwedon’treallyknowwhatitis,onlythatiscorrespondstothewatervaporpressureat20°C.Fornowspecifyavalueof0.1bar;we’llfixitlater.Weknowthatthisisacondensingsteamturbine.ThedefaultfortheTurbinemodelisthatonlyvaporwillexit,sothiswillhavetobechanged.ClickontheConvergencetab.PulldownthelistforValidphases&changetoVapor‐Liquid‐FreeWater.
Nowlet’sdefinetheoperatingconditionsforthesteamcondenser.Doubleclickontheexchangericontoopenitsinputform.Wewanttospecifytheoutletassaturatedliquid.WewanttomakesurethatoneoftheFlashTypeoptionsisVaporfraction&settheappropriatevalueas0(i.e.,saturatedliquid).Wealsowanttospecifyazeropressuredrop(i.e.,letthedischargepressuresettingfromtheturbinecontrolthis).MakesurethatoneoftheFlashTypeoptionsisPressure&settheappropriatevalueas0(i.e.,zeropressuredrop).Wenowhaveenoughsettingstobeabletorunthesimulation.Openthecontrolpanel(itemundertheHometab)&pressRun.Somewarningsmaycomeupbuttheywillbeaddressedlater.WecansummarizetheresultsontheflowsheetbymodifyingtheStreamResultssettings.SelecttheMainFlowsheet.SelecttheModifytab&selecttheTemperature,Pressure,&VaporFractionitems.Clickinthelowerleft‐handcorneroftheStreamResultssection.Onthepop‐upformselectthe
Rev0.0 ‐10‐ January1,2015
Heat/Workitem.Also,changetheformatforthePressurevaluetoshowthreedecimalplaces(i.e.,as“%.3f”).DothesamefortheVaporfractionformat.ClickOK.
Wecannowseeasummaryoftheresultsontheflowsheetbelow.Onethingtonoteisthatourguessfortheturbine’sdischargepressurewasinerror.Thepressureshouldactuallybe0.019bartocorrespondwithacondenseroutlettemperatureof20°C.Wecouldgobackandchangethevaluemanually.However,we’lluseoneofAspenPlus’soperationstoautomaticallysetittomatchthecondenseroutlet.
WewillusetheCALCULATORoperationto“feedforward”theCondenser’spressuretotheturbine’sdischargepressure.Eventhoughwecoulduseacalculatorwithoutseeinganyindicationontheflowsheetwe’llinsteadputaniconontheflowsheettogiveanindicationthatitisthere.
Rev0.0 ‐11‐ January1,2015
FromtheModelPalette,chooseManipulators,Calculator,&selectICON1.Placeitontheflowsheetneartheexhauststream.(Fortheflowsheetshownitisrotatedverticallysoitcan“hang”belowtheline.)RenameitSET‐P.Double‐clickontheicontoopenupitsinputform.DefinethevariablePCNDSRasthepressurecalculatedforstreamCONDNSAT(i.e.,thesaturationpressureat20°C).SpecifythisasanImportvariable(i.e.,thevaluehastobecalculatedbyAspenPlus&willbe“read”bythecalculatoroperation).
NowdefinethevariablePTURBNasthesteamturbine’sdischargepressure.SpecifythisasanExportvariable(i.e.,thevaluebe“written”asaparameterinadownstreamoperation).
Rev0.0 ‐12‐ January1,2015
Finally,definetherelationshipintheCalculatetab.UsingtheFortranmethodenterthestatement“PTURBN=PCNDSR”(startingincolumn6).
Nowwecanrerunthesimulationandgettheresultssummarizedbelow.WecanseethattheCALCULATORhasdoneitsjob;theoutletpressurefromthesteamturbineisnowthesameastheinlettothecondenser.However,thetemperaturesaredifferent.What’swrong?
TheproblemisthatmostofthecalculationsaredonewiththedefaultPENG‐ROBproperties,notthedesiredSTEAM‐TAproperties.TheexceptionistheoutletoftheturbinewhichrecognizestheliquidformedasFreeWater&usestheSTEAM‐TAoptionforitsproperties.Hence,theinconsistency.WecanforcetheunitstousetheSTEAM‐TAoptiontodothecalculationsbymakingmodificationstoeachunit’sBlockOptionssettings.IntheSimulationtreestructureforeachoperationselectBlock
Rev0.0 ‐13‐ January1,2015
Options.Underthepull‐downlistforPropertymethodselectSTEAM‐TA.TheformforSTMTRBNisshownasanexample.
Nowwhenwererunthesimulationwegetconsistentresults.Noticethattherearesubtlechangestotheheat&workstreams.Forexample,theboilerheatisnow2,581kJ/sec;itwas2,808kJ/secwhencalculatedbythePENG‐ROBmethod(adifferenceof9%).
Rev0.0 ‐14‐ January1,2015
InpreparationforadditionalchangesweneedtomodifythesettingsforSTMTRBN.OnitsinputformclickontheConvergencetab.ChangetheValidphasestoVapor‐Liquid‐Liquid.Whenwererunwegetaminorwarningthattheoutletisbelowitsdewpoint(whichwealreadyknowsincethisisacondensingturbine).
Whendealingwiththepositive&negativevaluesfortheheat&workstreamsrememberthetwoconventionsusedbyAspenPlus:
IftheheatorpowerstreamisanoutletofaunitthenAspenPlushascalculatedthevaluetomakeotheroperatingspecifications(suchastheoutlettemperatureinanexchanger).IfitisaninlettoaunitthenAspenPlususesthevaluetodeterminetheoutletconditions.
Heatrepresentsenergytoorfromtheunitoperation;itisinthedirectionofthearrowiftheheatispositiveorintheoppositedirectionifitisnegative.Work,ontheotherhand,representsenergytoorfromtheuniverse;theenergyflowisintheoppositedirectionasthatforheat.
SinceQ‐BOILERisnegativeforaheatstreampointingawayfromtheBOILER,thentheenergyflowsintotheboiler’sfluid.SinceW‐TURBNisnegativeforaworkstreampointingawayfromtheSTMTURBN,thentheenergyflowsoutoftheturbine’sfluid.Fromtheresultsshownwecancalculatethethermalefficiencyofthissteamcycle.Weshouldalwaysmakeuseoftheabsolutevaluesfortheheat&workstreams.Forthissteamcycle:
netth
boiler
W‐TURBN W‐PUMPW 1078 130.4126
Q Q‐BOILER 2581
.
Rev0.0 ‐15‐ January1,2015
Fuel&CombustionSystem
Wewillwanttocreateasimplenaturalgasburner/boilerwiththefollowingprocessconditions: Naturalgasisavailableatindustrialdeliverypressure,20bar‐g&15°C.Wewill
characterizethenaturalgasas100%methane. Airisavailableat25°C.Wewillcharacterizetheairasa21/79O2/N2molarmixtureand
bonedry(i.e.,nowater).Wewanttoaddenoughairsothatthereis20%excessoxygenbasedoncompletecombustionofthenaturalgas.
Thecombustionprocessoccursnearatmosphericconditionssothenaturalgasmustbeletdowninpressure.However,ablowerisneededtopushtheairintothecombustionchamber.
Thepressuredropthroughtheburner/boiler/fluecombinationis0.3bar. Thefluegasisemittedat120°Ctopreventanyliquiddropout&subsequentcorrosion
problems.Let’splacethefollowingunitsfromtheModelPalettetotheflowsheet:Valve,Compressor2,RGibbsReactor,&Heater3.Ultimatelyitwillbedepictedasfollows.(We’lldiscusstheSETcalculatorsaswego.)
Connecttheunitswiththefollowingstreams:
IntheModelPaletteclickontheMaterialstreambutton.Drawasfollows:o DrawastreamintothebluearrowoftheLETDOWNvalve;callitFUELGAS.o DrawastreamfromthebluearrowoutoftheLETDOWNvalve&intothebluearrowof
theCOMBSTNreactor;callitLP‐GAS.o DrawastreamintothebluearrowoftheAIRBLWRcompressor;callitAIR.o DrawastreamfromthebluearrowoutoftheAIRBLWRcompressor&intotheblue
arrowoftheCOMBSTNreactor;callitAIR‐2.o DrawastreamfromthebluearrowoutoftheCOMBSTNreactor&intothebluearrow
oftheHRSGexchanger;callitCOMBGAS.o DrawastreamfromtheredarrowoutoftheHRSGexchanger;callitFLUEGAS.
IntheModelPaletteclickontheHeatstreambutton.Drawasfollows:
2Notethatthecompressorhasbeenrotatedverticallytogettheinletstreambelowthecompressor&theoutletstreamabove.3Notethattheheatexchangerhasbeenrotatedverticallytogettheheatstreambelowtheexchanger.
Rev0.0 ‐16‐ January1,2015
o DrawastreamoutofthebluearrowoftheHRSGexchanger;callitQ‐HRSG. IntheModelPaletteclickontheWorkstreambutton.Drawasfollows:
o DrawastreamoutofthebluearrowoftheAIRBLWRcompressor;callitW‐BLOWER.Let’sstartsettingparametersfortheinletstreams.Let’sinitializethenaturalgasstreamfirst.Double‐clickontheFUELGASstream.SelectTemperature&PressurefortheFlashType.Enter15CfortheTemperature&20bargforthePressure.Enter1fortheC1valueasMole‐Frac.Let’suseaflowbasisof1kg.mol/sec.Nowlet’sinitializetheAIRstream.Double‐clickontheAIRstream.SelectTemperature&PressurefortheFlashType.Enter25CfortheTemperature&0bargforthePressure.Enter0.21fortheO2&0.79fortheN2valuesasMole‐Frac.Asastartingpointlet’sdefinetheflowrateas12kg.mol/hr.Let’sspecifytheoutletpressureof0.3bar‐gafterthelet‐downvalve.Double‐clickonLETDOWN.Specify0.3bargastheOutletpressure.
Rev0.0 ‐17‐ January1,2015
Wewanttomaketheairbloweranidealreversiblecompressor.Double‐clickonAIRBLWR.SelecttheCompressorasModel.PulldowntheTypelist&chooseIsentropic.Specify1fortheIsentropic&MechanicalEfficiencies.
Nowit’stimetomodelthecombustionportionofthefuelgasburner.Therearevariousoptionsfordoingthis.Oneofthesimplest(andwouldnormallybedoneforhandcalculations)wouldbetodefineallcombustionreactions&specifytheextentofconversionforeach.Instead,we’regoingtotakeadvantageofthefullthermodynamiccapabilitiesofAspenPlus&useareactorthatwillminimizetheGibb’sfreeenergy.Allwehavetodoislisttheexpectedproducts&AspenPluswillcalculatetheresultingproductdistributionthathonorsthematerial&energybalancesaswellasanychemicalequilibriumlimitations.DoubleclickontheRGibbsReactoricon.SetPressureto0(torepresentazeropressuredrop)&specify0fortheHeatDuty(tosignifyadiabaticoperation).That’sprettymuchit.Thedefaultistoincludeallspeciesinthecomponentlistaspotentialproducts.
Nowlet’sseehowmuchheatcanbetransferredoutofthecombustiongasesbyspecifyingthecombustiongassideoftheboiler.Doubleclickontheheatericon.Settheconditionstotheoutletconditionsoutthestack:120C&0barg.
Rev0.0 ‐18‐ January1,2015
Wehaven’taddressedthecalculatoroperationsyetbutwecanstillrunthesimulation.TheresultsaresummarizedontheFlowsheetshowthatthecombustiontemperaturewillbe1734°C.Wecandouble‐clickontheCOMBGASstream&seethattherewillbesomeCO&NOxformedattheseconditions.
Therearestillacoupleitemstobedoneto“cleanup”thesimulation&formatoftheresults.Thefirstisforamatterofconvenience–howshouldwespecifythepressureoftheAIR‐2streamoutoftheairblower?RightnowthepressureintotheCOMBSTNoperationissetseparatelyforthetwoinletstreams(LP‐GAS&AIR‐2).Ifastudywastobeperformed&thepressureweretochangethenhavingthespecificationsintwoseparatelocationscouldleadtothembeingchangeddifferently.Itsurewouldbenicetosetitonlyinonelocation&thenhavetheotherlocationupdateautomatically.WecandothiswithaCALCULATORoperation.FromtheModelPalette,chooseManipulators,Calculator,&selectICON1.PlaceitontheflowsheetneartheAIR‐2stream.(Fortheflowsheetshownitisrotatedtotheleftsoitcan“hang”offtheline.)RenameitSET‐AP.
Rev0.0 ‐19‐ January1,2015
Double‐clickontheicontoopenupitsinputform.DefinethevariablePFUELasthepressureforstreamLP‐GAS(i.e.,thepressureoutofthelet‐downvalve).SpecifythisasanImportvariable(i.e.,thevaluehastobecalculatedbyAspenPlus&willbe“read”bythecalculatoroperation).
NowdefinethevariablePAIRastheairblower’sdischargepressure.SpecifythisasanExportvariable(i.e.,thevaluebe“written”asaparameterinadownstreamoperation).
Finally,definetherelationshipintheCalculatetab.UsingtheFortranmethodenterthestatement“PAIR=PFUEL”(startingincolumn6).
Thesecondchangeinvolvesaconvenientwaytomakesurethatthecorrectamountofairisaddedtomatchthe“excessoxygen”spec.Theamountofstoichiometricoxygenisdeterminedfromthecombustionreactions.Formethane,ethane,&propanethereactionsare,respectively:
Rev0.0 ‐20‐ January1,2015
CH4+2O2CO2+2H2O C2H6+3.5O22CO2+3H2O C3H8+5O23CO2+4H2OThisshowsthatweneedtoknowthecompositionofthefuelgas(inmolaramounts)todeterminethestoichiometricamountofoxygenneeded.The“excess”partisadditionaloxygen(asamultiplier)thatisadded.ThefinalconsiderationisthatthespecificationinAspenPlusisnotjustfortherateofoxygenbutratheroftheair;sowehavetotakeintoaccountthecompositionoftheairaccountforthelargeamountofnitrogenalsobeintroducedintotheCOMBSTNoperation.Sincewehavesetthecompositionofthefuelgastobepuremethane&thebasisflowrateto1kg.mol/secthenthestoichiometricoxygenflowrateistwicethis,2kg.mol/sec.Wealsoneedtoincreasethisby20%toincludethedesiredexcess.Andweneedtotakeintoaccounttheoxygencontentintheairtodeterminetheairrate.Sooverall:
2
2
O
air
O
1 2 1 0.211.43kg.mol/sec
0.21
excessstoichn f
ny
.
WecoulddothesecalculationspriortorunningAspenPlusandentertheairrate.OrwecoulddothecalculationswithinAspenPlus.FromtheModelPalette,chooseManipulators,Calculator,&selectICON1.PlaceitontheflowsheetneartheAIRstream.(Fortheflowsheetshownitisrotatedtotherightsoitcan“hang”offtheline.)RenameitSET‐AFLO.Double‐clickontheicontoopenupitsinputform.DefinethevariableAIRFLOasthemolarflowofthestreamAIR(i.e.,thepressureoutofthelet‐downvalve).SpecifythisasanExportvariable.
Rev0.0 ‐21‐ January1,2015
Nowlet’sstartdefiningImportvariables.FirstdefinethevariableYO2astheO2molefractionintheair.SpecifythisasanImportvariable.
Nextlet’sdefineImportvariablesforthecombustibleportionsofthefuelgas(eventhoughwe’veonlyusedmethanewehaveincludedthepossibilityforethane&propane,too).DefinethevariablesC1FLO,C2FLO,&C3FLO.MakesurethesearespecifiedasImportvariables.
Finally,definetherelationshipintheCalculatetab.UsingtheFortranmethodenterthestatement:AIRFLO=2.*C1FLO+3.5*C2FLO+5.*C3FLOAIRFLO=AIRFLO*(1.+0.2)AIRFLO=AIRFLO/YO2(startingincolumn6).
Thesimulationcanbererungivingtheresultssummarizedbelow.Notethatcorrectairflowhasbeencalculated,11.43kg.mol/sec.
Rev0.0 ‐22‐ January1,2015
Onemoremodification,thattodirectlyshowthemolefractionsofallofthestreams(sincerightnowtheresultsareonlyshownasmolarflows).ExpandtheSetupoptionsintheleft‐handSimulationtreestructure.SelectReportOptions.NotethatMoleFlowbasisoptionisspecifiedbutnoneoftheFractionbasisoptions.SelecttheMoleoption.
Rev0.0 ‐23‐ January1,2015
Rerunthesimulation.Nowwhenyoudouble‐clickontheCOMBGASstreamyouwillnotonlyseethecompositionoutofCOMBSTNinmolarflowsbutalsoasmolefractions.
TyingtheTwoSystemsTogether
Eventhoughthesteamcycle&fuelgassystemsareinthesameAspenPlusflowsheettheyarereallymodeledseparately.Thesteamcyclehasconvergedwithabasisof1kg/secwatercirculationrate&thefuelsystemhasconvergedwithabasisof1kg.mol/secfuelgas.Wewilltiethesystemstogetherby“pushing”thedutyfromthefuelsideoftheboilertothesteamside&adjustingthewatercirculationrateinthesteamcycletoensurethisistheonlyheatneededforthesteamcycle.Nowlet’sconnectthetwosystems.
RenamethestreamQ‐BOILERtoQ‐RESID(for“residual”). RenamethestreamQ‐HRSGtoQ‐BOILER. Right‐clickonQ‐BOILER,selectReconnect,ReconnectDestination,&attachtoblueinlet
arrowontheBOILERexchanger.
Rev0.0 ‐24‐ January1,2015
Runthesimulation.Noticethatforthecombinationoffuelgasrate&watercirculationratethereistoomuchgeneratedfromthecombustionsideoftheboilertobeabsorbedbythesteam.Wecanseethisbecausethe“residual”heatfromthesteamside,Q‐RESID,is763,426kJ/sec.Since766,007kJ/secwasgeneratedfromthecombustionsidethenonly2,581kJ/secwasneededinthesteamside.
Theresultsshowthatwereallyneed296.8kg/secwatercirculatinginthesteamcycletoabsorballoftheheatfromthecombustionside.Wecouldenterthisvaluemanuallybutthenwewouldhavetodothehandcalculationoveragainifanyconditionsweretochange.InsteadwewillletAspenPluscalculatetheproperflowrate.FromtheModelPaletteselectaDesignSpec(theoneshowninthePFDistheDesignoption&rotatedtotheright).ChangethenametoADJ‐WFLO.Double‐clickonADJ‐WFLOtogetitsinputforms.CreateavariableRESIDUALtorepresenttheresidualheataroundtheboiler(i.e.,thedifferencebetweentheheatgeneratedonthecombustionside&theheatneededonthesteamside).
Rev0.0 ‐25‐ January1,2015
SelecttheSpectab.DesignatetheRESIDUALvariableastheSpecvariable,setitsTargetvalueto0(I.E.,tomatchupthecombustionside&steamsiderequirements).SetitsconvergenceToleranceto0.5.SelecttheVarytab.ToadjustthemassflowoftheCONDENSATstreamfirstchooseStream‐VarastheType4.Let’sassumethattheUpperlimitislessthan500kg/sec;we’llsettheLowerlimitas0.1(aslightlypositivenumber).SettheStepsizeas0.01&theMaximumstepsizeas0.1.
Wecanlookattheresults&seethattheanticipatedwatercirculationratehasbeenfound,296.8kg/sec.
4DonotchooseMass‐FlowastheType;thiswillpointtotheflowofanindividualcomponent,nottheentirestream.
Rev0.0 ‐26‐ January1,2015
AdditionalStream&UnitAnalyses
Thereareadditionalanalysesthatwemaywanttoperformforthissimulation.Sincethegoaloftheprocessistocreatepowerweshouldbeveryinterestedtodeterminethevariousthermalefficienciesofthesystems.Tocalculatetheefficiencyoftheboilerweneedtodeterminetheheatingvalueofthefuelgasused.Todothiswewillmakeuseofthebuilt‐innet&grossheatingvalues(lower&higher,respectively).ExpandtheSetupitemintheleft‐handtreestructureoftheSimulationitems.UnderPropertySetscreateaNewsetcalledHEATVALS.Editthatpropertyset&addthepropertiesQVALNET&QVALGRS.
Nextwewanttoaddthesepropertiestothesimulationreport.UnderSetupintheleft‐handtreestructurechooseReportOptions.GototheStreamtab&clickonPropertySets.
Rev0.0 ‐27‐ January1,2015
SelectHEATVALSintheAvailablepropertysetslist&press>.ThiswillmoveHEATVALStotheSelectedpropertysetslist.ClickonClose.
Nowwecanrerunthesimulation.NowwhenwelookattheResultsforastreamwewillseethenet&grossheatingvaluesatthebottomofthelist.
Wecannowstarttocalculatevariousefficienciesforthecombinedfuel/steamsystem.
Boilerefficiency.Thiswillbetheamountofheatthatistransferredoutofthecombustionsectionofthesystemintothesteamsystem.Thiscanbebasedeitheronthelower(net)heatingvaluebutmorenormallyonthehigher(gross)heatingvalue:
boilerHHV
766,007kJ/sec0.8601
HHV 55515.1kJ/kg 16.043kg/sec
Qm
.
Steamcyclethermalefficiency.Thishasalreadybeencalculatedastheratioofthenetwork
producedbythesteamcycletotheboilerheatin:
turbine pump
th
boiler
319,838kW 3,716kW0.4127
766,007kJ/sec
W W
Q
.
Overallefficiency.Thisisnormallycalculatedastheproductofthecombustionside’s
efficiency&thesteamcycle’sefficiency:
HHV th 0.8601 0.4127 0.3550 .
Rev0.0 ‐28‐ January1,2015
However,thisdoesnottakeintoaccounttheenergyneededtoruntheairblower.Instead,weshouldusetheratioofthenetworkproducedtotheenteringheatingvalue(again,intermsofHHV):
turbine pump
total,HHV
319,838kW 3,716kW 7622kW0.3464
HHV 55515.1kJ/kg 16.043kg/sec
blowerW W W
m
.
Let’ssetupanExcelspreadsheettodothesecalculations.Youcanstartwithaspreadsheetwithlabelsthatlooklikebelow.NotethatvaluesthatwillbedeterminedfromtheAspenPlussimulation(eitherasaninputoracalculatedvalue)areinabluefont&willhavealightgreenbackground.
Theinformationwewanttoputintothistable&useforcalculationswillcomefromstreamresults(Material,Heat,&Work)aswellasequipmentinformation(i.e.,modelresults).Wecouldcopy&pasteindividualdatavaluesbetweentheAspenPlussimulationandthespreadsheet;itismoreflexibletocopyentiretablesofresultstothespreadsheet&thenpickoutthevaluesdesired.Performthefollowingsteps:
Inyourspreadsheetcreatethreenewstabs&callthemMaterialTable,HeatTable,&WorkTable.
InyourAspenPlussimulationselecttheStreamsoptionunderResultsSummaryintheleft‐handtreestructure.ThedefaultshowstheMaterialtabselected.ClicktheCopyAllbutton.GototheMaterialTabletabinyourspreadsheet&selectcellA1.Right‐click&selectPaste.Youmaywanttoadjustcolumnwidthssoyoucanmorereadilyreadallofthevalues.
Rev0.0 ‐29‐ January1,2015
InyourAspenPlussimulationselecttheHeattab.Selectthesquareintheupperleftpartofthetable&click(youshouldseetheentiretablehighlighted).Right‐clickthisupperleftsquareofthetable&selectCopy.GototheHeatTabletabinyourspreadsheet&selectcellA1.Right‐click&selectPaste.Youmaywanttoadjustcolumnwidthssoyoucanmorereadilyreadallofthevalues.
Rev0.0 ‐30‐ January1,2015
InyourAspenPlussimulationselecttheWorktab.Selectthesquareintheupperleftpartofthetable&click(youshouldseetheentiretablehighlighted).Right‐clickthisupperleftsquareofthetable&selectCopy.GototheHeatTabletabinyourspreadsheet&selectcellA1.Right‐click&selectPaste.Youmaywanttoadjustcolumnwidthssoyoucanmorereadilyreadallofthevalues.
Rev0.0 ‐31‐ January1,2015
InyourAspenPlussimulationselecttheModelsoptionunderResultsSummaryintheleft‐handtreestructure.ThedefaultshowsasummaryreportwiththeHeatertabselected.ClicktheSendtoExcelbutton.UsethedefaultformofOnetableperExcelworksheet.SelecttheoptiontoAddtablestoexistingworkbook;clicktheBrowsebutton&findthespreadsheetthatyou’vecreated.ClickontheExporttablestoExcelbutton.WhendoneclickOKforOpenExcelFile.Youshouldseetabsforthevarioustypesofequipmentinyoursimulation.
Rev0.0 ‐32‐ January1,2015
Rev0.0 ‐33‐ January1,2015
Nowthatwehavetheresultsinthespreadsheetlet’sstarttoconnectingthecellvaluesintheSummarypage.Manyofthevaluescanbereferencedtoasinglecell,e.g.,themassflowrateofthefuelgasas“='MaterialTable'!I6”,thesteamturbinepoweras“='WorkTable'!D2”,orthesteamturbinemechanicalefficiencyas“=Compr!E17”.Thetotalmolarflowrateofthefuelgasisalittlemorecomplicatedsincethetotalvalueisnotreportedinthematerialtable;itcanbedeterminedasthesumofallthemolarflowratesoftheindividualcomponents,“=SUM('MaterialTable'!I11:I21)”.NotethateventhoughtheunitsonthevaluescouldbeextractedfromtherowdescriptionincolumnAofthesheetsitiseasiertoenterthemastextvalues.
Someadditionalcleanup:
Itisconvenienttoformatthenumberslargerthan1,000toanumberwithnodecimalplaces&commaseparators.
Thesignsontheheat&worktermsaredependentonwhetherthevaluesaretransferringinoroutofaparticularunit.Onlytheabsolutevaluesshouldbereportedhere(importanthereonlyforthepowertermassociatedwiththesteamturbine).
Rev0.0 ‐34‐ January1,2015
Nowwewanttoaddformulastocalculatetheefficiencyvalues:
CellE2,“=B3*B4” CellE3,“=B3*B5” CellH2,“=E4/E2” CellH3,“=E4/E3” CellH5,“=(E8‐E7)/E4” CellH7,“=(E8‐E7‐E6)/E2” CellH8,“=(E8‐E7‐E6)/E3”
WenowhaveaspreadsheetcreatedwithafairlyflexibleformatthatallowsustocalculatenewefficienciesformodificationstotheAspenPlussimulation.Allwewouldhavetodoiscopyinthenewstreamtables&modelresults.Forexample,wecangetderivenewefficiencyvaluesforthefollowingchangesinoperatingparameters:
Pressuredropthroughthefuelgassystemis0.2bar(not0.3bar). Theisentropicefficienciesofallrotatingequipmentis85%(not100%)&themechanical
efficienciesare95%(not100%). 150°Cofsuperheatsuppliedtothesteam.
Rev0.0 ‐35‐ January1,2015
We’llskipthedetailsofallofthechangestotheAspenPlussimulation.Howeverthespreadsheetshownbelowshowsallofthestepsoftheefficiencycalculations.