Exploring the Possibility of Using Molten Carbonate Fuel Cell ...
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High temperature fuel cells such as molten carbonate fuel cells and solid oxide fuel cells produce significant amounts of heat that can be used ... ThisarticleispartoftheResearchTopic MoltenCarbonateFuelCellsforSimultaneousCO2Capture,PowerGeneration,andHydrogenProduction Viewall 8 Articles Articles BarbaraBosio UniversityofGenoa,Italy TimothyA.Barckholtz ExxonMobil(UnitedStates),UnitedStates MASSIMILIANODELLAPIETRA ItalianNationalAgencyforNewTechnologies,EnergyandSustainableEconomicDevelopment(ENEA),Italy JakubKupecki InstituteofPowerEngineering,Poland Theeditorandreviewers'affiliationsarethelatestprovidedontheirLoopresearchprofilesandmaynotreflecttheirsituationatthetimeofreview. AbstractIntroductionCoproductionandPoly-GenerationFuelCellTheoryandModelingHydrogenProductionUsingIR-MCFCsResultsandComparisonwithIR-SOFCStudyConclusionDataAvailabilityStatementAuthorContributionsFundingConflictofInterestPublisher’sNoteSupplementaryMaterialFootnotesReferences SuggestaResearchTopic> DownloadArticle DownloadPDF ReadCube EPUB XML(NLM) Supplementary Material Exportcitation EndNote ReferenceManager SimpleTEXTfile BibTex totalviews ViewArticleImpact SuggestaResearchTopic> SHAREON OpenSupplementalData ORIGINALRESEARCHarticle Front.EnergyRes.,24August2021 |https://doi.org/10.3389/fenrg.2021.656490 ExploringthePossibilityofUsingMoltenCarbonateFuelCellfortheFlexibleCoproductionofHydrogenandPowerUtkarshShikhar*,KasHemmes*andTheoWoudstraFacultyofTechnology,PolicyandManagement,DelftUniversityofTechnology,Delft,NetherlandsFuelcellsareelectrochemicaldevicesthatareconventionallyusedtoconvertthechemicalenergyoffuelsintoelectricitywhileproducingheatasabyproduct.Hightemperaturefuelcellssuchasmoltencarbonatefuelcellsandsolidoxidefuelcellsproducesignificantamountsofheatthatcanbeusedforinternalreformingoffuelssuchasnaturalgastoproducegasmixtureswhicharerichinhydrogen,whilealsoproducingelectricity.Thisopensupthepossibilityofusinghightemperaturefuelcellsinsystemsdesignedforflexiblecoproductionofhydrogenandpoweratveryhighsystemefficiency.Inapreviousstudy,theflowsheetsoftwareCycle-Tempohasbeenusedtodeterminethetechnicalfeasibilityofasolidoxidefuelcellsystemforflexiblecoproductionofhydrogenandpowerbyrunningthesystematdifferentfuelutilizationfactors(between60and95%).Lowerutilizationfactorscorrespondtohigherhydrogenproductionwhileatahigherfuelutilization,standardfuelcelloperationisachieved.ThisstudyusesthesamebasistoinvestigatehowasystemwithmoltencarbonatefuelcellsperformsinidenticalconditionsalsousingCycle-Tempo.Acomparisonismadewiththeresultsfromthesolidoxidefuelcellstudy.IntroductionTherehasbeenanincreaseddemandforrenewableenergyinrecenttimes.Populationandeconomystillrelyheavilyonfossilfuelsandthereisanurgentneedforchange.Hydrogenhasbeenidentifiedasoneofthecleanfuels,andwhensuppliedtotheanodeofafuelcellproduceselectricity,heat,andwaterinconventionalapplications.Fuelcellsareelectrochemicaldevicesthatconvertfuelintoelectricity.Themaximumpotentialoffuelcellsisyettoberealizedastheycanbesuitableforvariousapplicationswhilealsooperatingatahigherefficiencythanconventionalcombustionengines.Therearevarioustypesoffuelcellsbut,inthisstudy,thefocusisonthemoltencarbonatefuelcell(MCFC),whilealsoacomparisonismadewithasolidoxidefuelcell(SOFC)system.Asfuelcellsrequirehydrogen,oftenanexternalreformerisusedtoreformconventionalfuelssuchasnaturalgaswithsteamintoagasmixturecontaininghydrogen.Thisendothermicprocesscalledsteammethanereforming(SMR)requireslargeamountsofheat.HightemperaturefuelcellssuchastheSOFCandMCFCprovideenoughexcessheatofsufficienttemperaturetofacilitatethisreaction.Thesefuelcellsthereforecanperformthisreforminginternallyinsidethefuelcellstackandarethenreferredtoasinternalreformingfuelcells(IR-FCs).WhilenaturalgasmaybepreferredwiththeseIR-FCs,theirfuelflexibilityisshownthroughstudieswithotherfuelssuchasmethanol(Ruetal.,2020),ethanol(Dogdibegovicetal.,2020),ammonia(Afifetal.,2016),andbiogas(Escuderoetal.,2021).Ithasbeenrealizedthatthesefuelcellsnexttotheconventionalproducts,electricpowerandheat,canalsoproducehydrogenwhenoperatedatlowfuelutilization,whereweemphasizethatthehydrogenisnotpurebutintheformofagasmixture.Sinceitisproducedinareformingreactionofahydrocarbon,itcontainsCOandCO2nexttosteamandperhapssomeunreactedhydrocarbonfuel.Toobtainpurehydrogen,theconventionalprocessstepssuchasaCOshiftreactorandhydrogenseparatormustbeaddedtothesystem.Nevertheless,sometimesthisisnotneededandtheremightbeadirectapplicationforthegasmixturesasitresemblessyngas,awellknowsynthesisgasinthechemicalindustry,albeitwithalowerhydrogenpartialpressuresincethefuelcellhasconvertedpartofthehydrogeninitselectrochemicalreactions.Thecompanyfuelcellenergy(FCE)hasrecognizedthecoproductionoptionanddevelopedapoly-generationsystembasedontheirMCFCtechnology(Leo,2016).InterestinIR-FCsforhydrogencogenerationhascontinuedtogrow.Recently,aprojectsupportedbytheEuropeanCommission’sHorizon2020programaimedatbuildingaprototypesystemforhydrogenrefuelingstationsbasedoncogenerationofhydrogenandpowerusingaSOFC(EuropeanCommission,2021).AnumberofstudieshavebeenpublishedovertheyearsonthepotentialofhightemperatureIR-FCsforimprovedefficiencyapplications(Vollmaretal.,2000;LealandBrouwer,2006;Zhuetal.,2008;Guerreroetal.,2010;Hemmes,2010;Hemmesetal.,2010;VerdaandNicolin,2010;Margalefetal.,2011;Adamsetal.,2012;Hemmesetal.,2012a;Hemmesetal.,2012b;Hemmes,2013;Lietal.,2013;Petersetal.,2013;MclartyandBrouwer,2014;Nguyenetal.,2014;ShafferandBrouwer,2014;Hemmes,2015;Rinaldietal.,2015;Fernandesetal.,2016;Hemmes,2016;Abdallaetal.,2018;Chenetal.,2018;Pernaetal.,2018;Baldietal.,2019;Panagietal.,2019;Pérez-Fortesetal.,2019;Ramadhanietal.,2019).Onesuchstudy,“FlexibleCoproductionofHydrogenandPowerUsingSolidOxideFuelCells”servesasthebasisforthisstudy(Hemmesetal.,2008).Theauthorsperformedflowsheetcalculationsonaninternalreformingsolidoxidefuelcell(IR-SOFC)systemtoshowthataflexiblecoproductionsystemcanbeobtainedwhichcanoperateinconventionalfuelcellmode,producingelectricpowerandheatand,inhighefficientcoproductionmode,producingalsohydrogennexttoelectricityandalittleheat.Moreover,whenproducinghydrogen,itmakessensetooperatethefuelcellinwhathasbeencalled“high-powermode,”thatis,athighercurrentandpowerdensitywithlowerelectricefficiencythanundertheusualoperatingconditions,becausethelargeramountof“wasteheat”isnotwastedbutisinsteadusedinternallytoreformmorenaturalgasintohydrogen.Hydrogenisconsideredavaluableproductjustlikeelectricity.Inthisstudy,weexploretheconceptofcoproductionwithinternalreformingmoltencarbonatefuelcell(IR-MCFC)inanidenticalmanneralsousingtheflowsheetsoftwareCycle-TempowhilekeepingtheparametersascloseaspossibletothoseusedintheIR-SOFCstudywithwhichwewillcompareourresults(Hemmesetal.,2008).UsingtheIR-SOFCcalculationsasareference,ourIR-MCFCwillberuninthesamethreemodes:high-efficiencymode,constantcurrentdensitymode,andhigh-powermode,whilealsovaryingthefuelutilizationfrom60to95%foreachmode.Nextinthisstudy,fuelcelltheoryandmodelingandtheconceptofcoproductionarebrieflyexplained.Then,hydrogenproductionusinganIR-MCFCissimulatedusingCycle-Tempo.Thisisfollowedbyasectioninwhichtheresultsofallthreemodesofoperationsarepresentedandexplained.Inthissection,thecomparisonbetweenIR-MCFCandIR-SOFCisalsomade.Finally,ourconclusionsaregiven.CoproductionandPoly-GenerationInthecaseofaconventionalpowerplant,thewasteheatthatisproducedcannotoftenbeutilized.Ifitcanbeused,onespeaksofcogenerationorcombinedheatandpower(CHP)operation.Cogenerationincreasestotalefficiencybyusingheatthatwouldbeotherwiselosttotheenvironment.Itiswidelyusedinheatandpowerapplications,alsousingfuelcells.Hightemperaturefuelcellscanrundirectlyonnaturalgasbyconvertingnaturalgasintohydrogeninternallyandutilizingtheheatthatwouldotherwisehavetoberemovedfromthefuelcell,usuallybyalargecathodeairflow.Asstatedintheprecioussection,ifasignificantpartofthefuelisnotconverted,thecellproduceshydrogencontaininggasblend.Thisisanexampleofpoly-generation,asinthiscase,electricpower,hydrogen,andheatareproduced.Poly-generationcanbeseenasanextensionofthecogenerationprinciple.Theconversionofnaturalgasintohydrogenwithinhightemperaturefuelcellsiscarriedoutbythewell-knownendothermicreactionknownas“steammethanereforming”(SMR):CH4 + 2H2O ⇒ 4H2+CO2 (1)Thehydrogenproducedinthisreactionisthenutilizedintheelectrochemicalreactionsinthefuelcelltoproduceheatandelectricity.ApartofthisheatisutilizedintheendothermicreformingreactionmentionedinEq.1.Thus,byreducingheatloss,theoverallefficiencyofthesystemisimproved.Itispossibletoincreasetheamountofhydrogenleavingthefuelcell.Thiscanbedoneintwoways:firstlybydecreasingthecurrentdensityorsecondlybyincreasingthefuelinput.Theexhaustfromafuelcell,whichisessentiallyreformednaturalgas,stillcontainsanamountofhydrogendependingonthefuelutilizationfactoruf.Similartotheprocessofconventionalhydrogenproductionbysteammethanereformingofnaturalgas,hydrogencanbeobtainedfromtheoff-gasfromthefuelcell.Instandard,conventionalfuelcelloperation,fuelutilizationis90–95%andthereforethepartialpressureofhydrogenatthefuelcelloutputisverylow(5–10%).Theenergycontentintheoff-gasisusuallyrecoveredbyconvertingitintoheatinacatalyticburner.However,iffuelutilizationisdecreased,thehydrogencontentbecomeslargeenoughtoberecoveredbyseparationfromtheanodeoff-gasorthegasmixturecanbeusedasasyngasforlocallyproducingchemicalsifneededorotherapplications.LowfuelutilizationandtheproductionofhydrogencomewithanotheradvantagewhichisreducingNernstloss.AlmosthalfofthelossesinhightemperaturefuelcellsunderstandardoperatingconditionsarefromNernstlosses(Hemmesetal.,2011).Theyarecausedbythelowhydrogenpartialpressureneartheoutletofthecell.Therefore,theseNernstlossescanbesignificantlyreducedbyproducinghydrogenintheseIR-FCsbecauseneartheoutletofthefuelcell,ahighpartialpressureofhydrogenisstillavailable.Accordingtoflowsheetcalculations,anoverallsystemefficiencyofmorethan90%fortheproductionofelectricpowerandhydrogenhasbeenachievedinanIR-SOFCsystemsimulation(Hemmesetal.,2008).Duetotheflexibilityinthecoproductionofhydrogenandelectricpower,itispossibletooperatesuchIR-FCsystemstomeetfluctuatingdemandsandoptimizethesystemforhigheconomicefficiency(Hemmesetal.,2011).Inthisstudy,thisflexiblecoproductionofhydrogenandpowerisexaminedforanIR-MCFCenergysystem.ThesimulationsuseamoreorlessstandardMCFCsystemlayoutdevelopedatTUDelft,modeledintheflowsheetprogramCycle-Tempo,andalsodevelopedatTUDelft,andnowcommerciallyavailable12.Additionally,somefuelcellmodelverificationshavebeenpreviouslydonewithCycle-Tempo(Auetal.,2001;Auetal.,2003).FuelCellTheoryandModelingInthissection,fuelcelltheoryandanalyticalmodelingarebrieflyexplainedforabetterunderstandingoftheIR-MCFCmodelpresentedinthefollowingsections.DetailedversionsofthistheoryaredevelopedanddescribedbyStandaertandHemmesetal.(Hemmes,2004;Hemmesetal.,2012a).FromthefuelcellmodelderivedbyStandaert,thecellvoltageofafuelcellisapproximatelyestimatedbythefollowingequation(Standaertetal.,1996):Vcell≈ OCV− 12αuf − ir.(2)Equation(2)waslaterverifiedonMCFCbenchcellsandwasfoundtobequiteaccurate(Auetal.,2003).Forconvenience,aquasi-ohmicresistance“r”constitutescombinedirreversible,ohmic-,kinetic-,anddiffusion-losses.Thesecondtermonther.h.s.representstheNernstloss,whileαistheslopeoflinearizedNernstpotentialasafunctionoffuelutilizationgiveninvolt.Theopencellvoltage(OCV)forfuelcellsingeneralandspecificfortheMCFCisgivenbyEqs.3,5,respectively(FuelcellHandbook,2004):OCV= E0+RTnFlnΠ[(Preactants)]xΠ[(Pproducts)]y.(3)Here,E0isthestandardcellpotential,PproductsandPreactantsarethepartialpressureoractivityofproductandreactantspecies,respectively.nisthenumberofelectronsinvolved,xandyarethestoichiometriccoefficients,FisFaraday’sconstant,Ristheuniversalgasconstant,andTistheabsolutetemperatureofthecell.Thisequationwillvaryaccordingtotheoverallcellreactionofdifferentfuelcells.ForMCFC,itisgivenbyEq.5basedontheoverallcellreactionofanMCFC(Eq.4):H2+ 12O2+CO2(cathode) ⇒ H2O(anode)+ CO2(anode)(4)OCVMCFC= E0+RT2Fln(pH2)a(pO2)c1/2(pCO2)c(pH2O)a(pCO2)a(5)SubscriptsaandcinEq.5representspeciespresentattheanodeandcathode,respectively.Additionally,thepotentialatstandardstate(E0)dependsontheGibbsfreeenergychange(ΔG0)oftheoverallfuelcellreaction,whereasusuallythesuffix0referstothestandardstate:E0= − ΔG0/nF(6)ΔG= ΔH−TΔS(7)whereΔHisthechangeinenthalpyoftheoverallreaction.TheTΔSterminEq.7equalsthereversibleheatproduction.TheirreversibleheatproductionisduetotheirreversiblepolarizationlossesotherthanT.ΔSandtheNernstlossandtheyincreasewithanincreaseincurrentdrawnfromthecell.ThefuelcellefficiencyisalsoproportionaltothechangeinGibbsfreeenergyandisgivenbyηfc = ΔG/ΔH = 1−TΔS/ΔH(8)Thefuelutilization(uf)isdeterminedbytheratioofthecurrentoutputandinputfuelflowandcanbedefinedasuf= iiin(9)whereiistheactualcurrentdensityandiinisahypotheticalcurrentdensityknownas“equivalentinputcurrentdensity.”Itcanbedefinedasthecurrentproducedbythefuelcellwhenalltheinputfuelwouldbeelectrochemicallyconverted(i.e.,atuf=1)dividedbytheactivecellareaAofthefuelcell.Theequivalentinputcurrentdensityiincanbecalculatedwiththefollowingequation:iin= n⋅F⋅minA(10)whereministhenumberofmolesoffuelenteringthefuelcellpersecond.GoingbacktoEq.2,itcanbeseenthatbykeepingtheresistanceconstant,Vcellcanbecalculatedbysubstitutingvaluesforiandiinintotheequation.Similarly,“i”canbecalculatedifthevaluesofiin(oruf)andVcellaregiven.Therefore,thefuelcellsystembasicallyhastwoindependentvariableswhichcanbeseenasthetwomaincontrolknobsthatcanbevariedindependently.Inpractice,thesearetheinputflowoffuelgasandthecurrentdensitycontrolledbytheelectricloadorelectronically.Withthehelpofthese“controlknobs,”variousoperatingconditionsarepossiblefortheproductionofhydrogen,electricpower,andheatatdifferentefficiencyrates.However,tokeepourstudyalignedwithourpreviousstudyonaSOFCsystem,threemainmodesofoperationareconsideredasfollows(Hemmesetal.,2008):1.High-efficiencymode:inputpoweriskeptconstantto2 MWequivalent.2.Constantcurrentdensitymode:currentdensityisfixedat1500 A/m2.3.High-powermode:cellvoltageisfixedat0.5 V.InthemodelingofthesemodesofoperationinCycle-Tempo,variousassumptionshavebeenmadeassummarizedinTable1.ItisassumedthatallchemicalreactionsareinthermodynamicequilibriumasassumedlikewiseintheIR-SOFCreferencestudy(Hemmesetal.,2008).Thisapproximationisjustifiedduetothepresenceofanodecatalystandthehighoperatingtemperatures.Itiswellknownthatthereformingreactioninhightemperaturefuelcellsisfastsincetheinletofthecelliscooleddowntoomuchifnoprecautionalmeasuresaretaken.Intheanalyticalcellmodelthathasbeenused,assumptionsregardingthegeometryandconstructionoftheMCFCarenotneeded.Onasystemlevel,thethermalbalancingofthestackisincludedintheCycle-Tempoflowsheetprogramwiththeremarkthatitisalumpsumenergybalanceofthestack.Itdoesnotprovideadetailedcalculationofthethree-dimensionalheatandtemperaturedistributioninsidethestackaswouldbeneededforadetailedengineeringofthestack.Cycle-Tempofocusesonsystemlevelengineeringwithproperoverallmassandenergybalancesandtherefordoesnotneedthedetailedtemperatureandheatflowdistributionsinsideastackoranyothercomponent.Insteaditisassumedthatthedetailsofeachcomponenthavebeenengineeredproperlysothatthecomponentcanfunctionproperly.Thisisclarifiedfurtherwiththeexampleofastackwithinternalreforming.Forexample,theseriousdropintemperatureduetoatoofastendothermicreformingreactionattheinletisdefinitelysomethingtobetakenintoaccountinthedetailedengineeringofthestackbutforoverallsystemengineering,onlytheoverallenergybalanceshouldbetakenintoaccountandthatiswhatCycle-Tempodoes.Forexample,Cycle-Tempowillwarnorgiveanerrorifthefuelutilizationbecomestoolowresultingininsufficientheatdissipationtoprovideheatfortheendothermicreformingreaction.Althoughinsomecasesalowerutilizationthan60%couldbeachieved,wekepttherangebetween60and95%.TABLE1TABLE1.SummaryofassumptionsmadeinthisMCFCstudy.HydrogenProductionUsingIR-MCFCsHightemperatureIR-MCFCsoperateatabout650°Candproduceheatfromreversibleandirreversibleprocesseswhicharepartlyusedforthereformingreactionofthefuel(mostlynaturalgas)toproducehydrogen.Itispossibletoobtainmorehydrogenthannecessaryfortheoperationofthefuelcellsbyadjustingtheoperatingconditions.Inthissection,theIR-MCFCmodeldevelopedinCycle-Tempoisbrieflyexplained.SimilartotheIR-SOFCreferencesystem(Hemmesetal.,2008),ourMCFCflowsheetsystemlayoutshowninFigure1wasdesignedtobeassimpleaspossible.Thisdesignhasnotbeenoptimizedinanyway,notforhighefficiencynoreconomically.ThenaturalgascompositionofthefuelwaschosentobethegascompositionfromthelargestDutchsource“Slochteren”asitisselectedtobethestandardgascompositionintheNetherlands.Thislowcalorificgaswasfoundtocontainabout14%ofnitrogen.FIGURE1FIGURE1.Cycle-TempoflowsheetdiagramofaninternalreformingMCFCsystemforcoproductionofhydrogenandpower.RecycleloopshavebeenappliedtotheanodeandthecathodeasshowninFigure1.InMCFCs,CO2thatisliberatedattheanodeneedstoberecycledbacktothecathodetoprovidethenecessaryCO2forthecathodereactionnexttotheO2intheair.Thisisdonethroughtheseparator(apparatus19)asshowninFigure1.TheroleoftheseparatoristoisolateCO2fromtheanodeoutputflow.Theseparatorinthismodelhasbeenassignedaseparationefficiencyof80%.IntheSOFCmodel,thereisnoCO2recycling;thisisinfacttheprimarydifferencebetweenthetwofuelcellsnexttothedifferenceintheoperatingtemperature.Recyclinghasthreemainbenefits.First,abettertemperaturedistributioncanbeachievedinsideafuelcellstackbecauserecyclingprovidesthenecessaryheatfortheendothermicreformingreactioninparticularatthebeginningofthecell(Hemmesetal.,2012a)[4].Thisisbeneficialasthesereactionsoccuratrapidspeeds;thus,theypredominantlyoccurtowardstheinletofthefuelcellstack.Secondly,thenecessarysteamrequiredforthereformingreactionisalsoprovidedbyrecycling.Inputgasstreamsarepreheatedbytheoutputstreamsthroughvariousheatexchangerspresentinthemodel.Third,asalreadymentioned,CO2recyclingprovidestheCO2requiredbythecathodeintheMCFCoperation.AfterCO2removal,apartoftheremaininggasfromtheanodeoutputisrecycledbacktotheanodeandtherestofthesyngasexitsthroughsink9.Avalve(apparatus16)determinestheamountofgasexitingthroughsink9andtheamountofgasbeingrecycledintotheanode.InthiscasewithanIR-MCFC,therecyclevalueissetto0.3 kg/sforallthreemodesofoperation.Thisvaluewaschosentoobtainresultsinallthreemodesofoperationintherequiredrangeoffuelutilizationvalues.Forothervalues,noconvergencecouldbeobtainedinrunningtheprogramforsomemodesand/oroperationparametersinthechosenvaluerangeoffuelutilization(0.6–0.95).TheoutputfrompipeNo.17containshydrogenandothergasessuchasCO,CO2,andH2O.Hydrogencanbeseparatedfromthismixture,butthatisexcludedinthisstudy.InordertostayconsistentwiththeIR-SOFCmodel,onlytheamountsofhydrogenandCOareconsideredintheresults,sincetheyarethecomponentsofthefuelcontainingchemicalenergyandknowingthatCOcanbeconvertedintohydrogenviathewell-knownshiftreactionwithsteam.Theirenergycontentsareaddedtogivetotalusefulgasoutput,inthisstudysometimesroughlyreferredtoas“hydrogen”output.Nevertheless,mostoftheheatingvalueoftheoff-gasiscontributedbyhydrogen,whileCOcontributesonlyaboutone-third.TheIR-MCFCmodelshowninFigure1isusedtoexaminetheinfluenceofchangingfuelutilizationinthefuelcell,gasinputrate,cellvoltage,andcurrentdensityonthecoproductionofpowerandhydrogen.Inthemodel,apparatus5istheIR-MCFCthatoperatesnearatmosphericpressure.Naturalgasandairaresuppliedthroughsources1and10,respectively.Airfromsource10iscompressedslightlybyanairblower(apparatus11).Thenaturalgasfromsource1isalreadyavailableataslightlyelevatedpressureasitisinthegasdistributiongridanddoesnotneedfurthercompressing.Ablower(apparatus4)isneededtodrivetheanoderecyclecircuitandanotherone(apparatus20)isusedtodrivetheCO2looptothecathode.Therearethreeheatexchangersinthemodel,twoofwhich(Apparatuses13and7)areusedtoheatthecathodeinletair,whilethethird(apparatus2)isusedtopreheatthefuelflow.Fixedparametersincludethefuelcelloutlettemperaturewhichisfixedat700°C,cellresistancewhichisassumedtobe1 ohmcm2,andcellareawhichissetat1200 cm2tobeconsistentwiththeSOFCmodelofourearlierreferencestudy.ResultsandComparisonwithIR-SOFCStudyInthissection,theresultsobtainedfromtheflowsheetcalculationsontheIR-MCFCsystemarepresentedinFigure1.ThreedifferentmodesofoperationshavealsobeenexploredinaccordancewiththeIR-SOFCmodelinthereferencestudy(Hemmesetal.,2008).Ineachmode,thefuelutilizationisreducedfrom95to60%toshowcasethegradualshiftfromconventionalpowerproduction(uf=95%)tohydrogenandCOcoproduction.Finally,tomakethecomparisonbetweenthetwoIR-FCmodels,thereadingsobtainedfrombothmodelsareplottedtogetherinonefigureforeachmodeofoperation.SincetheSOFCcalculationswereperformedsomeyearsago,theywererepeatedtohavealltheresultdataavailableforcomparisonwiththeMCFCsystem.Efficiencydefinitionsusedinthisarticleandinthegraphspresentedlaterareasfollows:Electricefficiency:ηElec= Pelec,fcPin,system(11)Gasefficiency:ηgas= Pgas,systemPin,system(12)Totalefficiency:ηtot= Pelec,fc + Pgas,systemPin,system(13)InEquations11,12,13,thevariablePin,systemisthepowerinputintothesystemthroughsource1asshowninFigure1;itistheMWequivalentofthenaturalgasthatisenteringthesystemperunittime.Pelec,fcistheelectricpoweroutputfromthefuelcellandPgas,systemistheH2+COenergyoutputfromthesystemperunittimeobtainedatsink9asshowninFigure1.Thefuelutilizationvaluesconsideredinallthreemodesofoperationsrefertothefuelutilizationinthefuelcell.ItisimportanttonotethatinPgas,system,weconsiderH2+CObecausecarbonmonoxidecanbeeasilyusedtoproducehydrogenthroughthewell-knownwater-gasshiftreactionasshowninEq.14: CO+H2O⇒CO2+H2(14)Inthisarticle,theH2+COpoweroutputreferstotheenergycontentinthemolespersecondofhydrogenandcarbonmonoxideobtainedatsink9asshowninFigure1.Powerlostinseparationofthegasesatsink9andwater-gasshiftreactionhavenotbeenconsideredinefficiencycalculations.High-EfficiencyModeInthismodeofoperation,theinputfuelflowiskeptconstantat“2 MWequivalent”(0.053 kg/satSource1)inordertomatchthearbitrarilychosenfuelcellsizeinconventionaloperation.Next,inthesimulations,thefuelutilization(uf)inthefuelcellisdecreasedinstepsfrom95to60%whilekeepingthetotalcellareaconstantasinthepreviousSOFCstudy(Hemmesetal.,2008).Thisresultsinadecreaseinthecurrentdensityfrom1,586to1,343 A/m2alongwithelectricpowerbetweentheufof95and60%.Atverylowutilization,itispossiblethatthefuelcelldoesnotproduceenoughheatfortheendothermicreformingreaction.Althoughinsomecasesafuelutilizationbelow60%ispossible,itisnotconsideredinthisstudyassuchverylowutilizationscannotbereachedinallmodesofoperations.Whilethecurrentdensitydecreasesbyreducinguf,theelectricpowerdoesnotdecreaseproportionallysinceVcellincreasessimultaneouslyasindicatedbyEq.2.InFigure2,aplotofthepoweroutputintheformofH2+COandelectricpowervs.ufisshown.Itcanbeseenthattheslightdecreaseinelectricpoweroutputfromuf95to60%isovercompensatedbytheincreaseinH2+COpoweroutput.Theelectricoutputcanbeconsideredtobemoreorlessconstant.However,thetotalpoweroutput(notcountingheat)ismorethanwhatcanbeattainedinconventionalfuelcelloperationwithonlyelectricpoweroutputandoverallefficiencyofover80%(atlowfuelutilizationuf=60%)canbeachievedasshowninFigure3.AsstatedabovetheenthalpycarriedbyhydrogenisroughlytwicethatofCO.FIGURE2FIGURE2.Poweroutputvs.fuelutilizationforhigh-efficiencymode.FIGURE3FIGURE3.Efficiencyvs.fuelutilizationforhigh-efficiencymode.Figure3showsagraphofefficiencyvs.ufforthehigh-efficiencymode.Here,gasefficiencyisdefinedasH2+COpoweroutputdividedbythepowerinput.Fromthefigure,itcanbeseenthatthetotalefficiencyincreasesatahigherratethanthedecreaseinelectricpowerefficiencyasufdecreases.Thereisaveryslightdecreaseintheelectricefficiency(about59–56%),soitcanbeassumedtobealmostconstantinthiscase.Thismodemaybethemostefficient,butitmightnotbethemosteconomicallyfavorablemode.Fromthecalculations,itcanalsobedeterminedthatitispossibletotradepowerforhydrogen,butitisnotaone-to-onetrade-off.Thismeansthatthesumofelectricityandhydrogenpowerisnotconstant.Astheheatlossacrossthesystemboundaryisgreatlyreduced,maximumtotalefficiencyof80%isobtainedat60%fuelutilization.Itisimportanttonotethatthisefficiencyisthetotalefficiencyfortheproductionofhydrogen+powerexcludingheat,sonotthetotalefficiencyofallpoweroutputincludingheat,whichisusuallydefinedastotalefficiencyinCHP(fuelcell)systems.AsshowninFigure2,atlowfuelutilizationofbelow75%theIR-MCFCsystemproduceshigherelectricpoweroutputthantheIR-SOFCsystem.Asthefuelutilizationincreasesabove75%,theelectricoutputfromtheIR-SOFCincreasesatahigherratethanIR-MCFCsystem,producingslightlyhigherelectricpoweroutputathigherfuelutilization.ThemaximumelectricefficiencyachievedbytheIR-MCFCisabout59%and,fortheIR-SOFC,itisabout63%.FromFigures2,3,observationsregardingthecoproductionofH2/COcanalsobemade.ThevaluesofH2+COarerepresentedas“totalgaspower”and“gasefficiency”inthegraphsplottedforthefuelcells.Asexpectedatlowfuelutilization,thetotalgaspowerishigherasmoreH2/COisproducedatloweruf.Atlowerfuelutilizationuf=60%,thetotalgaspowerismuchhigherfortheIR-SOFCsystem(816 kW)thanitisfortheIR-MCFCsystem(475 kW).Athigherfuelutilization,asthefuelisalmostcompletelyutilizedforproducingelectricpower,theamountofH2/COliberatedfromthefuelcellsystemdiminishes.TheoverallenergyefficiencywhichhasbeencalculatedasthesumofelectricefficiencyandthetotalgasefficiencyinthisstudyisalsoplottedinFigure3.Thereisadifferencerangingfromroughly8to13point%,withtheincreaseinufbetweenthetwofuelcellsystems,andwiththeIR-SOFCmodelhavinghigheroverallefficiencythroughout.Theoverallefficiencyincreasesastheutilizationdecreases;thus,themaximumisachievedatthelowestutilizationuf=60%,being93%fortheIR-SOFCmodeland80%fortheIR-MCFCmodel.Fromtheseobservations,itcanbeconcludedthat,inthehigh-efficiencymode,intherangeofobservedfuelutilizationvalues,theelectricefficienciesoftheIR-MCFCsystemarealittlelowerbutsimilartotheelectricefficienciesachievedbytheIR-SOFCsystem.Theoverallefficiency,however,ismuchlowerfortheIR-MCFCsystem,whichresultsfromthesignificantlylowergasefficiency.Despitethis,still,overallefficiencyofover80%isachievedwiththeIR-MCFCsystem.ConstantCurrentModeIntheconstantcurrentmode,wekeepthecurrentdensityconstantandthefuelutilizationisdecreasedbyincreasingthenaturalgasinputflow.Thecurrentdensityiskeptconstantat1,500 A/m2asitrepresentsconventionaloperationatreasonablepowerdensity.Inthismode,Cycle-Tempoisallowedtochangethegasinputflowtomeetboththefixedvaluesofufandi.Theresultsobtainedinthismodearefoundtobeinbetweenhigh-power(seesectionHigh-PowerMode)andhigh-efficiencymode(seesectionHigh-EfficiencyMode).FromFigure5,itcanbenoticedthat,inbothfuelcellsystems,thetotalefficiencyincreaseswithadecreaseinuf.Inordertokeepthecurrentdensityconstant,thefuelcellsystemsrequireahigherfuelinputatloweruf.Asaresultofhigherfuelinput,higherelectricpoweroutputsarealsoobservedatlowerfuelutilization.Theelectricefficienciesvarysimilarlytothoseofthehigh-efficiencymodewithmaximumsof57%(forIR-MCFC)and62%(forIR-SOFC)occurringatuf=95%.Thetotalgaspoweroutputforboththefuelcellsystemsishigherthanwhatwasobtainedinthehigh-efficiencymode,becauseofthehigherfuelinputatlowerfuelutilization.Atuf=60%,atotalgaspoweroutputof591 kWisobtainedfortheIR-MCFC,whiletheIR-SOFCsystemproducesalmostdoublethisamountbygenerating1,062 kWofgaspower(seeFigure4).Thevariationofgasefficiencywithufgivesanearlyidenticalplottotheoneobtainedinthehigh-efficiencymode(asseenfromFigures3,5).Similarly,theoverallefficiencyisfoundtocloselyresemblethevaluesfromthehigh-efficiencymodeaswell.Themaximumvalueofoverallefficiencyis80%fortheIR-MCFC,and92%fortheIR-SOFCisachievedagainatthelowestfuelutilizationwesimulated,i.e.,uf=60%.Thisalsoholdsintheconstantcurrentmodebecausejustlikeinthehigh-efficiencymode,nocompromisehasbeenmadeintheelectricalefficiencyofthefuelcellsystems.Inotherwords,whilefuelinputisallowedtochangetokeepcurrentdensityconstantinthismode,asignificantdropinelectricalefficiencyisnotobserved.FIGURE4FIGURE4.Poweroutputvs.fuelutilizationforconstantcurrentdensitymode.FIGURE5FIGURE5.Efficiencyvs.fuelutilizationforconstantcurrentdensitymode.Toconclude,inthismode,maximumpoweroutputoccursatthelowestfuelutilizationduetomuchhigherfuelinput.Justlikeinthehigh-efficiencymode,theelectricefficiencyofIR-MCFCisintherangeofwhatisachievedbytheIR-SOFCsystem.Again,thedifferenceintheoverallefficiencyfortheIR-MCFCsystemcanbeattributedtothelowergasefficiencyintheMCFCsystem.ButtheIR-MCFCsystemwasstillabletoachieveanoverallefficiencyof80%.High-PowerModeHigh-powermodeisofgreatinterestfromaneconomicpointofview.Inthismode,largecurrentdensitiesareobtainedbykeepingthecellvoltagefixedataverylowvalue.Similartotheconstantcurrentmode,thismodeachievesadecreaseinfuelutilizationufbyincreasingthenaturalgasinputfuelflow.Asthecellvoltageislow(setat0.5 V),thecurrentdensityishighandsoistheamountofheatdissipated.Thisheatcanbeusedfortheinternalreformingreactionofthenaturalgasfuel,andalargerquantityofnaturalgascanbereformedthaninpreviousmodes.Butitisalsonecessarytohavealargerfuelinputtoprovideenoughelectronsforthelargercurrent.TheresultsforthismodeofoperationareshowninFigure6(poweroutputvs.fuelutilization)andFigure7(efficiencyvs.fuelutilization).Asveryhigh-poweroutputvaluesareobtainedinthismode,thisisanextremeoperationmode.FIGURE6FIGURE6.Poweroutputvs.fuelutilizationforhigh-powermode.FIGURE7FIGURE7.Efficiencyvs.fuelutilizationforhigh-powermode.Althoughthecellvoltageislowerthanintheothermodes,thecurrentincreasessomuchmorethatstillasignificantlylargerelectricpoweroutput(currenttimescellvoltage)isachievedinthismode.ThisincreaseinpoweroutputcanbeseeninFigure6,whereatuf=60%,thecurrentdensitywasfoundtobei=3,428 A/m2.Inthishigh-powermode,celloperationiscarriedoutnearthemaximuminthepoweroutputvs.currentdensitycurveattheexpenseofalowerelectricefficiency(Hemmesetal.,2008).Byusingwasteheatforproducinghydrogen,wecanoperateatornearmaximumpowerforelectricityproductionwhileatthesametimeproducingasimilarhighoutputintheformofH2/COalbeitattheexpenseofadropinefficiencycomparedtothetwomodesdescribedabove.Atlowuf,lowelectricpoweroutputispartlycompensatedbythehigherH2/COproduction,andthetotalefficiencyforcoproductionofgasandelectricpowerwasfoundtoreach56%.Itisseenthatthemaximumelectricpoweroutputobtainedinthehigh-efficiencymode(1,153 kW)is58%ofthatobtainedinthehigh-powermode(1,980 kW).So,roughlyestimating,itcanbesaidthatthehigh-powermodeproduceselectricoutputthatisalmosttwicethatofthehigh-efficiencymode.Additionally,1,344 kWofH2+COgaspoweroutputisobtainedinthismode,bringingthetotalusefuloutputtoover3,300 kW.Thisis2.9orabout3timestheelectricpoweroutputobtainedintheconventionaloperation(1,153 kWe)carriedoutwiththesamefuelcell.Itshouldbenotedthatalthough,atlowfuelutilization,thesystemisinH2/COproductionmode,theelectricpoweroutputincreasesaswellasthegasoutput.Thisisbecause,inthismodeofoperation,theutilizationfactorisdecreasedbyincreasingthenaturalgasinput.Hence,byallowingmoreJoulespersecondtoflowintothesystem,weareincreasingbothhydrogenproductionandelectricpoweroutput.Moreover,Nernstlossissignificantlyreducedduetohigherpartialpressureofhydrogeninparticularattheoutputsideofthefuelcellatlowerfuelutilization,resultinginanimprovementofcellvoltageandthusfuelefficiencyasindicatedbyEq.2.Theelectricefficiencyincreaseswithanincreasingfuelutilization,butitismuchlowerthanintheothertwomodes.Theelectricefficiencyvariesalmostidenticallybetween32and45%forboththefuelcellsystemsasthefuelutilizationincreasesasshowninFigure7.Thedifferenceingasefficiencybetweenthetwofuelcellsystemsismuchlargeratlowerfuelutilizationandisalmostthesamebeyonduf=85%.Justlikeintheothertwomodesofoperation,themaximumgasefficiencyremainsaround25%fortheIR-MCFCsystemand40%fortheIR-SOFCsystem.ThemaximumtotalefficiencyoftheIR-MCFCsystemisfoundtobeover56%whilefortheIR-SOFCmodel,itisfoundtobeabout73%.ThemaximumtotaloutputfromtheIR-MCFCsystemis3,325,and5,667 kWfortheIR-SOFCsystem.AlthoughoutputsashighasthosefortheIR-SOFCsystemmaynotbeobtainablewiththeIR-MCFCsystemusedhere,weseethatthemaximumtotaloutputfromtheIR-MCFCsystemcanstillbealmostthreetimeshighercomparedtoconventionaloperation.Therefore,thisoperationmodemightbethemosteconomiconeprovidingathreetimeshigherproductionrateofvaluableeconomicgoods(electricityandhydrogen)forthesamecapitalcostofthesamefuelcellstack,providedthecoursethatthestackcanhandlethehighergasflowsandhighercurrentdensitiesandthattheelectrodesarestillstableatalowcellvoltageofaround0.5 V.GasCompositionoftheOutputGasAsthefuelutilizationvalueisvariedfromuf=60%touf=95%,thecompositionofgasesintheMCFCoutputchangesasshowninFigure8forthehigh-powermodesimilartowhathasbeenshownfortheSOFCmodel(Hemmesetal.,2008).TheanodeoutputisfoundtocontainagasmixturecontainingH2,CO,H2O,andCO2withanobviousdecreaseinH2andCOasthefuelutilizationincreases.ThecathodeoutputmainlyconsistsofamixtureofN2andO2(N2isnotshowninFigure8).ThegasoutputcompositionsaremostlysimilartothoseobtainedfromtheIR-SOFCmodel;however,amajordifferencewasobservedattheanodesideinvolvingamuchhigherCO2flowfortheMCFC.Thisisexpectedduetothedifferenceinthefuelcelloperatingprinciples.InaSOFC,whichoperatesatmuchhighertemperaturesofupto1,000°C,thechargecarriersaretheO2-ions,whileintheMCFCoperatinghereat650°C,thechargecarriersaretheCO32-ions.TheseCO32-ionstravelfromcathodetoanodethroughtheelectrolyte,whiletheelectronstravelfromanodetocathodeinanexternalcircuit.Asaresultofthis,ahigherCO2concentrationisfoundattheanodeofanMCFC.ItisimportanttonotethatthehighconcentrationofCO2intheanodeoutputisnotreflectedinthegascollectedatsink9inFigure1astheCO2intheanodeoutputisrequiredbythecathode.TheCO2isseparatedandrecirculatedfromtheanodeoutputtothecathodeinputwitharecycleloopasshowninFigure1.FIGURE8FIGURE8.Maingasoutputcompositionvs.utilizationfactorforhigh-powermodeattheMCFCoutput.Cycle-Tempoalsoprovidestheexergyefficiencyofthefuelcellsystems.Forthehigh-efficiencymodeandtheconstantcurrentdensitymode,themaximumexergyefficiencyobservedfromtheIR-SOFCsystemwasabout59%whiletheIR-MCFCsystemachievedamaximumofabout54%.Inthehigh-powermode,thesystemexergyefficiencywasalsofoundtobecloselyidenticalinboththefuelcellsystemsanditwasfoundtovaryintherangebetween30and40%.Acomparisonofresultsbetweenthetwofuelcellsatfuelutilization(uf)of60%whereoverallefficiencyismuchhigherthanconventionalfuelcelloperationhasbeenpresentedinTable2.TABLE2TABLE2.Comparisonofresultsbetweenthetwofuelcellsatfuelutilization(uf)of60%wheretheoverallefficiencyismuchhigherthanconventionalfuelcelloperation.TheresultsforSOFChavebeenreproducedbasedoninformationprovidedinHemmesetal.(2008).ReasonsforLossinEfficiencyinIR-MCFCComparingthetwofuelcellsystemsitwasfoundthattheelectricefficiencieswereclosertoeachotherthanthegasefficienciesforallthreemodesofoperation.Thedifferenceinoverallefficienciesbetweenthetwofuelcellsystemsisthereforeprimarilyduetodifferencesingasefficiency.WhiletheIR-SOFCsystemcanachieveagasefficiencyofupto40%,theIR-MCFCsystemexaminedinthisstudywasabletoachieveonly25%atbest.WhilecarehasbeentakentokeeptheparametersinMCFCascloseaspossibletotheSOFCreferencestudy,thereareafewdifferencesintheoperatingprinciples,systemparameters,andmodels.Itshouldbenotedthattheoperatingparametersofthetwofuelcellsaredifferent.TheIR-MCFCsystemiskeptat650°CwhiletheIR-SOFCiskeptat900°C.FromFigure8,wealsoseethatwhileoperatinginthehigh-powermode(alsotrueforothermodes),theanodeoutputgascompositionobtainedfromtheIR-MCFCsystemcontainsamuchhigherCO2concentrationthanintheIR-SOFCsystem,whichontheotherhandismuchricherinsteam.ThisisduetothedifferenceintheoperationofthetwoIR-FCssystemsandthereactionstakingplaceinthefuelcellsduetotheneedforCO2atthecathodeofanMCFC,whereastheSOFConlyneedsair.IntheMCFCmodelasshowninFigure1,CO2generatedintheanodeoutputisrecycledtothecathodethroughaseparator(apparatus19).Theseparationefficiencyoftheseparatorissetat80%.TheCO2thatisseparatediscompressedinablower(apparatus20)intherecyclelooptoprovideCO2atthepressureoftheairenteringthecathode.Theremaininggasoftheanodeoutletismadetopassthroughthevalve(apparatus16),whereaportionofthegasisinjectedintothefuelstreamthroughpipe18.Theremaininggasfromthevalvepassesthroughheatexchangers(apparatus2andapparatus7)throughpipes19and15,respectively.ThesetwostreamsafterpassingthroughheatexchangersultimatelycombineattheendtosupplyhydrogenandCOfromtheoutletofpipe17.ThisarrangementthroughthevalveisnearlyidenticaltotheSOFCmodel.ThemaindifferenceisthatinthecaseoftheSOFCmodel,theinputflowtopipe18isfixedat0.4relativetopipe5(anodeoutlet).Thismeansthat40%oftheanodeoutputisinjectedbackintothefuelstreamheadedtotheanodeinlet.Therecyclingintotheanodeinletisneededtoprovidesufficientsteamfortheinternalreformingreaction.DuetothecomplexityarisingfromtherecycleloopforCO2fromanodeoutputtocathode,asimilarflowdivisioncannotbespecifiedforpipe18inthisCycle-TempoMCFCmodel.Theotheroptionforspecifyinginputdataforapipe(pipe18inthiscase)thatisleavingavalveisbyfixingitsabsoluteflow.IntheMCFCmodel,theflowforpipe18issettoafixedvalueof0.3 kg/s.Thisisa“bestfit”valuechosentooperateinallthreemodes,acrosstheentirerangeoffuelutilizationvaluesanalyzed.Inhindsight,thisappearstobeaquitehighvaluepossiblycausingoratleastcontributingtothelowerefficienciesfortheMCFCsystem.Itistobecomparedforexamplewiththeinputflowofnaturalgasfuelof0.053 kg/satSource1.Duetofixingtheflowinpipe18to0.3 kg/s,themajorityofthegasfromtheanode(afterCO2separation)isactuallyrecycledintothefuelstreamtowardstheanodeinlet.ThismeansmuchmoreoftheanodeoutputincomparisontotheIR-SOFCisactuallygettingrecycledbackintotheanodeinputinthecaseofIR-MCFC.ThisstreamisrichinhydrogenandthussuppliesadditionalfueltotheIR-MCFCalongwiththenaturalgaswhichisenteringthesystem.Bylookingatthehigh-efficiencymodewherefuelsenteringthesystemisconstantandanalyzingthepoweroutputs,itwouldimplythattheIR-SOFCconfigurationismoreefficient.Theremaininggasconstitutesthesyngasproductionatsink9asshowninFigure1,whichislowerforallfuelutilizationvaluesinIR-MCFCthanIR-SOFC.Bydefinitionwiththeincreasedfuelutilizationinthefuelcell,H2/COintheanodeoutletdecreases;thisresultsinthegaspoweroutputlineofIR-MCFCinthegraph(e.g.,Figure2)approachingzero.InthecaseofIR-MCFC,theamountofnaturalgasfuelenteringthesystemintheconstantcurrentdensitymodeandthehigh-powermodeislessthanintheIR-SOFCsystemsforallutilizationfactors.Aseitherthecurrentdensityvalueorthevoltageinthesemodesisfixedinthefuelcell,thevariationintheamountoffuelmaybeduetothedifferenceintheamountofhydrogenfromvalve16beingrecycledintheanodeinputinthetwofuelcellsystems.Thisdifferenceinthefuelinputcanbeashighas1,700 KWequivalenttothatinthehigh-powermodeoperatingatfuelcellutilizationofuf=60%.Withaloweramountoffuelenteringthefuelcells,outputslowerthanIR-SOFCcanbeexpected.Moreover,therearetwootherblowers,one(apparatus4)beforetheanodeinletthatprovidespressurizedfuelmixturetotheanodeandtheother(apparatus11)thatcompressestheairenteringthesystem.Asaresultofthemuchhigherflowinpipe18,theflowthroughtheblower4islargerintheMCFCmodel(thantheSOFCmodel),requiringmorepowerforcompressionthanintheSOFCmodel.Duetotheincreasedmassflowintotheanodeofthefuelcell,bothanodeandcathodeoutputsarelargeraswell.Themassflowfromthecathodeoutputisatahightemperature(700°C)anditpassesthroughaheatexchanger(apparatus13)beforeexitingthroughsink15atareducedtemperatureof100°C,whichisalowerexitingtemperaturethanthecathodeexhaustintheIR-SOFCmodel.Asaresultofthelargeamountofheatavailableat(heatexchanger)apparatus13,thereisanincreasedairflowintothesystemthroughcompressor11.Thisairisultimatelysuppliedtothecathodeinlet.ThisresultsinhigherpowerconsumptionintheIR-MCFCsystemthanintheIR-SOFCcaseforblower11.Withanadditionalblower(apparatus20)forseparatedCO2,alongwiththehigherpowerconsumptionbytheothertwocompressors(apparatuses4and11),thepowerconsumedbytheauxiliarycomponentsofthesystemismuchhigherthanintheSOFCcase,resultinginadditionallossofefficiencyintheIR-MCFCsystemsaswell.ConclusionItwasfoundthroughflowsheetcalculationsonanIR-MCFCsystemthatitispossibletodesignacoproductionsystemthatcanfunctioninaconventionalmodeproducingmainlyelectricpowerandheatandincoproductionmodeproducingelectricpower,hydrogen,andverylittleheat.Byusingwasteheatintheendothermicreformingreactiontoproducehydrogen,hightotalefficiencyofover80%forhydrogen+powerproductionispossible.Aswasteheatiseffectivelyutilizedintheproductionofhydrogen,theIR-MCFCcanbeoperatedataveryhighpowerdensity.Inthehigh-powermode,itispossibletoachieveaveryhighelectricpoweroutputthatisnearlytwicethatofthesameMCFCwhenoperatedinaconventionalmode,whileatthesametime,anadditionallargeamountofpowerintheformofhydrogeniscoproduced.Thetotalefficiency,however,dropsbelow60%inthishigh-powermode.•High-efficiencymode:IR-MCFCachievedamaximumtotalefficiencyofover80%forelectricityplushydrogenproduction.•Constantcurrentdensitymode:IR-MCFCalsoachievedamaximumtotal(gaspluspower)efficiencyofover80%.•High-powermode:IR-MCFCachievedamaximumoverallefficiencyofover56%atatotal(gaspluspower)outputthreetimeshigherthaninthehigh-efficiencymode.IncomparisontotheIR-SOFCsystem,theIR-MCFCsystemproducessimilarelectricoutputatsimilarefficiencybutwiththegaspoweroutputintheformofhydrogenandCO;hence,thegasefficiencyismuchlower.Thisresultsinlowertotalefficiency.Inallthreemodesofoperation,theIR-MCFCoverallefficiencywasatleast10percentagepointslowerthantheIR-SOFCmodel.Thegasefficienciesmaybelowerduetoreasonsassociatedwithoperatingprinciples,valverecyclingratiosetting,andincreasedpowerconsumptionbytheblowers.Despitethis,IR-MCFC,liketheIR-SOFCsystem,allowsforaflexibleoperationofacoproductionsystemthatcanmeetvaryinghydrogendemandandelectricdemandsathighefficiencies,thusmakingthemtechnicallyfeasibleforpoly-generationapplications.DataAvailabilityStatementTheoriginalcontributionspresentedinthestudyareincludedinthearticle/SupplementaryMaterial,furtherinquiriescanbedirectedtothecorrespondingauthors.AuthorContributionsTheresearchthatformsthebasisforthisarticlewasperformedbyUSaspartofhisMSc-thesisworkatTUDelftunderthesupervisionofKHasafollow-uponthesimulationworkperformedbyAnishPatilalsounderthesupervisionofKH.USalsowrotethefirstconceptofthisarticle,furthercommentedanddiscussedintheusualiterativeprocessbyKHandUSafterthegraduationofUS.FundingThisresearchwasperformedfundedbytheregulareducationalfundsofTUDelft(“firstmoneystream”)withoutexternalfunding.ConflictofInterestTheauthorsdeclarethattheresearchwasconductedintheabsenceofanycommercialorfinancialrelationshipsthatcouldbeconstruedasapotentialconflictofinterest.Publisher’sNoteAllclaimsexpressedinthisarticlearesolelythoseoftheauthorsanddonotnecessarilyrepresentthoseoftheiraffiliatedorganizations,orthoseofthepublisher,theeditorsandthereviewers.Anyproductthatmaybeevaluatedinthisarticle,orclaimthatmaybemadebyitsmanufacturer,isnotguaranteedorendorsedbythepublisher.SupplementaryMaterialTheSupplementaryMaterialforthisarticlecanbefoundonlineat:https://www.frontiersin.org/articles/10.3389/fenrg.2021.656490/full#supplementary-materialFootnotes1Cycle-TempoisnowdistributedbyAsimptote(www.asimptote.nl/software/cycle-tempo/).2Cycle-Tempooperationguideandtechnicalnotes(http://www.asimptote.nl/software/cycle-tempo/cycle-tempo-documentation/).ReferencesAbdalla,A.M.,Hossain,S.,Petra,P.M.,Ghasemi,M.,andAzad,A.K.(2018).AchievementsandTrendsofSolidOxideFuelCellsinCleanEnergyField:APerspectiveReview.Front.Energ.14(2),359–382.doi:10.1007/s11708-018-0546-2CrossRefFullText|GoogleScholarAdams,T.A.,Nease,J.,Tucker,D.,andBarton,P.I.(2012).EnergyConversionWithSolidOxideFuelCellSystems:AReviewofConceptsandOutlooksfortheShort-andLong-Term.Ind.Eng.Chem.Res.52(9),308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protected];KasHemmes,[email protected] COMMENTARY ORIGINALARTICLE Peoplealsolookedat SuggestaResearchTopic>
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