煤制甲醇工艺9.docx
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煤制甲醇工艺9
AIChE2008NationalStudentDesignCompetition
CoaltoMethanolChemicalPlantReport
ChiHangLee
ManKitChan
ChanYauAo
UniversityofCalifornia,SanDiego
DepartmentofMechanicalandAerospaceEngineering
ChemicalEngineeringProgram
9thJune,2008
ProfessorPaoChau
Contents
ExecutiveSummary……………………………………………………..……...……….1
OverallProjectScopeDescription……………………………………………….………1
DesignBasis,PrincipleandLimitations……………………………………….………...2
TechnologySelectionCriteriaandConclusion……………...…………….……………..5
ProcessPerformanceSummary………………………………………………………….9
ProjectEconomicsSummary…………………………………….………...………….17
ProjectDescription……………………………………………………………………...18
ProcessFlowDiagram……………………………………………………...…………...19
MajorEquipmentandList……………………………………………………...……….21
EnvironmentalandProcessSafety…………………………………………………...….21
AppendixA:
CoalInputCalculations
AppendixB:
HigmanGasificationSimulationOutput
AppendixC:
WaterGasShiftReactionCalculations
AppendixD:
MethanolSynthesisRateCalculations
AppendixE:
Temperaturevs.CO2andH2SwithNMP
AppendixF:
NMPCostCalculation
AppendixG:
ASPENInputFile
AppendixH:
ASPENSimulation
AppendixI:
EquipmentSizingCalculation
1.GoalGasifier
2.AcidGasRemovalTower
3.WaterGasShiftReactor
4.FlashDrum
5.DistillationTower1
6.DistillationTower2
AppendixJ:
EconomicAnalysisforPFR
AppendixK:
CAPCOSTModel
AppendixL:
OverallProcessFlowDiagram
ExecutiveSummary
Asthepriceofcrudeoilcontinuestoincrease,thereisaraisingneedtoproduceanalternatefuelsourceMethanolisanattractivecontestandinthisproject,theeconomicfeasibilityandapreliminarydesignforachemicalplanttoproducemethanoltocoalisexplored.DesignwillbecompletedwiththecomputermodelASPEN,whiletheeconomiciscarriedoututilizingCAPCOST.Thedesiredoutputofmethanolis5000MT/dayandmustalsomeettheAAgraderequirement.Thispreliminarydesigniscapableofproducing5065MT/dayofmethanol,theplantisdesignedbasedon292daysperyearand24hoursoperationschedule.Theinternalrateofreturnoninvestmentis0.13%andapaidbackperiodof19.3year.
OverallProjectScopeDescription
Thisstudyservestoprovideapreliminarydesignforacoal-to-methanolprocessandtodeterminetheeconomicfeasibilityoftheproject.LocationoftheplanthasbeendecidedtobeontheUSTexasGulfCoast,andacapacitytoproduce5000MTperdayofmethanolisdesired.MethanolproducedmustmeettheAAmethanolgradepurityspecification.Theprocesswillstartbyselectingacoalsourceoutofthreetypesofcoal.Itisassumedthattheselectedcoalhasbeenpre-processedatanestimatedcostandtransferredintoagasifierinwhichcoalisreactedwithsteamandoxygenproducingasyngascontainingunreactedsteam,H2,N2,CH4,H2S,CO2,COandNH3.Thesyngaswillthenbesubjectedtoaseparationunitforacidgasremoval.TheH2Sconcentrationinthetreatedsyngaswillbereducedtolessthan0.1ppmvbeforeenteringthewatergasshiftreactor.Inthewatergasshiftreactor,thestoichiometricratiobetweenH2andCOinthecleansyngasisshiftedtothedesiredratioof2:
1.Thisspecificratioisneededtofavortheproductionyieldofmethanolinthemethanolsynthesisprocesswhichconsistsofaseriesoffiveadiabaticplugflowreactorswithinter-stagecoolingsystems.ThemethanolproducedwillthenberefinedinordertomeetthespecificAAgraderequirement.TheoverallprocessofthedesignispresentedinFig.1below.
Fig.1.Blockflowdiagramofcoal-to-methanolprocess.
Methanolproducedcanbesoldatapriceof$320/MT(USGulfCoastFOB).Aneconomicanalysisofthecoal-to-methanolprocesswillalsobeperformedtoevaluatetheeconomicfeasibilityoftheplant.Keynumberssuchascapitalcost,operatingcost,projectinternalrateofreturn(IRR),sensitivityoftheprojecteconomicandpaybackperiodwillallbeconsideredwhendeterminingtheoveralleconomicfeasibility.Besides,theenvironmentalandsafetyofthemethanolproductionplantwillalsobeanalyzedandconsideredwhenevaluatingtheenvironmentalfeasibilityofthedesign.
DesignBasis,PrinciplesandLimitations
CoalGasification
VariouscalculationsinthisdesignareperformedusingMT/dayasthebasis.Inthecoalgasificationprocess,thegoverningchemicalreactionscanbegeneralizedasthefollowingreaction:
CxHy+x/2O2→xCO+y/2H2
(1)
Sincethegasifieroperatesathightemperature(inexcessof1500°C)andpressure(3200kPa),itcanbemodeledasequilibriumreactorsassumingnear-completecarbonconversionusingthefollowingsetofreactions:
CO+H2O↔CO2+H2
(2)
C+CO2↔2CO(3)
C+H2O↔CO+H2(4)
Thesereactionsareassumedtoatthermodynamicequilibriumandareusedasabasistodeterminetherelativeconcentrationsinthesyngasgeneratedfromthegasifier.
AcidGasRemoval
Thesyngasproducedfromthegasifieristreatedbyanacidgasremovalprocess.Therearemanycommercialacidgastechnologiesintheindustryandoneofthetechnologieswillbeusedasabasisofthedesign.ThechosenacidgasremovaltechnologyshouldhaveahighselectivityforH2SrelativetoCO2andbeablereducethesulfurlevelofthetreatedsyngasto0.1ppmvorlower.Inthisdesignproject,theacidgasremovalprocessisapproximatedasasimpleseparationunittoachievethespecifiedsulfurlevelofthetreatedsyngas.TheremovalofCO2duringthisprocesswillalsobeconsideredtoinordertoaccountforthecarbonlossduringthecoal-to-methanolprocess.
WaterGasShiftReactor
Thebasicchemistryinthewatergasshiftreactorcanberepresentedasthefollowingreaction:
CO+H2O↔CO2+H2(5)
ThepurposeofthewatergasshiftreactionistoadjusttheratioofH2toCOto2:
1.Thetemperatureofthewatergasshiftreactorrangesfrom600-900˚F(315.6-482.2˚C)andthepressureisapproximatelyat500lb/in2(3447kPa).Theequilibriumconstantatdifferenttemperaturescanbecalculatedusingtheequationbelow:
(Eq.1)
Basedonthecalculatedequilibriumconstant,theamountofsteamfeedingtothewatergasshiftreactorcanbedetermined.
MethanolSynthesis
Duringthemethanolsynthesisprocess,threechemicalreactionshavetobeconsidered:
CO+2H2↔CH3OH(6)
CO2+H2↔CO+H2O(7)
CO2+3H2↔CH3OH+H2O(8)
2CO+4H2↔C2H5OH+H2O(9)
Thesereactionsaresimultaneousreactionsinthemethanolsynthesisreactors.Reaction(5)isthewatergasshiftreaction,reaction(8)isthemethanolsynthesisfromcarbondioxide,reaction(9)istheproductionofbyproduct(ethanol)andreaction(6)isconsideredtobethebasicreactionforthesynthesisofmethanolbecauseCOisthemosteffectivecomponentforproductionofmethanolandreaction(6)istheratedeterminingstep.Theexpressionofequilibriumconstantforreaction(6)withtemperaturerange(373–673K)is:
(Eq.2)
Thekineticsofthereactionsabovecanbefoundfromtheliterature.Basedonthekineticsofthosereactions,theproductionyieldofeachchemicalcomponentinthesyngascanbecalculated.Thekineticrateexpressionsforeachreactionarepresentedasfollows:
(Eq.3)
(Eq.4)
(Eq.5)
Thesearethekineticrateexpressionsforreaction(6),(7)and(8).ThevalueoftheparametersaredescribedandgiveninAppendix.Thekineticrateofreaction(9)isassumedtobe100timesslowerthantheproductionrateofmethanol,sothekineticrateexpressionforethanolsynthesiswillbeequation(6)dividedby100.
AdiabaticquenchedbedreactorswithCu-Zn-Alcatalystsareusedformethanolsynthesis.Consideringthekineticrateexpressionsandreactionsabove,theproductionyieldofmethanolcanbefoundfromAspensimulation.Themethanolproductionrateisrequiredtobeslightlygreaterthan5000MT/daypriortothemethanolrefiningprocess.Suchmethanolproductionratecanbeachievedbyvaryingtheamountofcatalystsandthenumberofreactors.
MethanolRefinery
ThedesignofthemethanolrefiningprocessmustbeabletoachieveAAmethanolgradepurityspecification.Thefinalproductshouldcontaingreaterthan99.85%w/wmethanol(drybasis),lessthan0.1%w/wwaterandlessthan50ppmwethanol.Morethanonedistillatormayberequiredtomeetthepurityspecification.
TechnologySelectionCriteriaandConclusion
CoalSelection
Thedesignofthecoal-to-methanolprocessbeginswithcoalselectionandpre-processing.Threecoalsourceswerebeingconsidered,whichareMartinLakeTexasLignite,MontanaSub-BituminousandIllinoisBituminous.MontanaSub-Bituminouswaschosentobethecoalsourcebaseduponthecharacteristicsofthethreecoalsprovided.Montanacoalcontainshighcarboncontentandtheleastmoistureandsulfurcontentsamongthethreecoals.Thegasificationofhighcarboncontentcoalcangeneratemorecarbon-containingsynthesisgassuchascarbonmonoxideandcarbondioxide,andthuscanleadtoabetteryieldofmethanolinthemethanolsynthesisprocess.Thelowsulfurcontentincoalcreateslessacidgas,andthusleadstoalowerwastetreatmentcostintheremovalofsulfurintheacidgasremovalstage.
Table1.CoalSourcesandComposition
GasificationTechnologySelection
Therearethreechoicesofgasificationtechnologieswhicharemoving-bed,fluid-bedandentrained-flowgasificationprocesses.Thechoiceofgasificationprocesshasbeendecidedtoemploytheuseofentrained-flowsinglestagegasifierbecausethisprocessgivesahighercarbonconversiontoCOthantheothertwoprocesses.ThelowCO2andhighcarbonconversionensuresthatalmostallcarboninthefeedisconvertedtoCO,andhenceanon-s