煤制甲醇工艺9.docx

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