process synthesis and global optimization of novel ammonia ... · process synthesis and global...
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ProcessSynthesisandGlobalOptimizationofNovelAmmonia
ProductionProcesses
C.Doga Demirhan1,2,WilliamW.Tso1,2,Efstratios N.Pistikopoulos1,21.ArtieMcFerrinDepartmentofChemicalEngineering
2.TexasA&MEnergyInstitute
November2,2017
AIChE AnnualMeeting,Minneapolis,MN
§ Worldpopulationisexpectedtoreach8.6billionby2035and9.4billionby2050andtheworldGDPwilldouble!
§ Ammoniawillcontinuetobeproducedandusedinextensiveamounts.
§ Biomassisanenvironmentallyfriendlyalternativehydrogensourcetonaturalgas withnonetCO2 emissions
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Introduction&Motivation
NRELGeospatialDataScienceReport,2014
365milliontons/yearofsolidbiomasswasavailablein2015!
Possible>1billiontons/yearwillbeavailableby2040!
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USCensusBureau, USGeologicalSurvey,WorldBank,USEIA
USDOE,2016Billion-TonReportEIAMonthlyEnergyReview,Sept2017
AIChE AnnualMeeting,Minneapolis,MN
Aim1: Mathematicalmodelingoftheprocessesinfossil- and/orrenewablefuel-based(hybridfuel)ammoniaproductionprocesses
§ Developadata-drivenmodelforammoniaconverter§ Presentmodelsforprocessalternativesforsyngasgeneration,syngascleaning,andammoniasynthesisloopsections
Aim2: Processsynthesisandglobaloptimizationofammoniaproductionprocesses
§ Incorporateallprocessalternativesinaprocesssuperstructurewithsimultaneousheat,power,andwaterintegration
§ Applyglobaloptimizationmethodstofindthegloballyoptimaltopologiesfordifferentfeedstockavailabilities,greenhousegasemissionreductions,andplantscales
11/2/17 2
AimsofthisWork
AIChE AnnualMeeting,Minneapolis,MN
Challengesofbuildingdata-drivenmodels:§ Howtofindthebestfittingmodel?§ Whichtermsshouldbeincludedinthemodel?§ Overfitting?
Oursolution:§ Wepreparedtrain/validation/test sets§ 5-fold cross-validation approachisappliedtocreate5models§ These5modelsaretestedwithnewdata(testset)§ Belowarethescatteredresultsofanexampletrain/validation/testwith55totalpoints(40-10-5)
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AmmoniaConverterModeling
Conversion = β+ +-β.
�
.
x.
Quadraticpressuretermisfoundtobe
insignificant!
Additionofquadratictermsof
temperatureandpressureresultedin
overfitting!
Linearmodelisselected!
Nowwecanmoveontotheprocessalternatives!
AIChE AnnualMeeting,Minneapolis,MN11/2/17
NaturalGas-BasedAmmoniaProduction
PrimaryReforming
SecondaryReforming
Water-Gas-Shift
SyngasPurification
AmmoniaSynthesis
Water
AirRecycle
Ammonia
PurgeCarbondioxideCompression
Oxygen
AirSeparationUnit
Nitrogen
Air
Nitrogen
4
Natural gasSyngas
AmmoniaSynthesisGas
H2-richSyngas
AIChE AnnualMeeting,Minneapolis,MN11/2/17
Biomass-BasedAmmoniaProduction
Water-Gas-Shift
SyngasPurification
AmmoniaSynthesis
AirRecycle
Ammonia
PurgeCarbondioxideCompression
BiomassGasificationBiomass
- Switchgrass- Hardwood- CornStover- MunicipalSolidWaste
Oxygen
AirSeparationUnit
Nitrogen
Nitrogen
SynGasCleaning
5
Carbondioxide
CleanBio-Syngas
AmmoniaSynthesisGas
H2-richSyngas
AIChE AnnualMeeting,Minneapolis,MN
§ Processsynthesisproblemisalarge-scalenonconvexmixed-integernonlinearoptimization(MINLP)problem
§ Binaryvariablesareusedfortechnology/reactortypeselection§ Modelincludes:
§ Mass&energybalanceequations§ Thermodynamicrelations(phaseandchemicalreactionequilibria)§ Simultaneousheatandpowerintegration§ Concavecostfunctionsforcalculationofunitinvestmentcosts
§ Nonlinearitycomesfromthefollowingterms:§ Bilinear: equilibriumreactors,splitters,flashcalculations,streamcompositions,etc.§ Trilinearandquadrilinearterms: Thermodynamicsandequilibriumcalculations
§ Objectivefunctionisminimizingthelevelizedcostofammoniaproduction:
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OptimizationProblem
MIN - Cost5667 + Cost6869:;.9.:< + Cost=>?A6BC6A:;D:.EF − CostHIJ + - CostCF.:A
�
C∈LMNO
�
5∈P667
TDC = (1 + BOP)C+SS+
A5
xC,CO,A[ − KC,A]H^ _ xC,C`,A
[ = 0
xC,C`,A[ _ NC,C`
b − NC,C`,A[ = 0
xC,Cc,=>[ _ xC,Cc,d?[ e − KC[f _ xC,Cc,=dg
[ _ xC,Cc,d?>[ = 0
AIChE AnnualMeeting,Minneapolis,MN
§ Weuseatailoredbranch-and-boundalgorithmcombinedwithadvancedterm-basedrelaxationtechniquestosolvetheproblemtoglobaloptimality.
§ Piecewiselinearunderestimatorsareusedwithlogarithmicpartitioningscheme.
§ TheproblemisdecomposedintoanMILPlowerboundandanNLPupperboundproblem.
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GlobalOptimizationAlgorithm
§ Feasibility- andoptimality-basedboundstightening(FFBTandOBBT)methodsareusedtoobtaingoodqualitybounds.
§ Branchingisdoneonthevariablewiththelargestrelaxationerror.
§ Theaimisthegetasolutionwithinafewpercentofthebestpossiblevalue.
MINLP
MILP
NLP
SolvetheMILPtogetalowerboundsolution(LB)
SolvetheNLPtogetanupperboundsolution(LB)
(LB-UB)/UB<ε-RelativeTolerance
Yes
No
Fixthebinaries!
BranchonvariablesandsolveOBBTtogetnewbounds!
Relaxtheproblem!
Globaloptimalityistheoreticallyguaranteed!
AIChE AnnualMeeting,Minneapolis,MN
§ Adata-drivenmathematicalmodelisdevelopedforammoniaconverter§ Aprocesssuperstructureissynthesizedandmodeledforbiomass-basedammoniaproductionandsolvedtoglobaloptimality
§ Casestudiesshowedthatforsingletypeoffeedstock:§ Ammoniaproducedfromhardwoodtypebiomasshadthelowestbreak-evenpriceofammoniawith50%reductioninGHGemissionsbeingpossible
§ Atsmallerplantsize,NG-basedproductionhaslowerbreak-evenprice;astheplantsizebecomeslarger,biomass-basedprocesshasthelowestbreak-evenprice
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Conclusions
Acknowledgements