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University of Pennsylvania University of Pennsylvania
ScholarlyCommons ScholarlyCommons
Senior Design Reports (CBE) Department of Chemical & Biomolecular Engineering
4-2016
C4 Operations Optimization C4 Operations Optimization
Michael Moroney University of Pennsylvania, [email protected]
Evan M. Smith University of Pensylvania, [email protected]
Marissa E. Thompson University of Pennsylvania, [email protected]
Fernando Torres University of Pennsylvania, [email protected]
Follow this and additional works at: https://repository.upenn.edu/cbe_sdr
Part of the Biochemical and Biomolecular Engineering Commons
Moroney, Michael; Smith, Evan M.; Thompson, Marissa E.; and Torres, Fernando, "C4 Operations Optimization" (2016). Senior Design Reports (CBE). 80. https://repository.upenn.edu/cbe_sdr/80
This paper is posted at ScholarlyCommons. https://repository.upenn.edu/cbe_sdr/80 For more information, please contact [email protected].
C4 Operations Optimization C4 Operations Optimization
Abstract Abstract The primary objective of the project chronicled in this report was to design a model that optimizes C4 operations. This model will optimize the options for processing both “crude C4” and “Cat BB” streams, taking the feed stream makeup, market pricings, and capacity constraints into account. Crude C4 streams contain butanes, butenes, and butadienes, while “Cat BB” streams are similar in makeup but do not include butadienes.
It is assumed that the equipment for all unit operations is readily available. In addition, the plant will already have a baseload of feedstock that does not fully utilize all the equipment in the plant, which allows for the purchase of feedstock that could potentially be profitable.
Available unit operations include Butadiene extraction, MTBE production, Metathesis, 1-Butene distillation, Skeletal Isomerization, Olefin Isomerization, and Alkylation. The model will be required to make choices about which unit operations to utilize based on the constraints input by the user. While the model will not directly produce revenue, it will allow the company to optimize processes within the plant, finding the most profitable situation. Thus, it will be possible to assess the program’s value based on its accuracy.
Disciplines Disciplines Biochemical and Biomolecular Engineering | Chemical Engineering | Engineering
This working paper is available at ScholarlyCommons: https://repository.upenn.edu/cbe_sdr/80
UniversityofPennsylvaniaSchoolofEngineeringandAppliedScienceDepartmentofChemicalandBiomolecularEngineering220South33rdStreetPhiladelphia,PA19104
April12,2016
DearProfessorFabiano,Dr.Shieh,andMr.Sawyer,
Thefollowingreportcontainsourproject,C4OperationsOptimization,whichwas
recommendedbyMr.GarySawyer.TheoptimizationprogramusesMicrosoftExcelto
determinetheoptimalprocessingofacrudeC4stream,andutilizesunitoperationsatan
existingpetrochemicalplant.Givenfeedstreammakeup,marketpricings,andcapacity
constraints,theoptimizationprogramwedesignedisabletodeterminethemostprofitable
courseofactionforthepetrochemicalplantinquestion.
Ourreportcontainsdetailedinformationontheprogramthatwasdesigned,aswellas
informationonunitoperations,marketanalysis,utilityandcapacityrequirements,and
customerrequirements.Adiscussionoftypicalscenariosisalsoincluded,aswellasasensitivity
analysisandaninvestmentopportunityanalysis.Theprogramisuser-friendlyandcanbe
modifiedtofitthespecificationsofthepetrochemicalplantinquestion,meetingthe
requirementslaidoutintheprojectstatement.Thegrouprecommendsthatthecompany
beginuseofthisprogramimmediatelybecauseitcansignificantlyincreasecompanyprofits.
Suggestionsforimprovementstothecodeoftheprojectprogramareincludedinthisreportas
well.
Sincerely,
________________________________________________________
MichaelMoroney EvanSmith MarissaThompson FernandoTorres
OptimizationModelforaCrudeC4Refinery
ReportAuthoredby:MichaelMoroney,UniversityofPennsylvania
EvanSmith,UniversityofPennsylvaniaMarissaThompson,UniversityofPennsylvaniaFernandoTorres,UniversityofPennsylvania
FacultyConsultant:
Dr.WenShieh,Professor,UniversityofPennsylvania
PrimaryIndustryConsultant:Mr.GarySawyer
April12th,2016
Table of Contents
Abstract..................................................................................................................................1
Introduction...........................................................................................................................1ProjectCharter.................................................................................................................................3
MarketandCompetitiveAnalyses..........................................................................................3MarketAnalysisforCompounds.......................................................................................................3
EffectofdecreaseinoilpricesoncrackersinEurope.........................................................................4Ethylene...............................................................................................................................................4Propylene.............................................................................................................................................41-Butene..............................................................................................................................................4Methanol.............................................................................................................................................5MTBE....................................................................................................................................................6Butadiene............................................................................................................................................6N-Butaneandi-Butane........................................................................................................................6
CompetitiveAnalysisforModel.......................................................................................................7
CustomerRequirements.........................................................................................................7
ProductConcepts....................................................................................................................7SuperiorConcept.............................................................................................................................8Assumptions....................................................................................................................................8DescriptionofModel........................................................................................................................9
SpreadsheetLayout.............................................................................................................................9TheLandingPage...............................................................................................................................103DSensitivityAnalysis.......................................................................................................................13InvestmentAnalysis...........................................................................................................................13ProfitBreakdown...............................................................................................................................16DetailedFlowDiagram......................................................................................................................17FeedInformation...............................................................................................................................19PricingInformation............................................................................................................................20ProcessSheets(ExtractiveDistillation)..............................................................................................21
UsingtheModel.............................................................................................................................22CaseStudy.....................................................................................................................................24UnitOperationsDescriptions.........................................................................................................29
ButadieneExtraction.........................................................................................................................29MTBEProduction...............................................................................................................................29Metathesis.........................................................................................................................................301-ButeneDistillation..........................................................................................................................30SkeletalIsomerization........................................................................................................................30OlefinIsomerization..........................................................................................................................31Alkylation...........................................................................................................................................32
Hydrogenation...................................................................................................................................32UtilityandCapacityRequirements.................................................................................................32
Metathesis(UOPOleflex)..................................................................................................................33Alkylation(DupontSTRATCO)............................................................................................................33MTBEProduction(UOPEthermax)....................................................................................................33ButadieneExtraction(BASF)..............................................................................................................34Hydrogenation(HülsSelectiveHydrogenationProcess)...................................................................34SkeletalHydrogenation(SKIPProcess)..............................................................................................341-ButeneDistillation..........................................................................................................................35
ConclusionandRecommendations.......................................................................................36
Acknowledgements..............................................................................................................36
WorksCited..........................................................................................................................38
1
AbstractTheprimaryobjectiveoftheprojectchronicledinthisreportwastodesignamodelthat
optimizesC4operations.Thismodelwilloptimizetheoptionsforprocessingboth“crudeC4”
and“CatBB”streams,takingthefeedstreammakeup,marketpricings,andcapacityconstraints
intoaccount.CrudeC4streamscontainbutanes,butenes,andbutadienes,while“CatBB”
streamsaresimilarinmakeupbutdonotincludebutadienes.
Itisassumedthattheequipmentforallunitoperationsisreadilyavailable.Inaddition,the
plantwillalreadyhaveabaseloadoffeedstockthatdoesnotfullyutilizealltheequipmentin
theplant,whichallowsforthepurchaseoffeedstockthatcouldpotentiallybeprofitable.
AvailableunitoperationsincludeButadieneextraction,MTBEproduction,Metathesis,1-Butene
distillation,SkeletalIsomerization,OlefinIsomerization,andAlkylation.Themodelwillbe
requiredtomakechoicesaboutwhichunitoperationstoutilizebasedontheconstraintsinput
bytheuser.
Whilethemodelwillnotdirectlyproducerevenue,itwillallowthecompanytooptimize
processeswithintheplant,findingthemostprofitablesituation.Thus,itwillbepossibleto
assesstheprogram’svaluebasedonitsaccuracy.
IntroductionCrudeC4sandCatBBsareproductsofthesteamcrackingprocessdesignedtoproduce
petrochemicals.Thesestreamscontainamixofbutanes,butenesandbutadienes.Often,
chemicalrefineryplantsopttoprocessandselltheseproducts,whichcallsfortheuseofan
optimizationprogramtodeterminethemostprofitablepathway.Bothbutadiene,whichcanbe
recoveredthroughextractivedistillation,and1-butene,whichcanberecoveredthrough
conventionaldistillation,arevaluablemonomersifhighinpurity.Inaddition,isobutylenecan
2
beprofitableasamonomer,butisoftenconvertedtomethyl-tertiarybutylether(MTBE),a
highoctanefueladditivethatistypicallymoreprofitable.Furthermore,therearemultiple
optionsfortheprocessingofcis-andtrans-2-butene.Theseoptionsincludealkylation,skeletal
isomerization,metathesis,andolefinisomerization.Alkylationrequiresisobutaneandproduces
alkylate,amotorfuel.Skeletalisomerizationallowsforanequilibriummixtureofbuteneand
isobutylenetoberecycledbacktotheMTBEreactionunittoincreaseprofit.Metathesis
requiresethyleneandproducespropylene,achemicaltypicallymorevaluablethanethylene.
Olefinisomerization,alsocommonlyknownasbuteneisomerizationorpositional
isomerization,allowsfortheproductionandrecuperationof1-butene,whichcanthenbesold.
Hydrogenationof2-buteneton-butaneisanadditional,albeitlessdesirable,option,wherethe
n-butaneissoldasfeedstock.
Thefocusofthisprojectwastocreateaprogramthatmadedecisionsbasedonfeedstock
composition,marketpricesofproducts,andcapacityconstraintsofunitoperationsintheplant
inordertomaximizeprofit.Theprogramwastoalsoexploretheopportunityofbuying
additionalfeedstockintheeventthatthebaseloaddidnotfullyutilizeequipmentcapacity.
Thisrequiredresearchonutilitycosts,capacityinformation,andthepetrochemicalmarket,as
wellasthecharacterizationoftypicalcrudeC4andcatBBstreams.Thesefactorsarediscussed
inthereport.ThemajorityoftheprojectinvolvedusingMicrosoftExceltobuildauser-friendly
modelthatcouldoptimizerefineryplantoperations.Additionalcalculationsincludedmaterial
balancesandprofitanalysis.
ThemodelinMicrosoftExcelwillbeusedbyalargepetrochemicalscompany.Itwillbe
designedtofitthespecificneedsofthecompany,andwillbeassessedbasedoneaseofuse
andonaccuracy.Itisassumedthatthecompanyinquestionalreadypossessesallofthe
necessaryequipmentfortheunitoperations,thusitwillnotbenecessarytopurchase
additionalunits.
3
ProjectCharter
Name:C4OperationsOptimization
ProjectStudents:MichaelMoroney,EvanSmith,MarissaThompson,andFernandoTorres
ProjectAdvisors:Mr.LeonardFabiano,Dr.WenK.Shieh,andMr.GarySawyer
SpecificGoals:ThedevelopmentofanoptimizationprogramtobeusedforC4optimization.
Scope:[InScope]
Capacityandutilitycostsofunitoperations
Typicalmarketpricingofproducts
EconomicAnalysis
ProgrammingandcodingtodesignoptimizationsprograminMicrosoftExcel
Massandenergybalances
[OutofScope]
ReactorDesign
Labworkandexperimentalprocedures
Deliverables:
Fullyfunctionaloptimizationprogramthatallowscustomizableuserinputs
Economicandmarketanalysis
Massandenergybalances(Incorporatedintomodel)
Timeline:Completionofdesignprojectwithinthe3monthsemester.
MarketandCompetitiveAnalyses
MarketAnalysisforCompoundsVolatilityinoilpricesgloballyfactorsintothepetrochemicalindustry.Withrecenthistorically
lowoilprices,manypetrochemicalcompanies,especiallythoseinEurope,havebenefitedfrom
anincreaseintheirmargins.
4
EffectofdecreaseinoilpricesoncrackersinEurope
CrackersinEurope(companieswhotakefeedstockandbreakitdowntomakeolefins)have
benefitedmostsincetheirmainfeedstockisnaphtha(C5-C8),adirectproductfromcrude.
Theirenergycostshavealsogonedown,sincetheyuseoiltofueltheircrackingoperations,as
opposedtotheUnitedStates,whichusesshalegas(andhasusuallyenjoyedmuchgreater
competitivenessthankstoitsprice).Thedropinoilpricesthencomesasareliefto
petrochemicalscompanies,consideringashowfeedstockandenergycostsaccountforcloseto
85%oftheoperatingcost.
However,theircustomershavenotenjoyedtheeffectsofthispricedrop.Manyofthese
companies,underthefinancialstraintheyusuallyface,failedtomakeadequateinvestments
thathavenowcostthemintheformofunprecedentedshutdowns.Thesehaveledtoa
decreaseinthesupplyoftheirproducts(ethylene,propylene,byproducts,andderivatives),
resultinginanincreaseinprice.16
Ethylene
Supplyforethylenewastightin2015,andlookstoremaintightin2016aswell.Priceshave
droppedingeneral,althoughthemarginfortheproducerhasincreasedbecauseofthelowoil
priceandthetightsupply.TheUSisexpectingtobeginatleast7large-scaleprojectstoincrease
theproductioncapacityofethyleneby50%overthenextfewyears.Itcanbeexpectedthatthe
increaseofethyleneproductioncapacitymayresultinagreaterquantityofcrudeC4.10,16
Propylene
Propylenesupplyisnotexpectedtobetightin2016.Demandforithasfallenrelativetothatof
ethylene,asitsderivatives’marketsdonothaveaspositive/steadyoutlooks.Themargingap
betweenethyleneandpropylenecontinuestobroaden.16,20
1-Butene
Linearlow-densitypolyethylene(LLDPE)iscurrentlythefastestgrowingapplicationforalpha
olefinssuchas1-butene,drivenbytheincreasingdemandforhigh-qualityplastics.Assuch,the
5
demandforalphaolefinsisexpectedtogrowglobally.Pricing,however,isinherently
dependentonthevolatilepricesoftherawmaterialsrequiredforproduction.
Methanol
Whilemethanolpricingshouldbeindependentofoilprices,becauseofMethanoltoOlefins
(MTO)andMethanoltoPropylene(MTP)processesthatareoperationalinChina,thepriceof
Methanolhasbeenimpacted.MTOandMTPprocessesthatproduceethyleneandpropylene
competewiththemoretraditionalapproachthatusesnaphthaasafeedstock.Sincethecosts
ofthistraditionalapproachwentdownbecauseofthedropincrudeprices,inorderto
compete,thepriceofmethanolalsodecreased.In2015,capacityintheUSformethanol
productionincreasedbymorethan75%.2016isexpectedtobestable.Pricingwasveryvolatile
duetotheuncertaintyinsupply,althoughcurrentpricesareata6-yearlow.3,21
Table 1: Chemical and Utility Prices
Material MED LOW HIGH CUSTOM Source Month YearEthylene $0.18 $0.15 $0.20 $0.18 Platt January 2016Propylene $0.30 $0.26 $0.34 $0.30 Platt January 20161-Butene $0.67 $0.64 $0.69 $0.67 Argus August 2015Methanol $0.41 $0.34 $0.29 $0.41 Platt January 2016MTBE $0.23 $0.20 $0.26 $0.23 Platt January 2016Butadiene $0.42 $0.36 $0.47 $0.42 Argus August 2015n-Butane $0.51 $0.51 $0.51 $0.51 Argus August 2015i-Butane $0.51 $0.51 $0.51 $0.51 Argus August 2015CrudeC4 $0.01 $1.26 $1.51 $0.01 Argus August 2015isobutylene $0.58 $0.55 $0.60 $0.58 Argus August 2015Alkylate $0.20 $0.20 $0.27 $0.20 OPIS February 2016Hydrogen $8.00 $8.00 $8.00 $8.00 Electricity $0.06 $0.06
“CostSheetOutline”onpage604ofDr.WarrenSeider’s
ProductandProcessDesign
Principles.
NA 2016
Steam(150psig) $10.50 $10.50Coolingwater $0.02 $0.02Processwater $0.20 $0.20boilerfeedwater $0.50 $0.50NaturalGas $3.20 $3.20ChilledWater $4.00 $4.00Steam(50psig) $6.60 $6.60
6
MTBE
ThemajorityofMTBE(95%)isusedtooxygenategasolineandboostitsoctanes.Althoughthe
supplyofMTBEisexpectedtodecreaseinEuropenextyear(2016),itisexpectedtogrowin
otheremergingeconomies.AsChinaandIndiaimposestricterenvironmentalrules,the
demandforMTBEisexpectedtoincrease.Throughout2015priceswerefairlyvolatile.7
Butadiene
MostButadieneisobtainedbyextractingitfromthecrudeC4whichresultsfromnaphtha
crackingtomakeolefins.IntheUS,roughly75%ofbutadieneisusedtoproducestyrene
butadienerubber(SBR),whichisusedintheproductionoftires.Ofthisabout80%isusedin
thereplacementtiremarket,whichhassufferedadropindemand.TheremainingButadiene
producedintheUSisusedtomakeacrylonitrile-butadiene-styrene(ABS),whichisusedto
makeplasticsforcars,amongstotherthings.Formostof2015,supplyremainedamplewitha
steadybutmediocredemand.Ingeneral,thepriceofButadienefellwiththepriceofoil,
althoughforperiodsin2015thepriceincreased,mostprobablyduetosupplyconstraints.
AnotherdevelopmenthasbeeninthetechnologiesusedtomakeButadiene.Whilethe
traditionalmethodemploysanaphthafeedstock,newmethodsexploreusinglighterfeedstocks
likeethane,whileothersexplorethedehydrogenationofn-butane.Overall,theviewofthe
Butadienemarketfromparticipantsispessimistic.ThemarketsofButadienecustomersare
expectedtodecrease,anddemandisexpectedtofurtherslow.6
N-Butaneandi-Butane
Abouttwo-thirdsofthebutaneproducedgloballyisusedinliquefiedpetroleumgas(LPG).
DemandforLPGasadomesticfuelhassurgedinbothcommercialandresidentialsectors,
leadingtothegrowthofthebutanemarket.Thetightsupplyofethylenehasalsocontributed
tothegrowthofthebutanemarket,sincebutanesareusedintheproductionofethylene.
Exceptionalgrowth,however,hasbeenheldbackbythevolatilecrudeoilmarketand
environmentalconcerns.Overall,themarketisexpectedtoincreasemodestly.16
7
CompetitiveAnalysisforModel
Althoughsimilarmodelsexistatcompetitorplants,becausethismodelisdesignedspecifically
fortheplantinquestion,thereisnodirectcompetitor.Sincethemodelhasbeencreatedfrom
scratchinMicrosoftExcel,therearenoconcernsaboutpatentinfringement.Thecompany
musthavealicenseforMicrosoftExceltorunthemodel,buttherearenootherroyaltiesor
feestooutsidepartiesthatthecompanyneedstopay.However,itisessentialthatthemodel
fitsallstandardssetbythecompanysothattheplantisabletoearnmoreprofitsandcompete
againstotherpetroleumplants.
CustomerRequirementsOurgrouphasbeenhiredbytheOperationsPlanningdepartmentofapetrochemicalcompany.
Aspreviouslystated,theprojectistodesignanoptimizationmodelthatwilldetermine
profitableopportunitiestobuyfeedstock.Thisprogrammustbeuser-friendly,andmustbe
demonstratedatthefinalpresentationsinAprilof2016.Thecustomerhasrequiredthatthe
modelfindoptimalprocessconfigurationsgivencapacityinformation,pricinginformation,and
thefeedcomposition.Typicalutilityinformationisalsorequiredforthemodeltofunction
correctly.Allofthesecustomerrequirementsareclassifiedasfitness-to-standard(FTS).Easeof
usecouldpotentiallybecategorizedasnew-unique-difficult(NUD),ascouldothervariables
suchaswarningsaboutunrealisticpricinginputs,orinfeasiblecapacityrestraintinputs.
Becausethisproductistobedesignedforaspecificcompany,itdoesnothavetocompetewith
thoseatothercompanies.However,itmustbeefficientandaccurate.Itmustoutperform
whateverpreviousmodelsthecompanyhasbeenusing,potentiallygivingthemacompetitive
edgeandallowingthemtoincreaseprofitsthroughthemostefficientuseofunusedcapacity.
ProductConceptsSeveraldifferentprogrammingtoolswereavailablefortheproductdesign.Thesetoolsincluded
MicrosoftExcel,Matlab,andpotentiallyASPENPlus.MicrosoftExcelfeaturesanadd-incalled
8
Solverthatservesasanoptimizationtool.Matlabcanalsobeusedtocreateextensive
operationsoptimization.Finally,ASPENPlusisanadditionaloption,howeveritrequires
differentinputsthantheMicrosoftExcelandMatlaboptions.
SuperiorConcept
TheprogrammingtoolselectedforthisproductdesignwasMicrosoftExcelandtheSolveradd-
in.Thisallowsforthedesignofanoptimizationmodelusingmultiplespreadsheetsforeachof
themassbalances.Inaddition,auser-friendly“landingpage”canbecreatedthatallowsthe
usertoinputthenecessaryconstraintsandprices.Furthermore,Solverblockscanbeeasily
troubleshootedandthefileitselfeasilyshared.TheExcelformatrequirescertainassumptions,
namelyutilitiesthatscalelinearlywithprocessthroughputinorderforthemodeltoprovidea
suggestedC4purchaseamountinatimelymanner.Whiletheassumptionofproportional
utilitiesintroducessomeerrorinthecostcalculations,particularlyinthe1-butenedistillation
andanyprocessunitrunningatverylowthroughput,themodelcanbeeasilyupdatedwith
utilityrequirementsobservedbyprocessoperators.
MatlabandASPENweredecidedagainstbecausetheydidnoteasilyallowforthesame
accessibilityandvisualoutputthatanExcelmodelcouldpossess.Matlabwouldhaverequired
theusertokeeptrackofaverylargeworkspaceofvariablesthatcouldcauseconfusionand
erroriftheuserdidnottakeextremecarewhenchangingmultipleprocessparameters.More
ofthecodingforgraphicalanalysiswouldhavebeenleftfortheusertoinput,restrictingthe
potentialuserstothoseinthecompanywithproficientMatlabskills.
Assumptions
Severalassumptionswerenecessaryinordertocreateaworkingoptimizationmodel.First,it
wasassumedthatutilitiesscalelinearlywiththroughput.Thisallowedthemodeltoquickly
provideapurchaseamountusingtheinformationavailabletothegroup.Itisalsoassumedthat
allunitoperationsexistatthegivenpetrochemicalsplant,andthattheseunitoperationsare
readilyavailable.Thereactorsintheseprocesseswereassumedtooperateunderthesame
9
conditionsregardlessofthroughput.Anyadditionalreactants,i.e.hydrogen,wereaddedin
stoichiometricproportion.Bydoingthis,thegroupisassumingthatthereisalreadyexcess
reactantthatisbeingrecycledintheprocess,requiringonlystoichiometricmakeupofthe
reactantfortheprocesstooperate. Varyingreactorconditionswasnotconsideredasan
optimizationparameter.Fortheprogramtofunction,itwasnecessarytoassumethattheunit
operationswerealreadyheatintegratedandnofurtherheatintegrationwasnecessary.For
theinvestmentpageoftheprogram,itwasassumedthattheinterestratewasconstant,the
pricesandutilitycostswereconstant,andthattherewasnoinflation.
DescriptionofModel
Theoptimizationmodelmustmakeaseriesofchoicesregardingthepossibleprocessesthat
canbecarriedoutintheplant.Bothbutadieneand1-butenecanbesoldasmonomers,andare
quiteprofitablewhensoldinpureform.Isobutylenecanalsobesoldasamonomer,butitis
oftenusedinthereactiontoformMTBE.2-buteneisnotasvaluableasamonomer,butthere
areseveralprocessesthatcanserveasprofitableoptionsfor2-butene.Theseoptionsinclude:
Alkylation,whichcreatesamotorfuelknownas“alkylate”;skeletalisomerizationtoform
isobutyleneandbutenes,whichinturncanbeconvertedtoMTBE;Metathesis,whichcreates
propylenethatcanbesoldforprofit;andolefinisomerization,whichcreatesanequilibriummix
ofboth1-and2-butenes,wherethe1-butenecanberecoveredandsold.Themodeloptimizes
theplantbyvaryingthesplitfractionsoftheRaffinate2streamleavingtheMTBEunit,thesplit
fractionsoftheRaffinate3streamleavingthe1-butenedistillation,andtheamountof
additionalcrudeC4purchased.
SpreadsheetLayout
Themodelcomespresetwithcapacity,utility,andchemicalpricevaluesascitedinthe
followingsectionsofthereport.However,theuserisfreetochangetheseparameters,
denotedbybluecellshading,towhatevervaluestheuserseesfit.Thisallowstheuserto
updatethemodeltoreflectchangesinpricesinthechemicalmarketplaceand/orchangesin
theoperatingcharacteristicsoftheplantbroughtonbymaintenance,fouling,etc.
10
TheLandingPage
OpeningthemodeldisplaystheLandingPage(Figure1),whichcontainsadetailedsummaryof
theplantoperationsattheprocesslevelwiththethroughput,throughputconstraints,capacity,
product,andprofitofeachunitdisplayedinthe“ProcessInformation”table.Inthetopleftof
theLandingPageisthe“FeedInformation”table,whichallowstheusertomanuallyinput:the
amountofcrudeC4incomingfromtheupstreamprocesses,aswellasthecompositionofthe
C4feeds.TheamountofExternalFeedisdeterminedbythemodelandisnotauserinput.
Compositioninputsarechangedusingdropdownmenus,whichreferencepresetstandard
compositionsanduserselectedcompositionslocatedintheFeedInformationsheet(the6th
sheetlisted).Totherightofthe“FeedInformation”table,the“PriceScenario”tableprovides
theuserwithdropdownmenusforeachoftherelevantreactants/productsintheplant.These
pricesreferencethePricingInformationsheet,whichcontainsthemostup-to-datepricesthe
teamcouldfind.Aspricescanvarygeographicallyandwillvaryovertime,acustompriceinput
isavailableforeachchemical.The“ResetPrice”buttonwillautomaticallyresetthepriceofall
chemicalstothe“Mid”valueaslistedinthePricingInformationsheet.Totherightofthe
“PriceScenario”tableisthe“UtilityInformation”table,whichhasutilitycostsfortherelevant
utilitiesintheunitsspecifiedinthetable.Thetablevaluesarepresetaccordingtothe“Cost
SheetOutline”onpage604ofDr.WarrenSeider’sProductandProcessDesignPrinciples.18Like
chemicalpricing,utilitycostscanvarybyregionandwillvaryovertime,sothemodelallowsthe
usertoinputupdatedutilityvaluesinthe‘PricingInformation’Sheet,automaticallyupdating
thoseintheLandingPage.Thecolumntotherightoftheaforementionedtablescontainsthe
buttonthattheuserclickstoruntheoptimizationsimulationwiththeselectedinputs.
Displayedbelowthebuttonisthetotalprofitfortheplantforaweekofoperation.The
opportunitycostlistedbelowthetotalprofitistheamountofmoneythecompanycouldexpect
tomakefromsellingaweek’sworthofupstreamcrudeC4productionatmarketpriceinstead
ofrunningitthroughtheplant.Thetabledirectlybelowtheopportunitycostisasummaryof
theprofitbreakdownbyproduct.Itshouldbenotedthattheprofitbreakdownforthe
productsreflectsthedifferencebetweentheproductrevenueandthetotalcostofoperation
fortheunitwhichdirectlyproducesthatproduct.Tomakethesumoftheprofitsequaltothe
11
totalprofit,theprofitofMTBEincludestheutilitiesoftheskeletalisomerizationunit,andthe1-
buteneprofitincludestheutilitiesoftheolefinisomerizationunit.Amoreaccurate
representationoftheprofitfromproducingeachchemicalwouldbegivenbyspreadingthe
utilitycostsofupstreamprocesseslikebutadieneextractiontodownstreamproductslike
propyleneandalkylate,whichneedtheseupstreamprocessesinordertobeproduced.Putting
apriceontheintermediatestreamscouldalsobeusedtoobtainmoreaccurateprofitmargins
forthechemicals.Theteamwouldmakethisimprovementinthenextversionofthemodelby
distributingutilitycosts,aspricingintermediatestreamsaccuratelywouldrequiremarketdata
fromtheuser,whichisexpensiveandmaynotbedirectlyavailable.Finally,thetwotablesat
thebottomoftherightcolumndisplaythesplitfractionsofthe
12
Figu
re 1
: Lan
ding
Pag
e
13
Raffinate2andRaffinate3streams,respectively.TheRaffinate2istheproductoftheMTBE
unit,andtheRaffinate3isthebottomsproductofthe1-butenedistillation.
3DSensitivityAnalysis
Thesecondsheetisthe3DSensitivityAnalysis.Thissheetallowstheusertoquicklyvisualize
theimpactofpricechangesoftwochemicalsand/orutilities,selectedbytheuser,onthetotal
weeklyprofitoftheplant.Theuseralsoselectsthepercentchangeintheselected
material/utilityprices.Themodelwillapplythispercentchangetotheaveragepriceofthe
material/utility,asgiveninthe‘PriceInformation’sheet,inordertogeteightdatapoints.The
“RunAnalysis”buttonexecutesamacrowhichrunstheoptimizationprogramvaryingthe
pricesoftheselectedchemicalsbythespecifiedincrements.Themacroalsoplotsthedata
automaticallyina3Dsurfaceplot.Whiletheusercanselectanytwopricestovary,themost
interestingandimportantresultsarisefromthevaryingofpricesoftwoproductsthatrequire
Raffinate2orRaffinate3asinputs.Thissetupwouldallowtheusertoseewhichproductholds
moreinfluenceovertheprofitabilityoftheplantandisthereforevitalindecidingwherethe
majorityoftheraffinategoeswhentheplantisrunningoptimally.Byvaryingthepriceofan
inputandproductofoneprocess,forexampleethyleneandpropylene,theuserwillbeableto
observehowchangesinprofitabilityofoneunitoperationimpactsoverallplantprofitability.
Thisanalysiscouldbeusedinconjunctionwitheconometricforecastingofchemicalpricesto
producearangeofforecastedprofitsfortheplant.Theoptimalsplitfractionsfortheunits
couldalsobeforecastedandpreparationscouldbemadetoscaleunitsupordowndepending
ontheanalysisresults.
InvestmentAnalysis
Thethirdsheet,InvestmentAnalysis,providestheuserwithawaytoquicklyexaminethe
cost/benefitanalysisofexpandingthecapacityofabottleneckedprocess.Theuserdecidesby
whatpercentagetoincreasecapacityandhowmuchitwillcostonaperpoundbasis.Theuser
alsoselectstheinterestrateusedtoevaluatethenetpresentvalueoftheinvestmentaswellas
thenumberofyearsthattheinvestmentwilllast.Theprocesstobeexpandedischosenbythe
user,butitisrecommendedthattheuserchooseaprocessthatisoperatingat100%capacity.
14
Basedontheseinputs,thesheetwillcalculatethenewcapacityoftheselectedprocessandthe
costofprocessexpansion.
Figu
re 2
: Sen
sitiv
ity A
naly
sis
15
Figu
re 3
: Inv
estm
ent A
naly
sis
16
Clickingonthe“InvestmentAnalysis”buttonwillexecutethatrunsthemacro.Itfirstoptimizes
theprocessusingtheoriginalcapacities.Themacrowillthenoptimizetheprocessusingthe
newcapacityfortheselectedprocess.Itwillthentaketheprofitbeforetheexpansionandafter
theexpansion,calculateanincrementalweeklyprofit,andannualizeitinordertodoa
discountedcashflowanalysisusingtheinterestrateandyearspreviouslyselectedbytheuser.
Theoutputofthisanalysisincludestheinvestmentcost,thediscountedfuturecashflows,the
yearbywhichtheinvestmentisexpectedtobreakeven,andthenetpresentvalueofthe
investment.
Anumberofassumptionshavebeenmadewhenconstructingtheinvestmentanalysisfeature.
Theinterestrateisassumedtoremainconstantthroughoutthelifeoftheinvestment.Future
versionscouldallowforavariableinterestratethatcouldbeprovidedbythecompany’s
econometricforecastingforeachyearintheperiod,increasingtheaccuracyofthediscounted
cashflowanalysis.Anotherassumptionisthatpricesforutilitiesandchemicalsareconstant
overthistimeframe.Thisassumptionreducesthecalculationaccuracy,aspricesarealmost
certaintochange.Futureversionscouldincludetheoptionofchangingthesetofchemical
pricesyearlyastheforecastingwingofthecompanyseesfit.Addingthisfunctionalitywould
onlyimprovethecalculationsforthefirstfewyearsatbest,however.Sincepricevolatility,
especiallyinthecurrenteconomicclimate,makeslongtermforecastinglosealotofpredictive
power,addingthisfunctionalitywouldonlyimprovethecalculationsforthefirstfewyearsat
best.Capacityexpansionalsoassumesthatconstructionwillnotimpactcurrentoperations.The
userisexpectedtoconsiderallcostsintheexpansionprocess,includinganystartupcosts
whentheexpansionisintegratedintotheexistingprocess.Ideallythesearecondensedinthe
perpoundcostthattheuserinputs.
ProfitBreakdown
TheProfitBreakdownsheetgivesagraphicaldepictionoftheprofitbreakdownbyproduct.
Thewaterfallchartautomaticallyupdateswhentheoptimizationmodelisrunand/orwhenthe
userchangesthepriceinputsinthelandingpage.AswasnotedintheLandingPagesection,
theprofitbreakdowniscalculatedbasedonthedifferencebetweentheproductrevenueand
17
theoperatingcostoftheunitthatproducesit.InthecaseoftheMTBEproduction,thecostsof
skeletalisomerizationhavebeenincludedwhencalculatingtheprofit.Similarly,thecostof
olefinisomerizationhasbeentakenintoaccountwhendeterminingtheprofitof1-butene
distillation.Thesecombinationsweremadebecausetheisomerizationunitsdonotdirectly
produceasellableproduct,astheirfunctionsaretoincreaseproductionoftheprocessunits
theircostshavebeencombinedwith.Thismethodofcalculatingprofitresultsinanaccurate
totalplantprofit,butitdoesnotincludethecostofrequisiteupstreamprocessesinthe
productionofdownstreamproductslikealkylateandpropylene.Futureversionsofthe
optimizationprogramwouldspreadthesecostsoutandprovideamoreaccurateaccountof
theprofitbreakdown.
Figure 4: Profit Analysis
DetailedFlowDiagram
Theusercangetaclearervisualoftheplantoperationsonthissheet.Thepossibleconnections
betweentheplantprocessesareshownalongwiththepercentageofaunit’soutput
intermediatestreamthatissentalongaparticularpath.Thepercentagesupdateautomatically
witheveryrunoftheoptimizationmacrofromtheLandingPage.Productstreamsareshown
asdashedlines,buttheflowratesmustberecordedfromtheLandingPage.Thegroup
18
Figu
re 5
: Pro
cess
Flo
w D
iagr
am
19
excludedtheproductflowratesbecausethelargenumberswouldovercrowdthediagram
whileonlyprovidinginformationthattheusercouldeasilyfindonanotherpage.
FeedInformation
ThissheetispreloadedwithdifferentcompositionsofcrudeC4basedontheproduction
specificationsoftheDowChemicalCompany.Themedium,high,andlowbutadienecontent
compositionsdisplayedinthetablearetheonesreferencedinthedropdownmenuonthe
LandingPage.Additionally,therearetwocolumnsforcustomcompositionsofcrudeC4.These
columnshavebeenincludedbecauseitisunlikelythatthecompany’sowncrudeC4
compositionandthecompositionofthecrudeC4availableforpurchasewillmatchthoseofthe
selectedDowChemicaloptions.AfterlabsamplingofboththeinternalandexternalcrudeC4,
theusercaninputtheresultsinthecustomcolumnsofthetable.Thesecanalsobereferredto
inthedropdownmenusontheLandingPage.Ifthecompositionsinputtedbytheuserlie
outsidetheDowChemicalspecsshownbelowthetable,thegreencirclewillturnrednextto
theoutlierspecies.Tohelppreventusererror,ifthesumofthecustompercentagesdoesnot
equal100%,thecellinthelastrowwillturnred.
Figure 6: Feed Information
20
PricingInformation
Themostrecentpricesthegroupcouldlocateforthechemicalsandutilitiesrelevanttothe
plantarelocatedinthetableontheleftofthissheet.Sourceanddateinformationarelocated
ineachrow,withthemajorityofpricescomingfromPlattandArguswithintheseveralmonths
ofthereport’spublishing.Itshouldbenotedthatthesepricesarenotfromthesamepointin
time,andwiththerecentvolatilityintheindustry,thevariedtimeframesmaycausetheresults
oftheoptimizationprogramtoreturnunrealisticprofitmargins,aswellasinaccuratesplit
fractions.Itisthereforerecommendedthatthecompanyfrequentlyupdatethepricesofthe
chemicalswiththeirmostuptodateinformation.Thecustomcolumnwascreatedforthis
purpose,althoughallothercolumnscanalsobeupdated.ForsomechemicalslikeMTBE,crude
C4,andalkylate,thepricesquotedareoftenonavolumebasis.Sincetheoptimization
programoperatesonamassflowbasis,thePricingInformationsheetconvertsthepriceper
volumetopriceperpoundinthetableontheright.Theusersimplyneedstoinputtheprice
pergallonandtheremainingcellsinthetablewillautofillwiththepriceperpoundincents.
Figure 7: Pricing Information
21
ProcessSheets(ExtractiveDistillation)
Thesheetsforeachoftheplantprocesseshavethesamebasicstructureandfunction,sofor
brevitythereportwillbasethediscussionoftheprocesssheetsontheExtractiveDistillation
sheet.Anydifferencesinotherprocesssheetswillbenoted.
Sinceextractivedistillationisthefirstprocessintheplant,itssheetisuniqueinthatitissetup
withadditionalinformationaboutthecrudeC4feed.Theselectedcompositionsfortheinternal
andexternalcrudeC4feedsaredisplayedinthetopleftofthesheet.Belowthepercentage
compositionsarethemassflowsforeachoftherelevantchemicalsineachofthefeeds.The
blockdiagramfortheprocessisseentotherightofthesetables.Forthestreamsshown,the
massflowratesareshowninthelargetableunderneaththediagram.Allprocesseshavea
maintablesimilartothisoneinwhichthemassflowsofinput,intermediate,andoutput
streamsarecalculated.TheoutputstreamforbutadieneextractionisRaffinate-1,whosemass
flowratesarereferencedasoneoftheinputflowstreamsoftheMTBEproductionsheet.The
restoftheintermediatestreamsarelinkedbetweenprocessesasdepictedintheDetailedFlow
Diagram.
Theprocessparametersof:distillationeffectiveness,cellJ33;fractionofunrecovered
butadienehydrogenated,cellO49;andfractionalconversionofhydrogenatedbutadiene,cells
R49-51,areusedincalculatingthemassflowsoftheintermediatestreamsandhydrogeninput.
Therequiredhydrogenisthenconvertedtolbsperlbbutadieneproductforthebutadiene
materialcostcellontheLandingPage.ForotherprocesseswithadditionalinputslikeMTBE
production,metathesis,andalkylation,theadditionalinputisalsocalculatedontherightofthe
mainprocessstreamtableandischangedtoalbperlbsproductbasis.Otherprocessesalso
haveparametersthataffectperformancethatcanbetunedtotheuser’spreference.This
freedomallowstheusertoaccountforchangesintheplant’sefficiencyastheplantagesor
betweenroutinemaintenance.
22
Thebutadieneextractionutilitydataiscollectedontherightofthesheet.Thedataforeach
processhasbeenselectedfromthesourceslistedineachprocessdescription.Theutility
requirementsarethencombinedwiththeutilitypricesontheLandingPagetoprovideatotal
utilitybillperlbofproductforagivenprocess.Thisnumberisthenbroughtbacktothe
LandingPageintheutilitycostrowfortheprocesses.Capacityconversionsareshownnextto
theutilityinformation.
UsingtheModel
Whenusingthemodel,theusermustfirstprovidetheamountofavailablecrudeC4feed
comingfromupstreamprocessesinthecompany,aswellasitscompositionandthe
compositionofthecrudeC4availableforpurchase.Themodelwillupdatetheprofitandmass
flowratesforthegivensplitfractionsimmediatelyaftereachinputvalueischanged.The
resultswillnotbeoptimized,however,untiltheuserclicksonthe“RunSimulation”button.
OncetheuserhasselectedthedesiredchemicalandutilitypricesonthePricingInformation
sheet,theusercanselectcapacityrestraintsforeachoftheprocesses.Itshouldbenotedthat
overconstrainingtheprocessescancausetheavailablecrudeC4flowtobeinsufficientor
overloadtheprocesses,dependingontheconstraintsselected.Forexample,ifahighflow
requirementisdesiredforeveryprocessthatreceivesaninputfrom1-butenedistillation,there
mightnotbeenoughflowthroughthedistillationprocesstosatisfytheconstraintsforthe
otherprocesses.Conversely,ifahighflowminimumisimposedonthe1-butenedistillation
andlowmaximumsareimposedonthedownstreamunits,theremightbetoomuchflowto
meettheconstraintsdownstream.Iftheselectedconstraints,whichcanbechangedbythe
user,arenotmet,thecircleinthe“percentcapacityused”columnwillchangefromgreento
redfortheprocess.Oncethepricesandcapacityconstraintshavebeenselected,theusercan
runthesimulationtooptimizetheplantbyclickingonthe“RunSimulation”button.The
ProcessInformationtablewillthendisplaytheoptimalsplitfractionsfortheplantalongwith
capacityusageandproductinformation.TheexternalC4willthenbesettotheoptimalvalue,
resultinginthetotalprofitbeingmaximized.IfthechangeinexternalC4andthesplitfractions
cannotsatisfycapacityconstraints,anerrorwindowwillpopupafterrunningtheoptimization
23
statingthattheconstraintscouldnotbemet.Adjustmentstothecapacityconstraintsor
externalC4compositioncanbemadetoattempttosatisfytheconstraints,rerunningthe
simulationaftereachchange.Inthedesignteam’sexperience,overloadedprocessesinthe
downstreampartoftheplantcanberectifiedbyincreasingbutadienecontentintheexternal
crudeC4compositionifadjustingthecapacityconstraintsisnotpossible.Iftheuserexhausts
allpossibleadjustmentoptionsandtheconstraintsarenotsatisfied,theyshouldconsider
takingactionlikesellingavailablecrudeC4orinputtingadditionalfeedatdifferentpointsinthe
plant,dependingoniftheplantisoverfullorrunningdry.Theusercanperformtrial-and-error
todeterminehowmuchavailablecrudeneedstobesold,butthemodeldoesnoteasilyallow
fortheadditionofexternalfeedatmultiplepointsintheplant.
Assumingtheconstraintsaremet,theusernowhastheoptimalamountofexternalcrudeC4to
bepurchasedandtheresultingprofits.NowtheusermayturntheirattentiontotheSensitivity
Analysispage.Theusercanthenselectthetwopricesthattheywanttovaryfromthedrop
downmenus.Theincrementsofchangecanbeinputtedaspercentagesforeachvariable.
Clickingonthe“RunAnalysis”buttonwillpresenttherelationshipbetweenthevariables’prices
andthetotalprofit.
TheInvestmentAnalysispageisstraightforwardtouse.Afterrunningtheoptimizationonthe
LandingPage,runningtheInvestmentAnalysisbyclickingthebuttonwillautomaticallylocate
thebottleneckoftheplantunderthecurrentconditions.Ifthereisnobottleneck,whichis
unlikelygiventheproportionalutilityassumption,theanalysiswillreportbackthatthereis
none.Theuserneedstosimplyinputthepercentexpansionoftheunit’scapacity,theinterest
rate,andthelifetimeoftheexpansion.Thecostperlbaddedcapacitymustalsobeprovided
bytheuserthroughanoutsidecostinganalysisfortheunit.Oncetheinputsareentered,the
additionalprofitperyeararedisplayed,andthepresentvaluefortheadditionalprofitandthe
expansionprojectaregiveninthetable.Therequisitelifetimefortheprojecttoturnaprofitis
displayedabovethetable.
24
CaseStudy
Togiveamoreconcreteexampleofhowthemodelisused,considerthepricingscenarioas
showninFigure8.
Figure 8: Pricing Scenario for Case Study
Assumeanavailablefeedof15,000,000lb/weekofcrudeC4atthecompositiongivenbyhigh
butadieneDowChemicalcrudeC4,andthecrudeC4availableforpurchasehasthesame
composition.Figure9hastheresultsoftheoptimizationmodelforthissituation,withthe
processflowconstraintsgivenintheProcessInformationtable.Theoptimizationhasthe
optimalpurchaseoftheexternalcrudeC4at4.57*10^6lbs/week.Thevaluationofaweek’s
worththeinternalC4,theopportunitycost,iscalculatedat$6,000,000.Theweeklyprofitfrom
operatingtheplantiscalculatedat$8,951,659.Therefore,thebenefitfromrunningtheplantis
$2,951,659/weekorroughly$153.5millionperyear.NotableresultsarethattheMTBEunit
and1-butenedistillationareat100%capacity.ThisarisesfromthefactthattheMTBEunithas
ahighercapacitythanthe1-butenedistillationcolumn,andtheMTBEunitcansendthe
differenceincapacitytothemetathesisunit.Theolefinisomerizationunitisalsooperatingat
maximumcapacity,whiletheskeletalisomerizationunitisoperatingagainstthelowerbound
ofitsflowconstraints.Thissuggeststhattheplantwouldneedtooperatebelowthelower
constraintoftheskeletalisomerizationunitfortheplanttoreachanunconstrainedprofit
maximum.
25
Figu
re 9
: Lan
ding
Pag
e af
ter s
imul
atio
n w
as d
one
usin
g th
e pr
ice
scen
ario
for t
he c
ase
stud
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26
Examiningthe3DSensitivityAnalysispage,aninterestingrelationshiptoexamineistheeffect
ofvaryingisobutaneandalkylatepricesonthetotalprofitoftheplant.Thegeneraltrendof
the3Dgraph(Figure10)isrisingprofitsasthepricespreadbetweenthechemicalsisthe
largest,withthealkylateatahighpriceandisobutaneatalowprice.Thisisshownonthe
graphwithlowerprofitatthenearrightcornerandhigherprofittowardsthebackleftofthe
graph.Thesteeperslopefromrighttoleftindicatesthatachangeinalkylatepricehasmuch
moreofanimpactoftheprofitthanachangeinisobutaneprice.Thisrelationshipmakessense
becausetheisobutanerequirementroughlyonepoundofisobutaneperfourpoundsof
alkylate.Thestandarddeviationoftheprofitrangesis$73,336,whichisarelativelysmallfigure
comparedtotheprofitsinthe$8millionrange.Thissmallstandarddeviationindicatesthatthe
plantprofitisrelativelyrobusttofivepercentvariationsinthepricesofisobutaneandalkylate.
LookingattheProfitBreakdownsheet(Figure11),thealkylaterepresentsasmallportionofthe
overallprofit.Therefore,thesmalldeviationsinoverallprofitinresponsetochemicalprice
changesinthealkylateprocessmakessense.ButadieneandMTBEpricechangeswouldshowa
greaterstandarddeviationintheoverallprofit.
TheInvestmentAnalysispageshowsaninterestingbutnotunexpectedresult(Figure12).The
bottleneckselectedbytheuseristheMTBEproduction.Althoughthe1-butenecolumnisalso
operatingat100%capacity,additionalflowthroughtheMTBEcolumnwouldallowthe
metathesisandalkylationprocessestofilloutmorewhilestillkeepingthe1-butenecolumn
operatingatmaxcapacity.Expandingthe1-butenecolumnwouldonlytakeawayflowfrom
themetathesispathway,sincetheMTBEprocessbottleneckrestrictsthedownstreamflow.In
thisscenariotheuserisevaluatinga15%expansionoftheMTBEunit.Forasampleexpansion
cost,$45.00perlb/weekisused.Notethatthisvaluehasnotbeencalculatedusingcosting
modelsandissolelyintendedforthepurposeofhighlightingtheInvestmentAnalysisfunction.
TheuserwouldhavetoperformthesecalculationswhenusingtheInvestmentAnalysissheet.
Aninterestrateof12%annuallyandaprojectlifetimeof15yearsisselected.Thecostof
expansioniscalculatedatroughly$57million,andthebreakevenpointoftheexpansionis
27
betweenyearstwoandthreeafterthecapacityisexpanded.Thenetpresentvalueofthe
processoverits15yearlifespanis$123million.
Figu
re 1
1: S
ensi
tivity
Ana
lysi
s res
ults
for t
he p
rici
ng sc
enar
ion
in th
e ca
se st
udy
Figu
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0: P
rofit
Bre
akdo
wn
for t
he p
rice
scen
ario
in th
e ca
se st
udy.
28
Figu
re 1
2: In
vest
men
t Ana
lysi
s res
ults
from
pri
cing
scen
ario
in c
ase
stud
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29
UnitOperationsDescriptions
ButadieneExtraction
ExtractiveButadieneDistillationisthefirstprocessintheblockdiagram,andthusthefirst
decisionpointfortheprocessoptimizationsmodel.Thisprocessremovesbutadienefromthe
mixedcrudeC4stream.Theresultingbutadienestreamishighinpurity.Butadieneisusedto
produceseveraltypesofrubbers.Extractivedistillationisnecessarybecausethesimilaritiesin
volatilitiesbetweentheproductsintheC4streampreventtheuseofconventionaldistillation.
ThespecificprocessdescribedinthisreportistheBASFbutadieneprocess,whichrequiresthe
useofN-methylpyrrolidinone(NMP)asasolvent.11NMPisnotcorrosive,whichallowsfor
carbonsteeltobeusedintheplantwithouttheriskofcorrosion.2
BASFbutadieneextractivedistillationrequiresthreeprocesses.Theseprocessesareextractive
distillation,degassing,anddistillation.Theextractivedistillationhasanoverheadproduct
containingbutenesandabottomsproductcontainingcrudebutadiene.Thesolventis
recoveredduringthedegassingprocess,whilethebutadieneispurifiedusingthedistillation
process,whichallowsforapurityof99.7%orhigher.Theunrecoveredbutadieneisthen
selectivelyhydrogenatedto90%butenesand10%butanesbeforeproceedingontothe
subsequentprocessesoftheplant.18
MTBEProduction
Methyltertiarybutylether(MTBE)isanoxygenatecommonlyusedingasoline,althoughitsuse
hasbeendecliningasenvironmentalconcernshavesurfaced.MTBEandotheroxygenates
becamepopularinthe1990sasconcernsaroseabouttheairpollutionresultingfromlead
octaneenhancers,aproblempartiallyalleviatedbytheuseofoxygenates.However,bythelate
1990sandearly2000s,thepopularityofMTBEdeclinedduetoproblemswithgroundwater
contaminationandleaksinundergroundstoragetanks.
30
ThespecificprocessusedinthisreportistheEthermaxProcess,licensedbyUOP.15Thisprocess
converts99%ofisobutylene.Theprocessrequiresanadiabaticreactor,wheretheprimary
reactionoccurs.Theeffluentrunstoadistillationcolumn,wherethebottomsistheMTBE
product.Unreactedcomponentsarefedthroughafractionatortopromoteconversion.The
methanolintheoverheadfromthedistillationcolumnisthenrecoveredthroughasystemof
separations.Althoughthiswastheprocesswiththebestcharacteristicsthegroupcouldfind,its
capacitycreatedacripplingbottleneckontherestoftheplant.Inordertoshowoffthe
model’scapabilities,thegroupassumedthattheplanthadaccesstomultipletrainsofthe
Ethermaxprocess.
Metathesis
Themetathesisreactionproducespropylenefrom2-butene,1-buteneandethylene.The
specificprocessdetailedinthisprojectreportistheUOPOleflexProcess.12Inthepropylene
productionprocess,afeedofliquefiedpetroleumgasisdepropanizedtoseparateandremove
thebutanesandotherhydrocarbons.ItisthensenttoanOleflexunitandreacted.Thetwo
resultingproductstreamsareavaporthatisrichinhydrogen,aswellasaliquidthatisrichin
bothpropaneandpropylene.
1-ButeneDistillation
1-Butenedistillationallowsfortherecoveryofhighpurity1-butene.The1-butenemonomer
canbeveryprofitableifitispure.Inaseriesoftwodistillationcolumns,theheavy
hydrocarbonsareremovedinthebottomsstreamfirst,while1-buteneisremovedasthe
bottomsfromtheseconddistillationcolumn.Thisprocessrequiresnobutadieneor
isobutene.17
SkeletalIsomerization
SkeletalIsomerizationinvolvesisobutylene,1-butene,and2-butene.Athightemperature,
theseconstituentsreachchemicalequilibrium.Skeletalisomerizationallowsfortheproductto
befedtoanMTBEunitandconverttheisobutyleneintoprofit.Theprocessdescribedinthis
31
reportistheskeletalisomerizationprocess(SKIP)process,introducedbytheTexasOlefins
Company.9Afeedof1and2-butenesarefirstvaporized,andsteamisadded.Thestreamis
heatedtoreactiontemperature,whichfallsbetween480-550°C.Next,thestreamisreactedin
afixed-bedreactor,wheresomeofthe1-and2-butenesareconvertedtoisobutylene.
Followingreactionandequilibrium,thestreamiscooledinaheatexchangerandawater-
quenchcolumn.Thehydrocarbonsarethenseparatedfromthestreamanddepropanizedto
recovertheisobutyleneforuseinotherprocesses.
TheSKIPprocess,likeothersimilarprocessesintroducedbyothercompanies,isoftenincluded
followinganMTBEprocess.TheisobutyleneisthenrecycledbacktotheMTBEunitforfurther
productionoftheprofitableMTBE.AnalternativeoptionforsetupistoincludetwoMTBEunits
withaSKIPunitbetweenthem.
OlefinIsomerization
OlefinIsomerization,alsocommonlyknownasbuteneisomerizationorpositional
isomerization,involvestheconversionof2-buteneto1-butene.Theprocessdescribedhereis
theComonomerProductionTechnology(CPT)byCB&I.4However,specificutilityrequirements
wereunavailableforanycommercialolefinisomerizationtechnology.Usingaratiocomparing
theutilitycostsofexistingskeletalandolefinisomerizationtechnologies,itwaspossibleto
obtainanestimateforolefinisomerization,atapproximately38%oftheutilitycostofskeletal
isomerization.8TheCPTProcessincludestwosections.Inthefirstsection,2-buteneis
isomerizedto1-butene.Thestreamisvaporizedandpreheatedbeforebeingfedtoareactor
wherethe2-buteneisisomerizedoveracatalyst.Theproductstreamcontainsboth1-and2-
buteneatthermalequilibrium.Thesecondsectionisthefractionationsectionwhere1-and2-
buteneareseparatedusingabutenefractionator.The1-buteneistheoverheadproduct,while
the2-buteneisthebottomswhichisthenrecycledtotheisomerizationreaction.However,
sinceourplantalreadyhasitsown1-butenedistillation,ourolefinprocessonlyrepresentsthis
firstsection.
32
Olefinisomerizationallowsforalargeincreasein1-butenerecovery,whichthenallowsittobe
soldforprofit.
Alkylation
Alkylationisaprocessbywhichtrimethylpentaneor“alkylate”isformedfromisobutane,
isobutyleneand2-butene.Alkylateisacomponentformotorfuel,whichwaspopularinthe
1940s.However,withthedeclineinpopularityofMTBEduetoseriousenvironmentalconcerns,
itispossiblethatalkylatewillincreaseinvalueinthecomingyears.Thespecificprocesslisted
hereistheSTRATCOAlkylationprocessbyDupont,whichusessulfuricacid.13Accordingtothe
processdescription,therearefivesectionsoftheprocess,whichincludethereactionsection,
therefrigeratorsection,theeffluenttreatingsection,thefractionationsectionandthe
blowdownsection.Thereactionsectionincludesthereactionbetweenthehydrocarbonstream
andthesulfuricacidcatalyst.Therefrigerationsectionremovesbothheatofreactionaswellas
lighthydrocarbons.Intheeffluenttreatingsection,freeacid,alkylsulfatesanddialkylsulfates
areremovedfromthestream.Thefractionationsectionfollowstheeffluenttreatingsection,
whereisobutaneisremovedandrecycledtothereactionsection.Finally,intheblowdown
section,theacidisdegassedandthepHofthewastewaterisadjusted.
Hydrogenation
Butenescanbehydrogenatedton-butane,whichallowsthemtobereturnedtothesteam
crackerasafeed.Thisoptionistypicallylessdesirablethantheotherunitoperationsthatcan
beusedtoprocess2-butene.ThehydrogenationprocesslistedhereistheHülsSelective
HydrogenationProcess(SHP).14Theselectivehydrogenationprocesscanbeusedwithvarious
feedstreams,includingC3-C5streams.
UtilityandCapacityRequirements
Overallutilityinformationisincludedbelowforeachoftheunitprocesses.Pricinginformation
wasobtainedfromtheProductandProcessDesignPrinciplesTextbookforthecostof
electricity,water,gasandsteam.11Pricingforvariousacidsolutions,includingthesulfuricacid
andsodiumhydroxidefortheAlkylationprocess,wereobtainedfromAlibaba.Itshouldbe
33
notedthatthisprojectcreatesanoptimizationprogramforanalreadyexistingpetrochemicals
plant,thusitisnotnecessarytopurchaseadditionalequipmentfortheunitoperationsbecause
itisassumedthatthecompanyalreadypossessesallnecessaryequipment.
Metathesis(UOPOleflex)
Utility Requirement
ElectricPower 6500kW/hBoilerFeedWater 10metrictonsperhourCoolingwater 6000m3/hFuelGas 13.1millionkcal/hCapacity 350,000MTA
Alkylation(DupontSTRATCO)
Utility Requirement(unit/barrel)ElectricPower 15kWCoolingwater 1370galProcesswater 4galSteam 194lbFreshacid 13lbNaOH .05lbCapacity 240MTperstreamday
MTBEProduction(UOPEthermax)
Utility Requirement
ElectricPower 177kWh
Medium-PressureSteam 7.9mtperhour
CoolingWater 52cubicmetersperhour
Condensate 7.9metrictonsperhour
Capacity 50,000MTA
34
ButadieneExtraction(BASF)
Utility Requirement
ElectricPower 100-200kWh
Medium-pressure 1.5-2.5t
CoolingWater 100-200cubicmeters
Solvent(Cost) $0.60(permetrictonproduct)
OtherChemicals(Cost) $2.50(permetrictonproduct)
Capacity 29,000to430,000MTA
Hydrogenation(HülsSelectiveHydrogenationProcess)
Utility Requirement
Power 46kWh
Mediumpressuresteam 798kg/hr
Condensate 798kg/hr
Coolingwater 51m^3/hr
Capacity 6373BPD
SkeletalHydrogenation(SKIPProcess)
Utility Requirement
ElectricPower 234.16kWh
Medium-pressure 1.735mt
Low-Pressure 1.739mt
CoolingWater 6.576GJ
NaturalGas 1.679GJ
Capacity 2400BPD
35
1-ButeneDistillation
Utility Requirement(unitperton1-butene)
Steam 4t
Water,cooling 110m3
Power 43kWh
36
ConclusionandRecommendationsThisreportchroniclesaprojectentitledC4OperationsOptimization,whichinvolvedthe
creationofacomputermodelthatcanoptimizeoperationsandprocessesforanexisting
petrochemicalsplant.Otherfeaturesoftheprojectincludeasensitivityanalysisand
investmentanalysisthatprovidetheuserwithanideaofhowtheplantprofitabilitywill
respondtochangesintheeconomicclimateandplantcapacity.Itisrecommendedthatthe
plantinquestionbeginusingthismodelpromptly,asitcanincreaseprofitsbyaconsiderable
margin.Forfurtherdevelopmentsinthemodel,werecommendmodificationstothemethod
bywhichittakesutilitycostsintoaccount.Insteadofassumingproportionalutilities,functions
relatingutilityrequirementstothroughputcouldbeincorporatedintothemodel.These
functionscouldbederivedfromplantobservationorfromASPENsimulations.
Withthecurrentmodel,profitabilityislistedbyproduct,butsubsequentversionscouldspread
theutilitycostssothatoneproductisnotabsorbingalltheutilitycosts.Anotherfeaturethat
couldbeaddedisasetofpurityconstraintsforeachproductasspecifiedbythe
company.Thesewouldbemostapplicableinthe1-buteneandn-butaneproductstreams,as
traceamountsofisobutyleneandisobutane,respectively,canentertheseproductstreamsand
lowerpurity.
AcknowledgementsWehavebeenluckytohavehadtheguidanceandsupportofseveralfacultymembersatthe
UniversityofPennsylvaniaaswellasfromindustryconsultants.Withouttheseindividuals,our
projectwouldnothavebeenpossible.
WewouldliketofirstthankMr.GarySawyerforintroducingourprojectandforhisconstant
adviceandhelpthroughoutthesemester.Herespondedtoallemailsandquestionsinatimely
andhelpfulmanner,andhissuggestionsonhowtoformattheprogramwereespecially
valuable.
37
Wewouldalsoliketothankourfacultyadvisor,Dr.WenK.Shieh,forhisassistancethroughout
thesemester.Dr.Shiehattendedallofourweeklymeetingsandprovidedadviceandsupport
forourproject.
WewouldliketothankDr.WarrenSeiderandDr.SeanHolleranfortheirguidanceandadvice
duringtheCBE459and460designcourses.Withoutthisintroductiontotheseniordesign
process,wewouldnothavebeenabletosuccessfullycompleteourproject.
WewouldliketothankProfessorLeonardFabianoforhissupportandguidancethroughthe
seniordesignprocess.Weespeciallyappreciatehimtakingthetimetoreviewourprojectand
report.
Weoweadditionalthankstothemanyindustryconsultantswhometwithusonaweeklybasis.
OursincerethanksgoestoDr.IvanBaldychev,Mr.DavidKolesar,Mr.StevenTieri,andMr.
BruceVrana.
38
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