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Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperiencebroaden ourunderstanding,changesinresearchmethods,professionalpractices,ormedicaltreatmentmaybecome necessary.Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuchinformation ormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers,includingpartiesforwhomthey haveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeany liabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligenceor otherwise,orfromanyuseoroperationofanymethods,products,instructions,orideascontainedinthematerial herein. BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress ISBN978-0-444-62700-1 ISSN1570-7946 ForinformationonallElsevierpublications visitourwebsiteatstore.elsevier.com PrintedandboundinPoland Preface WelcometothesecondeditionofIntegratedDesignandSimulationofChemicalProcesses.Thebody of work has been greatly expanded, improved and updated. Five new chapters have been added on ProcessIntensification,BatchProcesses,ChemicalProductDesign,Health,SafetyandEnvironment and Sustainability Analysis. The chapters on Dynamic Simulation and Plantwide Control were fully rewritten.Thenewmaterialrepresents35%ofthebook,about50%ofthecontentissignificantlyim- provedversustheoriginalversionandtherestwasupdatedasdeemednecessary.Thetheoryisamply illustrated with 432 figures, 167 tables, 3 case studies and numerous examples spread across the chapters. The book is a comprehensive body of work that covers the fundamentals of modern Conceptual ProcessDesign.Theemphasisisondevelopingcreativitytodesigninnovativeandsustainablechem- icalprocessesbyusingthesystemsapproach,systematicmethods,advancedthermodynamictoolsand computer simulation. The book comprises five sections: Process Simulation, Thermodynamic Methods,ProcessSynthesis, ProcessIntegration andDesignProject. ThisneweditionissuitableasgeneralteachingmaterialforChemicalProcessandProductDesign courses for students aiming at an MSc degree in Chemical Engineering. The book is intended to respond to the European education needs using the ECTS system but is compatible with academic requirements worldwide. Advanced features such as process intensification and plantwide control aresuitableforpostgraduatestudieslikePhDorDrandPDEng(ProfessionalDoctorateinEngineer- ing). Professional engineers will find here an update on the latest developments in modern process designas well asthe efficient useof computersimulationtools. Whatsetsthisbookapartistheintensiveuseofprocesssimulationforanalysis,designandeval- uation.Threechaptersaredevotedtovariousgenericaspectsincludingdynamicsimulationwithpro- cess control implementation. Another unique characteristic is the emphasis on thermodynamic modelling and on the computation of physical properties, including those with an impact on health, safetyandtheenvironment.Moderntrendsinequipmentdesignareillustratedbyprocessintensifica- tion.Finally,thisbookdevelopsanoriginalapproachforintegratingprocessdesignandplantwidecon- trol that is particularly useful for complex plants with recycles. These features involved original research bythe authors, their teams and their collaborators. Despiteallofoureffortsintherevision,weareawarethatsomeerrorsmightstillbepresent.Weare open toany remarksand therefore grateful inadvancefor feedback from our readers. AlexandreC.Dimian Costin S. Bildea Anton A.Kiss xix Acknowledgements Completingthesecondeditionofthisbookhasbeenaconsiderablechallengefortheauthorsconsid- eringtheamountofnewmaterialandthevarietyoftopicsadded.Wehadthechancetoknoweachother forabout15yearsandtocooperatecloselyinbotheducationalandresearchactivities,whichmadethis ambitious endeavourpossible andenjoyable. Firstly,wewouldliketoexpressourcommitmenttotheEuropeanculturalvaluesthatshapedour educationandskills.WesharethesevalueswithcolleaguesfromdifferentEuropeancountries,namely by actively participating in different research and academic exchange programmes supported by the EuropeanUnion.TheannualmeetingsESCAPEorganisedbytheEuropeanComputer-AidedProcess Engineering (CAPE) community with worldwide participation play in particular a major role in disseminating the latest developments inour field. Thematerialofthisbookhasbeentaughtforabout20yearsatdifferentgraduateandpostgraduate courses in The Netherlands and Romania. We thank so many students and colleagues from TheNetherlandsandallovertheworld,whohelpedustodevelopandrefineoureducationalapproach. WearegratefulnamelytotheUniversityofAmsterdam,UniversityofTwente,TechnicalUniversityof Eindhoven,DelftUniversityofTechnologyandUniversity‘Politehnica’ofBucharestfortheirsupport. WearethankfultoElsevierfortheprofessionalsupportandkindlyassistance,andtoourcollab- orators inthe research programmesthat we are carrying out. Finally,weareindebtedtoourfamiliesfortheirlong-standingencouragementandunderstanding, namely for the late-evening call conferences andlong working weekends. AlexandreC.Dimian, Costin S. Bildea Anton A.Kiss xxi CHAPTER 1 INTEGRATED PROCESS AND PRODUCT DESIGN 1.1 INTRODUCTION 1.1.1 MOTIVATION TheproductsmanufacturedbytheChemicalProcessIndustries(CPIs)arevitalforfulfillingtheneeds ofthemodernsociety.Theprocessdesigneristhepersoninchargeoftransformingavaluableideaor experimentintoanindustrialprocess.Thecreativeeffortshouldberewardedbysubstantialtechnical and economic advantages. Thus, novelty and efficiency are key motivations for process designers. Today,sustainabledevelopmentsetsnewchallengesfordesigners,namelythetransitiontorenewable resources, aswell as the protection ofthe natural environment. Thejobofaprocessdesigneristofulfilnotonlyoriginality,efficiencyandsustainabilitycriteria,but toconsideralargenumberofconstraints,oftencontradictory.Forexample,usingbiomassasrenewable feedstockimpliestypicallyacomplexchemistry,withmanyby-productsandimpurities.Betterselec- tivitymaybeachievedworkingatlowerconversion,butwithsupplementarycostsinequipmentand energyforhandlingtherecycles.Theenvironmentalregulationssetseveretargetsforwasteandemis- sions,addingsupplementarycosts.Modernplantsshoulduselessland.Intheend,thedesignerhasto find an optimum ensuring high valorisation of materials, low energy requirements and no pollution, byemployingcompactandefficientequipment.Thecombinationofsomanyaspectsgiveshighlyin- tegrated processes. Their optimal design makes useof systematic conceptualmethods and powerful computersimulationtoolsformingthecoreoftheProcessSystemsEngineering(PSE)discipline. Etymologically,thewordengineercomesfromtheLatiningeniummeaningtheskillstounderstand, createandinvent.Today,theCPIsareconfrontedwithmultiplecrisesandchallenges,butinnovationis ultimatelythekeyissue.Inthiscontext,enhancingthecreativityofdesignersplaysacentralrole.We believe thatthecreativityshouldbeaccessibletoeveryone havingadequateprofessional knowledge andmotivationfordiscovery.Creativitycanbelearnedandteachingthecreativityofprocessdesigners isthe goal ofthis book. Theintellectualsupportforenhancingcreativityistheemploymentofasystemsapproachandsys- tematicmethods.Thishasatleasttwomerits:(1)Itprovidesguidanceinidentifyingthefeasibilityof theprojectbeforethedesignofunits.(2)Notjustasinglesolutionbutseveralalternativesaregenerated andevaluated,correspondingtodesigndecisionsandconstraints.Afterrankingbysomeperformance criteria,themostconvenientalternativesarerefinedandoptimised.Notethatbyapplyingsystematic methods, quasi-optimal targets for unitscan beset well ahead oftheir detailed sizing. Theassemblyofthesystematicmethodsemployedfordevelopingprocessflowsheetsandensuring the optimal use of materials andenergy forms the paradigm of Integrated ProcessDesign (IPD). Its application relies on the intensive use of Process Simulation. This approach allows the engineer to 1 ComputerAidedChemicalEngineering.Volume35.ISSN1570-7946.http://dx.doi.org/10.1016/B978-0-444-62700-1.00001-2 ©2014ElsevierB.V.Allrightsreserved. 2 CHAPTER 1 INTEGRATED PROCESS AND PRODUCT DESIGN understandthebehaviourofcomplexprocesssystems,explorealternativesandproposeeffective in- novative solutions. Traditionally, process design was oriented to commodity chemicals. Recent years have seen an increasinginterestinamoresystematicapproachtoProductDesign,whichdealswithmanufacturing ofhighervalue-addedchemicals.Thus,theintegratedparadigmconcernstodaybothprocessandprod- uct design. 1.1.2 THE ROAD MAP OF THE BOOK Thebookcontainsfivesections:ProcessSimulation,Thermodynamics,ProcessSynthesis,ProcessIn- tegrationandDesignProject.Eachsectionhasseveralchapters,21intotalplusappendices.Theroad map depicted inFigure 1.1 shows anoverview ofthe chapters. The main avenue links the introductory chapter on IPD with the section devoted to the Design Project, the final goal, and at the same time allows the circulation of information between different sectionsandchapters.Doublesenseroadsindicatethattheinformationgoesinandoutbetweensec- tions andsomechapters. Inthisbook,weadoptedthestrategyofteachingtheprinciplesbytheassignmentofadesignpro- ject.Forthisreason,therearenoproblemsattheendofchapters.Instead,studentswillbetrainedby applying the theoretical concepts totheir own project. Guiding examples can be found in the book published by Dimian and Bildea (2008) containing 11 detailed computer-aided case studies. Viewedfromthetop,therightsideoftheavenuedealswithissuesregardingthetools,andtheleft side handles the principles ofIPD.A rapidtour presents the key topics of each chapter. ThejourneybeginswithanintroductorychapteronIntegratedProcessandProductDesign.This canbedescribedasthemarriageoftwotypesofactivities:ProcessSynthesis,asarchitecturaldesign, andProcessIntegration,asdevelopmentandoptimisationofsub-systems.Keytopicsaresystemsap- proach, sustainable development andproduction-integrated environmentalprotection. ThefirstsectionteacheshowtouseefficientlythepowerfulcapabilitiesofProcessSimulation.The treatmentisgeneric, notdedicated to specific commercial software. Chapter2servesasanIntroductioninProcessSimulation.Particularattentionispaidtosystems analysisbysimulation,commonlycalledflowsheeting.Thischapterprovidesanoverviewofcomputer simulationinprocessengineering,includingthekeystepsinasimulationapproach,thearchitectureof flowsheeting software and the integration of simulation tools. Chapter3presentsthefundamentalsofSteady-StateFlowsheetingsuchasdegreesoffreedomanal- ysis, efficient use of sequential-modular approach, equation-solving approach, thermodynamic tools and the treatment of convergence and optimisation. Mastering the flowsheeting techniques allows the user to get valuableinsightsinto more subtle aspects, such asplantwide control. Chapter4isdevotedtoDynamicFlowsheeting,nowadaysamajorinvestigationtoolinprocessop- erationandcontrol.Keytopicsarehowsettingupadynamicsimulationmodel,dynamicsimulation tools, numerical problems, dynamic simulation ofkey unitsand process control tools. ThesecondsectiondealswithThermodynamicMethodsusedincomputer-aidedprocessdesign.It islargelyrecognisedthatinappropriatethermodynamicmodellingisthemostfrequentcauseoffailure whenusingcomputersimulationforpredictingthebehaviourofrealsystems.Therefore,thissectionis highly recommended asself-study for upgradingthe knowledgein thermodynamics. 1.1 INTRODUCTION 3 1-INTEGRATED PRODUCT & PROCESS DESIGN III – PROCESS SYNTHESIS I - PROCESS 8 – Reaction 9 – Separation SIMULATION System System 2 - Introduction 7 - Process 10 - Process Synthesis Intensification 3 - Flowsheeting 11 - Batch 12 - Product 4 – Dynamic Processes Design Simulation IV-PROCESS INTEGRATION 13 - Pinch Point 14 – Applied II-THERMODYNAMICS Analysis Energy Integration 5 - Computational 15 - Plantwide Methods Control 16 – Health, Safety, 6 - Phase Environment Equilibria 17 - Sustainability Analysis 19 – Economic 18 - Design Project Analysis 20 - Equipment 21 - Case Studies sizing V- DESIGN PROJECT FIGURE1.1 Theroadmapofthebook. Chapter5describestheGeneralisedComputationalMethods,namelythePVT(pressure/volume/ temperature)behaviouroffluids,thermodynamicproperties,generalisedcomputationalmethodsusing PVT relationshipand the estimationofphysical properties. Chapter6developsthecomputationofPhaseEquilibriabyvariousthermodynamicmodels,suchas equationsofstateandliquidactivity.Particularattentionispaidtotheregressionofparametersfrom experimental data. Thethirdpart,ProcessSynthesis,entersthecoreoftheconceptualdesignandteacheshowtoinvent processflowsheets bya generic approach based on systemsanalysisand systematic methods. 4 CHAPTER 1 INTEGRATED PROCESS AND PRODUCT DESIGN Chapter7presentsthedevelopmentofflowsheetsbyapplyingtheHierarchicalApproach.Thein- put/outputanalysisisextendedtocapturetheessentialofecologicalanalysis.Emphasisisonthema- terialbalanceenvelopeformedbythesub-systemsofreactionsandseparationsconnectedbyrecycles. Here, the structure called Reactor-Separation-Recycle dominates the conceptual frame of the whole flowsheet.Thisisthebasisforsettinguptheplantwidecontrolofthematerialbalance,whichinturn dominates the operation costs. Separate chapters present a deeper analysis of the synthesis of sub- systems. Sinceflowsheetsynthesisstartsfromthereactor,Chapter8dealingwiththeSynthesisofReaction Systemsisparticularlyimportant.Akeyissueisthechemistry,includingtheformationofby-products andimpurities.Anothercentralsubjectisreactorselectionanditsintegrationwiththeutilitysystem. Chapter9presentstheSynthesisofSeparationSystems.Thischapterdevelopsagenericknowledge- basedframework.Theapproachreliesongeneratingalternativetaskstakingintoaccounttherelation betweencharacteristicpropertiesofthecomponentsandthetargetassignedforseparation,aswellas the evaluationof the appropriate separation methods. Chapter10,ProcessIntensification,presentsmoderntechniquesforincreasingtheeco-efficiency ofthechemicalequipmentwiththebenefitoflowercapitalcosts,substantialenergysaving,reduced footprintandsafetybydesign.Centraltopicsarereactiveseparationdevices(e.g.reactivedistillation, reactive absorption), and more advanced distillation technologies such as the dividing-wall column (Kiss, 2013). Chapter 11, Chemical Product Design, presents an approach that integrates both product and processdesign.Wesharetheviewthatallprocessdesignsaredevotedtoproducts.Inthecaseofcom- modities,focusissetonflowsheetdesignthatensuresthelowestcapitalandoperationcosts,whilefor industrial and consumer-configured goods the emphasis is on specifications satisfying the customer needsforwhichaprocessdesignshouldbefound,inmanycasesemployingmultipurposeequipment. Chapter12,BatchProcesses,coversthedesignofprocessestypicallyemployedformanufacturing specialitychemicals.Keytopicsarebatchdistillationandbatchreactors.Here,processoperationissues rather than flowsheet synthesis are important, such as productivity improvement, energy saving and safety preservation. Thefourthsectionofthebook,devotedtoProcessIntegration(PI),addressesthecombinationof individualunitsinanoptimalsystemfromtheperspectiveoflowenergyconsumption,goodcontrol- labilityproperties and superior environmental performance. Chapter13,devotedtoPinchAnalysis,addressestheprinciplesofachievingoptimalenergyutili- sation.Theprincipleisthattheanalysisoftheprocessasasystemleadstomuchmoreefficientsolu- tions for saving energy than by just optimising the stand-alone units. Namely, this method can set optimumenergytargetswellaheadthedetaileddesignofheatexchangers.Theappropriateplacement ofunitoperationswithrespecttoPinchgivesvaluableinsightsforimprovingtheenergeticandenvi- ronmental efficiency ofthe whole process. Chapter 14 deals with Applied Energy Integration in process industries, more specifically with combinedheatandpowerproduction,newrefrigerants,wasteheatrecovery,energysavingindistil- lation, integration ofchemical reactors and site utilitysystem. Chapter15isdevotedtoPlantwideControlasaholisticapproachtointegratingprocessdesignwith processcontrolatthelevelofthewholeplant.Morespecifically,thechapterdealswiththestabilityand flexibilityinoperationrelatedtothedesignofreactorsandseparators.Akeytopicisthebifurcation analysisof the Reactor/Separator/Recycle system characterisingthe process. 1.2 INTEGRATED PROCESS AND PRODUCT DESIGN 5 Chapter 16 handles the basics of Health, Safety and Environment (HSE) activities in conceptual process design. The first section describes impact factors on health, as well as estimation methods assistedbycomputersimulation.SafetyisatbestachievedbyInherentlySaferDesign.Theprotection oftheequipmentbysafetyvalvesisbrieflycovered.Thechapterendswithmethodsfortheassessment and preventionof technological risks. Chapter17dealswithSustainabilityAnalysis,animportantsubjecttodayforbothsocietyandin- dustry. Central issues are the concept of life cycle assessment (LCA), eco-cost value ratio, eco- efficiency analysisand sustainability metrics. Thelastpartofthebookisdevotedtotopicshelpingtheplanningandtheexecutionofaconceptual designproject. Chapter18onProcessDesignProjectdiscusseseducationalaspects.Guidelinesareprovidedfor developingcoursesandprojectsatMScleveladaptedtotheEuropeanCreditTransferSystem,aswell as topostgraduate and continuouseducation activities. Chapter 19 handles the Economic Evaluation of a conceptual design project. Central topics are time-value of money, estimationof capital and operationcostsand profitability analysis. Chapter20 presents guidelines for EquipmentSelectionand Sizing, namely shortcut methods for quickassessmentofreactionvessels,separationcolumns,heatexchangersanddevicesforthetransport of fluids, which associated with the sizing capabilities of a simulation package can be used for esti- mating the total investmentcost. Chapter21presentsCaseStudiesillustratinginmoredetailsomeexamples,includingfulldynamic simulationwithcontrol implementation. HelpfulengineeringdatafordesignprojectsaregiveninAppendices,suchasestimationofcostsfor equipmentandutilities,materialsofconstruction,steamtables,vapourpressureofsomekeyfluidsand conversion factors. ThematerialofthisbookissuitableforsettingupcoursesinChemicalProcessandProductDesignfora MScdegreeinchemicalengineering.Thematerialshouldbeadaptedtospecificteachingenvironments, namelythebackgroundknowledgeinchemicalengineering,aswellthetimeallocationinthecurriculum. AdvancedfeaturesareofinterestforPhDandpostgraduatestudentsinvolvedindesignorresearchprojects. Finally,thebookwillbehelpfultoprofessionalengineersasanupdateonthelatestconceptualdevelop- mentsindesigningsustainableprocesses,aswellasontheefficientuseofcomputersimulationtools. Thebestmannertoconsolidatethecreativeskillsacquiredduringaconceptualdesignprojectisby workingoutacomprehensiveplantdesignproject,whichissuitedfordevelopingprofessionaldesigner expertiseasrequiredinengineeringcompanies.Ascomplementarymaterial,werecommendtherecent book of Towler and Sinnott (2013). 1.2 INTEGRATED PROCESS AND PRODUCT DESIGN 1.2.1 CREATIVE ASPECTS IN PROCESS DESIGN Thefollowing definition of Douglas (1988) highlights the roleof creativity: ProcessDesignisthecreativeactivitywherebywegenerateideasandthentranslatethemintoequip- ment and process for producing new materials or for significantly upgrading the value of existing materials. 6 CHAPTER 1 INTEGRATED PROCESS AND PRODUCT DESIGN ConceptualDesignreferstothatpartofadesignprojectthatdealswiththefundamentalelementsofa process:layoutoftheunitsorflowsheet,materialandenergybalances,specifications,performanceand sizingoftheequipment,energyrequirements,safety,hazardandenvironmentalissuesandeconomic efficiency.Attheconceptualdesignphase,theemphasisisonthebehaviouroftheprocessasasystem of connections of functional units rather than on the detailed sizing of the equipment and the plant design. It is important to note that conceptual design isresponsible for the largest part ofthe investment costs in a process plant, even if its fraction of the total project’s fees is very limited. An erroneous decisionattheconceptuallevelwillpropagatethroughoutthewholechainoftheequipmentprocure- mentandplantdesign.Eventuallymuchhighercostswillariselaterinoperationwhencorrectingde- sign misconceptions. Figure1.2illustratestheeconomicincentivesofaplantproject,fromtheconceptualphasedownto constructionandcommissioning(Pingen,2001).Theconceptualphasetakesonly2%ofthetotalpro- jectcost,althoughitcouldcontributemorethan30%incost-reductionopportunities.Atthedetailed designphase,thecostofengineeringrisessharplyto12%,whilesavingopportunitiesfalltoonly15%. In contrast, the cost of procurement and construction increases to more than 80%, while the saving opportunities drop to10%. At the commissioning stage, the total cost isfrozen. Thelongroutefromanideatoarealprocesscanbebestmanagedbymeansofasystemsapproach forevaluatingtheprocessasawholeandbysystematicmethodsfordesigningthesub-systems,suchas reaction, separations and utilities. Asystematicmethodconsistsinacombinationoftwosteps,analysisandsynthesis.Inthiscontext, theAnalysisstepdealswiththeknowledgeoftheelementsdefiningthesystem,suchasthephysical propertiesofthechemicalcomponentsandmixtures,theperformancecharacteristicsofreactorsand unitoperations,theecologicalaspectsandtheprofitabilityissues.Ontheotherhand,theSynthesisstep 30% 2% 25% 40% 20% Cost Total reduction project opportunity cost 15% 44% 10% 12% 5% 2% Concept Design Procure Construct Commission FIGURE1.2 Economicincentivesinaproject. 1.2 INTEGRATED PROCESS AND PRODUCT DESIGN 7 handlesthearchitectureofthesystem,theselectionandthepre-designofthesuitablefunctionalunits, as well asthe effect ofinteractions of materials, energy andinformation. Inthepast,thedevelopmentofanewprocesshasbeendescribedoftenasakindof‘art’.Thestrat- egy,calledsometimestheengineeringmethod,consistedofdrawinganinspiredsketchandthenim- provingitbysuccessivelayersofrefinementandevaluation,uptothefinaloptimisation.Theskillsof the designer, the expertise of the company and the availability of plant operation knowledge were crucial. Nowadays,theconceptualprocessdesignisbecomingincreasinglyanappliedchemicalengineer- ingscience.Engineerswithasolidscientificbackgroundandmasteringcomputerdesigntoolsareca- pable of finding valuable innovative ideas. Inspiration and expertise, as well as the availability of corporate knowledge, still play an important role, but these can be greatly enhanced by employing a systematic approach. Actually, it is the combination of science and engineering art that makes the conceptual process design such a fascinating challenge! A design problem is always under-defined, either by the lack of data or by insufficient time and resources.Moreover,adesignproblemisalwaysopen-ended.Thereisneverasinglesolution,butal- ternativesdependingonthedesigndecisionsthattheengineerhastotakeatdifferentstagesofthepro- jectinorder tofulfilthe constraints oftechnical, economical and environmental nature. Thesystematicgenerationofalternativesisthemostimportantfeatureofthemodernconceptual design.Then,thebestdesignisidentifiedastheoptimalsolutioninthecontextofconstraintsbyusing consistent evaluationand ranking ofalternatives. 1.2.2 PROCESS SYNTHESIS AND PROCESS INTEGRATION ProcessIntegrationemergedinthe1980sasanewdisciplineinchemicalengineeringwithemphasison theefficientuseofenergy.PIrevealedthatsignificantenergysavingcanbeachievedbyanalysingthe probleminthecontextofthewholeprocess(system),contrarytotheviewpointofthestand-aloneunits. The traditional process design comprises a hierarchy of activities, which can be depicted by the successivelayersofanOnionDiagram,asillustratedinFigure1.3(Linnhoffetal.,1994).Thedevel- opmentbeginswiththechemicalReactor(R),afterwhichitcontinueswiththesystemofSeparations (S).Then,thedesignaddressestheHeatExchange(H)andUtility(U)layers.Ideally,thesolutionofthe designproblemshouldbeglobal,sinceacompleteseparationoftheaboveactivitiesisnotpossible.For example, the separation system is intimately linked with the reactor design. Similarly, the heat R R – Reactor system S S – Separation system H – Heat Recovery system H U – Utility system U FIGURE1.3 HierarchicaldescriptionofprocessdesignbytheOnionDiagram.