959D65539D8C7AAAF46C8643A4D185A

Process Safety in BatchReaction Systems

1.1.Scope

TheCenterforChemicalProcessSafety(CCPS)hasidentifiedtheneedforapublicationdealingwithprocesssafetyissuesuniquetobatchreactionsystems.Thisbook,GuidelinesforProcessSafetyinBatchReactionSystems,attemptstoaidinthesafedesign,operationandmaintenanceofbatchandsemi-batchreac-tionsystems.Inthisbooktheterms“batch”and“semi-batch”areusedinter-changeably for simplicity. The objectives of the book are to:

•Provideahow-toguideforthepracticingengineertoidentify,define,andaddressuniquesafetyissuestypicallyencounteredinbatchreactionsystems.

•Providearangeofcriteriaandtechniquestobeconsideredinthedevel-opment,design,operation,andmaintenanceofbatchreactionsystemstoreduce risk and ensure safety of people, environment, and property.•Provideanaidtoidentifypotentialsourcesofunsafeconditionsencoun-tered in batch reaction systems.

•Provideguidanceinapplyingappropriateprocesssafetypracticestopre-vent accidents.

•Identify sources for specific expertise and reference them accordingly.Thebookdoesnotfocusonoccupationalsafetyandhealthissues,althoughimprovedprocesssafetycanbenefittheseareas.Detailedengineeringdesignsareoutsidethescopeofthiswork.Thisbookintendstoidentifyissuesandcon-cernsinbatchreactionsystemsandprovidepotentialsolutionstoaddresstheseconcerns.Thisshouldbeofvaluetoprocessdesignengineers,operators,main-tenancepersonnel,aswellasmembersofprocesshazardsanalysisteams.Whilethisbookofferspotentialsolutionstospecificissues/concerns,ultimatelytheuserneedstomakethecaseforthesolutionsthatprovideabalancebetweenrisk

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reductionandcost.Thesolutionspresentedinthebook,arepossibleapproachesfordealingwithaparticularissue.Theauthorsofthisbookcouldnotanticipateallthepossibleissues,orallapplicablesolutionsforaspecificissue.Therefore,itisintendedthattheuseofthesuggestedsolutionsbecom-binedwithsoundengineeringjudgmentandconsiderationofallrelevantfac-tors.Furthermore,allthesolutionspresentedmaynotbeapplicabletoagivensituation.Itshouldalsoberecognizedthatthesolutionspresentedmightthem-selvesintroducepotentialhazardsthatwerenotoriginallypresent.Therefore,itisnecessarytousetheinformationinthecontextofthetotaldesignconcepttoensurethatallhazardshavebeenconsidered,andthatallapplicablelawsandregulations have been complied with.

1.2.Special Concerns of Batch Reaction Systems

Batchreactionsystemspresentuniquechallengesforprocesssafety(Hendershot1987).Batchoperationsconsistofaseriesofprocessingsteps,whichmustbecarriedoutintheproperorder,andatthepropertime.Bytheirverynature,batch-typeprocessesdonotoperateinasteadystate.Astheprocessisbeingcar-riedout,theholdupofmaterialsinthevesselvarieswithtimeasmaterialsarecharged,reactedandperhapswithdrawn,thuschangingmixingcharacteristicsandeffectiveheattransferarea.Thereisacontinuousvariationinthephysicalproperties,chemicalcompositions,andphysicalstateofthereactionmixturewithtime.Thismakesitmoredifficult,bothfortheoperatorsandcontrolsys-tems,tomonitoranddiagnosetheprocess.Thesequenceofprocessingsteps,andfrequentstart-upsandshutdownsincreasetheprobabilityofhumanerrorsandequipmentfailures.Moreover,batchreactionsystemsoftenhandlemultipleprocessesandproductsinthesameequipment.Thiscanalsoleadtoincreasedprobability of human error.

Batchplantsareoftendesignedforgeneraluse,ratherthandedicatedtoaspecificprocess.Thepipingandlayoutoftheequipmentisoftenmodifiedtomeettheneedsofthecurrentprocess,ortheprocessismodifiedtousetheexist-ingequipment.Useofthesameequipmentindifferentcampaigns,complexpro-cesspiping,andtheuseofsharedauxiliaryequipment,suchascolumnsandcondensers,presentsgreaterchallengesinpreventingcrosscontamination;inselectingmaterialsofconstruction;andinselectinginstrumentationandcontrolsystems.Additionally,thecomplexityofequipmentandthefrequencyofchangescomplicatetheprocessdocumentationtask.Thesefrequentchangesoften result in complex management of change (MOC) issues.

Thenatureofbatchoperations(unsteady-state),frequentlyinvolvingmanualintervention,createssignificantissuespertainingtothedesignofcon-trolsystems,designofoperatingprocedures,andtheinteractionbetweenthe

1.3.Approach Used in Guidelines

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controlsystemandtheoperators.Theoperatorisamoreintegralpartoftheprocesscontrol,supervisionloop,andthesafeoperationoftheprocess.Theoperatormanagingabatchprocesshasagreaternumberofdutiesandresponsi-bilitiesthanhiscounterpartinacontinuoussystem.Severalofthesedutiesareeitherspecifictobatchoperationsoraredonemoreofteninbatchoperationsthanincontinuousprocesses.Thenumberandvarietyoffunctionsthattheoperatorhastoperformduringabatchprocessrequireseffectivemanagementsystems,includingmorerigoroustraining,tominimizehumanerror.Further-more,thebatchoperatorismoreinvolvedandisoftenincloserproximitytotheprocess.Thiscloseproximityputstheoperatoratincreasedrisktodirectexpo-suretothehazardsassociatedwithlargerinventoryofrawmaterialsandsemifinished products than continuous systems with comparable throughput.

Alloftheseissuesmakebatchreactionsystemsunique,intermsofthechal-lenges they pose for managing process safety.

Figure 1 shows a typical batch reaction system.

1.3.Approach Used in Guidelines

Thebookpresentsinformationpertainingtothesafetyissuesinbatchreactionsystems in five chapters.

Eachchapterstartswithadescriptionofthetopiccoveredinthechapter.Thisisfollowedbyashortexamplehighlightingareportedincidentinvolvingabatchreactionsystem.Thecasestudyisfollowedbyalistingofkeyissuesandprocesssafetypracticesuniquetothetopic.Theissuesandconcernspresentedinthisbook,aswellaspotentialdesignsolutionsandsourcesofadditionalinfor-mationarepresentedinthetables.Thisformatconciselyconveysthenecessaryandrelevantinformationinafamiliarandconvenientformat.Theorganizationof the tables is described below.

•Concern/Issue:Identifiesaspecificsafetyissueorconcernanditssafetyimplications.

•PotentialSolutionsandControlMechanisms:Liststhepotentialsolu-tionsandcontrolmechanismsthatmaybeemployedtoreducetheriskofa specific issue or concern.

•AdditionalResources:Providesadditionalsourcesofinformationontheconcerns/issuesidentifiedinthetables.Pleasenotethatthe“AdditionalResources”columndoesnotattempttoincludeallsourcesofadditionalinformation.

Itshouldberecognizedthatthesolutionsandcontrolmechanismspre-sentedinthetablearepossibleapproachesfordealingwithaparticularissue.

4Figure1.Typicalbatchreactionsystem.

1.3.Approach Used in Guidelines

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Theyaresolelymeanttocreateawarenessandassistdesignersandoperators,andarenotmeanttoimplythatthesesolutionsandcontrolmechanismsareRecog-nizedandGenerallyAcceptableGoodEngineeringPractices(RAGAGEP).Theauthorsofthisbookcouldnotanticipateallthepossibleissues,orallapplicablesolutionsforaspecificissue.Thepotentialsolutionandcontrolsareintendedtostimulatethoughtandinitiatediscussionsabouttheappropriatenessofthepotentialsolutionspresented,andpotentiallystimulatethegenerationofothersolutions not included in the table.

Itisintendedthattheuseofthetablesshouldbecombinedwithsoundengi-neeringjudgmentandconsiderationofallrelevantfactors.Furthermore,allthesolutionspresentedmaynotbeapplicabletoagivensituation.Itshouldalsoberecognizedthatthesolutionspresentedcouldintroducepotentialhazardsthatwerenotoriginallypresent.Therefore,itisnecessarytousethetableinthecon-textofthetotaldesignconcepttoinsurethatallhazardshavebeenconsidered.

Theinformationpertainingtothesafetyissuesinbatchreactionsystemsispresented in the following chapters:

Chapter 2.Chemistry

Understandingthebehaviorofallthechemicalsinvolvedintheprocess—rawmaterials,intermediates,productsandby-products,isakeyaspecttoidentifyingandunderstandingtheprocesssafetyissuesrelevanttoagivenprocess.Thenatureofthebatchprocessesmakesitmorelikelyforthesystemtoenterastate(pressure,temperature,andcomposition)whereundesiredreactionscantakeplace.Theopportunitiesforundesiredchemicalreactionsalsoarefargreaterinbatchreactionsystemsduetogreaterpotentialforcontaminationorerrorsinsequenceofaddition.Thischapterpresentsissues,concerns,andprovidespotential solutions related to chemistry in batch reaction systems.

Chapter 3.Equipment Configuration and Layout

Properequipmentconfigurationandlayoutcanmakeasignificantcontributiontothesafetyofaprocessingfacility.Inbatchprocesses,wherethematerialhan-dledbytheprocesscanchangefrequently,providingsafeseparationdistancespresentsanevengreaterchallengethancontinuousprocesses.Otherimportantconsiderationsforfacilitylayoutaretheelectricalclassificationandfireprotec-tionrequirements.Italsoisquitecommonforbatchprocessestobelocatedinsidebuildings.Thisleadstotheneedtoprovideadequatebuildingventilationtoavoidbuildupofhazardousvapors/gasesduetoleaks.Thischapterpresentsissues/concerns,andprovidespotentialsolutionsrelatedtoequipmentconfigu-ration and layout in batch reaction systems.

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1.PROCESS SAFETY IN BATCH REACTION SYSTEMS

Chapter 4.Equipment

Frequentlyapieceofequipmentisusedindifferentprocessesduringitslifecycle.Thiscouldresultinprocessconditionsthatexceedthesafeoperatinglimitsoftheequipment.Equipmentinspectionmayprovideapoorpredictionoftheequipment’susefullifeandreliability,duetothechangeofmaterialhandledorchangeinprocesschemistryoverthelifeofequipment.Batchoperationsarealsocharacterizedbyfrequentstart-upandshut-downofequipment.Thiscanleadtoacceleratedequipmentagingandmayleadtoequipmentfailure.Thischapterpresentsissuesandconcernsrelatedtothesafedesign,operation,andmaintenanceofvariouspiecesofequipmentinbatchreactionsystems,andpro-vides potential solutions.

Chapter 5.Instrumentation/Control Systems

Thefactthatbatchprocessesarenotcarriedoutatsteadystateconditionsimposesbroaddemandsonthecontrolsystem.Theinstrumentationandcontrolsystemhavetobeselectedtoprovideadequatecontrolforawidevarietyofoperatingconditionsandawidevarietyofprocesses.Inaddition,basicprocesscontrolandshutdownsystemshavetodealwithsequencingissues.Thischapterpresentsissuesandconcernsrelatedtosafetyofinstrumentationandcontrolinbatch reaction systems, and provides potential solutions.

Chapter 6.Operations and Procedures

Theoperatorisanintegralpartoftheprocessinabatchreactionprocess.Someofthefunctionsatypicaloperatorworkinginabatchprocessingfacilitymayhavetoperformarescheduling,equipmentsetup,cleaning,charging,executingandcontrollingprocedure,monitoring,faultdiagnosisandcorrectiveaction,sampling,handlingoffinishedandoff-spec/partiallyfinishedproducts,mainte-nance,emergencyresponse,processloggingandcommunication.Severaloftheseareeitherspecifictobatchoperations,oraredonemoreofteninbatchoperationsthanincontinuousprocesses.Thegreaternumberandvarietyoffunctionsthattheoperatorhastoperformduringabatchprocesspresentsmoreopportunitiesforerrorsthanforcontinuousoperations.Thischapterpresentsissuesrelatedtooperationsandproceduresinbatchreactionsystems,andpro-vides potential solutions.