types of exchangers

7/31/2019 Types of Exchangers

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TYPESOFAIRFINEXCHANGERS1. UseofExchangers2. TypesofExchangers3. TypesofShellandTubeExchangers4. LayoutofShellandTubeExchangersinBanks5. AlterationsThatCanBeMadetoShellandTubeExchangers6. EstablishingElevationsofExchangers7. Piping8. LayoutofExchangersOtherThaninBanks9. TypesofAirFins10. LayoutofAirFins11. Piping12. FinTubeExchangers13. Chillers1.UseofExchangersHeatexchangerstransferheatfromonemediatoanother.Inthepetrochemicalindustry,theycanbegenerallyclassifiedunderthefollowingheadings:Exchanger:Heatsonestreamandcoolstheother.Thereisnoheatlossandphysicalchangeineitherflowingmedia.Cooler:Coolsliquidorgaseswithoutcondensation;appliesalsotointercooler

andaftercooler.Condenser:Condensesvapourorvapourmixture.Canbewater-cooledorbysufficientlycoldprocessstreamwhichrequiresheating.Chiller:Usesrefrigerantforcoolingprocessstreambelowfreezingpointorbellowprevailingcoolingwatertemperature.Heater(nonfired)Heatsprocessstreamgenerallyuptoitsboilingpointwithoutappreciablevaporization.Heatingmediumisusuallysteam;appliesalsotopreheaters.Reboiler:Reboilsthebottomstreamoftowerforthefractionationprocess.Heatingmediumcanbesteamorhotprocessstream.Whenlargequantitiesofvaporhavetobeproducedthekettletypereboilerisused.Wasteheatboiler:Useswasteheat,suchasinternalcombustionexhaustfromgasturbinesorsimilardriversforsteamgeneration.

Steamgenerator:Usesheatofprocessliquidorgasforproducingsteam.Vapourizer:Vapourizespartofaprocessliquidstreamasdoesanevaporator.2.TypesofExchangersBriefly,exchangers,etc.,canbedividedintothefollowingthreegroups:Shellandtube:Whichcanbeverticalorhorizontalwiththehorizontalonessingleorstackedinmulti-units.Asthenamesuggests,theyconsistofacylindricalshellwithanestoftubesinside.Fintube:Thisconsistofafinnedtubethroughwhichpassesonemediajacketedbyanothertubethroughwhichpassestheothermedia.Theycanbeusedassingleormulti-units.Airfins:Comeintwoshapes;flatboxunitsandaframeunits.Bothconsistofboffinnedtubesthroughwhichpassesthemediatobecooled.Largefansblowair

fromatmospherethroughthebanks,thuscoolingtheflowingmedia.Thereareothertypes,suchasplateexchangers,carbonblockexchanger,etc.,buttheseareusedinfrequently.3.TypesofShellandTubeExchangersFloatingheadexchangersareusedwhenthemediabeinghandledcausesfairlyrapidfouling,andthetemperaturecreatesexpansionproblems.Tubescanexpandfreely;channelheadandshellcoverarrangementisconvenientforinspection,andthetubebundlecaneasilyberemovedforcleaning.U-tubeexchangersareusedwhenfoulingofthetubesontheinsideisunlikely.


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Thetubesarefreetoexpandandthebundlecanberemovedfromtheshellforcleaningontheshellsideoftubes.Fixedheadexchangershavenoprovisionforthetubeexpansionandunlessashellexpansionjointisprovidedcanonlybeusedforrelativelylowtemperatureservice.Theendcoversareremovablesothattheinsideofthetubescanbecleanedbyroddingorothersimilartools.Thistypeofcleaningisusuallycarriedoutinsitusosomespaceshouldbeallowedinthepipinglayouttoallowforthis.4.LayoutofShellandTubeExchangersinBanksForgoodmaintenanceandsafeworkingconditions,itisnecessarytospaceexchangerssuchthatsurroundingareaisadequateandclear.Theymaybespacedapartandgroupedinpairs.Whenapart,aclearaccesswayof750mmisconsideredadequate,thisbeingtheclearspacebetweentheshellsand/ortheassociatedpipeworkandinsulation.Forpairedexchangersasimilarconditionisrequiredbetweenpairsandadjacentsingles,butbetweeneachshellofthepairthismaybereducedto450mmbetweenheadflanges.Exchangersshouldalwaysbearrangedsuchthattheideallythereisaminimumof150mmclearattherearforremovalofthebonnetandspaceprovidedfordroppingitclearoftheworkingarea.Atthefrontorchannelend,aminimumdistanceofthetubelengthplus2500mmisconsideredgood.Thislatterdoesnotofcourseapplytoexchangerslocatedinstructureswereatotalof1500mmwouldbesufficient.Pipingconnectedtoheatexchangersisgenerallysimple.Pipingeconomyandgoodengineeringdesigndependlargelyonknowingwhatalterationscanbemadetoex

changers.Inotherwords,thepipingdesignercaninfluencetheexchangerdesign.Forexample,thedirectionofflow,nozzlelocations,etc.Alterationstoexchangersofcourse,shouldnotaffecttheirdutyandcost.Moneysavedonsimplerpipingshouldnotbespentoncostlyalterationstoexchangers.Theaccompanyingchartshowsthepossiblealterationsthatmaybeinstigatedbythepipingdesignerstotypicalshellandtubeexchangerswithoutaffectingthethermaldesign.Whencontemplatingsuchachangeitshouldberememberedthatgenerallytheheatedmediashouldflowupward,andthecooledmediaflowdownward.Thisisparticularlyimportantifthereisaphysicalchangetakingplacewithintheexchanger,suchasvaporizationorcondensation.Typicalexampleofthisare:Reboilerswheretheprocessstreamenterstheshellatthebottomsasaliquidandleavesatthetopasavapourafterflowingthroughthetubes,andstreament

erstheshellnearthetopofthetubesandleavesatthebottomontheshellascondensate.Condenserswheretheprocessstreamenterstheshellatthetopasavapourandleavesthebottomasaliquid,whilstcoolingwaterentersthetubessideatthebottomandleavesatthetop.5.AlterationsThatCanBeMadetoShellandTubeExchangersInterchange,flowingmediabetweenthetubeandshellside.Thischangeisoftenpossible,moresowhentheflowingmediaaresimilar,forexample,liquidhydrocarbons.Preferablythehottermediashouldflowinthetubesidetoavoidheatlossesthroughtheshell,orthenecessityforthickerinsulation.Changedirectiononflowoneithertubeorshellside.Onmostexchangersinpetrochemicalplants,thesechangesarefrequentlypossiblewithoutaffectingther

equireddutyoftheexchangerifthetubesareindoubleormulti-passarrangementandtheshellhascrossflowarrangement.Inexchangerswherecounterflowconditionscanbearranged,changingofflowdirectionshouldbemadesimultaneouslyintubeandshell.Somepointstoconsiderwhencontemplatingaflowchangeare:Shellleakage:Whenwatercoolinggases,liquidhydrocarbonsorotherstreamsofdangerousnatureitisbettertohavethewaterintheshellandtheprocessinthetubes,sinceanyleakageofgas,etc.,willcontaminatethewaterratherthanleakingtoatmosphere.Highpressureconditions:Itisusuallymoreeconomicaltohavehighpressurein


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thetubesthanintheshellasthisallowsforminimumwallthicknessshell.Corrosion:Corrosivefluidsshouldpassthroughthetubes,thusallowingtheuseofcarbonsteelfortheshell.Fouling:Itispreferabletopassthecleanstreamthroughtheshellandthedirtythroughthetubes.Thisallowsforeasiercleaning.Mechanicalchanges,suchastangentialorelbowednozzlescansometimesassistsinsimplifyingthepipingorloweringstackedexchangers.6.EstablishingElevationsofExchangersWhereprocessrequirementsdictatetheelevation,itwillusuallybenotedonthePandIdiagram.Fromtheeconomicpointofview,gradeisthebestlocation,whereitisalsomoreconvenientforthetubebundlehandlingandgeneralmaintenance.Exchangersarelocatedinstructureswhengravityflowisrequiredtothecollectingdrum,orwheretheoutletisconnectedtoapumpsuctionwhichhasspecificNPSHrequirements.Toelevateexchangerswithoutspecificrequirements,thefollowingprocedureisrecommended:Selecttheexchangerwiththelargestbottomconnection;addtothenozzlestandoutdimension(centerlineofexchangertofaceofflange)thedimensionthruhubofflange,elbow(11/2dia),one-halftheO/Spipediameterand300mmforclearanceabovegrade.Nowsubtractthecenterlinetounder-sideofsupportdimensionfromabove,andthedimensionremainingisthefinishedheightofthefoundationincludinggrout.

Itispreferableifthisfoundationheightcanbemadecommonforalltheexchangersinthebank.Ifthisisimpracticableduetoextremesofshelland/orconnectionpipesizes,thenperhapstwoheightscanbedecidedupon.Whenstackingexchangers,twoorthreehigh,itisdesirablethatoverallheightdoesnotexceed120(3650mm)duetotheproblemofmaintenance,bundlepullinc.7.PipingPlan-wisetheexchangerbankshouldbelaidoutspacedasnotedpreviously,andallthechannelnozzlesonacommoncenterline.Thisisparticularlyimportantifthecoolingwaterheadersareunderground,astheCWinletscanriseintothelowerchannelnozzles.Theendoftheexchangeradjacenttotherackwillnormallybethefixedend,if

theCWheadersareundergroundthefixedendwillbecomethechannelend.AllchangesproposedmustbediscussedfullywithProcessEngineerandClientEngineerorVesselDepartment.Linesturningrightintheyardshouldberightfromtheexchangercenterlineandthoseturningleftshouldapproachtheyardontheleft-handsideofexchangercenterline.Linesfrombottomconnectionsshouldalsoturnupontherightortheleftsideofexchangersdependinguponwhichwaythelineturnsintheyard.Lineswithvalvesshouldturntowardstheaccessaislewithvalvesandcontrolvalvesarrangedclosetoexchanger.Utilitylinesconnectingtoaheaderintheyardcanbearrangedonanysideofexchangercenterlinewithoutincreasingpipelength.Accesstovalvehandwheelsandinstrumentswillinfluencepipingarrangementaroundheatexchangers.Valvehandwheelsshouldbeaccessiblefromgradeandfroma

convenientaccessway.Theseaccesswaysshouldbeutilizedforarrangingmanifolds,controlvalvesandinstruments.Inthepipingarrangement,provisionfortuberemovalaccessshouldbeprovided.Thismeansaspoolpieceofflangedelbowinthepipelineconnectingtothechannelnozzle.Therequirementsofgoodpipinglayoutgenerallyapplytothedesignofheatexchangerpiping.Theshortestlinesandleastnumberoffittings-temperaturepermitting-willobviouslyprovidethemosteconomicalpipingarrangement.Thedesignershouldavoidloops,pocketsandcrossovers,andheshouldinvestigate,nozzletonozzle,thewholelengthofpipingroutedfromtheexchangertosomeothe


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requipment,aimingtoprovidenotmorethanonehighpointandonelowpoint,nomatterhowlongtheline.Veryoftenaflatturnintheyard,analternativepositionforcontrolvalvesormanifold,changednozzlelocationontheexchanger,etc.,canaccomplishthisrequirement.Avoidexcessivepipingstrainsonexchangernozzlesfromactualweightofpipeandfittingsandfromforcesofthermalexpansion.Forvalvesandblindesthebestlocationisdirectlyattheexchangernozzle.Inthecaseofanelbownozzleonanexchangeritshouldbecheckedthatsufficientclearancesareprovidedbetweenvalvehandwheelandoutsideofexchanger.Elevatedvalvesmayrequireachainoperation.Thechainshouldhangfreelyataccessiblespotneartheexchanger.Belowfigureshowssketcheshighlightingexchangerpipingdetails.Orificeflangesinexchangerpipingareusuallyinhorizontalpiperuns.Theselinesshouldbejustaboveheadroomandtheorificeitselfaccessiblewithmobileladder.Orificesinaliquidlineandmercurytypemeasuringelementrequiremoreheight.AtgaslinestheU-tubecanbeabovethelinewithorifice,consequentlytheheightisnotcritical.Lineswithorificeflangesshouldhavethenecessarystraightrunsbeforeandaftertheorificeflangesrequiredinspecificationorstandards.Locallymountedpressure-andtemperatureindicatorsonexchangernozzles,ontheshellorprocesslines,shouldbevisiblefromtheaccessaisles.Similarlygaugeglassesandlevelcontrollersonexchangersshouldbevisibleandassociatedvalvesaccessiblefromthisaisles.Whenarranginginstrumentconnectionsone

xchangerssufficientclearancesshouldbeleftbetweenflangesandexchangersupportbetweeninstrumentsandadjacentpiping.Insulationofpipingandexchangersshouldalsobetakenintoaccount.8.LayoutofExchangersOtherThaninBanksProcessequipmentinmostplantsisarrangedinthesequenceofprocessflow.However,whateverlayoutsystemisused,thegeneralevaluationregardingexchangerpositionsisverysimilar.Inlayoutthefractionationtowersshouldbelocatedinpropersequencefirst,althoughoftenthearrangementofotherequipment-forexample,condensersdependdirectlyuponthetowerorientation,andsometimesthedecisionwhethertouseastructureornotdependsuponthis.Thisrelativepositionofexchangerscanbereadilyevaluatedfromflowdiagrams.Forexchangerpositionsinapetrochemi

calplantthefollowinggeneralclassificationcanbemade.Exchangerswhichmustbenexttootherequipment.Suchexchangersarethereboilerswhichshouldbelocatedtotheirrespectivetowers,orcondenserswhichshouldbenexttotheirrefluxdrumsclosetothetower.Exchangerswhichshouldbeclosetootherprocessequipment.Forexample,exchangersinclosedpumpcircuitssuchassomerefluxcircuits.Overheadcondensersshouldalsobeclosetotheirtowertoensurethatthelinepressuredropinminimal.Incaseoftower-bottom-draw-off-exchanger-pumpflow,exchangersshouldbeclosetothetowerordrum,togiveshortsuctionlines.Exchangerslocatedbetweendistantitemsofprocessequipment.Theseareforexample,exchangerswithprocesslinesconnectedtobothshellandtubeside.Whereparallelrunistheideallocationforthistypeofexchanger.Onthatsideoftheyard,wherethemajorityofrelatedequipmentisplaced.Otherlocationswil

lcostmoreinpiperuns.Exchangerslocatedbetweenprocessequipmentandtheunitlimit.Suchexchangersareforexampleproductcoolers.Thesearefrequentlylocatedneartheunitlimit.Stackedexchangers.Afurtherstepinthelayoutistoestablishwhichexchangerscanbestackedforsimplifyingpipingandsavingplotspace.Mostunitsinthesameservicearegroupedautomatically.Twoexchangersinseriesorparallelareusuallystacked.Sometimes,smalldiameterexchangersinseriescanbestackedthreehigh.Twoexchangersindissimilarservicescanalsobestacked.Sufficientclearancemustbeprovidedforshellandchannelsidepipingbetweenthetwo


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exchangers.Reboilersandsinglecondensersusuallystandbythemselvesbesidetheirrespectivetowers.Verticalthermosyphonreboilersareusuallyhungfromthesideoftheirassociatedtower.9.TypesofAirFinsTherearetwotypesofairfinconstruction:theboxtypeandtheAframetype.Theboxtypecanbedividedintotwoforms:forceddraughtandinduceddraught.Forceddraftairfinsarethemostcommonlyusedtype,possiblybecausemaintenanceofthefaniseasyfromanunderslungplatform.Aframetypeairfinslesscommonthantheboxtype.Theyoffertheadvantageofrequiringlessplotareathanboxtypeairfinsofthesamecapacity.Theydo,however,presentafewproblems.Duetophysicalshapeofthem,i.e.triangularsectionwiththeapexuppermost,theinletheaderislocatedattheapex,withthecollectingheadersatbothbottomcorners.Thismeansthatcooledproductlinesarecomingoffbothsidesoftherackwhichcanpresentpipingproblems.Also,with60osidescontainingtheproduct,itispossibletogetunevencoolingduetothesunbeingononeside,ortheprevailingwindtendingtoblowintothetubebankagainstthefan.10.LayoutofAirFinsAirfinsarelargecomparedwithshellandtubeexchangers,anditisnotuncommonforthemtooccupyseveralthousandsquarefeetofplotareaonaunit.Ifthisplotareaisrequiredatgrade,therecouldwellbesitingproblems,butfortunatelymostprocessusingairfinsrequireagravityfeedthroughthem,wh

ichmeanstheymustbeelevated.Themostcommonsatisfactorylocationisontopofthemainpiperack.Piperackwidthisinvariablydeterminedbytubelengthofairfinunits.Intheabsenceofsufficientroomontherack,theymaybelocatedontopofanysuitablestructure,oranelevatedstructuremaybebuiltforthepurpose.Whenlocatingairfinsontheplotanumberofpointshavetobeborneinmind.Airfinofagivencapacitycouldbemadeupofseveralunitseachweighingseveraltons.Itisimportantthateachunitbereachedbythesitecraneforerectionandmaintenancepurposes.Therefore,theoverallplotlayoutmustprovideforthiscraneaccess.Asmostairfinswillbecondensingoverheadsfromtowers,itisimportanttoconsidertheexplanationproblemsoftheoverheadlinewhensitingtherelevantai

rfin,asairfinsareunsuitableforacceptinghighloadsonthenozzles.Accessplatformsarealwaysprovidedeithersideoftheairfinforaccesstotheheaderboxes,andunderneaththeunitsforaccesstofansandmotors.Provisionmustbemadeforgradetoalltheseplatformsatleastateitherend.Itisagoodideatoinvestigateconnectingtheseaccesswaystoadjacentstructurestoprovideintermediateescapeandforoperationalconvenience.11.PipingTherearefourmajorproblemswhenpiping-upairfins:1. Correctconfigurationsofpipingtogiveequalorasnearequaldistributionaspossibleoftheproductthrougheachunitofmulti-unitairfins.2. Makepipingfromtoweroverheadasshortaspossibletominimizepressuredrop.

3. Obtainingapipingsystemthatissufficientlyflexibletoavoidoverloadingtheunitnozzles.4. Providingsufficientlysuitablepipesupportsandanchors.Belowfigureshowsdiagrammaticallythreemethodsofpipingfordistribution:1. Showinggooddistribution2. Showinggooddistribution3. ShowingbaddistributionWhendesigningthepipingforairfinexchangers,thebasicrulesofpipingstillapply,thatthepipingrunsshouldbeasshortanddirectaspossible,butatthesametimebesufficientlyflexibletoavoidoverloadingtheairfinnozzles.


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Thebelowfigureshowstwomethodsofrunningproductheaderstoairfins:Byrunningtheinletheaderdownthecenteroftheunits,theoff-takestotheunitdropoutofthebottomoftheheader,runacrosstheunitsanddropintothenozzles.Thus,wehaveaseriesofoff-takessufficientlylongtoabsorbexpansion,atthesametimehavingtheminimumofelbowsresultinginminimumpressuredrop.Supportscanusuallybeattachedtothesteelmembersthatrunbetweenunitsandarethusshortandminimal.Theheadermustbeflangedatintervalsalongitslengthtofacilitatetheremovalofunitsbycraneformaintenance.Thepreferredpositionfortheheaderisdirectlyabovetheinletnozzles,keepingthebranchesasshortaspossible.Makesurethattheairfiniscapableofexceptingthemovementimposedontheheader.Supportfromtheracksteelisbetweentheheaderboxes.Outletheadersarelessofaproblembecausethetemperatureislowerandthepipesizeusuallymuchsmaller.Theycanusuallybesupportedofftheairfinlegsbeneaththeheaderboxplatform.Anyvalvesrequiredtoisolateunitsarethebestlocatedontheunitnozzles.Sometimesairfinshandlinglighthydrocarbonsmayrequiresnuffingsteamsupply.Theseshouldbetreatedinthesamewayassnuffingsteamtoheaters,insomuchasthevalvesshouldbelocatedatleast15metersradiusplanwisefromtheperimeteroftheairfin.Pipingrunsthatplaceloadsofanysortontheairfinstructuresshouldbeavoidedifpossible,orcommunicatedtothevendorassoonaspossible.

12.FinTubeExchangersFintubeexchangersconsistofahairpinshapedinnertubewithheattransferfinsontheoutside,exceptforthereturnbend.Thetwolegsarejacketedwithlargerborepipe.Theheatexchangeisachievedbythestreampassingthroughthehairpin,andtheotherpassingthroughthejackets.Theymaybeusedsinglyorinmultiples.Theprimaryusesareforheathersorcoolers;thatis,theprocessstreampassesthroughtheinnertubeandeithersteamorcoolingwaterpassesthroughthejackets.Theyareusedmainlyasasourceoflocalheatexchange,suchasoutletheatersfromthetanksanddrumstopumps,etc.Ourimportantpointtorememberwhenlocatingfintubesisthatthehairpintubedrawsoutfromthebackend,thatis,theoppositeendfromthenozzles,andsu

fficientroommustbeallowedforthispurpose.Pipingdesignconsiderationsaresimilartothoseonshellandtubeexchangers.13.ChillersChillersareusedwheretheprocessstreamrequirescoolingtolowertemperaturethanpossiblewithcoolingwater,andforthispurposeitisnecessarytousearefrigerant.Dependinguponthesizeofthechillersinstallation,therefrigerantcaneitherbesuppliedbyaproprietarypackageunit,oracustom-builtjobusingLPG.Theconstructionissimilartofintube,insomuchasthetubewithinatubefeatureiscommon.Chillersusuallyconsistofamulti-unitbankwiththeprocessstreampassingthroughtheinnertubeandtherefrigerantpassingthroughthejackets.Onceagain

spacemustbeallowedattherearfortubewithdrawal.Animportantthingtorememberwhenlayingouttheseexchangers,istheconsiderablethicknessofinsulationrequiredonallthepipe-work,necessitatinglargerthannormalpipespacing.FiguresTYPICALEXCHANGERS-SHOWSPOSSIBLEALTERATIONSFORBETTERPIPING


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TYPICALEXCHANGERS-SHOWSPOSSIBLEALTERATIONSFORBETTERPIPINGTYPICALEXCHANGERGROUPINGSTYPICALEXCHANGERGROUPINGSMINIMUMCLEARANCESFORHEATEXCHANGERSNOZZLEARRANGEMENTFORBETTERPIPINGNOZZLEARRANGEMENTFORBETTERPIPING

NOZZLEARRANGEMENTFORBETTERPIPINGNOZZLEARRANGEMENTFORBETTERPIPINGEXCHANGERPIPINGARRANGEMENT

BETTERPIPINGARRANGEMENTSTYPESOFAIRFINEXCHANGERSPLOTACCESS&SECTIONOFAIRFIN

AIRFINMANIFOLDLAYOUTHEADERMOUNTINGSFORAIRFIN NoIframes


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