KLMTechnology
Group
ProjectEngineering
Standard
Rev:01April2011
www.klmtechgroup.com
KLMTechnologyGroup#03-12BlockAronia,JalanSriPerkasa2TamanTampoiUtama81200JohorBahruMalaysia
PROCESSDESIGNOFAIRCOOLEDHEAT
EXCHANGERS(AIRCOOLERS)(PROJECTSTANDARDSANDSPECIFICATIONS)
TABLEOFCONTENT
SCOPE
REFERENCES
DEFINITIONSANDTERMINOLOGYSYMBOLSANDABBREVIATIONSUNITSGENERAL
HORIZONTALTYPEFANS
NumberofFans
FansinVariousDutiesTypes
RUSTPREVENTION
CHEMICALCLEANINGCONNECTIONS
OPERATINGTEMPERATUREANDPRESSUREAIR-SIDEDESIGN
GeneralRequirementsDESIGNCONSIDERATIONS
TUBE-SIDEFLUIDTEMPERATURECONTROLCOLDCLIMATECONSIDERATION
HighViscosity-HighPour-PointServicesWinterizationAPPENDIXAAPPENDIXBAPPENDIXC
2223334445566777810111112161719
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KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
SCOPE
ThisProjectStandardsandSpecificationscoverstheminimumprocessdesignrequirements,fieldofapplication,selectionoftypesanddesignconsiderationforaircoolers.REFERENCES
ThroughoutthisStandarddatedandundatedstandards/codesarereferredto.Thesereferenceddocumentsshall,totheextentspecifiedherein,formapartofthisstandard.Fordatedreferences,theeditioncitedapplies.TheapplicabilityofchangesindatedreferencesthatoccuraftertheciteddateshallbemutuallyagreeduponbytheCompanyandtheVendor.Forundatedreferences,thelatesteditionofthereferenceddocuments(includinganysupplementsandamendments)applies.
DEFINITIONSANDTERMINOLOGY
Bank-Oneormoresectionsincludingoneormoreunitsarrangedinacontinuousstructure.
BareTubeSurface-Outsidesurfaceofprimetubesbasedonlengthmeasuredbetweenoutsidefaceofheadertubesheetsinsquaremeters.
Bay-OneormoreK-Finsections,mountedonaselfsupportedstructurecompletewithmechanicalequipment.
FinnedTubeSurface-Totaloutsidesurface(exposedtoair)basedonlengthoftubesmeasuredbetweenoutsidefaceofheadertubesheetsinsquaremeters.ForcedDraftType-Designedwithtubebundleslocatedonthedischargesideofthefan.
InducedDraftType-Designedwithtubebundleslocatedonthesuctionsideofthefan.
Section-Assemblyoftwoheaders,finnedtubesandsidechannels.TubeBundle-Assemblyofheaders,tubesandframes.
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KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
Unit-Theair-cooledheatexchangeequipmentcoveredbyoneequipmentnumber,comprisingoneormoresections,thebundlestoperformonespecificduty.
SYMBOLSANDABBREVIATIONSSYMBOL/ABBREVIATIONA/VDNMAPNPSPUo
DESCRIPTIONAutovariable
DiameterNominal,mmManualAdjustablePitchNominalPipeSize,inch
Air-sidestaticpressuredrop,mbar(0.1kPa)
OverallHeatTransferCoefficient,W/m2.K(W/m2.°C)
UNITS
ThisStandardisbasedonInternationalSystemofUnits(SI)exceptwhereotherwisespecified.GENERAL
1.Aircooledexchangersareusuallycomposedofrectangularbundles
containingseveralrowsoftubesonatriangularpitch.Heattransferisgenerallycountercurrent,thehotfluidenteringthetopofthebundleandairflowingverticallyupwardthroughthebundle.
Aircooledunitshavebeensuccessfullyandeconomicallyusedinliquidcoolingforcompressorengineandjacketwaterandotherrecirculatingsystems,petroleumfractions,oils,etc.andalsoincondensingserviceforsteam,highboilingorganicvapors,petroleumstillvapors,gasoline,ammonia,etc.
2.Sinceairisauniversalcoolant,therearenumerousapplicationswhere
economicandoperatingadvantagesarefavorabletoair-cooledheattransferequipment.However,applicationsarelimitedtocaseswheretheambientairdrybulbtemperatureisbelowthedesiredcoolingorcondensingtemperature.
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KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
3.Whereexpensiveorinsufficientwatersuppliesareencounteredorwhere
coolingwaterpumpingortreatingcostsareexcessive,itisoftenfoundthatair-cooledunitsaredesirableforseveralservices.Theadverseconditionsofhighrelativehumidityorexcessivespacerequirementsoccasionallycreatehighcostsorinstallationdifficultiesforcoolingtowers.Insomeofthosecases,air-cooledheattransferequipmentoffersasatisfactorysolution.4.Fullconsiderationshouldbegiventoadequatewinterprotectionofair-cooled
unitsinstalledincoldclimates.Itisessentialthatallpossibilitiesoffreeze-upbeeliminatedandexternalrecirculationofhotairisnecessaryforseverewinterconditionswhentheunitissubjecttofreezingandheatingcoilsprovidedforprotectionagainstfreeze-upshallbeinaseparatebundleandnotpartoftheprocesstubebundle.5.Ifthefluidbeinghandledissubjecttowidevariationsinviscosityoverthe
rangeofatmospherictemperaturesencountered,provisionsmustbemadetocontroltheextentofcoolingatthelowerambientairtemperatures.6.Bundlesmaybefabricatedinwidthsto3.65m(12ft)anddepthsto8rows.
Usuallythemaximumdimensionsaredictatedbyshippingrequirements.Althoughstandardbundlesareavailableinlengthsof2.44m(8ft),3.05m(10ft),4.57m(15ft),6.07m(20ft),7.31m(24ft),10.36m(34ft),and12.2m(40ft).Bundlesmaybestacked,placedinparallel,orinseries,foragivenservice.Also,severalsmallservicesmaybecombinedinonebay.
Ingeneral,thelongerthetubesandthegreaterthenumberoftuberows,thelessexpensivethesurfaceonasquaremeterbasis.
7.Inmoderateclimatesaircoolingwillusuallybethebestchoiceforminimum
processtemperaturesabove65°C,andwatercoolingforminimumprocesstemperaturesbelow50°C.Betweenthesetemperaturesadetailedeconomicanalysiswouldbenecessarytodecidethebestcoolant.HORIZONTALTYPE
Unlessotherwisespecified,thehorizontaltypeispreferred.FANS
NumberofFans
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KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
Atleasttwofansshallbeprovidedforeachbay.AnydeviationfromthisrequirementwillneedthepriorapprovaloftheCompany.FansinVariousDuties
Where,forreasonsofcontrol,anair-cooledheatexchangerhastobeprovidedwithautomaticvariable-pitchfans,asinthecaseofoverheadcondensers,itshallnotshareitsfanswithair-cooledheatexchangersonotherduties,forexampleproductrun-downcoolers.Types
1.Twogeneralclassificationsofair-coolerfansare:
a.forceddrafttypewhereairispushedacrossthetubebundle;
b.induceddrafttypewhereairispulledthroughthebundle(seeFig.1).2.Forceddraftshouldbeselectedforallnormalapplications.Amongstother
reasons,theaccessibilityoffans,actuatorsanddrivesismuchbetterformaintenanceandthereisthusastrongpreferenceforthisarrangement.
Forceddraftshallbeselectedforcriticalandcondensingdutieswherethedifferencebetweenthedesignproductoutlettemperatureandthedesignairinlettemperatureis15°Corhigher.
Forceddraftshallbeselectedforallcoolingdutieswhereairoutlettemperatureswouldbehigherthanthosespecifiedaslimitingfortheinduced-draftarrangement.
3.Forcriticalcoolingorcondensingdutieswheretheproductoutlettemperature
fallsbelowapoint15°Cabovethedesignairinlettemperature(*),induceddraftmaybeconsideredprovidingtheairoutlettemperaturewillnotrisetoalevelhigherthanisacceptableforthefan,fanhubandbearingsforthegreasingsystemandforallstructuralcomponentsexposedtothehotairstream.ThedegreeofacceptabilityissubjecttotheCompany’sapproval.
Undernormaloperatingconditions,airoutlettemperaturesshouldnotexceed:--60°Cwithfansinoperation.
80°Cwithfreeconvectionontheairside.
Ahigheroutlettemperaturemaybeconsideredprovidingitdoesnotexceedtheoperatingtemperaturelimitsforthefanblades,thehub,thefanblade
Page6of19
KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
adjustingmechanismandthebearingswhentheheatexchangerisatmaximumoperatingtemperaturewithfreeconvectionontheairside.Thetemperatureeffectofradiationundertheseconditionsshallalsobetakenintoaccount.Forthepowerfailurecase,takeamaximumairoutlettemperatureof15°Cbelowthemaximumproductinlettemperature.
*UnlessotherwiseagreedbytheCompany,theproductoutlettemperatureshallnotbelessthan10°Cabovethedesignairtemperature.
4.TheadvantagesofforcedandinduceddrafttypesarelistedinAppendixD.
Theseshouldbeweighedcarefullybeforedecidingonthechoiceofunit.5.Recommendations
a.Induced-draftunitsshouldbeusedwheneverhot-airrecirculationisapotentiallycriticalproblem.
b.Forced-draftunitsshouldbeusedwheneverthedesignrequirespour-pointprotection,orwinterization.However,considerationofpossiblesummerrecirculationmustbeaccountedforinsizingthefanstominimizethiseffect.RUSTPREVENTION
Thestructuralpartscanbegalvanizedorpickledandpaintedtopreventrustingofthesteel.
CHEMICALCLEANINGCONNECTIONS
Ifchemicalcleaningmaintenanceisspecified,connectionsshallbeprovidedperthefollowing:
a.ConnectionsshallbeinstalledonlyinnozzlesDN100mm(NPS4inch)andlarger.Forsmallernozzles,connectionswillbemadeintheattachedpipingbythepurchaser.
b.TheminimumsizeconnectionshallbeDN50mm(NPS2inch).
c.Connectionsshallbeinstalledhorizontally.Orientationwillbespecified.
d.Forbundlesinseriesorseries-parallelarrangement,onlyonechemicalcleaningconnectionneedbeprovidedintheinletnozzleandoneintheoutletnozzleofeachseriesgroup.
Page7of19
KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
OPERATINGTEMPERATUREANDPRESSURE
ThemaximumanticipatedprocessoperatingtemperaturewillbeindicatedontheProcessDataSheet.AirCoolersshallbedesignedforatemperatureatleast28°Cabovethemaximumanticipatedtemperature.
Themaximumanticipatedoperatingpressure,whichshallincludeanallowanceforvariationsinthenormaloperatingpressurewhichcanbeexpectedtooccur,willbeindicatedontheAirCoolerSpecificationSheet.
Exceptforaircoolersoperatingunderavacuum,theinternaldesignpressureshallbe10%greaterthanthespecifiedmaximumoperatingpressure,butinnocaseshallthedifferencebelessthan2bar(200kPa).Theheadersonaircoolersoperatingunderavacuumshallbedesignedforaminimumexternalpressureof1bar(100kPa)unlessotherwisespecified.DesignpressuresshallbeindicatedontheProcessDataSheet.AIR-SIDEDESIGNGeneralRequirements
1.Suchenvironmentalfactorsasweather,terrain,mounting,andthepresence
ofadjacentbuildingsandequipmentinfluencetheair-sideperformanceofanair-cooledheatexchanger.
ThepurchasershallsupplytheVendorwithallenvironmentalfactorspertinenttothedesignoftheexchangeraspertheTable1.Thesefactorsshallbetakenintoaccountintheair-sidedesign.
2.AirCoolersshallbedesignedforsummerandwinterconditions.Thesummer
andwinterdesignairtemperaturesandhumiditiesshallbespecifiedinthejobspecifications.3.Forwinterdesignconditionstheminimumtubewalltemperatureshallbeat
least22°Chigherthanpourpointtemperatureforbothnormalandminimumdesignthroughput.4.Properfoulingresistanceshallbeappliedtotheinsidesurfaceofthetube.
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KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
5.Allheattransfersurfacesandcoefficientsshallbebasedontotaleffective
outsidetubeandfinsurface.6.Whencalculatingheattransfercoefficients,theinsidefoulingandinsidefluid
filmresistanceshallbemultipliedbytheratioofthetotaleffectiveoutsidesurfacetothetotaleffectiveinsidesurface.7.Theeffectivetubewallandfinmetalresistanceshallbeincludedin
calculatingheattransfercoefficients.8.Pressuredropsshallnotexceedthemaximumallowedvaluesspecified.
Theseindicatethetotalpressuredropsacrossnozzles,headersandtubes.9.Foulingfactoronairsideofexchangersshallbe0.35m2.K/kW(0.002
h.ft2.°F/Btu).10.Theneedforairflowcontrolshallbeasdefinedbythepurchaseronthebasis
ofspecificprocessoperationrequirements,includingtheeffectofweather.Variousmethodsofcontrollingairflowareavailable.
Thetypeultimatelyselectedisdependentonthedegreeofcontrolrequired,thetypeofdriverandtransmission,equipmentarrangement,andeconomics.Asaguide,thevariousmethodsinclude,butarenotlimitedto,simpleon-offcontrol,on-offstepcontrol(inthecaseofmultiple-driverunits),two-speedmotorcontrol,variable-speeddrivers,controllablefanpitch,manualorautomaticlouvers,andairrecycling.
11.Fanselectionatdesignconditionsshallbesuchthatatconstantspeedthe
faniscapableofproviding,byanincreaseinbladeangle,a10percentincreaseinairflowwithacorrespondingpressureincrease.12.Intheinquirythemaximumandminimumdesignambienttemperaturesunder
whichfansanddriverswilloperate,aswellasanyspecificrequirementsrelatingtothesizingofdriversandtransmissionsshallbestated.13.Formechanicalcomponentslocatedabovethetubebundledesign
temperatureshallbeequaltomaximumprocessinlettemperatureunlessotherwisespecified.DESIGNCONSIDERATIONS
1.Designmaximumambientairtemperatureshouldbeselectedsothatitwill
notbeexceededmorethan1-2percentofthetotalannualhourlyreadingsbasedonatleast5consecutiveyears.Lowerfiguresmeanasmaller
Page9of19
KLMTechnology
Group
ProjectEngineeringStandard
PROCESSDESIGNOFAIRCOOLEDHEATEXCHANGERS
(AIRCOOLERS)(PROJECTSTANDARDSAND
SPECIFICATIONS)
Rev:01
April2011
exchangerbuttheyalsoindicateaquestiononperformanceduringhottestweather.Dailytemperaturechartsaswellascurvesshowingnumberofhoursandtimeofyearanygiventemperatureisexceededvaluableandoftennecessaryinestablishinganeconomicaldesigntemperature.SeeTableA.1inAppendixAasatypicalstudy.
thetheareair
2.Unitsshouldpreferablybeplacedintheopenandatleast23-30mfromany
largebuildingorobstructiontonormalwindflow.Ifcloser,therecirculationfromdowndraftsmayrequireraisingtheeffectiveinletairtemperature1-2°Cormoreabovetheambientselectedforunobstructedlocations.
Ifwindvelocitiesarehigharoundcongestedareas,theallowanceforrecirculationshouldberaisedabove2°C.
3.Unitsshouldnotbelocatednearheatsources.Experiencecautionsthatunits
nearexhaustgasesfromenginescanraiseinletair8°Cormoreabovetheexpectedambient.4.HotAirRecirculation
Problemsassociatedwithhotairrecirculationarethedirecteffectofpoorexchangerdesignandlocation.Minimumallowabledistancesbetweenaircoolersandotherprocessequipmentshouldbeconsidered.These,however,arebasedonsafetyrequirementsandshouldbeaccordinglyincreasedifrecirculationposesapotentialproblem.Otherrecommendationsforcombatinghotairrecirculationinclude:---Usinginduceddraftfanswhichforcetheairawayfromthebundle.
Bafflesand/orastackontopofthebundleforaforceddraftunit(orfanonaninduceddraftunit)willalsodirecttheairawayfromthebundle.
Humidificationsectionsorairwashers:Ifthegeographiclocationissuchthattherelativehumidityislowmostoftheyear,ahumidificationsectioncouldbeinstalledbelowtheunit.This,ineffect,moisturizestheinletairdowntoitswetbulbtemperaturewhichcouldbe5°Cto11°Ccoolerthanambient.However,careshouldbetakentoinsurethatairenteringthetubebundleisdry.
A-Frame,V-Frameandverticalbundlearrangementsshouldnotbeusedifrecirculationisapotentialproblem.
Watersprayingisnotrecommendedforalleviatingexistinghotairrecirculationproblemsexceptasatemporarysolution.Ifthebundleissprayeddirectly,tube-to-finbonding,fouling,andcorrosionproblems
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