板壳换热器在Steam manual 的应用.docx

板壳换热器在Steam manual 的应用.docx

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板壳换热器在Steammanual的应用

ARO

ManualforAPSuseinsteamprocessesandpowerplants

9.7.2013

Customerversion

Index

ManualforAPSuseinsteamprocessesandpowerplants1

Index2

Introductiontothetopic4

1APSdesignprinciplesforsteamprocesses5

1.1Condensers5

1.1.1Construction5

1.1.2Thermaldesign5

1.1.3Subcooling6

1.1.4De-superheating7

1.1.5Pressuredrop7

1.1.6Steamvelocity9

1.1.7Condensateremoval9

1.1.8Flowdirectors10

1.1.9Twophasecondenser11

1.2Controlmethodsforcondensers11

1.2.1Steamsidecontrol12

1.2.2Condensatesidecontrol13

1.2.3By-passcontrol（watersidecontrol）16

1.3Evaporators18

1.3.1Construction19

1.3.2Thermaldesign21

1.3.3Dropletseparation22

1.3.4Steamvelocity23

1.3.5Reactionspeed,dryevaporation23

1.3.6Minimumload24

1.4Materialsandcorrosion24

2DesignandexamplesofAPSinsteamprocessuse26

2.1Ventcondensers26

2.2Steamgenerators27

2.2.1Externalcirculation28

2.2.2Internalcirculation29

2.3Inlinecondensaterecoveryunit（ICHRU）30

3DesignandexamplesofPSHEinPowerPlantuse32

3.1Hotwater–thermo-oilheaters32

3.2Highpressurepreheaters32

3.3Lowpressurepreheaters33

3.4Districtheatingcondenser33

3.5Turbineby-passcondensers33

4Start-upanduseofPSHEinsteamapplications35

4.1Recommendedmeasurements35

4.2Start-up35

4.3Shut–down38

4.4StorageofthePSHEandlongtimeshutdowns38

4.5RecommendedperiodicalinspectionsofPSHEandPRHEheatexchangers39

4.6Recommendationsforcleaning40

4.6.1Backflushing40

4.6.2Chemicalcleaning41

4.6.3Openablemodel42

4.7Repairingtheunit42

Introductiontothetopic

AROAPSiswidelyusedinapplicationswherewaterexistsbothinliquidandvapourphase.Inmostcasesitisamatterofheatingproductswithsteam,butthepurposecanalsobetoconvertsteambacktoliqud（Figure1）.TherequirementtoevaporateorcondensewaterexistsinallpowerplantsandenergydemandingindustriesandthismanualaimstogivebetterunderstandingofPSHEintheseapplications.Themostimportantdesignrulesareshowninboldandtheserulesmustbecarefullyfollowed.

Figure1.TypicalAPSsteamcondenser.

1APSdesignprinciplesforsteamprocesses

ThischaptergivesinstructionsonhowtodesignPlateandShellheatexchangersforcondenserandevaporatorduties.ControlmethodsandtheeffectofthecontrolsystemtoPSHEarediscussedinchapter1.2.andPSHEmaterialselectionsinchapter1.4.

1.1Condensers

Condensersconvertsteamintoliquid.Steamcondensesonthesurfacewhichiscolderthanthesaturationtemperatureofthesteam.Inaplateheatexchanger,condensingisfilmcondensing.Thismeansthatthecondensingliquidcreatesafilmwherethesteamcondenses.Alsodirectcondensingontheplatesurfaceoccursoccasionally.

1.1.1Construction

Condensingofwatervapourmustalwaysbearrangedsothatthevapourisintroducedtoheatexchangereitherfromtoporfromtheside.Vapourinletfromthebottomoftheexchangerisonlyallowedinspecialcircumstances.Thereasonforthetoptobottomflowarrangementistherequirementforcondensatedraining.Ifvapourisintroducedfromthebottom,condensatewillblocktheheattransfersurfacefromnewvapourentering.

InPSHEthecondensingmediaisusuallyplacedontheshellsideduetothelargerinletnozzlesandbetterdistributionofsteamtotheplatesurfaces（Figure1）.

1.1.2Thermaldesign

Inmostcasesk-valuesof2000–3500W/m2KcanbeachievedwhenusingPSHEforsteamcondensing.Thisisvalidwithwaterasacoolingmediaandsensiblepressuredrop（10–100kPa）.Withvacuumcondensationandhighrateofsuperheat,k-valuesarelower.

Minimumapproachtemperaturebetweencoldsideoutletandsteamcondensingtemperatureis2K,maxtemperatureefficiencyis97–98%.Figure2showsthepossibletemperaturesifthesteamissuperheated.

Itmustbenotedthatcoolingwatersidepressuremustbehigherthansteampressureincondensatesidecontrolledunit.Ifthepressureislower,coolingwatercanevaporateandthereisariskforplatedamage.Asimilarsituationcanhappeninsteamsidecontrolledunit,ifthesteamisonplatesideandthecoolingwateronshellsideincrossflowconfiguration.

Figure2.Temperaturesofsteamandliquidside.

1.1.3Subcooling

SubcoolingofthecondensatecanonlybeachievedinoneunitifacondensateliquidleveliskeptinsidethePSHE.Thiscanbedoneonlywithcondensatesidecontrol（chapter1.2.2）.

Outlettemperatureofsubcooledcondensateislimitedtothecoldsideaveragetemperature（Figure2）.

Example:

Steamcondensingtemperature150°C,coolingwater60–120°C

→Condensateminimumtemperaturewithcondensatesidecontrolis90°C.

Ifsubcoolingisneededinsteamsidecontrolsystem,aseparatesubcoolerisrequired.ThesubcoolercanbeseparateorintegratedintothecondensatereceiverwhichistypicalforPowerPlantcondensers.

1.1.4De-superheating

De-superheatingcanbedoneinacondensertoacertainextent.Whenthesuperheatingismorethan50°C,theuseofseparatede-superheaterhastobeconsidered.

1.1.5Pressuredrop

Pressuredroponthecondensingsideisverycriticalandmustbealwayscheckedincondenserdesigns.

Pressuredropshouldnotexceedthesteamsideinletpressure!

Nozzlepressuredropshouldnotbeover30%oftotalpressuredrop.

Also,itmustbenotedthat,duetothepressuredrop,thesaturationtemperaturecanchangeandthatwillchangethethermalperformanceoftheheatexchanger.

Table1.indicatestheavailablepressuredropifthesaturationtemperatureisreducedby1K.Table2indicatesthedecreaseincondensingtemperaturewithdifferentpressuredrop.

Example:

Condensingtemperatureis100°Candpressuredropofheatexchangeris3kPa,condensingtemperaturewillbedecreased1K.

Table1.Availablepressuredropswithdifferentcondensingtemperatures.

Condensingtemperature（°C）

[C]

Saturatedpressure（bara）

[bara]

AvailablePressuredropfor1K（kPa）

[kPa]

40

0.073

0.3

60

0.2

1

80

0.47

2

100

1.01

3

120

2.0

6

140

3.6

10

200

15.5

32

Table2.Decreaseofcondensingtemperatureswithdifferentpressuredrops.

Condensingtemperature（°C）

Saturatedpressure（bara）

Pressuredrop（kPa）

Decreaseofcondensingtemperature（K）

100

1.01

3

1

100

1.01

7

2

100

1.01

10

3

100

1.01

15

4,5

Ifthepressuredropistoohighinthesteamcondenser,thefollowingcanbedone:

-IncreaseInletconnectionsize

-ChangePlatetype

-UseShorterflowdirectors（seeFigure4）

-Usethenextlargestshellsize

-Nonconcentricassemblyofplatepacktoshell（Figure3）

Figure3.Eccentricunit.

1.1.6Steamvelocity

Steaminletvelocityisrecommendedtobe20–30m/s.Itisdependantonthesteamcontrolsystem.Ifsteamissuperheated,aninletvelocityupto60m/scanbeallowedforsteam.Excessiveportvelocitywillcauseerosionandincreasepressuredrop.

1.1.7Condensateremoval

Condensateremovaliscrucialforproperoperationofacondenser.Goodremovalallowsanemptyanddrycondenserwithoutanunplannedliquidlevelinside.Recommendedcondensatevelocityattheoutletconnectionis0.3–0.5m/s.However,ifthecondenserisverylong,itisrecommendedtouseatleasttwooutletconnections.

Inlargecapacitycondenserswithsteamsidecontrol,itisrecommendedtohavea“hotwell”–condensatereceiverwith20–120secondscondensatevolume.Thiscondensatereceivercanbeplacedunderthecondenserandcanalsobeusedforsubcoolingduty.Liquidleveliscontrolledinsidethecondensatereceiver.

1.1.8Flowdirectors

Inordertoavoidby-passontheshellside,flowdirectionsarerequired.Flowdirectorsaremadeofmetalplateswithsuitablesealingmaterial.PermissibleflowdirectorsealingmaterialsforsteamcondensersareEPDM,PTFEandgraphite（Table2）.ShortandlongtypeofflowdirectionsbetweentheshellandtheplatepackareshowninFigure5.

Anytypeofsiliconecannotbeusedwithwatervapour!

Table3.Flowdirectionmaterialsandmaximaltemperatures.

Flowdirectormaterial

Maxtemperature（°C）

EPDM

150

PTFE

260

Graphite

>260

Figure4.Condenserwithshortandlongflowdirections.

1.1.9Twophasecondenser

Twophasecondensersarecondenserswithbothliquidandsteamattheinlet.Thisismostoftenthecaseinafterturbinecondensers,whereitistypicaltohave3-8%ofliquidintheflow.

AnothertypicaltwophasecondenserisanInlinecondenser-seechapter2.3formoreinformation.

1.2Controlmethodsforcondensers

AROdoesnotdesigncontrolsystemsorsupplyanyadditionalcomponentstocontrolsystems.However,itiscrucialtounderstandPSHEuseindifferentsystems.

1.2.1Steamsidecontrol

Thecontrolvalveisinstalledinthesteaminletline.ThevalveregulatesthepressureinthePSHE.Whenmoredutyisneeded,thevalveopens,increasingthepressureandflow.Theincreasedpressuregivesahighercondensingtemperaturewhichgivesmoreheattransfer.Thecondensatetemperaturewillbeequaltothesteamcondensingtemperature.

Figure5.Steamsidecontrolsystem.

Advantages

-Fastcontrol

ATTENTION!

-Oversurfacingmayleadtohighvelocitiesinplategapscausingerosionproblems

-Oversurfacingmayleadtotoolowsteampressurecausingproblemstodrainthecondensate.Thisconditionmaydamagetheheatexchanger.

-Recommendedmaximumsteamsidevelocity50m/s（ifitsuper-heatedthesteamvelocitycanbeeven60m/s）

-Recommendedmaximumliquidsidevelocity5,5m/s

-Thecondensatehastobedrainedfromthecondenserinallconditions

oThecondensateremovalsystemhas