喷射器具体资料.docx

喷射器具体资料.docx

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喷射器具体资料

SteamJetEjectors

SteamjetEjectorsarebasedontheejector-venturiprincipalandoperatebypassingmotivesteamthroughanexpandingnozzle.Thenozzleprovidescontrolledexpansionofthemotivesteamtoconvertpressureintovelocitywhichcreatesavacuumwithinthebodychambertodrawinandentraingasesorvapours.Themotivesteamandsuctiongasarethencompletelymixedandthenpassedthroughthediffuserortail,wherethegasesvelocityisconvertedintosufficientpressuretomeetthepredetermineddischargepressure.

VacuumEjectorsareusedinavarietyofapplicationsintheprocess,food,steelandpetrochemicalindustries.Typicaldutiesinvolvefiltration,distillation,absorption,mixing,vacuumpackaging,freezedrying,dehysratinganddegassing.Ejectorswillhandlebothcondensibleandnonecondensiblegasloadsaswellassmallamountsofsolidsorliquids,howeveraccidentalentrainmentofliquidscancauseamomentaryinterruptioninvacuumbutthiswillnotcausedamagetotheejector.

Primaryadvantagesoverothervacuumpumpscanbeseenbelow:

∙NoMovingParts-Ejectorsareexceedinglysimpleandreliable.Therearenomovingpartstowearorbreakinabasicejector.

∙LowCost-Unitsaresmallinrelationtotheworktheydoandcostiscorrespondinglylow.

∙Versatile-Variouspipingarrangementspermitadaptingtoenvironmentalconditions.

∙SelfPriming-Ejectorsareself-priming.Theyoperateequallywellincontinuousorintermittentservice.

∙EasytoInstall-Relativelylightinweight,ejectorsareeasytoinstall,andrequirenofoundations.Evenmultistageunitsarereadilyadaptabletoexistingconditions.

∙CorrosionandErosionResistant-Becausetheycanbemadeofpracticallyanyworkablematerial,orcoatedwithcorrosion-resistantmaterials,ejectorscanbemadehighlyresistanterosionandcorrosion.

∙HighVacuumPerformance-Ejectorscanhandleairorothergasesatsuctionpressuresaslowas3micronsHgA.

EjectorsrangefromSingleuptoSixStageunits,andcanbeeitherCondensingorNon-Condensingtypes.ThenumberofEjectorstagesrequiredareusuallydeterminedbytheeconomyoftheejectorsandthelevelofvacuumrequired.TheoperatingrangeforeachstageofVacuumEjectorcanbeseenbelow,alsoforreference1BarA=760mmHgA.

1stStage:

810mmHgA-30mmHgA

2ndStage:

130mmHgA-3mmHgA

3rdStage:

25mmHgA-0.8mmHgA

4thStage:

4mmHgA-75micronsHgA

5thStage:

0.4mmHgA-10micronsHgA

6thStage:

0.1mmHgA-3micronsHgA

SingleStageEjectors

SinglestageVacuumEjectorsgenerallycovervacuumrangesfrom30mmHgAuptoatmosphericpressure.Tomaximiseperformanceeightdifferentdesignsareavailablewitheachejectorbeingoptimisedtooperateinaspecificvacuumrange.Thisallowsthemotivesteamconsumptiontobekeptataminimumfortheselectedejector,andalsoensuresthatoperationwillbestable.Allsinglestageejectorsaredesignedtodischargeeitheratorslightlyaboveatmosphericpressure.Sizesrangefrom1Inchto6Inch,howeverlargesizeareavailableifrequired.Standardmaterialsofconstructionarecarbonsteelorstainlesssteel,bothofwhicharefittedwithastainlesssteelnozzle.

TwoStageEjectors

StagingofEjectorsisrequiredformoreeconomicaloperationwhentherequiredabsolutevacuumlevelisreduced.TwostageVacuumEjectorsgenerallycovervacuumrangesbetween3mmHgAto130mmHgA,howeverdependinguponactualoperatingconditionsaSingleStagemaybemoreeconomicalifattheupperlimitoftheoperationalenvelope,oraThreeStageEjectorSystemifconditionsareatthelowerend.

InoperationatwostagesystemconsistofaprimaryHighVacuum（HV）EjectorandasecondaryLowVacuum（LV）Ejector.InitiallytheLVejectorisoperatedtopullvacuumdownfromthestartingpressuretoanintermediatepressure.OncethispressureisreachedtheHVejectoristhenoperatedinconjunctionwiththeLVejectortofinallypullvacuumtotherequiredpressure.

TwostagesystemscanalsobeeitherCondensingorNon-condensingtypes.Condenserscanbeusedaspre-condensers,inter-condensers,andafter-condensers,allofwhichhelptoreducethegasloadbeingpassedontothenextejectorstage.Thishelpstoreducemotivesteamconsumptionandalsoallowssmallerejectorstobeusedwithinthesystem.DependingupontheapplicationNon-condensingsystemscanalsobeused,howeverthiscanbelessefficientthanCondensingTypesaseachejectormustentrainthefullgasloadfromthepreviousstage.Thiscanleadtoejectorsbecominglargeandalsoincreasesmotivesteamconsumption.Non-condensingtypesareusuallyusedwhereitisnotfeasibletoinstallcondensers,orwhereserviceisintermittent,makingoperatingcostsasecondaryconsideration.

ThreeStageEjectors

ThreestageVacuumEjectorsgenerallycovervacuumrangesbetween0.8mmHgAto25mmHgA,howeverdependinguponactualoperatingconditionsaTwoStageEjectorsystemmaybemoreeconomicalifattheupperlimitoftheoperationalenvelope,oraFourStageEjectorsystemifconditionsareatthelowerend.

InoperationaThreeStagesystemconsistofaprimaryBooster,asecondaryHighVacuum（HV）Ejector,andatertiaryLowVacuum（LV）Ejector.AspertheTwoStageSystem,initiallytheLVejectorisoperatedtopullvacuumdownfromthestartingpressuretoanintermediatepressure.OncethispressureisreachedtheHVejectoristhenoperatedinconjunctionwiththeLVejectortopullvacuumtothelowerintermediatepressure.FinallytheBoosterisoperated（inconjunctionwiththeHV&LVEjectors）pullvacuumtotherequiredpressure.

ThreestagesystemsarealsousuallyoftheCondensingtype.AgainaspertheTwoStagesystem,condenserscanbeusedaspre-condensers,inter-condensers,andafter-condensersinordertoreducethegasloadbeingpassedontothenextejectorstage.DependingupontheapplicationNon-condensingsystemscanalsobeusedhoweverthisislessefficientthanCondensingTypesaseachejectormustentrainthefullgasloadfromthepreviousstage.

Four,Five&SixStageEjectors

ThesesystemsaresimilartoThreeStageSystems,howevertheyincludeadditionalboosterswhichareequippedwithSteamJacketstopreventiceformingwithintheejectors.ThesesystemsareusuallyoftheCondensingtypetoincreaseefficiencyandreducemotivesteamconsumption.

KeepEjectorsOnline

Theperformanceofsteam-jetejectorscanbe

maintainedbyfollowingtheseguidelines

（SpecialSharedContentfromCrollReynolds）

Figure1.Intotal,thisillustrationrepresentsafour-stageejectorsystemwithtwosurface-contactintercondensers.Asimplesingle-stagesystemwouldcompriseonlythesectionintheoutlinedbox.Ineithercase,motiveforceisprovidedbysteamjets,whichdrawvaporfromavesselandthroughthesystem.Thecondensersacttoreducetheloadonthenextejector.

Steamjetejectorsofferasimple,reliablemeansofproducingvacuum,andhavealowinstalledcostaswell.Theyarecommonlyfoundinprocessplantshavingavailablesteam.Thevacuumproducedisusefulformanyprocesses,includingevaporation,

cooling,hydration,crystallization,deaerationandfiltration.

Throughthesimplicityofitsconstruction（Figure1）,thesteam-jetejectorprovidesmanyyearsoftroublefreeoperation.Whenaproblemdoesoccur,manyplantpersonneldonothavetheexperiencetoeffectivelytroubleshootanejectorsystem,andpreciousproductiontimeislost.

Forexample,alossofvacuuminamultistageejectorsystemmighthavemanyplantpersonneldisassemblingthefirst-stageejectorbooster,ontheassumptionthatonemustcheckaunitfrominlettooutlet.Infact（aswillbeshownlaterinthisarticle）,thisisthelastplacetolook.Fortunately,downtimecanbekepttoaminimumwhenalogicalsequenceofsteps--achecklist--isfollowedtolocatethesourceoftrouble.

Ejectorbasics

Ejectorscanbeclassifiedassingle-stageormultistage.Multistageejectorsmaybefurtherdividedintocondensingornoncondensingtypes.Thesingle-stageejector,thesimplestandmostcommontype,isgenerallyrecommendedforpressuresrangingfromatmosphericpressure（30in.Hgabsolute）to3in.Hgabs.Dischargeistypicallyatornearatmosphericpressure.TheboxedsectionofFigure1showsasingle-stagesystem.Theeffectsofinjectedsteamonprocessvaporsisshowninfigure4.Multistagenoncondensingejectors（MNEs）areusedtoproducesuctionpressureslowerthan3or4in.Hgabs.SteamconsumptioninanMNEisrelativelyhigh.Eachsuccessivestageisrequiredtohandletheloadplusthemotivesteamfromthepreviousstage.MNEsarefrequentlyusedwhenlowfirstcostismoreimportantthanlong-rangeeconomy.Theyarealsousedforintermittentserviceorwhencondensingwaterisnotavailable.MNEsareusuallytwo-stage,althoughsix-stageunitshavebeenusedsuccessfully.

Multistagecondensingejectors（MCEs）areavailableintwothroughsixstages.Intercondensers（surfaceordirect-contact）betweenstagescondensesteamfromtheprecedingstage,reducingtheloadtobecompressedinthesucceedingstage.AmultistagesystemisshowninFigure1.

Four-,five-andsix-stageejectorsareusedtoachievesuctionpressuresaslowas5祄Hgabs.Undersuchvacuumconditions,pressurebetweenthepreliminarystagesistoolowtopermitcondensationofejectorsteam,andonlythefinaltwostagesarefittedwithcondensers.MCEsremovecondensablevaporaheadofagivenejectorstage.Theyalsopermituseofasmallerejector,andareductionintheamountofsteamrequired.Condensernomenclatureisdeterminedbythecorrespondingoperatingconditionsandfunctions.

Precondensersareusedwhenthea