深冷液体存贮与输送的实现

CryogenicStorageandDelivery

WhyitWorks

深冷液体存贮与输送的实现

Jan.5th,2012CHTRAMAT-EN-003(2012)Overview概述Gassesarestoredasliquidforseveralreasons气体之所以液化存贮Higherstoragedensity高存贮密度EasierDeliverylogistics容易输送EasierPumping易泵输送Useoftherefrigerationcontent制冷技术的使用WhatastorageTanksDoes贮罐可以做到StorestheLiquid,keepingitcold.贮存液体,使其保持低温AllowsforRefilling可重新充装MaintainsPressure保持压力AllowsforLevelMeasurement保持液位AllowsforWithdrawal使用Gasapplications气体使用LiquidApplications液体使用Protectsitselffromoverpressurization.防止罐体超压UnderstandingaLiquefiedGas理解液化气体Importantfluidpropertiesinclude重要的液体参数包括Pressure压力Temperature温度Density密度Energy能量Therelationshipbetweenthesepropertiesisfixedforafluid.Knowinganytwoallowsustopredicttherest.对任一液体而言,这些参数之间的关系是确定的,任何两个已知的参数都可以推导出其他的参数.Theleastintuitive,butmostinfluentialistheenergyofthefluid.最直接也是最有影响的参数是能量.UnderstandingtheInfluenceofenergyonthefluidiscriticaltounderstandwhycryogenicsystemsworkthewaytheydo.理解液体能量有助于理解深冷系统工作的原理Thermodynamicsisthestudyofhowenergyaffectsthestateofafluid.此处的热力学是解释能量如何影响液体状态的学科Energy(heat)willmovefromonebodytothenextifthereisatemperaturedifferencebetweenthem.Thehigherthedifference,thefastertheenergyistransferred.Energyisalsointroducedwhenworkisdoneontheliquid.Anytimetheliquidistransferred,thereisanincreaseintheenergyoftheliquid.两个物体之间存在温差时即可产生传热.温差越大,传热越快.对液体做功也能产生能量.输送液体时液体的能量会增加.IntuitiveMaterialProperties物质特性参数Property特性Description描述Units单位ExampleofInfluenceondesign设计相关示例Pressure压力Force/UnitArea单位面积受力PSI,PSIA,PSIGPa,MpaInnerVesselThickness内容器壁厚OuterVesselThickness外容器壁厚Temperature温度Responsethatanamountofmaterialhasbasedontheenergyitiscarrying表示物体冷热程度Fahrenheit,Rankine华氏度Celsius,Kelvin摄氏度MaterialSelection材料选择Vaporizers汽化器PBCoils自增压器Density密度Mass/UnitVolume单位体积的质量SpecificVolume=1/Density#/Ft3#/Gal.Kg/literKg/NM^3Heat(Energy)Property能量参数Property特性Description描述Units单位ExampleofInfluenceondesign设计相关示例InternalEnergy内能(U)Energymeasurethatincludesmolecularenergyatconstantvolume.物体在恒定体积下包括分子运动的能量总和dU/dT=CvBTU/lbJ/kgHoldTime压力保持时间(analysiswherepressurechangeswithinacontrolmass研究在恒定质量下压力变化)Enthalpy焓(H)Energymeasurethatincludesmolecularenergyandworkenergyatconstantpressure.物体在恒压下的能量和功的总和dH/dT=CpH=U+PVBTU/lbJ/kgPBCoilsizing自增压器计算VaporizerSizing汽化器计算NERCalculation蒸发率计算(analysiswheremasschangeswithinacontrolvolume研究在恒定体积下质量变化)Entropy熵(S)Energymeasurethatisusedtomeasurelostworkpotentialandenergyefficiency.Tds=dU=PdVTds=dH-VdPBTU/lb-RJ/kg-KUsedindesigningefficientliquefactionsystems.Helpfulinevaluatingtheenergyaddedbypumps.Page7名词解释Cryogenic深冷Abranch

ofengineeringthatrelatestotheproductionandeffectsofverylowtemperature,usually-230°Fandcolder.Heat

leak热泄漏Cavitation气穴PartialorfulllossofpumpprimeduetoinsufficientsubcoolingorNetPositiveSuctionHeadDepressurizationFlashLossVaporizationcausedbyreducingthegasphasepressuretosomethinglessthansaturatedvaporpressureoftheliquid.Page8Condensation冷凝The

conversionofvaporsintoliquidbycoolingthevapors.Equilibrium平衡Astatewheretheliquidandgasphasescoexistathesametemperatureandvaporpressure.Saturation饱和Astatewheretheliquidandgasphasescoexistin

equilibrium.名词解释Page9Subcooling过冷度RaisinggasspacepressureabovethenormalvaporpressureofasaturatedliquidcreatingNetPositiveSuctionHead(NPSH).Stratification分层Averticaltemperaturegradientwithcolderproductatthebottomandwarmerproductatthetop.Entrainment雾沫Liquiddropletscarriedalongwithaflowinggasstream.名词解释Page10三相点三相点triplepoint是指在热力学里，可使一种物质三相（气相，液相，固相）共存的一个温度和压力的数值三相共存时具有固定的温度和压强氦，是唯一没有三相点的物质例：水的三相点在0.01℃（273.16K），611.73Pa..\LNGStation\Water_boil.wmv水的蒸发过程开始水的温度：78℉（25.5℃）饱和蒸汽压：3.169x103Pa水开始沸腾：79℉（26.1℃）饱和蒸汽压：3.3x103PaPage11Page12临界点临界点criticalpoint一种热力学状态，此时在最高可能温度下物质的液态和气态可以平衡共存临界温度criticaltemperature物质处于临界状态时的温度。物质以液态形式出现的最高温度。温度不超过某一数值，对气体进行加压，可以使气体液化，而在该温度以上，无论加多大压力都不能使气体液化，这个温度叫该气体的临界温度。在临界温度下，使气体液化所必须的最小压力叫临界压力。临界压力criticalpressure物质处于临界状态时的压力（压强）。在临界温度时使气体液化所需要的最小压力。液体在临界温度时的饱和蒸气压。Page13饱和状态、饱和蒸气压、饱和温度饱和状态saturationcondition液体汽化时，其分子不断从液体中逸出，同时也有分子从蒸气中进入液体，当达到同一时间进出液体的分子数相等并平衡时的状态。饱和蒸气压saturatedvaporpressure

在一定温度下，与液体或固体处于相平衡的蒸气所具有的压力称为饱和蒸气压。同一物质在不同温度下有不同的蒸气压，并随着温度的升高而增大。饱和温度saturationtemperature是指液体和蒸气处于动态平衡状态即饱和状态时所具有的温度ts。饱和状态时，液体和蒸气的温度相等。饱和温度一定时，饱和压力也一定；反之，饱和压力一定时，饱和温度也一定。温度升高，会在新的温度下形成新的动态平衡状态。物质的某一饱和温度必对应于某一饱和压力。Page14蒸发、汽化、沸腾和沸点汽化vaporization物质从液态转变为汽态的过程蒸发evaporation物质从液态转化为气态的相变过程沸腾boiling在液体表面和内部同时发生的剧烈汽化现象沸点boilingpoint液体沸腾的温度蒸发和沸腾的联系它们都是液体汽化的方式，即都属于汽化现象，液体在蒸发和沸腾的过程中，都需要吸收热量。..\VCD\Nitrogen_boil.wmvPage15沸点、沸腾和蒸发蒸发和沸腾的区别蒸发是液体在任何温度下都能发生的汽化现象，而沸腾是液体在一定温度（沸点）下，并继续加热，才能发生的汽化现象。蒸发是只在液体表面发生的缓慢的汽化现象，而沸腾是在液体表面和内部同时发生的剧烈的汽化现象。蒸发时液体温度会下降，而沸腾中液体温度保持不变（在液体表面上压强不改变的前提下）。影响蒸发速度的因素是：液体的表面积，液体的温度，液体表面附近的空气流速；影响沸点的因素是：液体表面上的气压，液体的纯净程度。影响沸腾速度的因素：液体体积和原先的温度沸腾时有气泡产生，而蒸发时则无气泡产生。蒸发的微观本质为：由于分子的热运动，使液体表面的分子离开液体，进入空气中。蒸发在任何温度都会进行，只是温度越高越快，反之越慢。而沸腾必须温度在沸点，且继续吸热。沸腾的微观本质为：由于汽化剧烈产生了气泡，不仅液体表面的分子要离开液体，液体内部气泡壁上的分子也要离开液体，进入空气中。沸腾现象中包含了蒸发现象，但蒸发现象却不包括沸腾现象。Page16汽化潜热汽化潜热latentheatofvaporization单位质量的液体转变为相同温度的蒸气时吸收的热量称为汽化潜热，简称汽化热它随温度升高而减小，因为在较高温度下液体分子具有较大能量，液相与气相差别变小。在临界温度下，物质处于临界态，气相与液相差别消失，汽化热为零。PVT/PETSurface压力/体积（能量）/温度Thereisarelationshipbetweenthepropertiesofafluidthatisknownforeachtypeoffluid.Wecandesignequipmentbasedonthisrelationship对任意一种特定流体，其特性之间都存在固定关系，可以利用其进行设备设计Anytwopropertieswilldictatethethird.Thiscreatesathreedimensionalpropertyrelationship任意两个参数可以确定第三个，以此确定三者函数关系Thephysicalstateofthefluidisbasedonwhereweareonthissurfacerelationship流体的物理状态是基于它处于关系函数中的位置Themostcriticalareaofthesurfaceisthevapordome.Inthisregionwedefinethetransitionfromliquidtogas.P-T曲线中关键区域是饱和区域（饱和液相线及饱和汽相线以下），此区域内液体汽化为气体。Abovethedome,thefluidactsinapredictablemannerandfollowsalinearrelationshipbetweenpressureanddensity.曲线以上，流体在压力和密度之间存在线性关系Pureliquidisessentiallyincompressibleduetopressure,yetitsdensitywillchangewithincreasingenergy纯液体是不可压缩的，但随着能量的变化它的密度会产生变化。PVT/PETSurface压力/体积（能量）/温度Saturation/Equilibrium饱和/平衡Fluidthatisonthedomespaceissaidtobeinequilibriumorsaturated饱和区内的流体处于饱和或平衡状态Asaturatedstateisoftenfurthernotedbythecoincidentcorrespondingpressureortemperaturetothisposition.饱和状态下压力或温度可以维持不变.WhenSaturatedapressure,anyreductioninpressure,orincreaseinheatwillresultinthefluidchangingfromliquidtovapor.Vaporizationorboiling饱和压力下，任何压力的降低或能量的增加都导致液体的汽化（汽化或沸腾）Commensuratelyanyincreaseinpressureorreductioninheatwillresultinthefluidchangingfromvaportoliquid.Condensation相应地，任何压力的升高或能量的减少都会导致气体的液化（冷凝）Afluidthatinliquidstateandmarginallyawayfromthedomebyvirtueofexcessivepressureissaidtobesub-cooled.Suchaliquidhascapacityabsorbheatand/orlosepressureandstillnotbegintovaporizeorboil液态的流体在增压会形成过冷。它在吸热并/或降压的情况下并不汽化或沸腾。Saturation饱和IncreasingTemperature增压IncreasingPressureRequiredtoKeepMoleculesfrombeingLiberated(Boiling)沸腾IncreasingDensity密度增加IncreasingHeatEnergy能量增加Sub-Cooled过冷Equilibrium平衡Boiling沸腾StorestheLiquid,keepingitcold液体存贮及保温Heattransfersslowlyintothestoredliquid热量会缓慢传导给液体Liquidnearthewallheatsupbeforetheinternalliquid靠近筒壁的液体首先升温Thereduceddensitycausetheliquidtomigratetothetopoftheliquid,separatinganddistributingtheheatunevenly升温后的液体密度降低,向上移动,导致了热量传递的不均匀Thesamehappensinthevaporsideofthetank罐的气相存在同样现象Thisunevendistributionoftheheatcreatessubcoolontheliquidandiscalledstratification热量的不均匀分布导致液体的过冷,称做分层Tostratify,thereneedstobeisolationbetweenthetemperatures.Horizontaltankswillstratifylessthanverticaltanks.Smalltankslessthanlargeones.Tanksinmotionwillnotstratifyatall.分层的形成需要温度的不均匀不分布.卧罐分层少于立罐;罐体积越大分层越明显;移动罐不分层AllowsforRefilling重新充装Asthetankislikelyattachedtoausedevice,interruptingtheuseofatankforfillingisundesirable,thereisaneedtomaintaintankpressurewhilerefilling罐总在使用当中,为了充装打断使用是不可接受的.因此充装时需要维持罐内压力Introductionofliquidtothetankwillcausethevaporinthetoptobecompressed.Thiswillraisethepressure充液时顶部液体汽化导致空间压缩、压力上升Introductionofliquidintothewarm,stratified,vaporspacewilltendtoremoveheatfromthevaporandinturncauseittocondense.Thiswillreducethepressureinthetank把液体注入暖的、分层的气相空间将导致气体的热量传到液体使之凝结。这将使罐的压力降低。Havingbothatopandbottomfillvalvesallowforthetanktobeconnectedtoauseapplicationandbefilledwithoutinterruption.Thefillingoperatorwillmanipulatethetopandbottomfillvalvewhilemonitoringthetankpressure.顶充和底充同时使用使得充装时不用停止罐的使用。操作者可以监控压力，选择使用顶充或底充。MaintainsPressure压力保持Inordertoincreasepressure,tanksareconfiguredwithapressurebuilding,orPB,circuit.贮罐配置PB来实现升压Theforceoftheweightofliquidisallowedtodriveliquidoutofthetankandthroughanambientairheatexchanger.液体自身的重量使液体流入热交换器Theliquidfirstabsorbsheatuntilitissaturatedatthetankpressure液体首先在贮罐压力下吸热至饱和Continuedheatingbeginstoboiltheliquid继续吸热至沸腾Someadditionalheatingofthevaporwilloccurbeforethegasisreturnedtothetopofthetank.气体回到罐内前将继续吸收一部分热量Themoreeasilythetankisstratified,themoreeffectivethePBsystemwillwork.Verticaltankshavetheadvantageofincreaseliquidhead(push)andmoreadvantageousdistributionofheat液体分层越容易，PB效率越高Somevapormaybereducedinvolumeonceitenterstheconfinesofthecoldtank进入冷罐后部分蒸汽的体积会变小.PBCircuit增压回路ThePBcircuitisintendedtoreplacethevolumeofliquidremovedwithgasatthesamepressure增压循环的目的是在同压下用气体取代减少的液体Onlyliquidheadisavailabletodrivethemassthroughthecircuit只有液柱压力能够驱动循环Liquidsideregulatorsdeliverhighercapacitiesbuttendtoovershootonrecovery液相调压阀能够提供更多的液体给气相空间以补足失去的液体AllowsforLevelMeasurement液位测量ThesamepressurethatdrivesthePBalsoisusedtodriveadifferentialpressuregaugeforestimatingthelevelinthetank.驱动增压的压力同样能够驱动差压式压力计显示贮罐内的液位Thegaugewillshowthelevelbetweenthesurfaceinthetankandthesurfaceofliquidintheliquidphaseline.Thisapproximatesthelevelinthetank表头能够显示罐内液面和液相管内液面之间的差值，近似于罐内的差值。AllowsforLevelMeasurement液位测量Abruptchangesinpressurewilleitherexpandorcompressthevaporportionoftheliquidphaseline.ThiswillinturnmaketheDifferentialpressuregaugevary.突然的压力变化将会导致液相管内蒸汽的膨胀或压缩，这将导致差压式压力表的变化Overtime,heatleakintotheliquidphaselinewillreturnthegaugetoanormalindication.Thishowevermaytakeseveralhours.Pressurechangesthatoccuroverminutescanresultinmisleadingindications.随着时间的变化，进入液相管的热量将使得表头回到正常的指示。然后需要也许几个小时，压力变化将很快导致不正确的指示Asimilarissuecanoccuriftheequalizationvalveisleftopenforaperiodoftime.Theequalizationvalveshouldonlybeopenedaftertheisolationvalvesareclosed当平衡阀打开时，类似情况也会出现。只有隔离阀关闭时才能打开平衡阀AllowsforWithdrawalLiquidApplications液体使用Asliquidiswithdrawn,thevaporinthetopofthetankwillexpandtoaccommodatethemissingliquidvolume.取液时，罐顶蒸汽将膨胀以充填液相空间Ifthiscontinuesuntilthepressuredropstothesaturationpressureoftheliquid,theliquidwillbegintoboil.压力将一直降低到液体的饱和压力，液体开始沸腾Liquidapplicationsthataredrivenbycryogenicpumpsareaspecialcase.Inefficienciesinpumpswilladdheattoandreducethepressureontheliquidthatisinthepump.Suchheatwillboiltheliquidinthepumpcausingthepumptostopworking.Excessiveboiling,orcavitation,inthepumpcancauseseveredamagetothepump.Maintainingsomesub-coolontheliquidisimportantforpumpperformance.Theliquidmusthavecapacitytoabsorbsomepressuredropandheatadditionwithoutboiling.用低温泵驱动的液体使用情况有所不同，泵做功会把热量带到泵里的液体使之压力降低。这些热量将会使液体沸腾并使泵停止工作。过度的沸腾或者气穴使泵损坏，保持一定的过冷对泵有利。液体应该有一定的吸纳压降和热量而不导致沸腾的能力。Tomaintainsub-cool,aPBsystemisemployed.TheamountofflowthroughhePBisverysmall.TheliquidthroughthePBisexpandedfromtheliquiddensitytothevapordensity.TypicallythePBflowrateonlyneedstobeabout5%oftheliquidflowratefromthetank.使用增压系统以维持过冷。通过增压系统的流量极小，它从液体膨胀为气体。一般而言通过增压系统的流量仅为液体使用流量的5%Athermo-Siphontankmaintainssub-coolattheinletofthepumpbycontinuouslyflowingcoldliquidfromthebottomofthetankacrossthepumpinletandbacktothebottomofthetank.Thisflowisinducedbytheinefficiencyheatofthepump.Astheheatwarmsthecoldliquid,itsdensityisreduced.Thisdifferenceindensitycreatesasmallpressuredifferenceandaconvectiveflow.Aslongastheconvectiveflowexceedsthepumpspeed,thetankswillkeepasmallamountofsubcoolontheliquidfromtheliquidheadofthetank.Ifthepumpspeedgreatlyexceedsthisconvectiveflow,aPBsystemmayneedtobeemployed.热虹吸罐通过不断地从罐底部抽取冷的液体通过泵入口并回到罐的底部来维持泵入口的过冷。泵的做功产生热量使流量降低。热量使冷的液体加热导致了液体密度的降低，密度的差异造成了极小的压力差异和对流。由于这一对流速度大于泵的速度，罐将保持液体一定的过冷度。如果泵速大于过渡，则需要使用增压系统。AllowsforWithdrawalLiquidApplications液体使用AllowsforWithdrawal

Gasapplications气体使用Gasapplicationsarethosewherethecustomerisgoingtousetheproductingaseousform.Thismeansthatthecryogenisgoingtobevaporizedtoagasbeforeitreachestheapplication.气体使用用于客户要求使用气态产品的场合，这意味着在使用前深冷液体应该已经蒸发成气体。Theliquidwithdrawnneedstohaveitsvolumereplacedasintheliquidwithdrawal,orthepressurewilldropandpotentiallydisrupttheenduser.提液后突出部分应被填充，或意味着压力将会降低并影响最终使用。Althoughmaintainingsub-coolisnotcritical,maintainingpressurefortheenduseapplicationis.HereagainthePBisusedtomaintainpressure.尽管维持过冷并不重要，但维持一定的压力以确保最终应用很重要。需要用增压系统来维持压力。.Agasuseapplicationalsoallowsustowithdrawfromthevaporphaseofthetankifdesired.如果有需要，同样可能从气相空间来提取气体供使用。Doingsocreatestheopportunitytoquicklycorrectanyover-pressureissuesinthetank.如此，将有机会快速纠正罐内的过高压力。Thiscircuit,calledandeconomizercircuit,iscontrolledbyaregulatorthatopensataprescribedpointtypicallyabovethePBsetpoint.这一循环被称为经济回路，它由一个在设定压力高于增压开启压力的调压阀控制。Vaporisdriventhroughthecircuitbytheliquidheadgeneratedinadiptubethatrunsthelengthofthetank.蒸汽由液柱静压力驱动通过回路，此回路为一根与罐体高度相同的下行的管路Whenopen,amixtureofliquidfromthebottomandvaporfromthetopisdrawnintothefinalvaporizerandtothecustomer.Sincetheyareusinggasphaseproduct,suchamixtureisofnoconsequencetothecustomer.当回路开启时，从底部的液体和顶部的气体混后后进入汽化器并供给用户。由于客户最终使用的是气体，因此气液混合物对用户没有影响。AllowsforWithdrawal

Gasapplications气体使用Gas-Use/PB气体使用/增压

Gas-Use/Economizing气体使用/经济回路P.B.Regulator增压调压阀EconomizerRegulator经济阀VaporizerDesign汽化器Vaporizersshouldbedesignedtoconsidericingeffectonefficiencies汽化器设计考虑结冰对效率的影响Excessivegasvelocitiescancreateentrainmentthatwilldecreaseexitgastemperatures过高气体流速引起的夹带会降低气体温度Exitgastemperaturescanonly“approach”ambient.(typically20degreeFisused)气体温度最高接近环境温度Protectsitselffromoverpressurization过压保护Asliquidabsorbsheat,itexpands.Ifthereisnoroomforsuchexpansion,thepressurewillrisequicklyinatank.液体吸热后会膨胀，如果没有可膨胀的空间，压力会急剧上升。Thetankshavereliefvalvesthatwillopeninsuchaninstance.Sincethevolumetricflowrateofthereliefvalveismanytimelargerthanthevolumetricgrowthrate,thepressurewillquicklycorrectitself.Indoingso,therewillbeliquiddischargefromthereliefvalve.Thisisundesirablesinceithardonthelifeofthevalve,itejectscryogenictemperaturefromthetankandthevalvemaybemorelikelytostickopen.在此情况下，贮罐的安全阀会打开。由于安全阀泄放量远大于压力上升速率，压