深冷液體存貯與輸送的實現

CryogenicStorageandDelivery

WhyitWorks

深冷液體存貯與輸送的實現

Jan.5th,2012CHTRAMAT-EN-003(2012)Overview概述Gassesarestoredasliquidforseveralreasons氣體之所以液化存貯Higherstoragedensity高存貯密度EasierDeliverylogistics容易輸送EasierPumping易泵輸送Useoftherefrigerationcontent制冷技術的使用WhatastorageTanksDoes貯罐可以做到StorestheLiquid,keepingitcold.貯存液體,使其保持低溫AllowsforRefilling可重新充裝MaintainsPressure保持壓力AllowsforLevelMeasurement保持液位AllowsforWithdrawal使用Gasapplications氣體使用LiquidApplications液體使用Protectsitselffromoverpressurization.防止罐體超壓UnderstandingaLiquefiedGas理解液化氣體Importantfluidpropertiesinclude重要的液體參數包括Pressure壓力Temperature溫度Density密度Energy能量Therelationshipbetweenthesepropertiesisfixedforafluid.Knowinganytwoallowsustopredicttherest.對任一液體而言,這些參數之間的關系是確定的,任何兩個已知的參數都可以推導出其他的參數.Theleastintuitive,butmostinfluentialistheenergyofthefluid.最直接也是最有影響的參數是能量.UnderstandingtheInfluenceofenergyonthefluidiscriticaltounderstandwhycryogenicsystemsworkthewaytheydo.理解液體能量有助于理解深冷系統(tǒng)工作的原理Thermodynamicsisthestudyofhowenergyaffectsthestateofafluid.此處的熱力學是解釋能量如何影響液體狀態(tài)的學科Energy(heat)willmovefromonebodytothenextifthereisatemperaturedifferencebetweenthem.Thehigherthedifference,thefastertheenergyistransferred.Energyisalsointroducedwhenworkisdoneontheliquid.Anytimetheliquidistransferred,thereisanincreaseintheenergyoftheliquid.兩個物體之間存在溫差時即可產生傳熱.溫差越大,傳熱越快.對液體做功也能產生能量.輸送液體時液體的能量會增加.IntuitiveMaterialProperties物質特性參數Property特性Description描述Units單位ExampleofInfluenceondesign設計相關示例Pressure壓力Force/UnitArea單位面積受力PSI,PSIA,PSIGPa,MpaInnerVesselThickness內容器壁厚OuterVesselThickness外容器壁厚Temperature溫度Responsethatanamountofmaterialhasbasedontheenergyitiscarrying表示物體冷熱程度Fahrenheit,Rankine華氏度Celsius,Kelvin攝氏度MaterialSelection材料選擇Vaporizers汽化器PBCoils自增壓器Density密度Mass/UnitVolume單位體積的質量SpecificVolume=1/Density#/Ft3#/Gal.Kg/literKg/NM^3Heat(Energy)Property能量參數Property特性Description描述Units單位ExampleofInfluenceondesign設計相關示例InternalEnergy內能(U)Energymeasurethatincludesmolecularenergyatconstantvolume.物體在恒定體積下包括分子運動的能量總和dU/dT=CvBTU/lbJ/kgHoldTime壓力保持時間(analysiswherepressurechangeswithinacontrolmass研究在恒定質量下壓力變化)Enthalpy焓(H)Energymeasurethatincludesmolecularenergyandworkenergyatconstantpressure.物體在恒壓下的能量和功的總和dH/dT=CpH=U+PVBTU/lbJ/kgPBCoilsizing自增壓器計算VaporizerSizing汽化器計算NERCalculation蒸發(fā)率計算(analysiswheremasschangeswithinacontrolvolume研究在恒定體積下質量變化)Entropy熵(S)Energymeasurethatisusedtomeasurelostworkpotentialandenergyefficiency.Tds=dU=PdVTds=dH-VdPBTU/lb-RJ/kg-KUsedindesigningefficientliquefactionsystems.Helpfulinevaluatingtheenergyaddedbypumps.Page7名詞解釋Cryogenic深冷Abranch

ofengineeringthatrelatestotheproductionandeffectsofverylowtemperature,usually-230°Fandcolder.Heat

leak熱泄漏Cavitation氣穴PartialorfulllossofpumpprimeduetoinsufficientsubcoolingorNetPositiveSuctionHeadDepressurizationFlashLossVaporizationcausedbyreducingthegasphasepressuretosomethinglessthansaturatedvaporpressureoftheliquid.Page8Condensation冷凝The

conversionofvaporsintoliquidbycoolingthevapors.Equilibrium平衡Astatewheretheliquidandgasphasescoexistathesametemperatureandvaporpressure.Saturation飽和Astatewheretheliquidandgasphasescoexistin

equilibrium.名詞解釋Page9Subcooling過冷度RaisinggasspacepressureabovethenormalvaporpressureofasaturatedliquidcreatingNetPositiveSuctionHead(NPSH).Stratification分層Averticaltemperaturegradientwithcolderproductatthebottomandwarmerproductatthetop.Entrainment霧沫Liquiddropletscarriedalongwithaflowinggasstream.名詞解釋Page10三相點三相點triplepoint是指在熱力學里，可使一種物質三相（氣相，液相，固相）共存的一個溫度和壓力的數值三相共存時具有固定的溫度和壓強氦，是唯一沒有三相點的物質例：水的三相點在0.01℃（273.16K），611.73Pa..\LNGStation\Water_boil.wmv水的蒸發(fā)過程開始水的溫度：78℉（25.5℃）飽和蒸汽壓：3.169x103Pa水開始沸騰：79℉（26.1℃）飽和蒸汽壓：3.3x103PaPage11Page12臨界點臨界點criticalpoint一種熱力學狀態(tài)，此時在最高可能溫度下物質的液態(tài)和氣態(tài)可以平衡共存臨界溫度criticaltemperature物質處于臨界狀態(tài)時的溫度。物質以液態(tài)形式出現的最高溫度。溫度不超過某一數值，對氣體進行加壓，可以使氣體液化，而在該溫度以上，無論加多大壓力都不能使氣體液化，這個溫度叫該氣體的臨界溫度。在臨界溫度下，使氣體液化所必須的最小壓力叫臨界壓力。臨界壓力criticalpressure物質處于臨界狀態(tài)時的壓力（壓強）。在臨界溫度時使氣體液化所需要的最小壓力。液體在臨界溫度時的飽和蒸氣壓。Page13飽和狀態(tài)、飽和蒸氣壓、飽和溫度飽和狀態(tài)saturationcondition液體汽化時，其分子不斷從液體中逸出，同時也有分子從蒸氣中進入液體，當達到同一時間進出液體的分子數相等并平衡時的狀態(tài)。飽和蒸氣壓saturatedvaporpressure

在一定溫度下，與液體或固體處于相平衡的蒸氣所具有的壓力稱為飽和蒸氣壓。同一物質在不同溫度下有不同的蒸氣壓，并隨著溫度的升高而增大。飽和溫度saturationtemperature是指液體和蒸氣處于動態(tài)平衡狀態(tài)即飽和狀態(tài)時所具有的溫度ts。飽和狀態(tài)時，液體和蒸氣的溫度相等。飽和溫度一定時，飽和壓力也一定；反之，飽和壓力一定時，飽和溫度也一定。溫度升高，會在新的溫度下形成新的動態(tài)平衡狀態(tài)。物質的某一飽和溫度必對應于某一飽和壓力。Page14蒸發(fā)、汽化、沸騰和沸點汽化vaporization物質從液態(tài)轉變?yōu)槠麘B(tài)的過程蒸發(fā)evaporation物質從液態(tài)轉化為氣態(tài)的相變過程沸騰boiling在液體表面和內部同時發(fā)生的劇烈汽化現象沸點boilingpoint液體沸騰的溫度蒸發(fā)和沸騰的聯系它們都是液體汽化的方式，即都屬于汽化現象，液體在蒸發(fā)和沸騰的過程中，都需要吸收熱量。..\VCD\Nitrogen_boil.wmvPage15沸點、沸騰和蒸發(fā)蒸發(fā)和沸騰的區(qū)別蒸發(fā)是液體在任何溫度下都能發(fā)生的汽化現象，而沸騰是液體在一定溫度（沸點）下，并繼續(xù)加熱，才能發(fā)生的汽化現象。蒸發(fā)是只在液體表面發(fā)生的緩慢的汽化現象，而沸騰是在液體表面和內部同時發(fā)生的劇烈的汽化現象。蒸發(fā)時液體溫度會下降，而沸騰中液體溫度保持不變（在液體表面上壓強不改變的前提下）。影響蒸發(fā)速度的因素是：液體的表面積，液體的溫度，液體表面附近的空氣流速；影響沸點的因素是：液體表面上的氣壓，液體的純凈程度。影響沸騰速度的因素：液體體積和原先的溫度沸騰時有氣泡產生，而蒸發(fā)時則無氣泡產生。蒸發(fā)的微觀本質為：由于分子的熱運動，使液體表面的分子離開液體，進入空氣中。蒸發(fā)在任何溫度都會進行，只是溫度越高越快，反之越慢。而沸騰必須溫度在沸點，且繼續(xù)吸熱。沸騰的微觀本質為：由于汽化劇烈產生了氣泡，不僅液體表面的分子要離開液體，液體內部氣泡壁上的分子也要離開液體，進入空氣中。沸騰現象中包含了蒸發(fā)現象，但蒸發(fā)現象卻不包括沸騰現象。Page16汽化潛熱汽化潛熱latentheatofvaporization單位質量的液體轉變?yōu)橄嗤瑴囟鹊恼魵鈺r吸收的熱量稱為汽化潛熱，簡稱汽化熱它隨溫度升高而減小，因為在較高溫度下液體分子具有較大能量，液相與氣相差別變小。在臨界溫度下，物質處于臨界態(tài)，氣相與液相差別消失，汽化熱為零。PVT/PETSurface壓力/體積（能量）/溫度Thereisarelationshipbetweenthepropertiesofafluidthatisknownforeachtypeoffluid.Wecandesignequipmentbasedonthisrelationship對任意一種特定流體，其特性之間都存在固定關系，可以利用其進行設備設計Anytwopropertieswilldictatethethird.Thiscreatesathreedimensionalpropertyrelationship任意兩個參數可以確定第三個，以此確定三者函數關系Thephysicalstateofthefluidisbasedonwhereweareonthissurfacerelationship流體的物理狀態(tài)是基于它處于關系函數中的位置Themostcriticalareaofthesurfaceisthevapordome.Inthisregionwedefinethetransitionfromliquidtogas.P-T曲線中關鍵區(qū)域是飽和區(qū)域（飽和液相線及飽和汽相線以下），此區(qū)域內液體汽化為氣體。Abovethedome,thefluidactsinapredictablemannerandfollowsalinearrelationshipbetweenpressureanddensity.曲線以上，流體在壓力和密度之間存在線性關系Pureliquidisessentiallyincompressibleduetopressure,yetitsdensitywillchangewithincreasingenergy純液體是不可壓縮的，但隨著能量的變化它的密度會產生變化。PVT/PETSurface壓力/體積（能量）/溫度Saturation/Equilibrium飽和/平衡Fluidthatisonthedomespaceissaidtobeinequilibriumorsaturated飽和區(qū)內的流體處于飽和或平衡狀態(tài)Asaturatedstateisoftenfurthernotedbythecoincidentcorrespondingpressureortemperaturetothisposition.飽和狀態(tài)下壓力或溫度可以維持不變.WhenSaturatedapressure,anyreductioninpressure,orincreaseinheatwillresultinthefluidchangingfromliquidtovapor.Vaporizationorboiling飽和壓力下，任何壓力的降低或能量的增加都導致液體的汽化（汽化或沸騰）Commensuratelyanyincreaseinpressureorreductioninheatwillresultinthefluidchangingfromvaportoliquid.Condensation相應地，任何壓力的升高或能量的減少都會導致氣體的液化（冷凝）Afluidthatinliquidstateandmarginallyawayfromthedomebyvirtueofexcessivepressureissaidtobesub-cooled.Suchaliquidhascapacityabsorbheatand/orlosepressureandstillnotbegintovaporizeorboil液態(tài)的流體在增壓會形成過冷。它在吸熱并/或降壓的情況下并不汽化或沸騰。Saturation飽和IncreasingTemperature增壓IncreasingPressureRequiredtoKeepMoleculesfrombeingLiberated(Boiling)沸騰IncreasingDensity密度增加IncreasingHeatEnergy能量增加Sub-Cooled過冷Equilibrium平衡Boiling沸騰StorestheLiquid,keepingitcold液體存貯及保溫Heattransfersslowlyintothestoredliquid熱量會緩慢傳導給液體Liquidnearthewallheatsupbeforetheinternalliquid靠近筒壁的液體首先升溫Thereduceddensitycausetheliquidtomigratetothetopoftheliquid,separatinganddistributingtheheatunevenly升溫后的液體密度降低,向上移動,導致了熱量傳遞的不均勻Thesamehappensinthevaporsideofthetank罐的氣相存在同樣現象Thisunevendistributionoftheheatcreatessubcoolontheliquidandiscalledstratification熱量的不均勻分布導致液體的過冷,稱做分層Tostratify,thereneedstobeisolationbetweenthetemperatures.Horizontaltankswillstratifylessthanverticaltanks.Smalltankslessthanlargeones.Tanksinmotionwillnotstratifyatall.分層的形成需要溫度的不均勻不分布.臥罐分層少于立罐;罐體積越大分層越明顯;移動罐不分層AllowsforRefilling重新充裝Asthetankislikelyattachedtoausedevice,interruptingtheuseofatankforfillingisundesirable,thereisaneedtomaintaintankpressurewhilerefilling罐總在使用當中,為了充裝打斷使用是不可接受的.因此充裝時需要維持罐內壓力Introductionofliquidtothetankwillcausethevaporinthetoptobecompressed.Thiswillraisethepressure充液時頂部液體汽化導致空間壓縮、壓力上升Introductionofliquidintothewarm,stratified,vaporspacewilltendtoremoveheatfromthevaporandinturncauseittocondense.Thiswillreducethepressureinthetank把液體注入暖的、分層的氣相空間將導致氣體的熱量傳到液體使之凝結。這將使罐的壓力降低。Havingbothatopandbottomfillvalvesallowforthetanktobeconnectedtoauseapplicationandbefilledwithoutinterruption.Thefillingoperatorwillmanipulatethetopandbottomfillvalvewhilemonitoringthetankpressure.頂充和底充同時使用使得充裝時不用停止罐的使用。操作者可以監(jiān)控壓力，選擇使用頂充或底充。MaintainsPressure壓力保持Inordertoincreasepressure,tanksareconfiguredwithapressurebuilding,orPB,circuit.貯罐配置PB來實現升壓Theforceoftheweightofliquidisallowedtodriveliquidoutofthetankandthroughanambientairheatexchanger.液體自身的重量使液體流入熱交換器Theliquidfirstabsorbsheatuntilitissaturatedatthetankpressure液體首先在貯罐壓力下吸熱至飽和Continuedheatingbeginstoboiltheliquid繼續(xù)吸熱至沸騰Someadditionalheatingofthevaporwilloccurbeforethegasisreturnedtothetopofthetank.氣體回到罐內前將繼續(xù)吸收一部分熱量Themoreeasilythetankisstratified,themoreeffectivethePBsystemwillwork.Verticaltankshavetheadvantageofincreaseliquidhead(push)andmoreadvantageousdistributionofheat液體分層越容易，PB效率越高Somevapormaybereducedinvolumeonceitenterstheconfinesofthecoldtank進入冷罐后部分蒸汽的體積會變小.PBCircuit增壓回路ThePBcircuitisintendedtoreplacethevolumeofliquidremovedwithgasatthesamepressure增壓循環(huán)的目的是在同壓下用氣體取代減少的液體Onlyliquidheadisavailabletodrivethemassthroughthecircuit只有液柱壓力能夠驅動循環(huán)Liquidsideregulatorsdeliverhighercapacitiesbuttendtoovershootonrecovery液相調壓閥能夠提供更多的液體給氣相空間以補足失去的液體AllowsforLevelMeasurement液位測量ThesamepressurethatdrivesthePBalsoisusedtodriveadifferentialpressuregaugeforestimatingthelevelinthetank.驅動增壓的壓力同樣能夠驅動差壓式壓力計顯示貯罐內的液位Thegaugewillshowthelevelbetweenthesurfaceinthetankandthesurfaceofliquidintheliquidphaseline.Thisapproximatesthelevelinthetank表頭能夠顯示罐內液面和液相管內液面之間的差值，近似于罐內的差值。AllowsforLevelMeasurement液位測量Abruptchangesinpressurewilleitherexpandorcompressthevaporportionoftheliquidphaseline.ThiswillinturnmaketheDifferentialpressuregaugevary.突然的壓力變化將會導致液相管內蒸汽的膨脹或壓縮，這將導致差壓式壓力表的變化Overtime,heatleakintotheliquidphaselinewillreturnthegaugetoanormalindication.Thishowevermaytakeseveralhours.Pressurechangesthatoccuroverminutescanresultinmisleadingindications.隨著時間的變化，進入液相管的熱量將使得表頭回到正常的指示。然后需要也許幾個小時，壓力變化將很快導致不正確的指示Asimilarissuecanoccuriftheequalizationvalveisleftopenforaperiodoftime.Theequalizationvalveshouldonlybeopenedaftertheisolationvalvesareclosed當平衡閥打開時，類似情況也會出現。只有隔離閥關閉時才能打開平衡閥AllowsforWithdrawalLiquidApplications液體使用Asliquidiswithdrawn,thevaporinthetopofthetankwillexpandtoaccommodatethemissingliquidvolume.取液時，罐頂蒸汽將膨脹以充填液相空間Ifthiscontinuesuntilthepressuredropstothesaturationpressureoftheliquid,theliquidwillbegintoboil.壓力將一直降低到液體的飽和壓力，液體開始沸騰Liquidapplicationsthataredrivenbycryogenicpumpsareaspecialcase.Inefficienciesinpumpswilladdheattoandreducethepressureontheliquidthatisinthepump.Suchheatwillboiltheliquidinthepumpcausingthepumptostopworking.Excessiveboiling,orcavitation,inthepumpcancauseseveredamagetothepump.Maintainingsomesub-coolontheliquidisimportantforpumpperformance.Theliquidmusthavecapacitytoabsorbsomepressuredropandheatadditionwithoutboiling.用低溫泵驅動的液體使用情況有所不同，泵做功會把熱量帶到泵里的液體使之壓力降低。這些熱量將會使液體沸騰并使泵停止工作。過度的沸騰或者氣穴使泵損壞，保持一定的過冷對泵有利。液體應該有一定的吸納壓降和熱量而不導致沸騰的能力。Tomaintainsub-cool,aPBsystemisemployed.TheamountofflowthroughhePBisverysmall.TheliquidthroughthePBisexpandedfromtheliquiddensitytothevapordensity.TypicallythePBflowrateonlyneedstobeabout5%oftheliquidflowratefromthetank.使用增壓系統(tǒng)以維持過冷。通過增壓系統(tǒng)的流量極小，它從液體膨脹為氣體。一般而言通過增壓系統(tǒng)的流量僅為液體使用流量的5%Athermo-Siphontankmaintainssub-coolattheinletofthepumpbycontinuouslyflowingcoldliquidfromthebottomofthetankacrossthepumpinletandbacktothebottomofthetank.Thisflowisinducedbytheinefficiencyheatofthepump.Astheheatwarmsthecoldliquid,itsdensityisreduced.Thisdifferenceindensitycreatesasmallpressuredifferenceandaconvectiveflow.Aslongastheconvectiveflowexceedsthepumpspeed,thetankswillkeepasmallamountofsubcoolontheliquidfromtheliquidheadofthetank.Ifthepumpspeedgreatlyexceedsthisconvectiveflow,aPBsystemmayneedtobeemployed.熱虹吸罐通過不斷地從罐底部抽取冷的液體通過泵入口并回到罐的底部來維持泵入口的過冷。泵的做功產生熱量使流量降低。熱量使冷的液體加熱導致了液體密度的降低，密度的差異造成了極小的壓力差異和對流。由于這一對流速度大于泵的速度，罐將保持液體一定的過冷度。如果泵速大于過渡，則需要使用增壓系統(tǒng)。AllowsforWithdrawalLiquidApplications液體使用AllowsforWithdrawal

Gasapplications氣體使用Gasapplicationsarethosewherethecustomerisgoingtousetheproductingaseousform.Thismeansthatthecryogenisgoingtobevaporizedtoagasbeforeitreachestheapplication.氣體使用用于客戶要求使用氣態(tài)產品的場合，這意味著在使用前深冷液體應該已經蒸發(fā)成氣體。Theliquidwithdrawnneedstohaveitsvolumereplacedasintheliquidwithdrawal,orthepressurewilldropandpotentiallydisrupttheenduser.提液后突出部分應被填充，或意味著壓力將會降低并影響最終使用。Althoughmaintainingsub-coolisnotcritical,maintainingpressurefortheenduseapplicationis.HereagainthePBisusedtomaintainpressure.盡管維持過冷并不重要，但維持一定的壓力以確保最終應用很重要。需要用增壓系統(tǒng)來維持壓力。.Agasuseapplicationalsoallowsustowithdrawfromthevaporphaseofthetankifdesired.如果有需要，同樣可能從氣相空間來提取氣體供使用。Doingsocreatestheopportunitytoquicklycorrectanyover-pressureissuesinthetank.如此，將有機會快速糾正罐內的過高壓力。Thiscircuit,calledandeconomizercircuit,iscontrolledbyaregulatorthatopensataprescribedpointtypicallyabovethePBsetpoint.這一循環(huán)被稱為經濟回路，它由一個在設定壓力高于增壓開啟壓力的調壓閥控制。Vaporisdriventhroughthecircuitbytheliquidheadgeneratedinadiptubethatrunsthelengthofthetank.蒸汽由液柱靜壓力驅動通過回路，此回路為一根與罐體高度相同的下行的管路Whenopen,amixtureofliquidfromthebottomandvaporfromthetopisdrawnintothefinalvaporizerandtothecustomer.Sincetheyareusinggasphaseproduct,suchamixtureisofnoconsequencetothecustomer.當回路開啟時，從底部的液體和頂部的氣體混后后進入汽化器并供給用戶。由于客戶最終使用的是氣體，因此氣液混合物對用戶沒有影響。AllowsforWithdrawal

Gasapplications氣體使用Gas-Use/PB氣體使用/增壓

Gas-Use/Economizing氣體使用/經濟回路P.B.Regulator增壓調壓閥EconomizerRegulator經濟閥VaporizerDesign汽化器Vaporizersshouldbedesignedtoconsidericingeffectonefficiencies汽化器設計考慮結冰對效率的影響Excessivegasvelocitiescancreateentrainmentthatwilldecreaseexitgastemperatures過高氣體流速引起的夾帶會降低氣體溫度Exitgastemperaturescanonly“approach”ambient.(typically20degreeFisused)氣體溫度最高接近環(huán)境溫度Protectsitselffromoverpressurization過壓保護Asliquidabsorbsheat,itexpands.Ifthereisnoroomforsuchexpansion,thepressurewillrisequicklyinatank.液體吸熱后會膨脹，如果沒有可膨脹的空間，壓力會急劇上升。Thetankshavereliefvalvesthatwillopeninsuchaninstance.Sincethevolumetricflowrateofthereliefvalveismanytimelargerthanthevolumetricgrowthrate,thepressurewillquicklycorrectitself.Indoingso,therewillbeliquiddischargefromthereliefvalve.Thisisundesirablesinceithardonthelifeofthevalve,itejectscryogenictemperaturefromthetankandthevalvemaybemorelikelytostickopen.在此情況下，貯罐的安全閥會打開。由于安全閥泄放量遠大于壓力上升速率，壓