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VariationofpropertiesinthedensephaseregionPart1PureCompounds

Inthistipofthemonth(TOTM)wewilldescribethedensephaseofapurecompound,whatitis,andhowitimpactsprocesses.Wewillillustratehowthermophysicalpropertieschangeinthedensephaseaswellasintheneighboringphases.Theapplicationofdensephaseintheoilandgasindustrywillbediscussedbriefly.InnextmonthTOTM,wewilldiscussthedensephasebehaviorofmulticomponentsystems.

Whenapurecompound,ingaseousorliquidstate,isheatedandcompressedabovethecriticaltemperatureandpressure,itbecomesadense,highlycompressiblefluidthatdemonstratespropertiesofbothliquidandgas.Forapurecompound,abovecriticalpressureandcriticaltemperature,thesystemisoftentimesreferredtoasadensefluidorsupercriticalfluidtodistinguishitfromnormalvaporandliquid(seeFigure1forcarbondioxide).Densephaseisafourth(Solid,Liquid,Gas,Dense)phasethatcannotbedescribedbythesenses.Thewordfluidreferstoanythingthatwillflowandappliesequallywelltogasandliquid.Purecompoundsinthedensephaseorsupercriticalfluidstatenormallyhavebetterdissolvingabilitythandothesamesubstancesintheliquidstate.Thedensephasehasaviscositysimilartothatofagas,butadensityclosertothatofaliquid.Becauseofitsuniqueproperties,densephasehasbecomeattractivefortransportationofnaturalgas,enhancedoilrecovery,foodprocessingandpharmaceuticalprocessingproducts.

Thelowviscosityofdensephase,supercriticalcarbondioxide(comparedwithfamiliarliquidsolvents),makesitattractiveforenhancedoilrecovery(EOR)sinceitcanpenetratethroughporousmedia(reservoirformation).Ascarbondioxidedissolvesinoil,itreducesviscosityandoilwaterinterfacialtension,swellstheoilandcanprovidehighlyefficientdisplacementifmiscibilityisachieved.Additionally,substancesdispersethroughoutthedensephaserapidly,duetohighdiffusioncoefficients.Carbondioxideisofparticularinterestindensefluidtechnologybecauseitisinexpensive,nonflammable,nontoxic,andodorless.Pipelineshavebeenbuilttotransportnaturalgasinthedensephaseregionduetoitshigherdensity,andthisalsoprovidestheaddedbenefitofnoliquidsformationinthepipeline.

Inthefollowingsectionwewillillustratethevariationofthermophysicalpropertiesinthedensephaseanditsneighboringphases.MethanepropertieshavebeencalculatedwithHYSYSsoftwareforaseriesoftemperaturesandpressures.Table1presents,thepressuresandtemperaturesandtheirpathsusedinthisstudy.

ThecalculatedthermophysicalpropertiesareplottedasafunctionofpressureandtemperatureinFigures2to9.Thethermophysicalpropertyisshownonthelefthandsideyaxis,temperatureonthexaxisandpressureontherighthandsideyaxis.

Table1.PressureTemperaturecombinationandthepathschosenformethane

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Density:

Figure2presentsthevariationofdensityindifferentphasesasafunctionofpressureandtemperature.IntheisobaricsubcoolingpathofAB,liquiddensityincreasesgradually.However,intheisothermalcompressionofBCpath,asmallincreaseofdensityisobserved.IntheisobaricCDpath,compressedliquiddensitydecreasesgraduallyastemperatureisincreasedwellintothedensephaseregion.However,asthetemperatureincreasesfurtherinthedensephase,densityreductionisaccelerated.ReductionofdensityisfurtheracceleratedduringisothermalexpansionofDE.IsobariccoolingofvaporalongEFpathcorrespondswithagradualincreaseindensity.Itcanbenotedthevaluesofdensephasedensityareclosetotheliquidphasedensityinsomeareasofthedensephaseregion,andisoverallsignificantlyhigherthanthevaporphasedensities.

Viscosity:

Figure3presentsthevariationofviscosityindifferentphasesasafunctionofpressureandtemperature.IntheisobaricsubcoolingpathofAB,liquidviscosityincreasesrapidly.However,intheisothermalcompressionofBCpath,averysmallchangeofviscosityisobserved.IntheisobaricCDpath,compressedliquidviscositydecreaseslinearlyandsharplyastemperatureisincreasedwellintothedensephaseregion.Asthetemperatureincreasesfurtherinthedensephase,viscosityreductionbecomesgradualandapproachesthegasphasevalues.ReductionofviscosityisquitesmallduringisothermalexpansionofDE.IsobariccoolingofvaporalongEFpathcorrespondswithnoappreciablechangeinviscosity.

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CompressibilityFactor:

Ingeneral,thecompressibilityfactorZ,calculatedbyanequationofstateisnotaccuratefortheliquidphase.Therefore,Figure4whichpresentscompressibilityfactorasafunctionofpressureandtemperatureshouldbeconsideredforqualitativestudyonly.IntheisobaricsubcoolingpathofAB,Zremainsalmostconstant.However,intheisothermalcompressionofBCpath,Zincreasesdrastically.IntheisobaricCDpath,Zincreasesgraduallyastemperatureisincreasedwellintothedensephaseregion.Asthetemperatureincreasesfurtherinthedensephase,theincreaseinZisaccelerated.TheincreaseinZisfurtheracceleratedduringisothermalexpansionofDE.IsobariccoolingofvaporalongFFpathcorrespondswithagradualdecreaseinZ.

SurfaceTension:

Figure5showsthatintheliquidphase,surfacetensionisastrongfunctionoftemperaturebutindependentofpressure.Abovethecriticaltemperature,surfacetensionisnotapplicableanditsvalueiszero.

HeatCapacity:

Generally,heatcapacityisapplicableinasinglephaseregionandshouldnotbeusedwhenthereisaphasechange.Figure6presentsthevariationofdensityindifferentphasesasafunctionofpressureandtemperature.IntheisobaricsubcoolingpathofAB,liquidheatcapacitydecreases.IntheisothermalcompressionofBCpath,asmalldecreaseofheatcapacityisobserved.IntheisobaricCDpath,compressedliquidheatcapacityincreasesgraduallyastemperatureisincreasedwellintothedensephaseregion.Asthetemperatureincreasesfurtherinthedensephase,heatcapacityreachesamaximumvalueandthenstartstodecrease.Thisisstrangebehaviorandsurprisinglyhighvaluesarecalculated.SimilarresultswereobtainedusingProMaxsoftware.ReductionofheatcapacityisfurthernoticedduringisothermalexpansionofDE.IsobariccoolingofvaporalongEFpathcorrespondswithagradualincreaseinheatcapacity.

ThermalConductivity:

Figure7presentsthevariationofthermalconductivityindifferentphasesasafunctionofpressureandtemperature.IntheisobaricsubcoolingpathofAB,liquidthermalconductivityincreases.IntheisothermalcompressionofBCpath,nochangeisobserved.IntheisobaricCDpath,compressedliquidthermalconductivitydecreasesgraduallyastemperatureisincreasedwellintothedensephaseregion.However,asthetemperatureincreasesfurtherinthedensephase,thermalconductivityreductionisaccelerated.ReductionofthermalconductivityisfurthernoticedduringisothermalexpansionofDE.IsobariccoolingofvaporalongEFpathcorrespondswithasmalldecreaseinthermalconductivity.

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7/21/2015 VariationofpropertiesinthedensephaseregionPart1PureCompounds|CampbellTipoftheMonth

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EnthalpyandEntropy:

Figures8and9presentthevariationofenthalpyandentropyindifferentphasesasafunctionofpressureandtemperature.Asshowninthesefigures,theirqualitativevariationsaresimilar.IntheisobaricsubcoolingpathofAB,liquidenthalpyandentropydecrease.IntheisothermalcompressionofBCpath,nochangeisobserved.DuringtheisobaricCDpath,compressedliquidenthalpyandentropyvaluesincreasegraduallyastemperatureisincreasedwellintothedensephaseregion.However,asthetemperatureincreasesfurtherinthedensephase,theenthalpyandentropyincreasebecomeslarger.TheincreaseinenthalpyandentropyisfurthernoticedduringisothermalexpansionofDE.IsobariccoolingofvaporalongEFpathcorrespondswithadecreaseinenthalpyandentropy.

Conclusions:

Densephasebehaviorisuniqueandhasspecialfeatures.Thethermophysicalpropertiesinthisphasemayvaryabnormally.Careshouldbetakenwhenequationsofstateareusedtopredictthermophysicalpropertiesindensephase.Evaluationofequationsofstateshouldbeperformedinadvancetoassuretheiraccuracyinthisregion.Manysimulatorsoffertheoptiontouseliquidbasedalgorithms(e.g.COSTALD)forthisregion.AsshowninFigure1,thereisagradualchangeofphasetransitionfromgastodenseanddensetoliquidphasesorviceversa.Densephaseisahighlycompressiblefluidthatdemonstratespropertiesofbothliquidandgas.Thedensephasehasaviscositysimilartothatofagas,butadensityclosertothatofaliquid.Thisisafavorableconditionfortransportingnaturalgasindensephaseaswellascarbondioxideinjectionintocrudeoilreservoirforenhancedoilrecovery.

Tolearnmoreaboutsimilarcasesandhowtominimizeoperationalproblems,wesuggestattendingourG40(Process/FacilityFundamentals),G4(GasConditioningandProcessing),PF81(CO2SurfaceFacilities),andPF4(OilProductionandProcessingFacilities)courses.

JohnM.CampbellConsulting(JMCC)offersconsultingexpertiseonthissubjectandmanyothers.FormoreinformationabouttheservicesJMCCprovides,visitourwebsiteatwww.jmcampbellconsulting.com,oremailyourconsultingneedstoconsulting@jmcampbell.com.

By:MarkBothamleyandMahmoodMoshfeghian

Reference:

1. ASPENone,EngineeringSuite,HYSYSVersion2006,AspenTechnology,Inc.,Cambridge,MassachusettsU.S.A.,2006.

7/21/2015 VariationofpropertiesinthedensephaseregionPart1PureCompounds|CampbellTipoftheMonth

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WrittenbyDr.MahmoodMoshfeghian

Dr.MahmoodMoshfeghianisaninstructorandconsultantwithJohnMCampbellandCompany(JMC).HeistheauthorofmostofCampbellTipsoftheMonthanddevelopstechnicalsoftwareforJMC.Hehas35yearsteachingexperienceinuniversities(OklahomaStateUniversity,UniversityofShiraz,UniversityofSydneyandUniversityofQatar)aswellasforoilandgasindustries.Dr.MoshfeghianjoinedJMCin1990asaparttimeconsultantandthenasfulltimeinstructor/consultantin2005.PrevioustojoiningJMC,Dr.MoshfeghianwasaSeniorResearchScientistatKuwaitInstituteforScientificResearchandProfessorofChemicalEngineeringatShirazUniversity.Dr.MoshfeghianisaseniormemberofAIChEandhaspublishednumeroustechnicalpapersonthermodynamicproperties,andProcessEngineering.Dr.Moshfeghianhaspresentedinvitedpapersininternationalconferences.HeholdsaB.S.,anM.S.andaPh.D.inChemicalEngineering,allfromOklahomaStateUniversity.

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1. TransportationofCO2inDensePhase|CampbellTipoftheMonthsays:January3,2012at8:35am

[]fluidtodistinguishitfromnormalvaporandliquid(seeFigure1forcarbondioxideinDecember2009TOTM[1]).Densephaseisafourth(Solid,Liquid,Gas,Dense)phasethatcannotbedescribedbythe[]

Reply2. TransportedelCO2enlaFaseDensa|CampbellTipoftheMonthSpanishsays:

January11,2012at2:57pm

[]M.,VariationofpropertiesinthedensephaseregionPart1Purecompounds,http://www.jmcampbell.com/tipofthemonth/2009/12/variationofpropertiesinthedensephaseregion,December[]

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Reply3. NonIsothermalTransportationofCO2intheDensePhase|CampbellTipoftheMonthsays:

February1,2012at6:01am

[]fluidtodistinguishitfromnormalvaporandliquid(seeFigure1forcarbondioxideinDecember2009TOTM[]

Reply4. TransporteNoIsotrmicodelCO2enlaFaseDensa|CampbellTipoftheMonthSpanishsays:

February8,2012at12:05pm

[]Parauncompuestopuro,porencimadelapresinytemperaturacrtica,selerefierealsistemaconfrecuenciacomounodefasedensa,ofluidosupercrticoparadiferenciarlodeunvaporolquidonormal(vaselaFigura1paraeldixidodecarbonoenelPDMdeDiciembre2009[1]).[]

Reply5. EffectofNitrogenImpuritiesonCO2DensePhaseTransportation|CampbellTipoftheMonthsays:

March1,2012at8:30am

[]fluidtodistinguishitfromnormalvaporandliquid(seeFigure1forcarbondioxideinDecember2009TOTM[]

Reply6. EffectofNitrogenImpuritiesonCO2DensePhaseTransportation|CampbellTipoftheMonthSpanish

says:March12,2012at2:27pm

[]M.,VariationofpropertiesinthedesephaseregionPart1Purecompounds,TOTM,http://www.jmcampbell.com/tipofthemonth/2009/12/variationofpropertiesinthedensephaseregion,Dec[]

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June22,2012at6:10am

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Reply8. TransportationofNaturalGasinDensePhase|CampbellTipoftheMonthsays:

October23,2012at8:14am

[]orsupercriticalfluidtodistinguishitfromnormalvaporandliquid(seeFigure1inDecember2009TipOfTheMont(TOTM)[1]forcarbondioxideandinJanuary2010TOTM[2]foratypicalnaturalgas).Densephaseisa[]

Reply9. TransportationofEthanebyPipelineintheDensePhase|CampbellTipoftheMonthsays:

March1,2014at11:12am

[]fluidtodistinguishitfromnormalvaporandliquid(seeFigure1forcarbondioxideinDecember2009TOTM[]

Reply10. TransportedelEtanoporGasoductoenlaFaseDensa|CampbellTipoftheMonthSpanishsays:

March2,2014at1:22pm

[]M.,VariationofpropertiesinthedesephaseregionPart1Purecompounds,TOTM,http://www.jmcampbell.com/tipofthemonth/2009/12/variationofpropertiesinthedensephaseregion,Dec[]

Reply11. retenciondeliquidoscausasyremediossays:

July13,2014at10:35am

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Reply12. RosarioBolmansays:

November17,2014at4:14am

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Reply13.MuhammadShehreyarKhansays:

January15,2015at4:10am

Infirst&2nddiagramsAB&CDarereferredasisobaricprocessesalthoughpressureseemstochangefromapprox4.4MPa(g)to5.4MPa(g)incaseofAB(asindicatedbyblackline).

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