CCS论文.docx
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CCS论文.docx
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CCS论文
InfluenceofMethaneinCO2TransportandStorageforCCSTechnology
Sunchenchen
(HuazhongUniversityofScienceandtechnology,Schoolofenergyandpowerengineering,HubeiwuhanM201270930)
abstract:
CO2CaptureandStorage(CCS)isagoodstrategytomitigatelevelsofatmosphericgreenhousegases.ThetypeandquantityofimpuritiesinfluencethepropertiesandbehavioroftheanthropogenicCO2,andsomustbeconsideredinthedesignandoperationofCCStechnologyfacilities.TheirstudyisnecessaryforCO2transportandstorage,andtodeveloptheoreticalmodelsforspecificengineeringapplicationstoCCStechnology.InthisworkwedeterminedtheinfluenceofCH4,animportantimpurityofanthropogenicCO2,withindifferentstepsofCCStechnology:
transport,injection,andgeologicalstorage.Forthis,weobtainednewpressure–density–temperature(PρT)andvapor–liquidequilibrium(VLE)experimentaldataforsixCO2+CH4mixturesatcompositionswhichrepresentemissionsfromthemainsourcesintheEuropeanUnionandUnitedStates.ThePandTrangesstudiedarewithinthoseestimatedforCO2pipelinesandgeologicalstoragesites.Fromthesedataweevaluatedtheminimalpressuresfortransport,regardingthedensityandpipeline’scapacityrequirements,andvaluesforthesolubilityparameterofthemixtures,afactorwhichgovernsthesolubilityofsubstancespresentinthereservoirbeforeinjection.WeconcludedthatthepresenceofCH4reducesthestoragecapacityandincreasesthebuoyancyoftheCO2plume,whichdiminishestheefficiencyofsolubilityandresidualtrappingofCO2,andreducestheinjectivityintogeologicalformations.
1、Introduction
CarbonDioxideCaptureandStorage(CCS)isoneofseveraleffectivestrategies(alongwithenergyefficiency,fuelswitching,anduseofrenewableenergysources)toreducegreenhousegas(GHG)levelsintheatmosphereinthemediumterm.(1-3)
CCSisusuallyconsideredasaprocessconsistingoffourmainseparatesteps:
CO2capture,CO2conditioning,CO2transport,andCO2injectionandstorage.
CO2capturecanbeperformedbydifferenttechniques(postcombustion,precombustiondecarbonization,andoxyfuelcombustion)andconditionedviadehydration,noncondensablegasseparationand/orliquefaction,andcompression/pumping.(4-8)EventhoughthisworkisnotdevotedtoCO2conditioningandcapture,thetechnologiesusedwilldeterminethecompositionofthegastobehandled.ItisalsoimportanttotakeintoaccountthatitseemsthatCO2purificationaftercapturewillbeveryexpensive.Thus,formanyoftheseparationtechnologiestheexpenseofpurificationgreatlyincreasesforahigherdegreeofpurityofgaseousmixture,(6)therefore,itisessentialthestudyofCO2behaviorwithdifferentimpurities.(9)Ontheotherhand,qualityspecificationsfortransportarenotcurrentlystated.Theelaborationofthecorrespondingregulationswillrequirestudyingtheinfluenceofimpuritiesonthethermodynamicpropertiesofthetransportedandstoredfluidaswell.Thisispreciselytheaimofourcurrentstudy.
Forover30yearsnow,andwithinthecontextofEOR(enhancedoilrecovery)andEGR(enhancedgasrecovery),long-distanceCO2transportandinjectiontechnologieshavebeendeveloped.Nevertheless,therearesomeimportantdifferencesbetweenthesetechnologiesandCCSsinceCO2capturedfrompowerstationsandindustrialsourcesmaycontaindifferentproportionsand/ortypesofimpuritiesfromthosefoundinthesourcesofCO2usuallyusedinEORandEGR.ThedesignandoperationofaCO2+impuritiesmanagingsystemiscomplicated,duetothehighlynonlinearthermodynamicpropertiesofthefluidandbecauseitisnormallytransportedasadense-fluid,foroperationalandeconomicreasons.(10)SincetheKyotoSummit,aninternationalnetworkwithspecificresearchprogrammesdevotedtoCCStechnologyhasbeenestablished.OnesuchschemeistheFP7CooperationWorkProgramme,whichincludesatopicentitled“ImpactoftheQualityofCO2onTransportandStorage”withintheEnergyTheme.(11)
Literatureshowsthatthepresenceandtypeofimpuritiesclearlyinfluencethefluid’spropertiesandbehavior,andasaconsequencethedesignandoperationofCCSfacilities.(12)KnowledgeofthethermodynamicpropertiesoftheCO2+impuritiesmixtures,especiallypressure–volume–temperature–composition(PVTxy)andvapor–liquidequilibrium(VLE),isthereforeessential.Thisinformationwillallowdeterminationofcompositionspecificationsandpurificationrequirements(ifnecessary)ofthefluidinthedifferentstepsofthistechnology,andwillenabledesignofefficient,safe,andeconomicalprocesses.(9)Thesedataarealsonecessarytodevelopreliabletheoreticalmodelsforengineeringapplications,coveringthelargerangeofoperativeconditions(fromatmosphericpressuretosupercriticalstates)ofmulticomponentmixturesinvolvedinCCSprocesses.Manyequationsofstate(EoS),suchasPR,RKS,SAFT,andGERGareavailableforthermodynamiccalculationsofCO2mixtures,butnoneofthemshowanyclearadvantageinCCSapplicationsforthecalculationsofallPVTxyproperties,thusareferenceEoSforCCSshouldbeafuturegoal.(9,13)
ThisisthefirstworkinasystematicstudyonbinarymixturesofCO2andthetypicalimpuritiesfoundinindustrialemissions.Inthisstudywepresentreliableexperimentaldataofpressure–density–temperature,PρT,andVLE,propertiesformixturesofCO2andCH4atthecompositions,P,andTrangesofinterestforthetransportandthestorageintheCCStechnologies.CO2andCH4aretwoofthesixGHGsthathavebeentargetedbytheinternationalcommunityascausingglobalwarming,beingtheenvironmentalimpactofmethaneemissions21timesgreaterthanthatofcarbondioxide.
(1)OurexperimentaldatawerecomparedwiththosepredictedbyGERGEoSwhichis,amongtheabove-mentioned,themostrecommendedbytheNISTforCO2+CH4mixturesandthemostusedforpetroleumfluidsandnaturalgas.(14)
FromthePρTexperimentalvaluesofCO2+CH4mixtures,weevaluatedtheeffectofimpuritiesonseveralparametersrelatedtotransport,injection,andstoragesuchastheminimalpressurefortransport,thesolubilityparameter,thenormalizedstoragecapacityofthereservoir,thenormalizedrisingvelocityoftheCO2plume,andthenormalizedpermeationflux.
2、ExperimentalSection
Materials
Carbondioxide(wt%>99.998)andmethane(wt%>99.995)wereobtainedfromAirLiquide.
InSpain,compositionsoftheemissionsfromdifferentindustriesarecharacterizedandrecordedbytheRegistroEstataldeEmisionesyFuentesContaminantes(PRTREspaña).(15)Thehighestcontentofmethane(wt%CH4≈6.0%)isfoundinemissionsfromwastemanagement(7%ofthetotalofCO2emittedinSpainin2010).Inadditiontothis,wt%CH4variesfrom≈1.0%forfarmingandlivestockemissionsto≈0.36%forotherindustriessuchasceramicsproduction.(15)Havingtakenthesefiguresintoaccount,wechosesixcompositionsrangingfrom0.14%to5.93%inwt%ofCH4allowingustostudyrepresentativeindustrialemissionsinSpain.InthiscompositionrangethepercentagesofmethanefromemissionsofthemainsourcesofanthropogenicCO2intheEUandtheU.S.(16-19)areincluded.ThetotalemissionsinSpain,EU,andU.S.containwt%ofCH4of0.15%,0.65%,and0.55%,respectively.Themixtureswerepreparedbysuccessiveweightingofthecomponentsinavariablevolumecellwithaprecisionof0.0002g.
ApparatusandProcedures
TheexperimentalsetupusedinthisworkforthedeterminationofPρTdataofCO2+CH4mixturesisthesameasthatdescribedinapreviousstudy.(20)Itwasdesignedforfast,reliable,andaccurategenerationofPρTdata.Theirquasi-continuousdataacquisitionalongsubcritical,critical,andsupercriticalregions(6000points/isothermevenlyreducedtoabout1000points/isothermforeasierhandling)allowstheaccuratedeterminationofthelimitsofVLEandthecalculationofderivedpropertiesfromtheexperimentaldata.
Theprecisionandaccuracyindensityresultsformixturesweredeterminedinapreviouswork;(20)themeanrelativedeviation,MRD(ρ)=0.7%andmeanstandarddeviation,S̅ρr=0.13%wereobtained.
3、ResultsandDiscussion
Inthisworkwepresent49experimentalPρTisotherms(containingatotalof49 000pointsavailableintheSupportingInformation)forsixCO2 +CH4mixtures(CO2molefraction,xCO2=0.8525,0.9719,0.9809,0.9902,0.9932,and0.9961)fromatmosphericpressureto20MPa,andat253.15,263.15,273.15,283.15,293.15,298.15,308.15,and333.15K.InthecaseofthemixturewithxCO2=0.8525theisothermat304.21K(TcofCO2)ispresentedtoo.PropertiesweremeasuredinPandTrangeswhicharewithintheestimatedpressuresandtemperaturesinCO2pipelines(7.5–20MPaand273–303K)(9)andingeologicstoragesitesonthebasisofageothermicgradient(21)of25K/kmandanaveragegradientofhydrostaticpressureof10MPa/km.
FromthesePρTexperimentaldataweobtainedthedewandbubblepressures,PdewandPbubble,andthedensitiesofthephasesinequilibrium(ρsat)foreachmixtureatthecorrespondingsubcriticaltemperatures,aswellasthederivativepropertiesαP(isobaricthermalexpansivity),κT(isothermalcompressibility),andπ(internalpressure).Besides,weevaluatedtheminimalpressuresfortransport,regardingthedensityandpipeline’scapacityrequirements,andtheeffectofimpuritiesonthesolubilityparameter,δ.ThisparameterwillgoverntheinteractionsbetweentheinjectedCO2andthesubstancespreviouslypresentinthereservoir,suchasmethaneitselfamongothers.Last,wecalculated,usingourexperimentaldata,valuesforotherparametersrelatedtostoragesuc
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