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ThermodynamicAnalysisandOptimization ofGeothermalPowerPlants

ThermodynamicAnalysis andOptimizationof GeothermalPowerPlants

Editedby CanOzgurColpan

MehmetAkifEzan

OnderKizilkan

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Contributors

Numbersinparenthesisindicatethepagesonwhichtheauthors’ contributionsbegin.

Sertaҫ Akar(17) NationalRenewableEnergyLaboratory (NREL),Golden,CO,UnitedStates

OlusolaCharlesAkinsipe(3) SchoolofEngineering&Built Environment,GriffithUniversity,Brisbane,QLD,Australia

PanagiotisAlexopoulos(131) LaboratoryofSoftEnergy ApplicationsandEnvironmentalProtection,Mechanical EngineeringDepartment,UniversityofWestAttica, Athens,Greece

SharjeelAshrafAnsari(249) DepartmentofEngineering Sciences,NationalUniversityofSciencesandTechnology,Islamabad,Pakistan

ChadAugustine(17) NationalRenewableEnergyLaboratory(NREL),Golden,CO,UnitedStates

MuhammadAziz(97) InstituteofIndustrialScience,The UniversityofTokyo,Tokyo,Japan

Young-JinBaik(315) ThermalEnergySystemsLaboratory,KoreaInstituteofEnergyResearch,Daejeon, RepublicofKorea

YusufBas ¸ ogul(113) DepartmentofMechanicalEngineering,EngineeringFaculty,AdıyamanUniversity, Adıyaman,Turkey

RiccardoBasosi(53) CenterforColloidandSurface Science,UniversityofFirenze,SestoFiorentino;R2ES Lab,DepartmentofBiotechnology,Chemistryand Pharmacy,UniversityofSiena,Siena;NationalResearch Council—InstitutefortheChemistryofOrganoMetallic Compounds,SestoFiorentino,Italy

JosephBonafin(43) TurbodenS.p.A.,Brescia,Italy

AriannaBonzanini(43) TurbodenS.p.A.,Brescia,Italy

GurcanC¸etin(263) DepartmentofInformationSystems Engineering,TechnologyFaculty,MuglaSıtkı Koc ¸ man University,Mugla,Turkey

GeorgeCharis(131) LaboratoryofSoftEnergyApplications andEnvironmentalProtection,MechanicalEngineering Department,UniversityofWestAttica,Athens,Greece

C.OzgurColpan(153) TheGraduateSchoolofNatural andAppliedSciences;FacultyofEngineering, DepartmentofMechanicalEngineering,DokuzEylul University,Buca,Izmir,Turkey

IbrahimDincer(207,225) CleanEnergyResearch Laboratory,FacultyofEngineeringandApplied Science,UniversityofOntarioInstituteofTechnology, Oshawa,ON,Canada

AnilErdogan(153) TheGraduateSchoolofNaturaland AppliedSciences,DokuzEylulUniversity,Buca,Izmir, Turkey

MehmetAkifEzan(153) TheGraduateSchoolofNatural andAppliedSciences;FacultyofEngineering, DepartmentofMechanicalEngineering,DokuzEylul University,Buca,Izmir,Turkey

MuhammadFarooq(315) DepartmentofMechanical Engineering,UniversityofEngineeringandTechnology,KSKCampus,Lahore,Pakistan

MiladFeili(167) DepartmentofMechanicalEngineering, FacultyofEngineering,UniversityofMohagheghArdabili,Ardabil,Iran

HikariFujii(83) GraduateSchoolofEngineeringand ResourceScience,AkitaUniversity,Akita,Japan

HadiGhaebi(167) DepartmentofMechanicalEngineering,FacultyofEngineering,UniversityofMohagheghArdabili,Ardabil,Iran

OnurVahipGuler(113) DepartmentofEnergySystems Engineering,TechnologyFaculty,MuglaSıtkı Koc ¸ man University,Mugla,Turkey

MuhammadImran(315) SchoolofEngineeringand AppliedScience,AstonUniversity,Birmingham,West Midlands,UnitedKingdom

MohammadAsharJamal(185) DepartmentofEngineeringSciences,NationalUniversityofSciencesand Technology,Islamabad,Pakistan

RaoHamzaJamil(185) DepartmentofEngineeringSciences,NationalUniversityofSciencesandTechnology, Islamabad,Pakistan

FirmanBagjaJuangsa(97) FacultyofMechanicaland AerospaceEngineering,InstitutTeknologiBandung, Bandung,Indonesia

KhurramKamal(249) DepartmentofEngineeringSciences,NationalUniversityofSciencesandTechnology, Islamabad,Pakistan

PrasadKaparaju(3) InstituteforAppliedSustainability Research(iiasur),Quito,Ecuador;SchoolofEngineering&BuiltEnvironment,GriffithUniversity, Brisbane,QLD,Australia

SpyridonKarytsas(65) GeothermalEnergyDepartment, DivisionofRenewableEnergySources,Centrefor RenewableEnergySourcesandSaving(CRES), Pikermi;DepartmentofHomeEconomicsandEcology, SchoolofEnvironment,GeographyandAppliedEconomics,HarokopioUniversity(HUA),Kallithea, Greece

KosmasA.Kavadias(131) LaboratoryofSoftEnergy ApplicationsandEnvironmentalProtection,Mechanical EngineeringDepartment,UniversityofWestAttica, Athens,Greece

AliKec ¸ ebas ¸ (113,263) DepartmentofEnergySystems Engineering,TechnologyFaculty,MuglaSıtkı Koc ¸ man University,Mugla,Turkey

ShoaibKhanmohammadi(279) Departmentof MechanicalEngineering,KermanshahUniversityof Technology,Kermanshah,Iran

OnderKizilkan(153,279) DepartmentofMechanical Engineering,FacultyofTechnology,IspartaUniversity ofAppliedSciences,Isparta,Turkey

ParthivKurup(17) NationalRenewableEnergyLaboratory(NREL),Golden,CO,UnitedStates

SaeidMohammadzadehBina(83) GraduateSchoolof EngineeringandResourceScience,AkitaUniversity, Akita,Japan

DiegoMoya(3) DepartmentofChemicalEngineering &GranthamInstitute—ClimateChangeandthe Environment,ScienceandSolutionsforaChanging PlanetDTP,ImperialCollegeLondon,London, UnitedKingdom;InstituteforAppliedSustainability Research(iiasur),Quito;CarreradeIngenierı´a Meca ´ nica,FacultaddeIngenierı´aCivilyMeca ´ nica, UniversidadTecnicadeAmbato,Ambato; Coordinacio ´ ndeInvestigacio ´ neInnovacio ´ n,ABREC, Quito,Ecuador

HafizAliMuhammad(315) ThermalEnergySystems Laboratory,KoreaInstituteofEnergyResearch, Daejeon,RepublicofKorea

FarayiMusharavati(279) DepartmentofMechanical andIndustrialEngineering,QatarUniversity,Doha, Qatar

GregF.Naterer(225) CleanEnergyResearchLaboratory, FacultyofEngineeringandAppliedScience,UniversityofOntarioInstituteofTechnology,Oshawa, ON;FacultyofEngineeringandAppliedScience, MemorialUniversityofNewfoundland,St.John’s, NL,Canada

Osman € Ozkaraca(263) DepartmentofInformation SystemsEngineering,TechnologyFaculty,MuglaSıtkı Koc ¸manUniversity,Mugla,Turkey

Murat Ozturk(207) FacultyofTechnology,Departmentof MechatronicsEngineering,IspartaUniversityof AppliedScience,Isparta,Turkey

MohammadMustafaPardesi(185) DepartmentofEngineeringSciences,NationalUniversityofSciencesand Technology,Islamabad,Pakistan

MariaLauraParisi(53) CenterforColloidandSurface Science,UniversityofFirenze,SestoFiorentino;R2ES Lab,DepartmentofBiotechnology,Chemistryand Pharmacy,UniversityofSiena,Siena;National ResearchCouncil—InstitutefortheChemistryof OrganoMetallicCompounds,SestoFiorentino,Italy

OlympiaPolyzou(65) GeothermalEnergyDepartment, DivisionofRenewableEnergySources,Centrefor RenewableEnergySourcesandSaving(CRES), Pikermi,Greece

TahirAbdulHussainRatlamwala(185,249) Department ofEngineeringSciences,NationalUniversityofSciencesandTechnology,Islamabad,Pakistan

ZabdurRehman(315) DepartmentofMechanicalEngineering,AirUniversityIslamabad,AerospaceandAviationCampus,Kamra,Pakistan

RonR.Roberts(225) CleanEnergyResearchLaboratory, FacultyofEngineeringandAppliedScience,University ofOntarioInstituteofTechnology,Oshawa,ON, Canada

HadiRostamzadeh(167) EnergyandEnvironment ResearchCenter,NirooResearchInstitute(NRI), Tehran,Iran

LalitChandraSaikia(293) DepartmentofElectricalEngineering,NationalInstituteofTechnology,Silchar, Assam,India

MuhammadNoumanSaleem(249) DepartmentofEngineeringSciences,NationalUniversityofSciencesand Technology,Islamabad,Pakistan

MuhammadAfzalSheikh(249) DepartmentofEngineeringSciences,NationalUniversityofSciencesand Technology,Islamabad,Pakistan

FarooqSher(315) SchoolofMechanical,Aerospaceand AutomotiveEngineering,CoventryUniversity,Coventry,UnitedKingdom

UzairAzizSuria(185) DepartmentofEngineeringSciences,NationalUniversityofSciencesandTechnology, Islamabad,Pakistan

WashimaTasnin(293) SchoolofElectricalEngineering, VelloreInstituteofTechnology,Vellore,TamilNadu, India

LorenzoTosti(53) CenterforColloidandSurfaceScience, UniversityofFirenze,SestoFiorentino;R2ESLab, DepartmentofBiotechnology,Chemistryand Pharmacy,UniversityofSiena,Siena,Italy

ShunsukeTsuya(83) GraduateSchoolofEngineeringand ResourceScience,AkitaUniversity,Akita,Japan

Variouscycleconfigurationsfor geothermalpowerplants

DiegoMoyaa,b,c,d,OlusolaCharlesAkinsipee,andPrasadKaparajub,e a DepartmentofChemicalEngineering&GranthamInstitute—ClimateChangeandtheEnvironment,ScienceandSolutionsforaChangingPlanetDTP, ImperialCollegeLondon,London,UnitedKingdom, b InstituteforAppliedSustainabilityResearch(iiasur),Quito,Ecuador, c CarreradeIngenierı´a Meca´nica,FacultaddeIngenierı´aCivilyMeca´nica,UniversidadTecnicadeAmbato,Ambato,Ecuador, d Coordinacio´ndeInvestigacio´neInnovacio´n, ABREC,Quito,Ecuador, e SchoolofEngineering&BuiltEnvironment,GriffithUniversity,Brisbane,QLD,Australia

1.1Introduction

Globally,thetransitionfromthepresentpetroleumdependentenergytechnologytogreenenergyisfundamentallycontingentonmakingadecisiononresult-driven renewablesystems [1].Mitigatingclimateissuesaswell aspromotingsustainabledevelopmentareunattainable withoutinnovativesystemsandtechnologytransfer.Featuressuchaslowgreenhousegasemissions,minimized environmentaldisruption,andtheviabilityoftechnology extractionhavedemonstratedgeothermalenergyasasustainableenergyresource [2] thatcouldbeharnessedand exploitedregardlessofclimaticfactors [3].TheEarth’s crusthousestherenewablegeothermalenergysource [4], usuallyassociatedwithtectonicactivityandvolcanicactivities [5].Typically,geothermalenergyislocatedasaheat sourceinhotrocks [6] aswellashydrothermalreservoirs intheEarth’scrust.

Geothermalenergyisconsideredasustainableclean renewableenergyresource.Theglobalinstalledgeothermal capacityisestimatedtobe12.729MWandthatisprojected togrowby68.46%in2020.Amongthegeothermalpower plantconfigurations,singleflash(41%)isthepredominant configurationfollowedbydrysteam(23%),doubleflash (19%),andbinary(14%).Thetripleflash(2%)andback pressure(1%)plantconfigurationsarelesspopular [7]

Factorssuchastheheatreinjectionmechanism,geothermal applications,andgeologictimescalearebackstoppingthe acceleratedgeothermalreservoirheatextractionincomparisonwiththereplacementofheatinthereservoirs. However,methodsforheatreinjectionhavebeendeveloped toensuregeothermalenergyasarenewableenergy resource.

Geothermalfluidsaregenerallyusedtocaptureheat energyfromtheEarth’scrustandtransportittothesurface throughproductionwellsdrilledintothegeothermal

reservoir [8].Dependinguponthelocation,temperature, anddepthofthegeothermalreservoir,geothermalfluids consistingofmineral-coatedhotwaterknownasbrine andsteam(vapor-dominatedfluids)aregenerallyused [9].Theheatenergythatistransportedtothegroundsurface isfurtherprocessedforelectricitygenerationand/ordirect uses [8].Dependingonthegeothermalsitefeatures,thermal energycanbeharvestedfromdepthsof300to3000mand beyond.Atgreaterdepths,thermofluidsarenaturally occurringastheporoushotrockofthehydrothermaland geopressuredgeothermalreservoirs [10].Harvestingthe hotfluidsisacontingentfeatureofthesereservoirs,and variouscontrolmeasuresarefactoredtomaximizetheutilizationofthisheatenergy [11].Finally,theelectricalpower generationisdependentupontheapplicationofvariousgeothermalheat [12].Inthischapter,currentgeothermalpower plantsystemsandtheirsignificanceinapplyingcuttingedgegeothermalconfigurationsaswellasundertaking researchonhybridconfigurationsarepresented.

1.2Geothermalpowerplantsystem

Theabundanceofhydrothermalresourceshasinfluenced thedevelopmentofgeothermalpowerplantarrangements andsystems [13].Geothermalpowerplantscanbeclassified assingle-flashsteampowerplants,double-flashsteam powerplants,drysteampowerplants,binary(Organic Rankine-KalinaCycle)powerplants,andadvancedgeothermalenergysystems.Theadvancedgeothermalenergy systemsarefurtherclassifiedashybridsingle-double-flash systems,hybridflash-binarysystems,hybridfossilgeothermaltechnologies,andhybridotherrenewableheat source-geothermalsystems [12].Geothermalpowerplants arebestgroupedintosteamandbinarycyclesforcycles forhigherwellenthalpiesandlowerenthalpies,respectively

[14].Thischapterwillassessthethermodynamicaspectsof thefivegeothermalpowerplantconfigurations.

1.2.1Single-flashsteampowerplants

Thesingle-flashsteampowerplantisthesimplestgeothermalpowertransformationarrangement.Thisconfigurationfacilitatesliquid-vaporproductionfromthe geothermalproductionwells.Basedontheirlargedensity disparity,theseareseparatedintotwodissimilarphases: steamandliquidwiththesupportofacylindricalcyclone pressurevessel [14].Theterm“single”depictsasingle flashingmechanismofthegeofluidobtainedbydepressuringthegeothermalfluidpressure [15].Thiscanbe achievedinaproductionwell,areservoir,oracycloneinlet tosupportthetransitionofpressurizedliquidtoliquid-steam mixtureproduction.A30MWsingle-flashgeothermal powerplantdemandsbetween5and6productionwells and2–3reinjectionwellsappropriatedalongwiththegeofluidresource [15].Further,pipesaredeployedformixture accumulationandtransportationfromthevariousgeo-

thermalproductionwells.Theidentifiedconstraintisthe dropinvaporpressureduetothepipefrictionalforceassociatedwithharvestingmechanisms [16].Empiricalcorrelationsareinvestigated,consideringtheircomplicationand reliability,bydeployingfactorssuchasthevapormassflow rate,thedensity,thepipediameter,thelength,andthecomponentsofthepipetoforecastpressureloss.Thevariables aresignificantcomparedtotheinvestmentcostofthepower plantandtheenergyconversiontechnology [16].Aturbine generatorproduceselectricalenergyfromvapor(around 99.95%dry)afterseparationofthevaporandliquid [15] Thechoiceofasingle-flashprocessisapplicablewhen thegeothermalfluidtemperatureexceeds260°Cwiththe attainmentofacapacityfactorbetween95%and100% [10]

Fig.1.1 showsthesingle-flashprocessofenergyconversiontechnology.Station1iswherethesingle-flash steampowerprocesscommenceswhilethegeothermalfluid accessestheproductionwellthroughthesourceinlettemperature.Betweenstations1and2(producingpipes),a pressuredropoccurs,andthisfacilitatestheboilingofthe fluid(avapor-liquidmixture)beforeitistransportedto

FIG.1.1 Single-flashgeothermalpowercycle [17].

station2.Atstation5,itcollectssteamfromthemixture fluidafterseparationwhilethebrine(mineral-ladenhot water)iscollectedatstation3beforereinjectingatstation4.

Atstation5,theinducedmotionoftheturbinegenerator supportstheelectricalenergyattheentranceofthesteam, followedbytheproductionofsteamexpansionalongwith theturbinetostation6atcondenserpressure.Anaircooler condensermaybeusedatstationc1toallowthecoolingof airandexitatstationc2 [15].Thesignificanceofcertain plantequipmentintheoperationofasingle-flashsteamgeothermalpowerplantisgreatlyacknowledged.Inthisconfiguration,largeamountsoffreshwaterarenotneededfor cooling [18].Nevertheless,coolingthetower,particularly thedryregionswithoutfreshwater,isachievedby deployingcoolingwaterobtainedfromcondensed steam [16].

Fig.1.2 isathermodynamicstate(T-s)diagramanalyzingthesingle-flashsteamconversionprocess.Itshould benotedthatmassconversionandtheenergyconversion

principle,thetwofundamentalthermodynamicprinciples, areconsideredintheinvestigationoftheprocesswiththe aidofthediagram.Inasingle-flashpowerplant,flashing occurswhenthegeothermalfluidunderpressureinitiates theprocessclosetothesaturationcurveatstate1 (Fig.1.2).Thechangeinthepotentialorkineticenergyis notconsidered,andtheenthalpy(h)isdesignedasconstant, h1 ¼ h2,ascanbeseeninEq.(1.1)in Table1.1.Afterthe flashingprocess,theseparationprocessoccursatstate2, andissimulatedatconstantpressure.Further,thevapor andliquidmixtureisshown,ascertainingthemixture qualityinthisstate.Thedrynessfraction(x2)drivesthis quality,asshownbyEq.(1.2)in Table1.1.Thequantity ofvaporenteringtheturbineisrepresentedbythesteam massfraction.Eq.(1.3)in Table1.1 showstheworkperunit mass(w1)generatedbytheturbineexpansionprocess betweenstates4and5.Thepotentialandkineticenergy arenotgenerallyconsidered,andheatlossesareneglected whenthethermalfluidentersandleavestheturbine. Eq.(1.4)in Table1.1 istheisentropicturbineefficiency, whichisdenotedby t.Thisisconsideredtheratioofthe actualworktothatoftheisentropicwork,whichistheideal processfromstates4to5.Eq.(1.5)indicatestheturbine grossmechanicalpower( _ Wt ).Theelectricalpoweroutput ofthegenerator(Eq.1.6)isgivenastheturbine’s mechanicalpowertimestheefficiencyofthegenerator ( g).Lastly,atstates5and6,thecondensationandcooling processesoccur,andEq.(1.7)givesthecoolingwaterflow rate [4]

Forthepurposeofanalyzingthewholeplantefficiency, thesecondlawofthermodynamicsisinvestigated [16].This allowsitsexaminationincontrasttotheactualpoweroutput towardthefinishofthesingle-flashprocessandtothe utmosttheoreticalpowerthatisgeneratedbythegeothermal fluid [15].Exergyistheenergyfeasibletobeusedandthe capacitytoproduceworkfromenergy [16].Eq.(1.8)presentedin Table1.2 definesthespecificexergy(ex)ofthe

FIG.1.2 Temperature-entropy(T-s)diagramofasingle-flashcycle [4]

TABLE1.1 Equationsusedforthermodynamicstateanalysis [15]

TABLE1.2 Exergyandpowerplantefficiency [19].

Thermodynamic dimensionEquation Equation number

Specificexergy ex ¼ h(T, P) h(TO, PO) TO[s(T, P) s(TO, PO)] (1.8)

Exergeticpower Ex ¼ m total ex (1.9)

Entirepowerplant efficiency

geothermalfluidforagivenpressure(P),temperature(T), ambientpressure(PO).andambienttemperature(TO). Eq.(1.9)showstheexergeticpower,alsoknownasthe maximumtheoreticalthermodynamicpower,whichisthe totalgeothermalmassflowratetimestheexergy.Finally, theexergyefficiencyoftheentirepowerplantisgivenby Eq.(1.10) [19].

Thereareseveralenvironmentalimpactsofsingle-flash geothermalpowerplants [15].Locationssuchasthecooling tower,theejectorvents,thepipelinedrains,thesteam tramps,thesilencers,themufflers,andthewellhead,which offersastructuralinterfacebetweenthewellsandtheproductionsystem,aretheprimeareasofpollution [18].The blendingofnoncondensablegasessuchasmethane (CH4),hydrogensulfide(H2S),andcarbondioxide(CO2) fromthesteamofgeothermalreservoirsisconsidereda mainenvironmentalconcern.Thesegasesare,however, subjectedtotreatmentandisolationbeforebeingdischarged intotheatmosphere [20].Further,inspiteofitsCO2 emissions,theGHGemissionsfromasingle-flashgeothermal powerplant(0.06kgCO2/kWh)aresignificantlylowerthan thetraditionalcoal-fired(1.13kgCO2/kWh)ornatural-gasfiredpowerplants(0.59kgCO2/kWh) [13].Withrespectto footprint,thelandrequirementsofacoal-firedpowerplant (40,000m2/MW)andasolarphotovoltaicpowerplant (66,000m2/MW)aremuchhigherthanthe1200m2/MW requiredforasingle-flashplant [15].Ingeneral,theloss ofcharacteristicbeauty,ozone-depletingsubstances,land andwaterutilization,visualandnoisepollution,andwater contaminationaresomeoftheotherenvironmental concernsassociatedwithgeothermalpowerplants [10] Strategiestomitigatetheenvironmentalimpactsof single-flashgeothermalpowerplantasproposedin [20] includemufflersandsilencerstoabatenoisepollution, air-cooledcondensers,reinjectionforsurfacewater,and preventingexpansionofgeothermalprojectsintonational parks.Byandlarge,theemissionsfromgeothermalpower plantsareinconsequentialcomparedtofossil-fuelconventionalpowerplants.

1.2.2Double-flashsteampowerplants

Thedevelopmentofthedouble-flashsteamgeothermal powerplantwastosupportpowergenerationbytheuse ofamixtureofvaporandliquidwatergeneratedinthegeothermalproductionwells [21].Adouble-flashpowerplant isconsideredmoreadvantageousthanasingle-flashpower plant,astheformercangenerate25%moreoutputpower thanthelatterunderthesamegeothermalfluidconditions [13].However,double-flashsteampowerplanttechnology ismorecomplexanditsoperationandmaintenanceare moreexpensivethansingle-flashpowerplants.Nevertheless,theefficientuseofthegeothermalresourceisa pointerthatasecondaryflashprocessisvaluable.Theuse ofasecondpressuredropinasecondaryflashprocess (secondseparator),afterthefirstpressuredrop,supports theproductionofextravaporfromtheseparatedliquid exitingthefirstseparator.Further,thecoupledturbinegeneratorisabletoproduceadditionalpowerduetothesupply oflower-pressuresteam [22] ortoaturbinedependingon theconfiguration [23].Thedouble-flashpowerplant’scompleteexergyperformanceisoptimallyboostedduetothe separatorofthegeothermalsteam-water,whichistheprincipaltechnologicaldevelopmentofthispowerplant technology.

Uponcomparisontoasingle-flashsystem(Fig.1.1),a double-flashconfiguration(Fig.1.3)usesadual-admission turbineandalow-pressureseparator.Forthepurposeof smoothcombinationwiththeexpandedhigh-pressure steam,thelow-pressuresteamissuppliedtotheturbineat therightstage [15] Fig.1.3 presentstheenergyconversion processinadouble-flashsteamgeothermalpowerplant. Thedouble-flashsteampowerprocesscommencesat station2;thesourceoftheinlettemperatureisthecorridor ofthegeofluid.Thefirstflashed-steamprocessoccurs betweenstations1and2,whenthepressuredropsandthe fluidsbegintoboil(mixturesteam-liquid)beforereaching theseparatoratstation2.Thefluidmixtureisthenseparated intothebrineandhigh-pressuresteam.Themineral-laden brinehotwater(station3)isthendownwardlycontrolled tolow-pressure(station8)andhigh-pressuresteam(station 5)withthesupportofaseparator.Thispromptsthesecond flashed-steamprocess.Thesecondpressuredropatstation9 willleadtotheproductionofasteam-brinemixtureandthe brineiscollectedbythelow-pressureseparator.Thesecond steamisinjectedintothesystematstation9andtheturbine collectsthesecondfreshlow-pressuresteam.Atstation5, thefirsthigh-pressuresteamgainsaccesstotheturbineafter theinitialsteaminjection.Theinducedmotionofthedualinjectionturbine,connectedtoagenerator,generateselectricalenergy.Thecondenserpressureatstation6,connected totheturbine,isthelocationwherethesteamexpansion happens [15].Withrespecttotheprocessdesign,thefirst stageadmissionorinjectionoftheturbineshouldhave

Production well Silencer

Well valves

Ball check valve

Injection well

Condensed water pump

High-pressure cyclone separator SV

Stop valve

Steam jet ejectors Condenser Condensate pump

High-pressure turbine

Low-pressure turbine

Low-pressure flash separator MR

thesamepressuredifferencebetweenthehighandlowseparators [24].Thehigh-pressurestagemassflowisexpected tobelowerthanthelow-pressurestagemassflow.The residualhotfluidsatstation6arecondensedbyusingan air-cooledcondenser.Coolairissuppliedatstationc1 andexitedatstationc2.Finally,theresidualbrinefrom thesecondflashedprocessatstation10andthecondensed fluidfromstation7isreinjectedintothesystematstation4 (Fig.1.3).

Thetemperature-entropy(T-s)ofadouble-flashpower plantispresentedin Fig.1.4.Thetwoflashprocessesthat existinstates1–2and3–6aresignificant,andtheyare studiedseparatelyasasingleprocess [15].Toascertain thequantityofsteamgeneratedintheseparatorsateach flashedprocess(x2 instates1–2and x6 instates3–6,theseparationprocess),Eqs.(1.11)–(1.14)in Table1.3 areapplied.

Further,theevaluationofthesteamatstate2andthe brineatstate6,obtainedfromdifferentseparatorsatthe high-andlow-pressurestages,wasachievedbyusingfour equations,asshowninEqs.(1.15)–(1.18).Again, Eqs.(1.15),(1.17)givethemassflowrateofsteamgeneratedathighpressure( _ m hps ,atstate5)aswellasatlow pressure( _ m lps ,atstate8),respectively.Also,Eqs.(1.16),

Moisture remover

Steam tramp

Control valve

Throttle valve Generator

Electric grid Wellhead

(1.18)areusedtocalculatethemassflowrateofbrineproducedathighpressure(m hpb ,atstate3)andlowpressure (m lpb ,atstate7).Thelow-pressureturbinestage(atstate 9)accommodatesthehigh-pressureandlow-pressure steamstogether.WiththeaidofEqs.(1.15)–(1.18),four valuesareappraised:thedisposedwasteliquid,the

FIG.1.3 Double-flashgeothermalpowerplantwithadualadmissionturbine [15,17]

FIG.1.4 Temperature-entropyprocessdiagramforadouble-flashpower plantwithadualadmissionorinjectionturbine [15]

TABLE1.3

Thermodynamicequationsfordouble-flashgeothermalpowerplants [14,15].

Flashprocess2Constantenthalpy

Separationprocess2Constantpressure Mixtureofliquidplusvapor

Massflowrateofsteam

Massflowrateofsteam generated

Massflowrateofbrine produced

Turbineexpansion process

High-pressurestage(Eqs.1.22–1.23arethe Baumannrule) whpt ¼ h4 h5 (1.19)

hpt ¼ h4 h5 h4 h5s (1.20)

W hpt ¼ m hps whpt ¼ x2 m total whpt (1.21)

h5 ¼ h4 A 1 h7 h8 h7 1+ A h8 h7 (1.22)

A ¼ 0.425(h4 h5s) (1.23)

Turbineexpansion process

Low-pressurestage

condenserheatdissipated,thecoolingwaterheatlosses,and theturbinepowerproduction.

Thissystemisappliedfortheillustrationofthetwo turbineexpansionprocesses.Eq.(1.19)istherepresentation ofthe firstturbineexpansionprocess producingwork(whpt) thatoccursbetweenstates4and5.Eq.(1.26)describesthe secondturbineexpansionprocess producingwork(wlpt).

m 5 h5 + m 8 h8 ¼ m 5 + m 8 ðÞ h9 (1.24)

h9 ¼ x2 h5 +1 x2 ðÞx6 h8 x2 +1 x2 ðÞx6 (1.25)

wlpt ¼ h9 h10 (1.26)

W lpt ¼ m 9 h9 h10 ðÞ (1.27)

h10 ¼ h9 Ax9 h11 h12 h11

1+ A h12 h11 (1.28)

A ¼ 0.425(h9 h10s) (1.29)

lpt ¼ h9 h10 h9 h10s (1.30)

W total ¼ W hpt + W lpt (1.31)

W e , gross ¼ g W total (1.32)

Thus,foratypicaldouble-flashpowerplantwiththe high-pressure( hpt)andlow-pressure( lpt)processes,two isentropicturbineefficienciesarederivedbyusing Eq.(1.20),andalow-pressureprocess( lpt)byusing Eq.(1.30).Thefirstturbinestagepowerproducedathigh pressure( _ W hpt )andthesecondstagepowerproducedat lowpressure(W lpt )aredefinedbyusingEq.(1.21)and

Eq.(1.27),respectively.Eq.(1.31)providestheaggregate turbinepowerproduced( _ W total ),whichisanadditionof individualturbinestagepowergenerated.Lastly,as explainedinEq.(1.32),theefficiencyofthegenerator ( g)impactstheelectricalpower(W e, gross ).Theefficiency oftheoverallpowerplant,theincominggeothermalfluid exergy,theenvironmentalimpacts,andthedeployed equipmentaresimilartothatofthesingle-flashprocess [24,25].

1.2.3Dry-steampowerplants

Studieshaveshownthatseverallocationsaroundtheglobe areendowedwithgeothermaldry-steam,particularlyin placessuchasthegeysersintheUnitedStatesandLarderello,Italy.Bothplaceshavethetwolargestdry-steam reservoirs.However,placessuchasCoveFort,Utah,United States;Wairakei,NewZealand;Matsukawa,Japan;and Kamojang,Indonesiaarecharacterizedbylimiteddrysteam [16,20].Intheeventthatageothermalreservoirdries, ZarroukandMoon [16] discussedthepossibilityof

convertingtheflashedgenerationsystemsintoadry-steam system.Consideringhighenthalpysystemconfigurations, dry-steamgeothermalpowerplantsarethemostefficient becausethehydrothermalreservoirssupporttheseconfigurationswithvapor-dominantgeothermalfluidathightemperatures [25,26].Thecoupledturbinegeneratorisable togenerateelectricalenergyusingthesteamsupplied directlyfromtheproductionwell [10]

Indry-steampowergeneration,between50%and70% ofthegeothermalfluidavailablework(exergy)isconverted intoelectricalpower [25].Uponcomparisonwiththesteamflashedprocess,thedrysteamhasasimplerconceptand requirescentrifugalcyclonestoseparateparticulatematters suchasrockchippingsanddust [25].Similarly,thecondensateiseliminatedbyusingdrainpots,andthelast moistureiseliminatedtoachievehigh-gradesteaminthe turbine.AVenturimeterisalsoneededfortheaccuratecalibrationoftheturbinesteamflowrate [13]

Themechanismofconversionofenergyinthedry-steam powerplantprocessisdescribedin Fig.1.5.Bothsingleflashanddry-steam(geothermalfluid)processesshare

FIG.1.5 Dry-steamgeothermalpowerplant [9,17]

similarfeaturesofthewholepowergenerationcycle,from theproductionwellstotheproductionturbine [15].Forboth smallerorlargerunitsofsingleflowordoubleflow,asingle pressureisperformedbythebladingturbineofimpulsereaction.Basedonthegraphs, Fig.1.1 (singleflash)shares thesamesimilaritywith Fig.1.5 withaparticulateremover ratherthanacycloneseparator.

Fig.1.6 istheT-sthermodynamicstateofthedry-steam system.Atstate1,saturatedsteamorlightlysuperheated steamisgeneratedintheproductionwells.Theexpansion oftheturbineoccursbetweenstates1and2whilethe coolingprocessisattainedbetweenstates2and3,where anemissionofheatviathecondenseroccurs.Thesingleflashgeothermalpowerplantsystemisequivalenttothe thermodynamicstudy [18] Table1.4 showstheequations inanalyzingthedry-steampowerplants.Intermsofimpacts ontheenvironment,thesingle-flashgeothermalpowerplant processhasalowerenvironmentalimpactthanflashed powerplants,asthesystemdoesnotusemineral-laden brine [15].

1.2.4Binary-organicRankinecycleand Kalinacyclepowerplants

Thebinarygeothermalpowerplant(B-GPP)generateselectricalenergyfromasecondaryseparatedprocess.Preheatingoftheworkingfluidisinvolvedandheatislost uponcontactingthegeothermalfluid [10].Geothermal resourceswithatemperaturerangeof20–150°C [25] or 85–170°C [27] arewellsuitedforbinaryconfigurations [25].Ahighertemperaturerangeprovidethermalstability oftheworkingfluidwhilethelowertemperaturesaremore feasibleintermsoftechnoeconomicandfinancialfactors. Further,theimpactsofcorrosionandscalingarenot apparentathightemperature,asthereisnocontactbetween thepowergenerationequipmentandthegeofluid.Undera conventionalRankinecycle,thereisthefunctionalityofthe secondaryfluid(workingfluid)inthebinarysystem [28], andthebinarycycleisidentifiedastheOrganicRankine Cycle(ORC)duetotheorganicnatureoftheworkingfluid.

Binarypowerplantsareversatileandthefunctionalityof thepowerplantisdecidedbythesecondarycycle.Different typesofconfigurationsofbinarypowerplantsareinoperation,includingB-GPPusinganORCwithaninternalheat exchanger(IHE),B-GPPwitharegenerativeORC,and B-GPPwitharegenerativeORCusingIHE [29].In1982, KalinapatentedavariationinB-GPP [30].Theworking fluidusedintheKalinacycleconsistsofwaterandammonia andcanbeusedindifferentcompositionstosuitvarious configurations [31].Athermalefficiencyof30%–40%is achievableandisconsideredmoreefficientthanthatof anordinaryB-GPP [28].

AclosedloopofathermodynamicRankineCycleused fortheenergyconversionsystemofabasicbinarygeothermalpowerplantisshownin Fig.1.7.Harvestingthe geothermalfluidviatheproductionwells(PW)andthen transportingitthroughvariousprimarycyclecomponents necessitatesthatpumpingsystemsaredeployed.The scouringanderosionofpipesandtubescanbeprevented byextractingsandfromthegeofluidbyemployingsand removers(SR).Finally,anevaporator(E)andapreheater (pH)areusedforcontinuousfluidflowwhilethegeothermalfluidisreinjectedintothereservoirnearthe injectionwell(IW)byusinganinjectionpump(IP).

Regardingtheworkingcycle,twoheating-boilingproceduresareincludedintheworkingfluid.ThePHisthe locationoftheboilingpointoftheworkingfluid.Upon contactofPHwithE,theworkingfluidbecomesasaturated vapor.Thisresultsintheexpansionandcondensationofthe workingfluidintheturbine.Theworkingfluidisthen returnedtotheevaporator,therebyconcludingtheloop processandbeginningtheprocessagain [31].Toprevent steameruptionandcalcitescalingwithinthepipes,monitoringthegeothermalfluidabovetheflashpressurepoint isnecessary [13].Thus,thelow-temperaturegeothermal

TABLE1.4 Thermodynamicequationsinthedry-steam processforturbineexpansionprocess [15]

FIG.1.6 Temperature-entropy(T-s)processdiagramforadry-steam powerplantwithsaturatedsteamattheturbineinlet [15,18]