Geo Thermal Energy Principle and Working

Geothermal Energy

1. 11
Geothermal Energy
•Geothermalenergyoriginatesfromtheearth’s
interiorintheformofheat
•Volcanoes,geysers,hotspringsandboilingmud
potsarevisibleevidenceofthegreatreservoirs
oftheheatthatliebeneaththeearth
•Althoughtheamountofthermalenergywithin
theearthisverylarge,usefulgeothermalenergy
islimitedtocertainsitesonly,asitisnotfeasible
toaccessandextractheatfromaverydeep
location
•Whereitisavailablenearthesurfaceandis
relativelymoreconcentrated,itsextractionand
usemaybeconsideredfeasible.Thesesitesare
knownasgeothermalfields

2. 22
Cont.,
•AsperUSGeologicalsurvey,theentireheatcontentof
theearth’scrustuptoadepthof10kmandabove15ºC
isdefinedasgeothermalresource
•Assuch,thegeothermalresourceoftheearthis
estimatedtobemorethan2.11x10
25
J,whichis
equivalentto10
9
MTOE(milliontonnesofoilequivalent)
•Thisisahugeamountofenergy,enoughtosupplyour
energyneedsatcurrentratesfor3,50,000years.Thus,
itisconsideredasinexhaustibleandrenewablesource
•However,itisalowgradethermalenergyandits
economicrecoveryisnotfeasibleeverywhereonthe
surfaceoftheearth
•Practically,itisnotthesizeoftheresourcethatlimitsits
usebuttheavailabilityoftechnologythatcantapthe
resourceinaneconomicmanner

3. 33
Cont.,
•Mostgeothermalresourcesproducelow-gradeheatat
about50-70ºC,whichcanbeuseddirectlyforthermal
applications
•Occasionally,geothermalheatisavailableat
temperaturesabove90ºC,andsoelectricalpower
productionfromturbinescanbecontemplated
•Theworld’stotalpresent(endofyear2005)installed
electricalpower-generatingcapacityfromgeothermal
resourcesisabout9,031MWanddirectthermaluse
installedcapacityis29,668MW
•Globally,generationofgeothermalpowerisgrowing
steadilyatarateofabove3%peryearaselectrical
energyand8.5%peryearasdirectthermalenergy

4. 4
Applications of Geothermal Energy
(i) Direct Heat Use:
•Ingeneral,althoughabundantgeothermalenergyis
accessible,itsthermodynamicqualityislow
•Thesourcesharesmanysimilaritieswithindustrial
wasteheat
•Thelowandmoderatetemperaturehydrothermal
fluidscanbeusedasdirectheatsourceforspaceand
waterheating,forindustrialprocessessuchasdrying
applicationsinfood,chemicalandtextileindustries,
cropdrying,washing,forwarmingfishpondsin
aquacultureandforagriculturalapplicationssuchas
soilandspaceheatingofglasshouses
4

5. 5
Cont.,
(ii) Electric Power Generation:
•Iftemperaturesarehighenough(>90ºC),thenthe
preferreduseofageothermalresourceisthegeneration
ofelectricity,whichwouldeitherbefedintotheutilitygrid
orbeusedtopowertheindustrialprocessesonthesite
•Itisnormallyusedforbaseloadpowergeneration
•Severalimportantelectricpowerplantsarefully
established,especiallyinItaly,NewZealandandUSA
•Electricitywasfirstgeneratedfromnaturallyoccurring
geothermalsteamatItalyin1940.Thiswasfollowedby
commercialplantsinNewZealandin1958andin
Californiain1960
5

6. 6
Types of Geothermal Resources
Four types of geothermal resources:
1.HydrothermalorHydro–geothermalenergyresources
(i)Vapour–dominated(or)drysteamfields
(ii)Liquid–dominatedsystemorwetsteamfields
(a)Theflashsteamopensystem(FSOS)
(b)Thebinarycyclesystem
2.Geopressuredresources
3.Petro-thermalsystemsorHotdryrock(HDR)
resources
4.Magmaresources(Molten-rock-chambersystems)
Thehydro-thermalconvectivesystemsarebest
resourcesforgeothermalenergyexploitationat
present.Hotdryrockisalsoconsidered.
6

7. 7
Hydrothermal Resources
•Hydrothermalresourcesoccurwhenundergroundwater
hasaccesstohightemperatureporousrocks,cappedby
alayerofsolidimperviousrock
•Thus,wateristrappedintheundergroundreservoirand
isheatedbysurroundingrocks.Heatissuppliedby
magmabyupwardconductionthroughsolidrocksbelow
thereservoir.Thus,itformsagiantundergroundboiler.
Underhighpressure,thetemperaturecanreachashigh
as350ºC
•Inordertoutilizethehydrothermalenergy,wellsare
drilledintothehydrothermalreservoirasshowninthe
nextslide
7

8. 8

9. 9
Cont.,
•Thehydrothermalresourcesarelocatedatshallowto
moderatedepths(fromapproximately100mto4,500m).
Temperaturesforhydrothermalreservesusedforelectricity
generationrangefrom90ºCto350ºCbutroughlytwo-
thirdsareestimatedtobeinthemoderatetemperature
rangeof150ºCto200ºC.
•Forpracticalpurposes,hydrothermalresourcesarefurther
subdividedinto(i)vapourdominated(drysteamfields),(ii)
liquid-dominated(wetsteamfields),and(iii)hotwater
resources.Vapour-dominatedfieldsdeliversteamwithlittle
ornowaterandliquid-dominatedfieldsproduceamixture
ofsteamandhotwaterorhotwateronly
•Thedrysteamhydrothermalsystemalonewillbe
discussedhere
9

10. 10
(i) Vapour –Dominated (or) Dry Steam Fields
•Drysteamfieldsoccurwhenthepressureisnotmuch
abovetheatmosphericpressureandthetemperatureis
high
•Waterboilsundergroundandgeneratessteamat
temperaturesofabout165ºCandapressureofabout7
atmosphere
•Themostimportantdrysteamfieldsare(a)TheGeysers
regioninCalifornia,whichmaybethelargest,(b)the
LarderelloandsomesmallerareasinItaly,and(c)small
fieldsatMatsukawa,Japan
•Adrysteamhydrothermalsystemisshowninthenext
slide
10

11. 11
(Centrifugal separator)

12. 12
Cont.,
•Steamisextractedfromthewell,cleanedinacentrifugal
separatortoremovesolidmatterandthenpipeddirectly
toaturbine
•Theexhauststeamoftheturbineiscondensedina
directcontactcondenser,inwhichthesteamis
condensedbydirectcontactwithcoolingwater
•Theresultingwarmwateriscirculatedandcooledina
coolingtowerandreturnedtothecondenser
•Thecondensationofthesteamcontinuouslyincreases
thevolumeofcoolingwater.Excesswaterisre-injected
intothegroundfordisposal.Thenon-condensablegases
areremovedfromthecondenserbysteamjetejection
12

13. 13
(ii) Liquid –dominated system or wet steam fields
(a) The flash steam open system (FSOS)
13

14. 14
Cont.,
Hotbrinefromthereservoirreachesthewellheadat
lowerpressurebythrottlingprocess.
Thislowqualitymixtureisthenthrottledinflash
separatorwhichimprovesthequalityofmixture.
Nowsteamisseparatedasadrysaturatedsteamand
suppliedtothestemturbine,whichproduceselectricity
powerthroughagenerator.
Thepowergenerationfromsuchsystemcanbemade
moreeconomicalbyassociatingchemicalindustrywith
powerplanttomakeuseofbrineandgaseseffluent.
14

15. 15
Cont., (b)The binary cycle system
15

16. 16
Cont.,
Thebinarycycleconceptisolatesthesteamturbinefrom
corrosiveornoncorrosivematerialsandto
accommodatehigherconcentrationofnoncondensable
gases.
ThisisbasicallyaRankinecyclewithanorganicworking
fluid.
Inthissystemisaheatexchangerisusedtotransfera
fractionofthebrineenthalpytovaporizethesecondary
workingfluid.
Inthissystemtherearenoproblemsofcorrosionor
scalingintheworkingcyclecomponents,suchasthe
turbineandcondenser.
Theheatexchangerisashell–and–tubetypessothat
nocontactbetweenbrineandworkingfluidtakesplace.
16

17. 17
Geo Pressured Resources
Thegeopressuredresourcescontainmoderatetemperature
brines(160
°
C)containingdissolvedmethane.
Thesearetrappedunderhighpressure(nearly1000bar)ina
deepsedimentaryformationsealedbetweenimpermeable
layersorshaleandclayatdepthsof2to10km.
Atgeopressured,dissolvedmethanegasisusually1.9-3.8
m3percubicmeterofwater.
Methanegasisseparatedfrombrinebysimpleand
economicalgravityseparationtechniqueandburningofCH
4
alsoproducesenergy.
Threesourcesofenergyareavailable
(i)Thermal
(ii)Mechanical-aspressure
(iii)Chemical-aspressure
17

18. 18
Petro-thermal systems or Hot dry rock (HDR)
Resources
Thesesystemsarecomposedofhotdryrock(HDR)butno
undergroundwater.Theyrepresentbyfarthelargest
geothermalresourcesavailable.
TherecoveryofheatfromHDRinvolvesdrillingdeepinto
hotrocks,thencrackingittoformcavityorfractures.
Thiscanbeachievedby
(i)Usinghighexplosivesatthebottomoftheman-made
well
(ii)Usingnuclearexplosion
(iii)Byhydraulicfracturing
ThethermalenergyoftheHDRisextractedbypumping
waterorfluidthroughawellatthelowerpartofthe
fracturedrockandwithdrawnbyanotherwellatadistance.
18

19. 19
Magma resources (Molten-rock-chamber systems)
Atsomeofplaces,especiallyinthevicinityofrelatively
recentvolcanicactivity,moltenorpartiallymoltenrock
(i.emagma)occuratamoderatedepth(lessthan5km).
Theveryhightemperatureabove650°Candthelarge
volumemakemagma asubstantialgeothermal
resources.
Thisresourcehasnotbeenusedyetduetothereason
thattheexistingtechnologydoesnotallowrecoveryof
heatfromtheseresources(Magmatechnologyrequires
specialmanufacturingtechnology).
19

20. 2020
ADVANTAGES
(i)Itisreliableandcheapsourceofenergy.
(ii)Itisavailable24hoursperday.
(iii)Itistheleastpollutingascomparedtoanother
conventionalenergysources.
(iv)Itisamenableformultipleusesfromasingleresource
(v)Itsavailabilityisnotdependentonweather.
(vi)Ithasinherentstoragefeatureandhencenoextra
storagefacilityisrequired.
(vii)Geothermalplantsrequirelittlelandarea.
(viii)Feasibilityofmodularapproachrepresentsalotof
opportunitiesforthedevelopmentofrelativelyquickand
cost-effectivegeothermalprojects.

21. 2121
DISADVANTAGES
(i)Lowoverallpowerproductionefficiency(about15%as
comparedto35%forfossilfuelplants).
(ii)Drillingoperationleadstonoisepollution
(iii)Largeareasareneededforexploitationofgeothermal
energy
(iv)Thewithdrawaloflargeamountsofsteamorwater
fromahydro-thermalreservoirmayresultinsurface
subsidenceorsettlement.

22. 22
APPLICATIONS
Generationofelectricpower.
Spaceheatingforbuildings.
Industrialprocessheat.
Cropdrying.
Plasticmanufacture.
Papermanufacture.
Mushroomculture.
Timberseasoning.
Productionofsaltfromsea.
Sewageheattreatment.
Greenhousecultivationusingdischargefroma
geothermalfield.
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23. 23
Geothermal Energy in India
•Asystematiccollaborative,research,developmentand
demonstrationprogammehasbeenundertakenwith
differentorganizations,viz,IITDelhi,NationalAeronautic
LimitedBangalore,GeologicalSurveyofIndia,National
GeophysicalResearchInstitute(NGRI)Hyderabad,Oil
andNaturalGasCorporation,etc
•Asaresultofvariousresourceassessmentstudies/
surveys,nearly350potentialhotsprings,distributedin
sevengeothermalprovinces,havebeenidentified
throughoutthecountry.Thesespringsareperennialand
theirsurfacetemperaturesrangefrom37to90ºCwitha
cumulativesurfacedischargeofover1000l/m.Mostof
themarelow-temperaturehotwaterresourcesandcan
bestbeutilizedfordirectthermalapplications

24. 24
Geothermal Energy in Indiacontinued…
•Onlysomeofthemcanbeconsideredsuitablefor
electricalpowergeneration.Thepotentialforpower
generationatthesesiteshasbeenestimatedtobe
around10,000MW
•Theuseofgeothermalenergyhasalreadybeen
demonstratedinthecountryforsmall-scalepower
generationandthermalapplications
•SmalldirectheatpilotplantshavebeeninstalledatPuga
andChumathang(inLadakhJammuandKashmir)and
Manikaran(HimachalaPradesh)
•Thesevengeothermalprovincesinclude
TheHimalayas:Sohana
Westcoast:Cambay
Sonata:GodavariandMahanadi