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Co-finanziato Dal Programma LLP dell’Unione Europea. GEOTHERMAL ENERGY. Geothermal energy is the energy generated by geological heat sources , exploiting the natural heat of the earth.
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Co-finanziato Dal Programma LLP dell’Unione Europea GEOTHERMAL ENERGY Geothermalenergyis the energygenerated by geologicalheatsources, exploiting the naturalheat of the earth. L’autore è il solo responsabile di questa comunicazione. L’Unione europea declina ogni responsabilità sull’uso che potrà essere fatto delle informazioni in essa contenute.
Geothermalenergyisnotwidelyusednowadays. In factthiskind of energy accounts for lessthan 1% of world total production, yetthere are countries in whichthiskind of energyisveryimportant; for example in Iceland 85% of houses are heatedthanks to this source of energy.
Pros and cons The greatestadvantages of thiskind of energyisitslowcost once the planthasbeenbuilt, becauseit exploits naturalforces. Moreovergeothermalplantsdon’tdamage the environmentbecausetheydon’thavewastewhichisharmful for men, animals or the earth.
THE GEOTHERMAL PRINCIPLE The exploitation of heatispossible once the underground heatconcentrationareashavebeenfound. These are caused by volcanic or tectonicphenomenons and are called hot springs
Hot springshavebeenusedsince the Paleolithic in China and shortlylater by the Romans aswell. Hot springs are used to heat up houses or greenhouses; low temperature fluids are used to produce electricenergy.
Industriesmainly use hydrothermalsystemsbutthere are otherkinds of systems, suchas the lowenthalpysystemwhich exploits the heatthanks to a heatpump.
SECONDARY VOLCANISM Because of the dangers of activevolcanos, the underground heatisusedthanks to the secondaryvolcanismphenomenons.Thesephenomenons are bornas a consequence of the coming out of magma from the crater.
After the activity of the volcnohasstopped, the magma chambergetcold. Lateritoriginatesphenomenonssuchas:
Geyser: periodicaleruptions of steamcharcterized by a siphonstructure, nearvolcanos. One of the mostfamousgeysersisGrand Geyser in Iceland.
Thermal Baths:thermalsprings are createdthanks to the degassing of magma in the magma chamber. Fumaroles: emanations of gas or heatnearvolcanos. They are clefts in the earth in which gas or steamdischargesoccur.
Boraciferous soffioni: structuresthat are bornduring the initialphase of the eruption; theyallow the coming out of ga es or steam in the magma chamber. The boraciferous soffioni in Larderello, Tuscany, are well-known.
Solfatara: the coming out of steam, carbon dioxide(CO2), hydrogen, from whoseoxidationwegetsulphur. Thesephenomenons in some cases originate sulphurexploitablesulphurdeposits.
Bradyseism. The lowering or raising of the soillevel,caused by the change in volume of the magma chambernear the surface, whichgetsempty and thenfills up
Geothermalplants exploit the heat of the earthdepthsbecause the inner temperature of ourplanetgrowsaswe go down towards the centre of the earth.
Thisincrease in temperature, calledgeothermalgradient, isaverage 3 degreesevery 100 metresdepthbut in some places, wherethere are geothermalsystems, itismuchhigher, up to 250-3050 degreesatabout 2000-40000 mt depth.
Through the clefts in the rock layers, the heatedvapours go up to the surface and are intercepted and produced by the geothermalwells.
The steamerogated by the wellsisconveyedintopipescalledsteampipes and sent to the turbine, whereeneryistransformedintomechanicalrotatingenergy.
The axis of the turbine isconnected to the engine of the alternator, that, rotating, trasformsmechanicalenergy in alternatingelectricenergywhichistransmitted to the transformer. Itraises the value of tension to 132000 volts and conveysitinto the distribution network. distribuzione.
The steamcoming out of the turbine isturnedinto a liquid in a condenserwhile the gases, contained in the steam, are dispersed in the atmosphere. .
A coolingtowerallows the cooling of the water produced by the condensation of the steam and italsoprovides the condenser with coldwater.Thecondensed water out of the plantisreinjected in the deeprocks from which the steamhasbeentaken.
When the wellssupply a liquidphase with a temperature belowabout 180 degrees C, the heat of the fluidisused to makeanotherlowboilingpointliquid (usuallyisobutane or isopentane) evaporate. Once ithasbeentransformedintosteamitwill be conveyed in the turbine, starting up the over describedprocess.
DIFFERENT KINDS OF GEOTHERMAL ENERGY Geothermalsources are essentially of threetypes: -Hydrothermal -pressurized -petrolchemical
Hydrothermalsystems are characterized by the presence of water or steam in underground pocketsheated by rocksat a high temperature and they are the onlygeothermalsystems to be exploted by industry. Hydrothermalsystems are dividedinto:dominantsteamsystems or water dominatsysyemsaccording to the predominance of one or the otherphase.
Geopressurizedsystems are verydeepdeposits(between 2500 and 9000mt)atrelativelylowtemperaturesbutat a very high pressure and full of naturalgases.
Petrothermalsystems or HDR ( Hard Dry Rock) are made of blocks of dry rocksat a small depth, the use of whichisnotdependent on the possibility to break the rock and insert water thatmay be able to take away the necessarythermalenergy. To thisaim large exchangesurfaces are needed, because of the moderate thermalconductibility of the rock.
