l'energie de la terre

Geothermal power stations
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/ GEOTHERMAL ENERGY AND ELECTRICITY PRODUCTION /

Currently, geothermal power stations produce electricity by using the fluids which escape from reservoirs underground. These are between 110°C and 350°C and can produce a flow of tens or hundreds of tonnes per hour, enough to produce a significant amount of electricity.

There are several different types of power stations, depending on the nature and characteristics of the energy source.
  • Dry steam or wet steam condensing power stations
These are the principle production facilities around the world. These are located on sites with proven geothermal potential (dry steam, very high temperature). These are often volcanic and hydrothermally active zones.
  • The power stations use the Organic Rankine Cycle (ORC) principle or binary fluid technology.
The industry primarily uses binary fluid technology to extract lower temperature sources, or sources where the fluid has special characteristics.
 

/ BINARY FLUID POWER STATION /
 
>> The principle behind a binary fluid power station is as follows:
  • the geothermal fluid, once extracted, is brought to a heat exchanger. Here, it transfers some of its energy to an organic fluid, which then evaporates.
  • For an identical pressure, this type of fluid has the particularity of vapourising at lower temperatures.
  • The vapour produced is then released into a turbine, then condensed upon contact with the condenser’s water cooling circuit.
  • Thus obtained, the liquid is then sent back to the exchanger using a pump. In this way, the cycle repeats: vapourisation, release, condensation, pressurisation.
  • The working fluid (organic fluid) is retained in a completely closed circuit. As for the geothermal fluid, it is reinjected into the underground reservoir. This type of power station is single-unit and modestly sized (only a few units or tens of MWe).

 

Principe de centrale à fluide Binaire - ADEME/BRGM
 

>> The principle of cogeneration

Instead of cooling the fluid in a cooling tower, the heat is recovered and reprocessed for a range of applications. This is how electricity and heat can be produced at the same time.

>> The dual advantage of cogeneration

 
Find out more:
Content and images taken from the book “La géothermie Quelles technologies pour quels usages?” (Geothermal energy: which technology for which purpose?)
2nd edition, November 2008
“Les enjeux des Géosciences” (The stakes for Earth Science) collection
ISSN: 17775-7533 - Joint edition ADEME/BRGM
© BRGM - www.brgm.fr - Autor. n° R12/38Ed.