Energy

Geothermoeletric plants

A geothermal field is the area that can be exploited within a geothermal system. A “high temperature field” can always be connected to a plant for the production of electric power. This plant is different from a thermoelectric plant only because the vapour needed to move the turbines and produce electricity is not obtained by burning fossil fuels, but it is a natural underground product. In a “dominant vapour” field, like in Larderello, the vapour is directly sent to the turbine. After the use, the vapour is condensed, depurated from non-condensable gases (i.e. carbon dioxide) and injected underground through special wells, so that the most adequate pressure level is kept in the tank. In a “dominant water” field, the water/vapour mix that comes out of the geothermal well passes through a “separator”. In this way the vapour, that has to be sent to the turbine, separates from the water that will be injected again or dispersed outside. Geothermoelectric plants can be of different types: “counter-pressure” if the vapour, after being exploited, is released into the atmosphere; “condensation” if the vapour, after being used, is condensed and injected underground through a special well. “Flash” plants are installed in water-dominated areas and are equipped with a separator that separates the vapour to be sent to the turbine from the water that is to be eliminated. In general, the geothermal fluid is used to vaporize a second liquid (i.e. isopentane), by means of a heat exchanger, at a boiling temperature that is lower than water boiling temperature. The resulting vapour is then sent to the turbine, condensed and sent to the exchanger in a closed circuit. The geothermal fluid, instead, is injected underground again. This is closed circuit is very ecological, as the pollutants contained in the geothermal fluid are not released into the external environment. In Italy in 2010 geothermal energy produces 5,876 GWh megawatts of electric power.