Geothermal Electric Power Plant

a steam electric power plant that converts the heat of the earth’s interior into electric energy.

The sources of the subsurface heat are the radioactive transformations, chemical reactions, and other processes that take place in the crust of the earth. The temperature of rock increases with depth and exceeds 100° C at depths of 2,000-3,000 m below the surface of the earth. Water circulating at great depths is heated to considerable temperatures and can be brought to the surface by wells. In volcanic regions, heated subsurface waters rise up through fissures in the earth’s crust. In these regions thermal water has a very high temperature and is located near the surface, sometimes escaping in the form of superheated steam. Subsurface drilling technology of the future will make it possible to harness the high temperatures of magma chambers. Thermal waters with temperatures of up to 100° C come to the surface in many regions of the USSR.

The first geothermal power plant (5 megawatt capacity) in the Soviet Union went into operation in 1966 near the volcanoes of Kosheleva and Kambal’naia Sopka in the valley of the Pauzhetka River in the southern part of Kamchatka. The steam-and-water mixture with a heat content of 840 kilojoules/kg (200 kilocalories/kg) is brought to the surface through wells and channeled into separation units where the steam is separated from the water under a pressure of 0.23 meganewtons/m² (2.3 atmospheres). The separated steam is fed into turbines and the hot water (120° C) is used for supplying heat to populated areas and for other purposes. The electric power plant is equipped with two 2.5 megawatt turbines. The geothermal power plant does not have a boiler room, fuel deliveries, ash traps, and the many other facilities required for conventional steam electric power plants; in practice, the geothermal plant consists of a machine room and sites for the electrical equipment. The net cost of electric power at this geothermal power plant is several times cheaper than the cost at local diesel power plants.

Electric power is produced at a geothermal power plant by either the direct or indirect method or by a combination of the two. Under the direct method, the natural steam from the wells is fed by pipes directly into turbines connected to electric generators. The steam and condensed water are sent on to district heating systems and sometimes to the chemical industry. Under the indirect method, aggressive (powerfully corroding) gases are first removed from the steam. In the combined system, the unpurified natural steam is fed to the turbines and then the undissolved gases are removed from the condensed water.

The energy of thermal waters with temperatures of approximately 100° C in nonvolcanic regions of the country can be converted by the use of vacuum turbines with several expanders or on the basis of a cycle process with low-boiling working agents, such as freons.

Geothermal power plants have also been built abroad in Italy (in the Larderello region of Tuscany), New Zealand (Taupo zone), the USA (in the Big Geysers area of California), and Japan. In Iceland geothermal waters are utilized for district heating systems in the vicinity of Reykjavik.