Dry Steam Geothermal

Dry Steam Geothermal Scheme

This type of formation is called a "dry steam" power plant because the steam is released from the pressure of a deep reservoir, through a rock catcher, and then past the power generator turbines. Many early geothermal projects, such as The Geysers dry steam power plant in Northern California, depend on high temperature steam formations to directly provide the energy to drive power generator turbines.

Production wells are drilled down to the aquifer and the superheated, pressurised steam (180°-350°C) is brought to the surface at high speeds, and passed through a steam turbine to generate electricity. Dry steam reservoirs use the water in the earth's crust, which is heated by the mantle and released through vents in the form of steam. The dry steam power plant is suitable where the geothermal steam is not mixed with water. In simple power plants, the low pressure steam output from the turbine is vented to the atmosphere, but more commonly, the steam is passed through a condenser to convert it to water. This improves the efficiency of the turbine and avoids the environmental problems caused from the direct release of steam into the atmosphere.

This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy where it has powered electric railroads for since 1904. At peak production, these dry steam geothermal power plants are the world's largest single source of geothermal power producing up to 2,000 megawatts of electricity an hour. That is about twice the amount of electricity a large nuclear power plant can produce. These dry steam power plants emit only excess steam and very minor amounts of gases. About 6 percent of the energy used in northern California is produced at 28 dry steam reservoir plants found at The Geysers dry steam fields in northern California.