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Geothermal energy
comes from within the earth, the result of the decay of radioactive
substances, chemical reactions, friction from the movement of the
continents and heat present when the earth formed.
Most of this heat is
at depths beyond the reach of current technology. The most famous example
of geothermal energy is the geyser Old Faithful in Yellowstone National
Park.
The four basic forms
of geothermal energy are dry steam, hot water or wet steam, hot dry rock,
and geopressurized systems. Dry steam occurs only in a few places,
but it is the only one of the forms that is in commercial use.
DRY STEAM runs
turbine generators at The Geysers plant north of San Francisco, producing
more than 500 megawatts of electric power.
Operators pipe dry
steam from natural underground reservoirs through a conventional steam
turbine-generator to produce electricity. The system converts the steam to
water in a condenser and returns the water to the earth.
HOT WATER: Hot
rock, far beneath the earth's surface heats underground water to
temperatures up to 2,200 degrees Fahrenheit. Pressure keeps the water in
liquid form. The hot water flows to the surface through wells. Deprived of
its pressure, it becomes steam to drive a steam turbine directly or to
heat another fluid to run a turbine.
Hot water geothermal
energy provides ides central heating for all the buildings in Reykjavik,
Iceland.
HOT DRY ROCK:
Extracting energy from subterranean hot dry rock means introducing a heat
exchange fluid (water) to carry the heat from the rock to the power plant.
Scientists inject water deep into fractured hot rock. Then they use the
heated water as geothermal water for conversion to useful energy.
GEOPRESSURIZED
SYSTEMS: Reservoirs of hot water mixed with methane gas, trapped
underground, offer the energy potentials of both pressure and burnable
methane, as well as the heat energy available from any geothermal resource. |
