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►Geothermal plant: Steam plants use hydrothermal fluids
that are primarily steam. The steam goes directly to a turbine, which
drives a generator that produces electricity. The steam eliminates the
need to burn fossil fuels to run the turbine. (Also eliminating the need
to transport and store fuels!) This is the oldest type of geothermal
power plant. It was first used at Lardarello in Italy in 1904, and is
still
Flash Steam Power Plants Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy.
Binary-Cycle Power Plants Most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants. Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants.
The Future of Geothermal Electricity Steam and hot water reservoirs are just a small part of the geothermal resource. The Earth's magma and hot dry rock will provide cheap, clean, and almost unlimited energy as soon as we develop the technology to use them. In the meantime, because they're so abundant, moderate-temperature sites running binary-cycle power plants will be the most common electricity producers.
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Geothermal Power Plant -
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