Flash

The most common type of power plant to date is a flash power plant, where a mixture of liquid water and steam is produced from the wells. At a flash facility, hot liquid water from deep in the earth is under pressure and thus kept from boiling. As this hot water moves from deeper in the earth to shallower levels, it quickly loses pressure, boils and ‘flashes’ to steam. The steam is separated from the liquid in a surface vessel (steam separator) and is used to turn the turbine, and the turbine powers a generator. Flash power plants typically require resource temperatures in the range of 350-500°F (177° to 260°C). A number of technology options can be used with a flash system. Double flashing, the most popular of these, is more expensive than a single flash, and could concentrate chemical components if they exist in the geothermal water. Even considering potential drawbacks, most geothermal developers agree that double flash is more effective than single flash because a larger portion of the resource is used. Steam processing is an integral part of the gathering system for flash and steam plants. In both cases, separators are used to isolate and purify geothermal steam before it flows to the turbine. A flash system requires three or more stages of separation, including a primary flash separator that isolates steam from geothermal liquid, drip pots along the steam line, and a final polishing separator/scrubber. A steam wash process is often employed to further enhance steam purity. All geothermal power plants require piping systems to transport water or steam to complete the cycle of power generation and injection. Figures 14.6 and 14.7 show schematics of single and double flash-type power plants.

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Figure 14.6 Single flash steam power plant schematic

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