Environmental Engineering Reference
In-Depth Information
in a low-pressure tank known as a separator. The emergence from very high pressure
underground to very low pressure in the separator causes the hot water to quickly evaporate
in so-called steam flashes. This blast of steam is drawn away to operate a turbine. Because
thetankismuchcoolerthantheundergroundreservoir,someofthesteamcondensesbefore
reaching the turbine. This water, together with the condensed water that has passed through
the turbines, is then pumped back into the geothermal reservoir.
Flash steam power plants work very well in places where the water or steam extracted is
already at a very high temperature. Unfortunately, sites like this, where hot magma occurs
close to the surface, are rare. However, some geothermal plants can generate power using
waterattemperatures aslowas60degreesCelsius.Theseareknownasbinarycycleplants,
because the geothermal energy is exploited in two stages; the hot water extracted from the
reservoir is first used to vaporize a secondary fluid, typically pressurized isobutane. Unlike
water, which boils at 100 degrees Celsius, the secondary fluid vaporizes at a much lower
temperature, and is therefore able to drive a (smaller) turbine. The binary principle allows
geothermal power to be viable in more places, and this model is likely to predominate in
the future.
Figure 4.55.
The Sonoma Calpine 3 geothermal power plant at The Geysers field, 70
miles north of San Francisco in California, which was developed commercially in the
1960s. The steam powers twenty-two power plants with a net generating capacity of
approximately 1 GW, enough to power the city of San Francisco.
Source:
Stepheng3 at
Wikimedia Commons.
