Power Plant Engineering

Fig. 2.33. A Geothermal Power Plant at the Geysers.
In the United States, the first attempt at developing the geysers field was made in 1922. Steam
was successfully tapped, but the pipes and turbines of the time were unable to cope with the corrosive
and abrasive steam. The effort was not revived until 1956 when two companies, Magma Power and
Thermal Power, tapped the area for steam and sold it to Pacific Gas and Electric Company. By that time
stainless steel alloys were developed that could withstand the corrosive steam, and the first electric-
generating unit of 11 mW capacity began operation in 1960. Since then 13 generally progressively
larger units have been added to the system. The latest is a 109 mW unit that began operation in September
1982 and which brought the Geysers total capacity to 909 mW. Two more units are under construction
and four more are planned, which will bring the total capacity to 1514 mW by the late 1980s.
Other electric-generating fields of note are in New Zealand (where the main activity at Wairakei
dates back to 1958), Japan, Mexico (at Cerro Prieto), the Phillipines, the Soviet Union, and Iceland (a
large space-heating program).
Future world projections for geothermal electric production, based on the decade of the 1970s,
are 7 percent per year. In the last four years of that decade, however, the growth rate was 19 percent per
year. In the United States, the projections are for growth between 13.5 and 22 percent per year through
the 1980s, which is 2.5 to 4 times the 5.3 percent per year growth rate of the total electric-generating
capacity. This includes the steam field at the Geysers and other fields of different types.
The U.S. Geological Survey predicts a U.S. potential from currently iden-tified sources to be
around 23,000 mW of electric power and around 42 × 10 SkJ of space and process heat for 30 years
with existing technology, and 72,000 to 127,000 mW of electricity and 144 to 294 × 10
15
Btu of heat
from unidentified sources. Areas of geothermal potential in the North American continent, Geysers
Region in Northern California, the Imperial Valley in Southern California, and the Yellowstone Region
in Idaho, Montana, and Wyoming.
Most power plants need steam to generate electricity. The steam rotates a turbine that activates
a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam.
Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of
miles or more below the Earth’s surface. There are three types of geothermal power plants: dry steam,
flash steam, and binary cycle.

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92
POWER PLANT ENGINEERING
Turbine
Generator
Condenser
Air and water
vapour
Cooling
tower
Air
Air
Water
Water
Water
Production well
Steam
Geothermal Zone
Injection
well