You are here
U.S. geothermal power plants use cooling towers or air-cooled condensers to reject waste heat into the atmosphere. Therefore, unlike most fossil fuel and nuclear power plants, they dump no waste heat into rivers or surface water. Waste heat can disrupt biota, such as algae and fish, in local water bodies.
Technology for the safe, nonpolluting use of geothermal fluids has been carefully developed and rigorously tested. Geothermal production and injection wells are lined with steel or titanium casing and cement to isolate fluids from the environment, including groundwater. Repeated examination—using sonic logging instruments and videography—of the casing and cement ensures that no leakage occurs. Spent geothermal fluids are then injected back into the reservoirs from which they were drawn. This solves the fluid disposal problem. It also prolongs the use of the geothermal reservoirs because it replenishes the fluids.
The Lake County Sanitation District (LACOSAN) in northern California found that injecting effluent from its wastewater treatment facility into several wells connected to The Geysers geothermal reservoir was environmentally superior to conventional surface disposal methods, such as surface water discharge or land irrigation. Rising production shows that this effluent injection also replenishes the steam resource at The Geysers, which was diminishing prior to this process. It has reduced the amounts of noncondensable gases, including hydrogen sulfide, in the steam too. The recycling of this wastewater also helps conserve water resources in this arid region.
For more information about effluent injection at The Geysers, see:
- The Geysers Pipeline Project, Geo-Heat Center Web site
- Lake County Effluent Recycling Pipeline
- City of Santa Rosa Geysers Recharge Project.
To conserve water, especially in arid regions, geothermal power plants can use air instead of water to condense spent steam/turbine exhaust fluid for injection back into the reservoir. The low profiles of air-cooled plants also blend in well with scenic areas.
U.S. Department of Energy (DOE) laboratories continue to work on ways to improve the efficiency of air-cooled condensers.
DOE laboratories also continue to work on improving the cements used in geothermal wells. Work on these cements resulted in an R&D 100 Awardin 2000.