About Geo!
The Northern California Power Agency is the owner and operator of two geothermal power plants and the associated steam field. The project is part of the Geysers Known Geothermal Resource Area (KGRA) located in the scenic Mayacamus Mountian Range 75 miles north of San Francisco. The Geysers KGRA is the largest producer of geothermal electrical energy in the world, providing clean (low emissions of the "green house" gas carbon dioxide and no emissions of air toxins associated with the combustion of fossil fuels), renewable energy for California. NCPA is proud to be part of this valuable "green" energy source. The NCPA power plants are registered by the California Energy Commission as a Registered Renewable Supplier I. D. Number CEC-40021.
The two NCPA power plants each house two 55 megwatt nameplate turbine generators and associated equipment. Dry superheated steam is delivered to the power plants from 65 to 70 production wells via approximately 8 miles of pipeline. The NCPA Plant 1 was first paralleled to the grid on New Year's Day 1983 with Plant 2 coming on line some twenty-two months later in November of 1985. Since that time the NCPA power plants have been a valuable and reliable generation asset for the members of NCPA, operating with a greater than 95% availability.
Toward the end of the 1980's reservoir engineers at the Geysers discovered that steam pressure within the geothermal reservoir was declining at a higher than expected rate due primarily to over porduction of the resource by the various companies operating power plants at the Geysers. Continued high decline rates threatened to significantly reduce the life of the Geysers as a valuable renewable energy source. NCPA was the first operator at the Geyers to aggressively take steps to try and reverse the pressure decline trend.
NCPA's initial effort to limit decline involved changing its mode of operation of the plants from a base loaded operation to a load following mode of operation, where electrical output of the plants was limited during off peak hours of the day and increased during peak hours. Annual average output from the plants was reduced from a high of 248 megwatts to 155 megwatts to obtain maximum long-term benefits from the geothermal project. The NCPA plants were the first geothermal plants to be cycled on a regular basis.
To fully utilize some of the lower pressure steam found in certain sections of the NCPA reservoir, NCPA modified its Plant 1, Unit 2 turbine to a low pressure turbine in 1996, along with the steam field piping and computer control systems. This allowed the lower pressure steam to be dedicated to the low-pressure turbine whereby turbine-generator outputs were maintained even at the lower pressure.
NCPA found that while reservoir pressure was declining, heat within the reservoir was not. Water injected into the reservoir via strategically selected production wells (typically low steam producing wells and/or wells with a communicating fracture system within the resevoir to other production wells) was readily converted to steam, helping to lessen the effects of the pressure decline. To this end, NCPA constructed two water retention dams near each of the power plants that collect rainwater runoff for injection into the resevoir. This rainwater supplemented the condensate blowdown from each plant that was already being injected. Resevoir testing found that the reservoir was capable of converting even more injection water to steam than there was water available. To maximize the benefits of augmented injection, NCPA partnered with other operators at the Geysers and the Lake County Sanitation District to pump treated effluent from the City of Clearlake, California some 28 miles up to the Geysers field for injection.This Effluent Pipeline Project has helped to further extend the life of the NCPA geothermal project by offsetting some of the pressure decline effects of the reservoir. Five to eight wells are utilized as injection wells to handle the augmented injection program.
A byproduct of the conversion of geothermal energy to electricity at the Geysers is elemental sulfur. The sulfur is produced during the chemical abatement of hydrogen sulfide gas, a naturally occurring noncondensible gas with a noxious order that is produced along with the geothermal steam. In the early years of the NCPA project, this sulfur was treated as a hazardous waste due to trace amounts of mercury, also a natural occurring constituent of the geothermal steam produced at the Geysers. Through technological innovation, a method to remove mercury was developed that now renders the sulfur nonhazardous. The sulfur is now utilized as a feedstock in the California agricultural fertilizer industry, benefiting the environment by eliminating the need to landfill the material. NCPA maintains an on-site laboratory certified by the California Department of Health Services as an Environmental Testing Laboratory. The laboratory tests every shipment of sulfur leaving the site to ensure that it meets all regulations connected to its classsification as a nonhazardous byproduct.
The NCPA geothermal project has established itself as a leader in the industry, and through the dedicated efforts of the NCPA staff, will continue to be a leader for many more years into the future.
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