ASME-Landmark:Geysers Unit 1


The largest geothermal field in the world, known as The Geysers, is located in the Mayacamas Mountains, approximately 72 miles (116 km) north of San Francisco. Geysers Unit 1, the first commercial geothermal electric generating station in North America, was a rebuilt kilowatt-size General Electric generator installed by the Pacific Gas and Electric Company engineers in 1960.

The field was first discovered in 1847 and minor attempts to develop it were made in 1922, but the steam that billowed from fumaroles was too corrosive for the piping and materials technology of the day. Today, the Geysers is the largest vapor-dominated geothermal system, ideal for electricity generation in that steam rises by natural means and can be applied directly to the turbine. It provides a fairly clean, slightly super-heated dry steam.

When the steam reaches the surface, it is first cleansed of solid impurities such as rock dust that could erode pipes and damage turbine blades. A closed loop system provides the necessary cooling water to condense the turbine exhaust steam. The warm water from the condenser is pumped to a mechanical draft cooling tower where its temperature is reduced, to be returned to the condenser again, thus closing the loop. Because there is very little surface or well water available at The Geysers, the make-up water required to replace what is lost through evaporation in the cooling tower is obtained by mixing the steam condensate with the circulating cooling water. The steam turbine drives the electric generator.

Today, more than 350 wells and 22 generators operate at The Geysers. [ ]