Technology

Our geothermal power plants employ binary systems and flash design.

Binary system
 
In a plant using a binary system, geothermal fluid, either hot water (also called brine) or steam, or both, is extracted from an underground reservoir. It flows from the wellhead through a gathering system of insulated steel pipelines to a heat exchanger, which heats a secondary working fluid which has a low boiling point. This is typically an organic fluid such as isopentane or isobutane, which is vaporized and used to drive the turbine. The organic fluid is then condensed in a condenser which may be cooled by air or by water from a cooling tower. The condensed fluid is then recycled back to the heat exchanger, closing the cycle within the sealed system. The cooled geothermal fluid is reinjected back into the reservoir.

The binary technology is depicted in the graphic below.

Flash design system
 
In a plant using flash design, geothermal fluid is extracted from the underground reservoir and flows from the wellhead through a gathering system of insulated steel pipelines to flash tanks and/or separators. There, the steam is separated from the brine and sent to a demister in the plant, where any remaining water droplets are removed. This produces a stream of dry steam, which drives a turbine generator to produce electricity. In some cases, the brine at the outlet of the separator is flashed a second time (dual flash), providing additional steam at lower pressure used in the low pressure section steam turbine to produce additional electricity. Steam exhausted from the steam turbine is condensed in a surface or direct contact condenser cooled by cold water from a cooling tower. The non-condensable gases (such as carbon dioxide) are removed through the removal system in order to optimize the performance of the steam turbines. The condensate is used to provide make-up water for the cooling tower. The hot brine remaining after separation of steam is injected back into the geothermal resource through a series of injection wells. The flash technology is depicted in the graphic below. In some instances, the wells directly produce dry steam (the flashing occuring under ground). In such cases, the steam is fed directly to the steam turbine and the rest of the system is similar to the flash power plant described below.