In high-temperature areas where geothermal fluid or steam can be found at over 200°C temperature at 1000 meter depth or less (Fridleifsson, 1979), flash steam or dry steam technology is most often applied. Flash turbines run on steam that has been separated from the geothermal fluid. Non-condensable gases are either scrubbed and collected or pumped back into the reservoir.
Geysir is the majority shareholder of HS Orka (formerly known as Hitaveita Sudurnesja), that generates electricity using flash and binary technology at its Svartsengi and Reykjanes geothermal power plants in Iceland.
High temperature geothermal areas are harnessed by drilling wells that reach the hot water or steam at depths of 1500 to 4000 meters. The geothermal fluid is brought to the surface normally as a two-phase mixture of steam and water. The steam is separated from the liquid brine and enters the turbine while the liquid (unflashed) brine is piped from the plant for re-injection. If applicable, the liquid brine can be used to generate more power or for heating before being re-injection into the geothermal reservoir.
The water fraction of the mixture must be removed before the fluid is sent to the turbine, both to increase the gaseous flow and to avoid damage to the turbine. During this separation of the steam and liquid, the enthalpy remains constant. The gaseous flow is then directed to the turbine where electricity is generated.
A double flash cycle can be applicable if the brine temperature and pressure are adequate; the medium pressure steam from the second flash chamber is injected to the turbine at an intermediate stage.
The steam exits the turbine as a saturated mixture and enters the condenser. The liquid brine exits the condenser and can be injected back to the ground or used for heating where it applies.
