Types of Geothermal Power Plants.
This was the original, and the least common type of geothermal power plant, utilizing the dry steam straight from the production well, drilled into the geothermal reservoir. The high pressure dry steam passes up the production well and through a rock catcher; a series of mesh filters which catch any rocks, stones or other debris, which would damage the turbine blades. The steam then passes through a steam turbine that drives an electrical generator, which produces electricity for the grid.
The steam exits the LP stage of the turbine and into the turbine condenser, that is under a vacuum. From here the condensate is pumped through a series of scrubbing towers that remove any residual non-condensable gasses. The condensate is then pumped to the water cooling towers, where it is cooled, with any remaining incondensable gasses re-circulated to the scrubbers before being re-injected with the cooled condensate down the injection well into the geothermal reservoir.
This type of plant injects water and condensate into the geothermal reservoir through the injection well that forces water at a high temperature (360°F) up through the production well. From the production well it is pumped through a series of pressure vessels which being at a lower internal pressure than the hot geothermal fluid, causes the water to flash off into low, medium and high pressure steam. The steam then passes through the steam turbine, condensing and being treated as per a dry steam plant, returning to the geothermal reservoir along with the non-condensable gasses through the injection well.
This type of plant uses high temperature geothermal water to heat another fluid which has a lower boiling point than water. The secondary fluid, (usually isobutene or isopentane), is heated by the geothermal fluid through a heat exchanger and flashes of to a vapour. This vapour is used to drive a turbine, similar to a steam turbine and condensed back to a fluid before returning to the heat exchanger to start the cycle again. Because the geothermal fluid passes from the production well, through the heat exchanger and back down the well in a continuous closed loop system. Therefore in this type of plant there is no escape of noxious gasses nor is there any gas scrubbing required. (Thus the plant type binary, meaning two, in this case referring to the two cycles).
1. Oregon Gov
2. Darvill Clara