How Binary Geothermal Plants Work

Binary plants differ from Dry Steam and Flash Steam plants in that no form of water passes through the turbine to power the generator. In a Binary system water is pumped at lower temperatures, between 225°F and 360°F, which is not hot enough to flash the water into steam. Instead, the water is passed through a heat exchanger where it heats a secondary (binary) fluid, such as Iso-Butane or Iso-Pentane, which flashes at a lower temperature than water. The vapor from the flashed binary liquid is passed through the turbine to power the generator. As this is a closed loop system, the vapor is recondensed after passing colder water to be reused in the heat exchanger. The pumped water is sent back down an injection well for later use. The only actual water usage is what is used in the cooling tower to recondense the binary vapor.