Prasun Barua
CHAPTER-14: TYPES OF GEOTHERMAL POWER PLANT AND HOW THEY WORK?
Geothermal power plants are of three types. They are - flash steam, binary cycle and small scale power plant.
Flash steam power plants: Here, geothermal tanks of water having temperatures higher than 183°C are used. This hot water flows up with its self-pressure through shafts in the ground. Pressure decreases with its upward flowing and some portion of hot water boils into steam. The steam is then separated from the water and used to rotate the turbine in order to generate power. Any excess water and compressed steam are injected back into the tank which is a significant example of sustainable resource.
Binary cycle power plants: These plants work on water at lower temperatures of about 108°-182°C. In order to boil a working fluid, these plants utilize the heat of hot water which is basically an organic compound having lower boiling point. In the heat exchanger, water fluid is evaporated which helps to rotate a turbine. For reheating, the water is then injected back into the ground. During whole process, working fluid and the water are kept separated. So, there is no possibility of air emissions.
Small-scale power plants: These plants are typically under 5 megawatts. They have good prospect of extensive application in rural areas as well as a distributed energy resource. Distributed energy resource is the diversity of small and flexible power producing technologies which is integrated to develop the process of the electricity delivery system.