Comparison of Thermodynamic Performances in Three Geothermal Power Plants Using Flash Steam

Abstract

Three geothermal systems, including single-flash, double-flash, and double-flash connected turbine flash geothermal power plants, are compared in terms of electrical power production and exergy efficiency. In the double-flash connected turbine (double-T) geothermal electrical power production systems, the outlet stream from the first steam turbine is recovered in the mixing chamber and combined with the vapor product of the second separator. The thermodynamic model for the single-flash, double-flash, and double-T geothermal systems is developed using energy and exergy balances for each component of the systems. From the thermodynamic model, the optimum flash chambers pressures, at which the electrical power production is a maximum, can be determined. It is found that, for an input geothermal source temperature of 230 °C and an input geothermal water mass flowrate of 230 kg/s, the optimum pressures for the first flash chamber are 300 kPa, 350 kPa, and 350 kPa for the single-flash, double-flash, and double-T geothermal systems, respectively. The electrical power produced in these systems at their corresponding optimum flashing pressures, respectively, are 16,000 kW, 19,500 kW, and 20,600 kW. Also, for the single-flash, double-flash, and double-T geothermal systems, the exergy efficiency at the optimum flash chamber pressures are found to be 44.2%, 47.1%, and 48.5%, respectively.