Optimization of an integrated gas turbine–geothermal power plant

Abstract

Geothermal resources represent an important renewable energy source for countries such as Italy, where steam dominated geothermal fields are present and have been exploited for decades. The main drawback in the direct use of geothermal steam is the low thermodynamic efficiency, due to its relatively low pressure and temperature. Steam from Italian steam dominated geothermal fields may be available up to 18 bar pressure and 207°C temperature, with a noncondensable gas content ranging from 4 to 10% by weight. In this paper the possibility to integrate geothermal power plants with a gas turbine is examined, in order to increase geothermal steam temperature through heat exchange with the gas turbine exhaust. The combination of ENEL standard sizes of geothermal power plants with commercially available gas turbines has been evaluated. In particular, an optimization of the gas turbine has been made in order to obtain the most suitable inlet conditions to the steam turbine and the highest overall efficiency.