Optimum Cycles for Geothermal Power Plants

Abstract

The optimum cycle for a geothermal power plant depends on the geothermal brine/steam characteristics and the site features. Selecting the most suitable configuration must therefore be based on the geothermal source and heat reject conditions (i.e. ambient conditions). This paper investigates the suitable plant configurations for four different kinds of geothermal sources, with increasing enthalpy, going from relatively low temperature (115 ?C) liquid brine to high temperature (250 ?C) superheated steam, and points out the best solution for each case. In order to do this, a sophisticated calculation model, which can manage different geothermal fluids, different working fluids and various plant configurations, is employed. The code is capable of optimizing the cycle thermodynamic parameters in order to get the highest economic return. The power conversion cycles considered include the ìtraditionalî flash and binary cycles and the ìadvancedî combined and mixed cycles, obtained respectively by: ï coupling a flash cycle (topping cycle) with a binary cycle (bottoming cycle) ï splitting the liquid and gaseous content of the source in two separate flows and then feeding a binary cycle with the liquid fraction, and a flash cycle with the gaseous fraction. The results show the optimum solution for each geothermal resource, the consequent economic return and power produced.