Combined cycles for hybrid fossil/geothermal power generation

The paper presents a preliminary technical and economic assessment of a combined cycle in which the bottoming cycle is fed both by the exhaust energy from a combustion engine topping loop and by moderate- temperature energy from a geothermal resource. It is shown that this arrangement offers significant performance and economic advantages over the separate utilization of the two energy inputs. A gas-turbine-topped dual pressure toluene bottoming system matched to a 300 F (-150 C) hydrothermal resource can produce 10 to 20% more power than would be obtained from two separate plants; a conventional flash or binary power plant for the geothermal fluid, and a 35%-efficient combustion power plant for the oil or natural gas burned in the topping loop. The superior performance of the hybrid plant results in a commensurate reduction in the cost of electricity.