Annual Simulation Results for an Air-Cooled Binary Power Cycle Employing Flash Cooling Enhancement

Abstract

Previous analysis and field tests have shown that the performance of air-cooled binary cycles can be significantly improved by employing evaporative cooling enhancement in hot weather. Because satisfactory cooling water is not always available, it has been proposed to flash a portion of the brine to provide it. A detailed hour-by-hour simulation model was developed for an air-cooled binary power cycle in which a portion of the geothermal fluid is first flashed to produce water for evaporative cooling enhancement of the air-cooled condensers. The model was run for separately optimized plants located in Reno, Nevada, at three different resource temperatures: 270ºF, 300ºF, and 330ºF (132ºC, 149 ºC, and 166 ºC). A constant price of electricity was assumed. Two types of evaporative cooling systems were analyzed: spray nozzles and evaporative media. The results show that for systems that are optimized to achieve the minimum specific cost (in $/kW), the amount of water produced by flashing and its associated cooling enhancement are insufficient to overcome the reduction in brine temperature caused by the flashing process and the parasitic power required to pump the water exiting the flash tank back to re-injection pressure.