Extraction turbines and feed-heating in geothermal binary plants: A thermodynamic performance assessment

Abstract

The use of extraction turbines in conjunction with multiple feedwater heaters is standard practice in conventional fossil or nuclear steam electrical generating stations as a way to conserve fuel by raising the final feedwater temperature entering the boiler. One way to improve the thermal efficiency of geothermal binary plants is to include a heat recuperator that uses the expanded, but still hot working fluid leaving the turbine to preheat the working fluid leaving the feed pump prior to reaching the main brine heat exchangers. However, the use of partially-expanded working fluid from an extraction turbine to further preheat the working fluid has not been widely deployed in geothermal binary plants. This paper will describe this technique in a feed-heating cycle, develop the working equations to assess the performance for a variety of geofluid temperatures, to determine whether or not this approach can be as effective in geothermal binary plants as it is in conventional nuclear power plants. Finally, we will discuss the practical aspects of this system in geothermal binary plants, and suggest some further studies to extend this concept to other geothermal applications.