Research on a Coupled Total-Flow and Single-Flash (TF-SF) System for Power and Freshwater Generation from Geothermal Source

Abstract

In response to the twin development challenges of energy shortage and water-scarcity in worldwide arid to semi-arid regions with geothermal resources, a new combined power and freshwater generation system is proposed for geothermal energy utilization. In this system, a total-flow turbine (TF) is employed to be coupled with the traditional single-flash (SF) system and thereafter the coupled TF-SF system is investigated in this work. In addition to power generation, the exhaust steam from turbines are recovered to produce freshwater through condensation. Based on the novel designed system, the production of both power and water are studied under variable wellhead conditions, including variable wellhead pressures, temperatures, mass flowrates, and vapor qualities. The temperature of the separating point at which the total-flow expansion ends and the steam expansion starts is studied for optimal system output. In addition, the efficiency effects of the total-flow turbine on performance of the combined system is also investigated. The power generation comparison shows good power potential of the proposed TF-SF combined system. An effective total-flow turbine with an average efficiency of 65% can lead to an optimal power capacity, exceeding the traditional single-flash (SF) system by 23.7%. Moreover, more than 1/3 of total wellhead discharge can be recovered as desalinated freshwater by the naturally equipped condensation process of the power plant, showing extra benefit from geothermal energy utilization.