Performance analysis of a hybrid hot spring thermal energy conversion system using self-supply water

The hybrid hot spring thermal energy conversion (H-STEC) system combines flash evaporation using hot spring water with an organic Rankine cycle (ORC). In this framework, vapor generated from flash evaporation helps remove contaminants from the hot spring water, thereby addressing the issue of scaling in heat exchangers. Furthermore, the condensate from the flash vapor is utilized as supply water for the cooling tower, addressing challenges related to water supply procurement. This study investigates the characteristics of the H-STEC system and examines the impact of evaporator performance on its power output and desalination rate. Key parameters included in the analysis are the overall heat transfer coefficient of the evaporator, non-equilibrium temperature difference in the flash chamber of the H-STEC system, and heat exchanger fouling coefficient of the ORC. The findings reveal that a higher overall heat transfer coefficient of the evaporator initially improves performance but subsequently exhibits a substantial decrease in this coefficient owing to the scaling phenomenon induced by the hot spring water, reducing the power output. The maximum power output of the H-STEC system at an NETD value of 1.0 °C aligned with that of the ORC system at an Rf value of 2.35 × 10−4 m2K/W. Additionally, as the non-equilibrium temperature difference in the H-STEC system increases, the temperature of the hot spring water vapor supplied to the evaporator decreases. This reduction lowers the effective temperature difference of the working fluid, which, in turn, diminishes the power output of the H-STEC system.