Improved layouts and performance of single and double flash steam geothermal power plants obtained by the HeatSep method

Single and double flash steam power plants are commonly used in the utilization of high enthalpy liquid dominated geothermal reservoirs. In these plants, the expansion line in the wet steam region results in significant penalties of turbine isentropic efficiency and power output. Accordingly, the “self-superheating” and “interstage heating” plant modifications have been recently proposed in the literature to address this issue. In the new flash steam layouts embedding these modifications, the saturated steam at turbine inlet is superheated by using the heat of the saturated liquid, which is cooled before the flashing process. In this study, the aforementioned and additional new flash steam plant layouts are generated by employing a systematic method, called HeatSep, for the optimum design of energy systems, which separates the parameter optimization of the basic plant configuration from the synthesis of the heat transfer network within the system. According to this method, all the thermal connections between consecutive basic plant components are “cut” to let these temperatures vary and in turn generate additional hot and cold streams, which are combined to enhance the overall performance of the system. For instance, the single flash plant with self-superheating is simply obtained by cutting the thermal links between production well and wellhead valve and between cyclone separator and steam turbine. In the double flash plant the higher number of basic plant components allows for a higher number of thermal cuts and heat integration options. Unlike the existing literature, the maximum power output is not constrained by a predefined heat transfer network, the structure of which is instead a result of the design optimization. A simulation model is developed in the Matlab/Simulink environment to explore the maximum potential of single and double flash geothermal power plants for power generation from liquid dominated reservoirs in the temperature range 200-320°C. The results show that the maximum power output of the novel single and double flash steam plants exceeds by 5.5-9.2% and 3.9-7.7% the maximum attainable by the corresponding traditional plants without internal heat integration. Moreover, the optimum heat transfer network obtained for the double flash system is found to be different from those presented in the literature.