Thermo-economic investigation of binary flashing cycle for enhanced geothermal system

Abstract

In this paper, as a promising technology, the binary flashing cycle (BFC) is proposed for enhanced geothermal systems (EGS) exploitation. The detailed thermo-economic model is developed. With the thermal efficiency, net power output, total investment cost and levelized energy cost (LEC) as evaluation criteria, the flowsheet modeling and thermo-economic analysis are conducted. It is revealed that larger geothermal well depth and geothermal brine flow rate are in favor for improving system thermal performance. However, it is not always beneficial for the economic performance. There exist the optimal depth (3300 m) and geothermal brine flow rate (57 kg/s), at which the LEC obtains the minimum (0.329 USD/kWh) and (0.328 USD/kWh), respectively. For an economic EGS operation, the geothermal brine flow rate should be no less than 50 kg/s. The influences of operating parameters, including generation temperature, dryness degree at the vapor generator outlet and flashing temperature, on the evaluation criteria are also discussed. To achieve better economic benefits, the generation temperature should be less than 110 °C and the dryness should be larger than 0.2. With the flashing temperature 72−82 °C, the EGS-BFC yields excellent thermodynamic and economic performance. The present investigation will be helpful for the geothermal well construction, resource mining and generation system operating parameters design.