Energy and exergy analysis of a hot dry rock geothermal resource power generation system based on organic Rankine cycle

Hot dry rock is an abundant, stable and low-carbon geothermal resource, which has a promising prospect for power generation in China. In this paper, a hot dry rock power generation system model based on conventional organic Rankine cycle was established. The performance of the system was evaluated by thermodynamic analysis, as well as energy and exergy analyses. Four types of organic working fluids were selected to investigate their effects on system energy efficiency. R114 had much higher energy efficiency (17.50%similar to 19.00%) than other three organic working fluids (R245fa, R245ca and R601) when water flow rate ranged from 80 t/h to 260 t/h. When R245fa was used as working fluid and power output was set at 4 MW, energy and exergy efficiency of the system were 15.27% and 50.42%, respectively. According to the energy flow analysis, the major energy losses (15.67 MW) in the system were attributed to the discharge temperature of turbine exhaust. However, exergy flow analysis indicated that the energy loss from turbine exhausts was not as serious as expected, since the work potential of that energy was limited. The exergy destruction of each component in the system was calculated, and the results showed that heat exchanger and the vapor separator were the weakness components in the system, and they respectively contributed to 44.8% and 29.8% of the total exergy destruction. The results obtained in this study provide possible strategies to improve the overall performance of the hot dry rock power generation system based on conventional organic Rankine cycle.