Effect of working fluid on super-long gravity heat pipe geothermal power generation system

Geothermal power generation is considered to have the potential as a basic power load, owing to its independence from ambient conditions, requiring no intermediate energy storage to cope with “peak clipping and valley filling”. The novel technical scheme of super-long gravity heat pipe (SLGHP) geothermal system in a single well has aroused widespread interest in the geothermal research and industry community. The advantage of this scheme is outputs saturated vapor, which can directly drive the turbine to produce electricity. For the SLGHP geothermal power system, the working fluid simultaneously affects the underground heat extraction process and the surface power generation system. In this study, a detailed analysis using the numerical and thermodynamic model is conducted based on the data from a real geothermal well in Xiong’an, Hebei Province of China. The appropriate production temperature was determined to maximize its power output. Thermodynamic analysis shows that under the same geothermal conditions, ammonia can produce higher power generation compared to water, although the exergy loss of water in ground power generation systems is relatively small. The difference narrows as geothermal conditions improve. This study unravels the generation performance of the two investigated working fluids, and the acquired knowledge can give the impetus required for further development of the SLGHP geothermal power generation system.