Techno-economic and environmental performance of combined heat and power for hot dry rock based on life cycle assessment

Hot dry rock (HDR) is considered a clean alternative energy source to fossil fuels. In order to comprehensively analyze the energy acquisition and energy conversion performance of HDR during the full life cycle, a Thermal- Hydraulic-Mechanical (THM) model is developed in this study to simulate the flow heat transfer in the geothermal reservoir fracture and obtain the production well outlet capacity during the full life cycle. Then, the organic Rankine cycle (ORC)-based stand-alone power (SP) and combined heating and power (CHP) system are built and optimized. Finally, the capacity of the two systems is compared during the full life cycle. The results indicate that the production well outlet temperature fluctuates around 169 degrees C in the first decade, then drops sharply from the tenth year and levels off after the twentieth year. The length of the decreasing trend of the production well outlet temperature is negatively correlated with the mass flow rate. Compared to the SP system, CHP system has increased the thermal efficiency by 11.44 times and shortened the payback period by three years. Furthermore, the CO2 reduction of the geothermal SP system compared to fossil fuel-based power generation can reach 2.88 x 108 kg.