Investigation of evaluation models for geothermal resources and intermittent operation/cycle thermal storage mode in closed coal mines

Abstract

The geothermal utilization of closed mines has a positive role to play in the reduction of fossil energy consumption, the development of renewable energy sources and the proper disposal of closed mine. In this work, for a more accurate evaluation of the sustainable geothermal production in closed mine, based on Xuzhou Jiahe coal mine, a 3D numerical model coupling roadway and goaf is established, and compared with other two numerical models. After analyzing the water storage space, flow field, temperature field, recovery well outlet temperature and heat recovery stability under long operation time, the roadway and goaf (RG) model performs more prominently and the results are more realistic. Both intermittent operation and cycle thermal storage mode have a higher recovery well outlet temperature in winter operation period, it can keep the heat supply at a high level, and accordingly the operational life of closed mine geothermal utilization system can be extended. COP (Coefficient of performance) of the system in winter operation period with different operation modes are basically the same when the recovery flow rate is low. As the recovery flow rate increase, COP of the system in cycle thermal storage mode has a significant advantage. In summer operation period, the outlet temperature in thermal storage cycle mode remains lower than the recharged hot water temperature, and it has a good cooling effect under high recovery flow conditions in the summer, contributes to the temperature return of thermal reservoir, and COP of the system in summer operation increase with recovery flow rate.