Performance Evaluation of Heat Storage in a Full Operation Cycle of Cross-Seasonal Thermal Energy Storage Systems in Coal Mine Underground Reservoirs

Coal mining has generated a large amount of underground space, which has traditionally been reused mostly as mine wastewater storage. Given the excellent thermal insulation properties of these mine reservoirs, their potential for seasonal energy storage is considerable. However, research on cross-seasonal thermal energy storage utilizing coal mine underground reservoirs remains limited, and the thermal storage characteristics of such systems throughout their entire operational cycle are not yet fully understood. This study employs numerical simulation methods to analyze the thermal storage performance of a cross-seasonal thermal storage system based on a coal mine underground reservoir throughout a fully operation cycle. Based on the actual geological conditions of the Daliuta Coal Mine in the Shendong Mining Area, we established a thermal-fluid coupling model for a coal mine underground reservoir. Using this model, we analyzed the entire process of the heat injection stage, heat storage stage, and heat production stage within the cross-seasonal thermal energy storage system. Based on the model, the feasibility of utilizing a coal mine underground reservoir for cross-seasonal thermal energy storage was evaluated, and the system’s thermal storage performance was assessed. Results indicate that under current geological conditions of the Daliuta Coal Mine and designed operating parameters, the effective heat storage rate of the cross-seasonal system can reach 78.16%. Through investigation of the thermal storage process, the distribution evolution of hot water and heat dissipation mechanisms were thoroughly analyzed. This study identified the heat storage phase as the primary stage controlling heat loss and discussed key influencing factors affecting the thermal storage process. These findings provide novel insights for utilizing coal mine goafs and residual underground spaces, offering a reference for developing and designing novel energy storage facilities.