Research on energy storage in coal mine goafs: geological model construction and application based on Nanshan Mine

To address the reuse of abandoned mine spaces and seasonal fluctuations of renewable energy, this study established an indoor simulation experiment based on the hydrogeological conditions of the Nanshan Mining Area to investigate the heat transfer and storage characteristics in goafs. The experiment consisted of four stages: heat storage, heat preservation, heat release, and recovery. During heat storage, the goaf temperature rose significantly, reaching a peak of 330.6 K. During heat preservation, the temperature decreased slowly (by approximately 17.3–17.4 K) before stabilizing. Heat release occurred mainly in the first six days, with the central goaf temperature dropping by 21.9 K, while the outlet water temperature remained stable under high flow rate. During recovery, the system temperature stabilized at 291–292 K. Spatially, during heat preservation, the temperature at the center of the fourth stratum dropped by 15 K, with the longitudinal temperature change rate decreasing from bottom to top; during heat release, the longitudinal temperature change rate was relatively fast. Under the traditional calculation method, the experimental heat storage efficiency was 54.52%, corresponding to heat storage capacities of the largest single goaf and all goafs in the Nanshan Mining Area equivalent to burning 7.745 × 10⁵ kg and 2.013 × 10⁶ kg of standard coal, respectively (initial temperature 20 °C, maximum temperature 60 °C, actual water storage at 75% of submerged area). Under the improved method, the efficiency reached 93.03%, corresponding to heat storage capacities equivalent to burning 6.608 × 10⁵ kg and 1.718 × 10⁶ kg of standard coal, respectively (initial temperature 20 °C, storage temperature 40 °C, actual water storage at 75% of submerged area).