Thermal-mechanical properties and heat transfer process of heat storage/energy storage backfill body in mine

There are abundant geothermal resources in underground mines in China, and the exploitation of mineral resources in deep mines provides some favourable conditions for the exploitation of geothermal resources. Combining backfill mining with geothermal resource exploitation, utilizing heat storage/energy storage functional backfill body to extract geothermal resource and providing guarantee for power supply and pipeline layout of geothermal resource exploitation with the aid of existing conditions of deep mining, can effectively save some drilling and mining costs required for geothermal resource exploitation and promote the long-term sustainable development of mining areas. The overall implementation plan of heat storage/energy storage functional backfill consists of three stages, which are backfill material preparation, pipe arrangement and heat storage/heat release of backfill body. In this study, the aspect of material preparation, the material characteristics and optimization objectives suitable for heat storage/energy storage functional backfill are put forward. The thermophysical properties of backfill material, which the part aggregate (such as tailings) was instead by using the paraffin as phase change material, were tested. The results show that the compressive strength of backfill body increases with the increase of cement-tailing ratio or slurry mass concentration. Meanwhile, the addition of paraffin will reduce the compressive strength and thermal conductivity of backfill body, while the specific heat capacity increases significantly. The characteristics of heat extraction system for different pipe arrangement and different heat transfer conditions were studied by experimental test. The total energy efficiency coefficient of the system was calculated based on the heat balance and the optimal layout and design parameters of the pipe were obtained, when the serpentine pipe arrangement is adopted, the inlet velocity of heat transfer fluid is 0.7 m/s and the surrounding rock temperature is 35 ℃, the energy efficiency coefficient is the highest, which is 0.48. The heat storage/heat release behavior of backfill body added with paraffin was studied by numerical simulation, the results show that: in the process of heat storage/heat release, the backfill body with 10% mass fraction paraffin can store 55.5% more heat capacity than the backfill body without paraffin, however, the heat release capacity is greatly reduced and the total energy efficiency coefficient is reduced. © 2021, Editorial Office of Journal of China Coal Society. All right reserved.