Synergetic mining of geothermal energy in deep mines: An innovative method for heat hazard control

The ongoing depletion of shallow resources has led to the mining of progressively deeper deposits, where high-temperature thermal stresses pose heat hazards and threaten worker safety. Mitigating geothermal hazards is therefore an essential component of mining operations in deep mines. In this paper, a novel synergetic mining approach is proposed that controls heat hazards at low cost and simultaneously exploits mineral and geothermal energy. Injection and production channels are designed below the ventilation tunnel to synchronously cool the tunnel surrounding rock and exploit mine geothermal energy. A fully coupled numerical model is established that simultaneously simulates heat and mass transfer in a large-scale ventilation network and geological reservoir. The cooling effect on the tunnel and heat recovery capacity of geothermal exploitation are investigated to assess the feasibility of the proposed scheme. Three case studies are presented to identify the impact of the water injection and production channel layout on the heat and mass transfer characteristics in the rock layer. The temperature of the tunnel surrounding rock is cooled over a few years via low-temperature water injection into the mine and heat production in the deep rock layer; this rapidly reduces the air temperature inside the tunnel. The total heat production rate initially rapidly increases and then gradually decreases. In the ninth year, the maximum heat production rate of the production channel reached 6.01 × 103 kW. The cooling effect on the roadway and heat production performance are optimal when the water injection channel is arranged under the air intake side of the main ventilation roadway of the mine and the heat production channel is arranged in the deep rock under the return air side of the roadway. After 4 years of water injection, the temperature at the end of the tunnel in Case 1 rapidly decreased to 30.9 °C; this temperature is 6.6 °C and 3.4 °C lower than those in Cases 2 and 3, respectively. Longer injection channel lengths can significantly reduce the injection pressure requirement in the injection channel. Shorter distances between the injection channel and tunnel are associated with faster reductions of the tunnel temperature. This technique significantly improves the thermal comfort inside the tunnel and produces considerable geothermal energy; a single heat production channel can produce 1.68 × 1015 J over a period of 10 years.