Ignition control and waste heat assessment of spontaneous combustion gangue hill by gravity heat pipe group: a case study in Shanxi Province, China.

Spontaneous combustion gangue hill has attracted great attention due to serious environmental pollution and terrible geological disasters. However, the rich thermal resources inside are often ignored. In order to control the spontaneous combustion of gangue hill and utilize the internal waste heat resources, this project studied the combined treatment effect of 821 gravity heat pipes, laid 47 sets of temperature monitoring devices, evaluated the storage of waste heat resources, and proposed different waste heat utilization methods. The results show that (1) the positions of spontaneous combustion are all located on the windward slope. The highest temperature is in the range of 6 ~ 12 m underground, exceeding 700 ℃. (2) The single-tube experiment of gravity heat pipe shows that the effective temperature control radius is 2 m. The cooling effect is obvious in the range of 3 ~ 5 m underground. However, the temperature rises at the depth of 1 m underground. (3) After 90 days of treatment of the gravity heat pipe group, the temperature at the depths of 3 m, 4 m, 5 m, and 6 m in the high-temperature zone dropped by 56 ℃, 66 ℃, 63 ℃, and 42 ℃, respectively. The maximum temperature drop exceeds 160 ℃. The average temperature drop in the middle- and low-temperature areas is between 9 and 21 °C. (4) The concentration of harmful gases (CO, SO, and HS) decreases by more than 90%. The hazard level is greatly reduced. (5) The amount of waste heat resources contained within 10 m of the spontaneous combustion gangue hill is 7.83E13J. Waste heat resources can be used for indoor heating and greenhouse cultivation. And, under the temperature difference of 50 °C, 100 °C, and 150 °C, the electric energy generated by the heat through the thermoelectric conversion device in the high-temperature zone of the gangue hill is 4056.8 kWh, 7468.2 kWh, and 10,603 kWh, respectively.