Study on the Heat Transfer Law of Coal Spontaneous Combustion in Open-Pit Mining Benches Under Varying Wind Speeds

The influence of external wind speed is critical for determining the spatial distribution of self-heating zones within open-pit mining benches. This study initially establishes the critical temperature required for the spontaneous combustion of the 13^# coal seam at the Hequ Open-Pit Mine. Subsequently, a comprehensive self-heating temperature rise model for coal bodies in open-pit mining environments is developed. This model integrates airflow dynamics, heat transfer, material transport, and chemical reactions. The model's predictions were then analyzed using COMSOL Multiphysics, focusing on the localization of high-temperature zones, and validated through similarity experiments. The findings indicate that an increase in wind speed causes the self-heating zone to extend deeper into the coal mass. Notably, the high-temperature region predominantly occupies the lower portion of the bench slope, with its external boundary located between 0.9 and 2.0 m horizontally from the slope surface. Vertically, the lower boundary of this high-temperature zone is situated 1.6 to 2.35 m above the base of the coal seam. Moreover, the study reveals that below a threshold temperature of 73°C, an increase in wind speed results in a decrease in temperature within the high-temperature zone. Conversely, above this threshold, further increases in wind speed lead to a rise in temperature.