Numerical Simulation of the Dynamic Change Law of Spontaneous Combustion of Coal Gangue Mountains

To further study the problem of spontaneous combustion of coal gangue mountains, a multifield coupled simulation model was established based on the mathematical models of temperature field, gas concentration field, and seepage velocity field. In addition, the dynamic development law of these three physical fields in the process of spontaneous combustion is numerically simulated, and the relationship between gas concentration and temperature is studied and verified by experiments. The results show that in the initial stage of the thermal storage and heating process of the coal gangue mountain, the overall heating rate is small. With the passage of stacking time, a high-temperature area will gradually form inside, and the high-temperature area is concentrated near the windward side first and then spread to the leeward side. The oxygen on the windward side keeps a high concentration all of the time and gradually attenuates after entering the interior, and the overall concentration decreases with the extension of stacking time. The distribution law of carbon monoxide concentration is opposite to that of oxygen concentration. The variation law of carbon dioxide concentration is the same as that of temperature, that is, the concentration near the windward side is the highest, and then, it shows a distribution trend of first concentration and then divergence. The vortex phenomenon formed on the leeward side of the mountain outside and the chimney effect inside will aggravate the gas convection inside the gangue mountain, which makes the reaction continue so that the temperature of the gangue mountain keeps rising until it spontaneously ignites. There is a correlation between temperature and gas concentration. Among them, the concentration of carbon monoxide and carbon dioxide can well reflect the temperature change inside the coal gangue mountain, and the effect of carbon dioxide is better in the high-temperature area. The research results provide a theoretical reference for the prevention and control measures of spontaneous combustion of coal gangue mountains and have certain guiding significance.