Research on the Characteristics of the Coal-Oxygen Reaction in a Lean-Oxygen Environment Caused by Methane
Coal mine fire often occurs in lean-oxygen environments caused by methane. To clarify the characteristics and mechanisms of the coal-oxygen reaction under these conditions, coal-oxygen reaction experiments were carried using thermogravimetric analysis (TGA)-gas chromatography (GC) combined technology in the range of 30-800 °C. The thermogravimetric subtraction/derivative thermogravimetric subtraction (TG-S/DTG-S) curves, which can more accurately reflect the coal-oxygen process, were obtained by subtracting the TG/DTG curve of coal pyrolysis under the condition of pure N2. Through TG-S/DTG-S curves, the coal-oxygen reaction was divided into the low-temperature oxidation stage, accelerated oxidation stage, and combustion stage. In the low-temperature oxidation and accelerated oxidation stages, methane delayed the coal-oxygen reaction as an inert gas. Under the same oxygen concentration, the effect of methane on reducing CO and CO2 production and increasing ignition temperature (Ti) of coal was more obvious than that of N2. In the combustion stage, the high-temperature environment (>500 °C) caused intense combustion and decomposition of surrounding methane, which consumed a lot of oxygen by direct combustion of methane and combustion of methane decomposition products (C and H2) and released a large amount of CO, CO2, and H2. When the temperature was >586 °C, the oxygen was completely consumed by methane and the coal-oxygen reaction was completely inhibited. With the decrease of the initial reaction oxygen concentration (the increase of methane concentration), the production of CO2 decreased gradually at the same temperature, while the changes of CO and H2 were more complex. The research results are of great significance to the prediction and prevention of coal mine fire in goaf.