Influence law of air flows on the risk of secondary oxidation spontaneous combustion of coal

In response to the issue that the self-ignition hazard of coal secondary oxidation under diverse air flow conditions has not been systematically investigated, this study carried out secondary oxidation experiments on lignite under four distinct air flow conditions. By measuring indicators such as the oxygen consumption rate, exothermic intensity, oxygen consumption activation energy, and limiting self-ignition parameters of the coal samples during the experiment, the characteristics of the secondary oxidation hazard of coal under different air flow conditions were deeply explored. The experimental findings indicate that within the air flow range of 25-100 mL/min during the entire oxidation process (40-170°C) and in the first oxidation stage (40-90°C) at 200 mL/min air flow, the oxygen consumption rate and exothermic intensity of the coal samples were significantly higher than those in the primary oxidation process; however, in the second and third oxidation stages (100-170°C) at 200 mL/min air flow, the opposite characteristics were manifested. Additionally, as the air flow decreased, the differences in oxygen consumption rate and exothermic intensity between primary and secondary oxidation gradually diminished. Regarding the oxygen consumption activation energy, the primary oxidation process exhibited lower values in the first and second stages, but in the third stage, the secondary oxidation process at 25 mL/min and 100 mL/min air flow had lower oxygen consumption activation energy, while at 50 mL/min and 200 mL/min air flow, the primary oxidation process had lower oxygen consumption activation energy. The study also discovered that the increase in air flow and the accumulation of oxidation times would significantly enhance the possibility of coal self-ignition and its sustainability.