Numerical study of pulverized coal ignition under different oxygen conditions based on solid-gas coupling

The plane hot plate test is the most commonly used method to evaluate the self-heating and ignition hazards of pulverized coal, especially for the accumulation of pulverized coal on the hot surface. In order to solve the problem of lacking of numerical study on the ignition characteristics of pulverized coal coupled with air based on hot plate experiment, a multi-physical field numerical model of coal spontaneous combustion with solid gas coupling is established on the basis of literature [9]. The simulation results show that the thickness of bituminous pulverized coal is 5 mm, 12.5 mm, 20 mm and 30 mm, and the diameter is 100 mm. When the thermal runaway of pulverized coal occurs, the bituminous pulverized coal slowly heats up to 170 ℃ before 30 min, and a high temperature region appears in the center of the coal layer, and the thermal runaway occurs suddenly at 37 min. When the thermal runaway of bituminous pulverized coal does not occur, the temperature of coal sample becomes stable after 30 min, and the temperature is lower than 150 ℃, without obvious high temperature point. The simulation results are in good agreement with the experimental results in literature 9. Under the condition of thicker bituminous pulverized coal, the minimum ignition temperature of the numerical model is compared with the results of literature 9, and the difference between the two is small, which verifies the reliability of the numerical model. Based on the numerical model, the spontaneous combustion characteristics of bituminous pulverized coal under different oxygen mass fractions are analyzed. ① As the thickness of bituminous pulverized coal increases, the minimum ignition temperature tends to decrease. ② In the thermal runaway stage, the high temperature area is located at the upper part of the pulverized coal center. ③ The temperature rise of pulverized coal in the early stage is caused by the heat transfer of hot plate. With the increase of pulverized coal temperature, the dominant factor of coal oxidation reaction changes from heat to oxygen. ④ The peak value of pulverized coal temperature increases linearly with the oxygen mass fraction, and the ignition delay time decreases exponentially with the oxygen mass fraction.