Study on the explosion characteristics of methane-air with coal dust originating from low-temperature oxidation of coal

The aim of this research was to reveal the explosion characteristics of methane-air with the admixtures of low-temperature oxidized coal dust. For this purpose, the particles (48-75 μm) of raw and oxidized coal dust with oxidation temperature of 80 °C, 160 °C and 240 °C were sampled. The industrial analysis and surface morphology of coal dust after low-temperature oxidation were comparatively investigated. In addition, the explosion parameters and flame propagation behaviors of methane-air/coal dust mixtures were monitored and analyzed by a 20 L spherical vessel reactor and a high speed camera, respectively. The results indicated that coal dust after low-temperature oxidation showed a significant decrease in the content of moisture and volatiles, and more cracks and pores were formed on their surface. The explosion experiments revealed that the coal dust after low-temperature oxidation of 240 °C had prolonged the combustion time of methane-air/coal dust mixtures by 81.69%, and increased the maximum overpressure from 0.67 MPa to 0.73 MPa as compared to the raw coal dust. The flame propagation behaviors of methane-air/coal dust mixtures showed that the coal dust after low-temperature oxidation displayed a lower flame propagation speed in the stage of gas phase combustion reaction, mainly due to the loss of volatile matter. This paper concluded that the reduction of volatile matter in the coal dust caused by the low-temperature oxidation inhibited the flame propagation of the methane-air/coal dust mixtures, but the cracks and pores formed during the low-temperature oxidation process promoted the combustion of coke in the coal dust.