Effect of particle size on indicator gas emission during high-temperature oxidation of weathered coal

Coal spontaneous combustion is one of the severe nature hazards among nature resources. There are many influence factors which control the development of spontaneous combustion such as particle size, oxygen concentration, etc. Weathering effects alter the spontaneous combustion characteristics of coal. To explore the effect of particle size on gas emission from weathered coal under high temperature oxygen deficiency, the macroscopic spontaneous combustion characteristics of weathered coal with various particle sizes in high temperature oxidation process were studied. The gas concentration of different particle sizes with weathered coal oxidation from normal temperature to 600 °C was tested by the self-built high temperature program experiment system, and the variation law of the indicator gas was analyzed. The results showed that there were different experimental phenomena in each particle size coal sample. The concentration of indicator gas neither increased nor decreased monotonically with the change of particle size. Roughly, 3 mm is the critical particle size in the process of high temperature oxidation of weathered coal. The experimental results provided a pivotal theoretical basis for the early prediction and the scientific prevention of the spontaneous combustion of the weathered coal during the mining process of the open pit and the shallow coal seam.