Role of the rapid gas desorption of coal powders in the development stage of outbursts

•Prove the necessity of coal powders in outbursts, which normally exist in the structural areas underground.•Take the outburst as a process of coal pneumatic conveying and obtain the different types of energy.•Obtain the critical coal diameter to provide adequately fast desorption for conveying the outburst coal.•Clarify the effect of rapid desorption on the outburst coal conveying. Summarize and deepen the outburst mechanism.

Based on the desorption experiments of coal particles with different sizes, the possibility of the existence of coal powders in the outburst development stage was studied from the perspective of energy balance and pneumatic conveying. The energy involved in outbursts (gas expansion energy, transport energy and remaining kinetic energy) and the general range of the transport critical particle size (TCPS, the coal particle size with the lowest gas desorption speed causing the outburst coal transport over a certain distance) were calculated. This study concludes that to convey outburst coal, it is necessary to capture the desorbed gas supply because the limited amount of free gas cannot meet the high energy demand. Rapid desorption within a short period is an essential condition for the development of an outburst. Only coal particles with small sizes can exhibit this high desorption speed. Based on the relationship between the initial desorption speed and the particle size, a mathematical model that could be used to estimate the TCPS of the Zhongliangshan outburst (117 μm) was established. Historical data regarding the Zhongliangshan outbursts and other mines support the results of calculations and certify the important role that coal powders play in outbursts.