Secondary Explosion Characteristics and Chemical Kinetics of CH4/Air Induced by a High-Temperature Surface

The gas explosion induced by the high-temperature surface of coal spontaneous combustion in goaf will cause a devastating blow to personnel and equipment in the process of coal mining. Secondary explosion may be induced by the high-temperature surface of coal spontaneous combustion after primary explosion with the continuous emission of gas and the ventilation of goaf. This will lead to new disasters for the ongoingrescue operation. A high-temperature source explosion experimental system consistent with the similarity and unity of goaf was designed and developed based on the similarity criterion in this study. A CH₄/air explosion experiment was carried out with the high-temperature surface as an ignition source. The characteristics of secondary explosion were studied, and chemical kinetics was analyzed. It is of great significance to the safety of the process of mining production. The results show that the secondary explosion limit (6.5–14%) is less than the primary explosion (5.5–14.5%). Its explosion risk (F) is reduced by 15.6%. The key parameters P_max, T_max, and (dP/dt)_max of secondary explosion at each concentration are lower than those of primary explosion. The t_e of secondary explosion is higher than primary explosion. The most dangerous concentration of primary and secondary explosions induced by the high-temperature surface is 11.5%. Carbon oxides (CO₂ and CO) and C₂ hydrocarbon gases (C₂H₂, C₂H₄, and C₂H₆) are generated after primary explosion. The chemical kinetics of secondary explosion was analyzed with CHEMKIN Pro 2021. When the CH₄ concentration is <11.5%, the formation of the key free radicals ·H, ·O, ·OH, and CH₂O is inhibited due to the formation of CO₂. When the CH₄ concentration is ≥11.5%, the formation of the key free radicals ·H, ·O, ·OH, and CH₂O is inhibited due to the generation of combustible gases (C₂H₂, C₂H₄, C₂H₆, and CO) and inert gas (CO₂). As a result, the limit range of secondary explosion and the explosion hazard characteristics are reduced. R156 and R158 played major roles in the process of secondary explosion with the analysis of reaction sensitivity.