Effect of flammable gases produced from spontaneous smoldering combustion of coal on methane explosion in coal mines

Methane released from underground coal mines forms a highly explosive mixture when combined with air, which can be aggravated by the flammable gases produced from spontaneous smoldering combustion of coal in the mines. In this work, the flammable gases from coal smoldering combustion under conditions close to those in a coal mine are experimentally characterized by a self-designed quartz cylinder. The flammable gases mainly consist of CO at the initial stage of the smoldering combustion while they are composed of CO, H2 and CH4 at temperatures above 300 °C. Then, their effect on explosion of methane-air mixtures is investigated via experiments and simulations. The explosion characteristics and flame propagation of the typical in-mine methane-air mixtures enriched by the smoldering combustion products are studied using a 20 L spherical vessel reactor and a high-speed camera. Among all the methane-air mixtures tested, the addition of the smoldering combustion products to fuel-lean methane-air mixtures most remarkably enhance methane explosion. In the simulations, a sensitivity analysis is conducted to identify the dominant elementary reactions during the explosion process. As the share of the smoldering combustion products added to the methane-air mixture increases, the dominant elementary reaction for methane consumption is found to eventually shift to enhance methane explosion by generating a high concentration of OH and O. The results of this work not only improve the understanding of methane explosion but also benefit the development of new methane explosion suppression technology for coal-mining industry.