Smoldering combustion of coal under forced air flow: experimental investigation

Coal can maintain smoldering combustion for a long time in the gob (mined-out) area which is a serious threat to the safety mining of a coal mine. However, few literatures can be obtained to well understand the smoldering phenomena of coal. To obtain the coal smoldering characteristics, vertical forward and reverse smoldering tests under different air flow rate were performed, and the smoldering combustion process, speed, and temperature were analyzed. It is found that although the combustion process of forward and reverse smoldering is significantly different, their smoldering speeds are the same and both increase monotonically with air flow rate as the higher the air flow rate is, the greater the oxygen consumption rate can reach. Even when the air flow rate is 0.074m/min in that the wind speed belongs to the suffocation zone of the gob, the coal can still undergo smoldering until complete combustion. This indicates that the smoldering fire cannot be effectively extinguished by only accelerating the stoping speed of the working face to create fire in the suffocation zone during the mining process. And for a sealed fire zone, it is also difficult for the smoldering fire to be completely extinguished as the fire zone cannot be absolutely sealed. Meanwhile, the risk of reverse smoldering is greater than forward smoldering due to its larger smoldering temperature.