Experimental study on the effects of coal particle size and fissure size on underground coal fires

Underground coal fire (UCF) widely spreads in many countries, which is a serious threat to the environment and the safety of coal mining industries. The cause of UCF is complex and affected by many factors such as fissures and coal seam porosity. For the first time, a novel experimental framework is proposed to simulate UCF. Two variables i.e., the coal particle size (6mm, 9mm and 15mm) and fissure size (1cm, 2cm, 4cm and 6cm) are considered in experiments. The peak temperature, air velocity and the propagation rates of dry front, pyrolysis front and oxidation front are analyzed. The results show that peak temperature and spread rate of UCF increase if the particle size or fissure size increase. In the smoldering stage, the ventilation is driven by buoyancy force produced by hot smoke. And this driving action increases with the particle size or fissure size, which further promotes smoldering by inhaling more air. The smoldering may turn to flaming combustion when the particle size is 9mm with fissure size ⩾ 4cm or the particle size is 15mm. (paper)