An experimental study on smouldering coal particles: Effects of air leakage and burning position in underground coal fires

The dominant combustion mode in underground coal fires (UCFs) is smouldering. A packed coal bed reactor with natural convection as the driving force was designed to represent the spatial features of three typical UCFs. Effects of air leakage through the left-hand wall and the burning position were investigated with three experi-mental cases. The ignition test showed that coarser particles (0.5-1 mm) failed to be ignited, while self-sustained smouldering was successfully initiated for finer particles (<0.5 mm). The repeatability test yielded reproducible results at a macroscopic level (maximum difference of 6.4%), with main uncertainties coming from the ignition stage when the formation of cracks introduces randomness. It was observed that air leakage through the left-hand wall enhanced the smouldering temperature near the wall boundary, and the enhancement became more prominent with the increasing depth. When ignition was initiated at the middle part of the reactor, the top region of the coal bed burned nearly twice faster. The quantitative results are dependent on specific conditions in the present study, while the relative differences among three cases could shed some light on smouldering propa-gation in actual UCFs from the perspective of fire safety.

Automated summary

Smouldering is the dominant combustion mode in underground coal fires (UCFs). This study investigated the effects of air leakage and burning position on smouldering propagation in UCFs. The results showed that coarser particles failed to ignite, while finer particles successfully initiated self-sustained smouldering. Air leakage enhanced the smouldering temperature near the wall boundary, and the ignition position influenced the burning rate of the coal bed.