Variations of smoldering spread characteristics of Shanxi anthracite during forward smoldering propagation: Effect of ventilation rate

•The derived theoretical critical ventilation rate is 0.01242 m/s.•The limit air-supply for coal-smoldering propagation is 0.18–0.27 m3h-1kg−1.•Ranked smoldering spread rates: AMEFSPR > APFSPR > ACOFSR > APTFSR.•Developed novel mathematical model for smoldering propagation with ventilation rates. In view of the increasing risk of smoldering fire in coal mines, and to study the effect of ventilation rate on smoldering propagation deeply, the forward smoldering propagation process of Shanxi anthracite (SXA) is studied for nine different ventilation rates (10.0–30.0 L/min). Both simulations and micro-structure testing were performed. The results show that there are five distinct combustion stages (t0-t5) for the coal samples in the temperature range between 25.0 and 800.0℃. With increasing ventilation rates (33.3 to 100.0 mL/min), both the characteristic temperature and the activation energy of the studied coal at each stage decrease first before they increase. The heat release, however, occurs in reverse order (all samples reach a turning point at 75.0 mL/min). The critical ventilation rate range for a unit mass of SXA coal to sustain smoldering propagation was 0.18–0.27 m3/h kg−1. With increasing ventilation (between 10.0 and 30.0 L/min), key parameters such as average peak smoldering-temperature, average peak smoldering-temperature rise rate, spread rate of the average moisture-evaporation front, and average peak-temperature front also increase before they decrease, reaching their maxima at 22.5 L/min. The smolder reaction occurs in the following sequence: The moisture evaporation occurs first, which is followed by the pyrolysis reaction and the char-oxidation reaction. Then, the temperature gradually decreases after reaching its maximum.