Investigate on spontaneous combustion characteristics of lignite stockpiles considering moisture and particle size effects

Coal spontaneous combustion (CSC) threatens the safety of the coal industry, with moisture content and particle size being pivotal factors. This study examines the heating dynamics and critical self-ignition temperatures (CSITs) of Baiyinhua lignite stockpiles through wire-mesh basket (WMB) tests at two scales. The CSC process in coal stockpiles unfolds in four stages. Notably, Stage II is notable for significant moisture evaporation between 43 and 84 degrees C, while Stage IV marks the onset of self-heating. Moisture evaporation absorbs heat, linearly prolonging the Stage II duration, which accounts for 0%-70 % of the total time. Conversely, larger particle sizes enhance pore seepage, effectively shortening the heating time. The time for d = 20 mm (particle size) coal sample to reach ambient temperature is roughly half that of 1.5 mm. CSITs of raw coal increase by 10-15 degrees C compared to the dry coal, and CSIT of coal samples with d = 50 mm has increased by 17.5 degrees C compared to 10 mm. Therefore, both an increase in particle size and moisture content increase the CSIT, thereby reducing the propensity for CSC. FrankKamenetskii theory and dimensionless analysis predict spontaneous combustion risks in field-scale coal stockpiles. This investigation contributes valuable insights to the estimation and prevention of CSC.