Numerical simulations on the self-heating behaviours of coal piles considering aging effect

In this study, the theoretical approach and numerical modelling of coal spontaneous combustion were investigated considering the aging effect. Numerical simulations of three-dimensional coal piles in cubic wire-mesh baskets (WMBs) were performed using ANSYS FLUENT. A theoretical heat generation model was constructed that incorporated aging effect (using a decay-power factor, γ), equivalent oxidation exposure time (EOE-time) theory, and moisture evaporation. The results from this model were compared with those obtained from the conventional Arrhenius equation, which does not take aging effect into account. The γ value required to accurately express the aging effect in conjunction with EOE-time theory was determined to be 4 × 10⁻⁵ s⁻¹ for the low-rank coal used in this work. This value was obtained by comparing simulated and measured coal temperature-time curves in WMBs. A moisture evaporation model that included an estimated evaporation heat rate was applied, based on the difference between coal moisture ratio and air relative humidity. These models were employed to simulate the self-ignition behaviour of coal piles and to explore the different heating processes of wet and dry coals. Finally, the relationships between pile volume and both critical self-ignition temperature and critical lead time were presented for industrial management of coal piles.