Numerical study on effects of air leakages from abandoned galleries on hill-side coal fires

• A novel approach was proposed to solve the varying timescales of transport and depletion of oxygen.
• A simplified formula of oxygen consumption rate at high temperature was proposed.
• Heterogeneous permeability induced by coal fires was considered.
• A two-dimensional unsteady-state model for hill-side coal fires was developed.
• Impacts of air leakage from abandoned gallery on hill-side coal fires was analyzed in detail.

In this paper, our main aims are to present a numerical model for hill-side coal fires and to analyze influences of air leakages from abandoned galleries on hill-side coal fires. A two-dimensional unsteady-state model for hill-side coal fires is developed. The coupling between chemical reactions in the coal seam and oxygen transport through adjacent rocks is involved. Heterogeneous permeability of different porous zones induced by rock mechanical failure is considered. Based on the single-particle reaction–diffusion model, a novel approach is proposed to estimate oxygen consumption rate controlled by oxygen transport at high temperature.Simulation results show that hill-side coal fires are remarkably intensified and accelerated by air leakage from the abandoned gallery: (1) the hottest spot is approximately 500 K higher than that for the case of no air leakage from the abandoned gallery; (2) temperature rise is much speedier than that in the case of no air leakage; (3) coal in the combustion zone starts to spontaneously combust approximately 50 days earlier compared to the sealed abandoned gallery; (4) high temperature zones including drying zone, baked zone and melting zone are larger than those in the condition of no air leakage from the abandoned gallery.