Modelling oxygen-limited and self-sustained smoldering propagation of underground coal fires driven by thermal buoyancy

Modelling oxygen-limited and self-sustained smoldering propagation is of significance for prevention of underground coal fire hazards. However, coupling oxidative reaction and oxygen transport in multi-scale porous media has been still a challenging issue and the conventional models have been questioned by inadequacy of TG-scale kinetic parameters applied to bed-scale propagation. In this work, an analytic expression of oxidative reaction rates limited by oxygen transport was derived from the conservation equations of oxygen species transport in gas and solid. Along with the Darcy air flow driven by thermal buoyancy, the oxygen-limited and self-sustained smoldering propagation of underground coal fires was modeled in this work. The model was compared with laboratory experiments and the conventional model. Results show that the proposed model well predicts the oxygen-limited and self-sustained smoldering propagations of underground bituminous and anthracite coal fires. The predictability of the proposed model is better than the conventional model in spite of great effort to modify kinetic parameters best fitting with experimental data. It is validated that the proposed model addresses the two puzzled issues in the conventional model with respect to buoyancy-driven, oxygen-limited, and self-sustained smoldering propagation of underground coal fires. This work may help to develop green countermeasures to mitigate underground coal smoldering fires.