Numerical study on thermal-hydro coupling characteristics of underground coal combustion under heterogeneous void fraction

Abstract

Coal seam mining will lead to the movement and fissures of the overlying strata, which makes a complex void condition between the mining area and the ground surface. The void condition plays a key role in the occurrence and expansion of underground coal fires. In this study, the void rate model and the coupled thermal-hydro model of the underground coal fire were constructed. The COMSOL Multiphysics was used to study the coupling law of the temperature field and gas flow field of coal seam spontaneous combustion. By setting different oxygen content and inlet gas velocity, the influence of the external environmental parameters on the expansion law of underground coal fire is analyzed. The results show that the void characteristics of the mining area and the overlying strata have an obvious influence on the expansion of underground coal fire, and there is also a two-way coupling effect of the temperature field and gas flow field. The analyses of the influencing parameters show that reducing the oxygen content or increasing the inlet gas velocity will have a certain inhibitory effect on the expansion of underground coal fires, which can reduce the risk of spontaneous combustion.

Keywords

• Underground coal fire
• Void characteristics
• Thermal-hydro coupling characteristics
• Oxygen consumption
• Gas velocity