Multi-physics coupling model of coal spontaneous combustion in longwall gob area based on moving coordinates

Abstract

The spontaneous combustion of coal in gob area that is caused by longwall mining techniques results from the coupling effect of air seepage, oxygen transport, heat transfer and exothermic reaction. Previous researches are neither able to systematically address the whole process of spontaneous combustion in longwall gob nor model the continuous expansion of gob area perfectly well. In this paper, the mechanism of multi-physics coupling of spontaneous combustion in longwall gob is illustrated in detail, and a technique of moving coordinates is introduced to convert the expanding gob area into a relatively fixed region to simplify solving. On this basis, a time-independent model of multi-physics coupling of spontaneous combustion in gob is established, which is discretized by a new algorithm based on tetrahedral mesh. A software system of COMBUSS-3D is developed independently to solve the discretized model. This model is verified by matching the field measurement. Thus, this software can be served as a crucial tool to predict spontaneous combustion and locate high temperature zone in longwall gob areas.The influence factors of spontaneous combustion in gob, such as longwall advance rate, thickness of crushed coal and ventilation flux, are also analyzed quantitatively through the software. The results reveal that (i) the high temperature zone of spontaneous combustion locates in the windward side of gob; (ii) increasing the advance rate, reducing the crushed coal and decreasing the ventilation flux are all able to effectively reduce the risks of spontaneous combustion of gob; (iii) the minimum advance rate, the maximum thickness of coal and the maximum ventilation flux are obtained as the technical targets to suggest how to suppress or even eliminate the spontaneous combustion through regulating on-site mining technology. These results are beneficial for preventing spontaneous combustion of coal in longwall gob areas.