Experimental study on the influence of ground temperature on coal spontaneous combustion characteristics with different metamorphic degree

Ground temperature affects the characteristics of coal spontaneous combustion, and then affects the distribution of coal spontaneous combustion danger areas in goaf. In order to explore the effect of ground temperature on coal spontaneous combustion, lignite, long-flame coal and 1/3 coking coal are selected as research objects. Thermogravimetric experiment is used to analyze the weight changes of coal samples at different ground temperatures during combustion. The characteristic temperature points are found out by TG/DTG curves, and the activation energy at pyrolysis stage is calculated by integral formula. The results show that under the same pretreatment temperature, the same characteristic temperature increases with the increase of coal sample metamorphism. For coal samples with the same metamorphic degree, the higher the pretreatment temperature, the lower the characteristic temperature during combustion, especially the dry cracking temperature, growth temperature and ignition point temperature. The activation energy in the pyrolysis stage is also reduced by 5%-30%, indicating that the higher the pretreatment temperature, the more easily the coal oxygen reaches the critical ignition temperature, thus achieving the conditions required for coal spontaneous combustion and accelerating the process of coal spontaneous combustion. The research results have guiding significance for the prevention and control of coal spontaneous combustion disaster under high ground temperature environment.