Study on low temperature oxidation heat release characteristics of bituminous coal at different heating rates

Coal spontaneous combustion is one of the important factors threatening the process of mining, storage and utilization. The oxidation exothermic reaction of coal at low temperature stage is also the main factor leading to coal spontaneous combustion. In order to study the heat release characteristics of bituminous coal at low temperature, three kinds of bituminous coal with different metamorphic degree were selected to study. Caojiatan (CJT) long flame coal, Dafosi (DFS) non caking coal and Dongtan (DT) gas coal were used as the coal samples. The micro calorimeter (C80) was used to monitor the change of heat flow of coal samples in the temperature range of 30～300 ℃, so as to explore the heat flow change law and exothermic situation of different bituminous coal low-temperature oxidation processes, and obtain the staged heat flow of the low-temperature oxidation process. features and corresponding mathematical models. In order to further study the effect of heating rate on the heat release characteristics of bituminous coal, the experiments were conducted at different heating rates of 0.2, 0.4 and 0.6 ℃ / min, respectively. Based on the heat flow model and heat formula, the index γ for judging the spontaneous combustion tendency was established, and the influence of different heating rates on the heat release characteristics and spontaneous combustion tendency of bituminous coal in low temperature oxidation process was analyzed. The results show that the low temperature oxidation of bituminous coal can be divided into four stages: endothermic, slow exothermic, accelerated exothermic and fast exothermic stages. With the increase of heating rate, the characteristic temperature point tends to move backward and the heat release decreases. The proportion of exothermic heat in the three exothermic stages did not change significantly, about 1%, 30%, and 70%. It was found that the lower the heating rate is, the smaller the activation energy value is, and the γ value of coal spontaneous combustion tendency index increases. By studying the heat release characteristics of bituminous coal and the influence of different heating rates on the heat release characteristics of bituminous coal,, this subject can have a clearer understanding of bituminous coal oxidation heat release so as to study fire extinguishing materials, and prevent and control coal spontaneous combustion.