Study on Spontaneous Combustion Characteristics of Coal Samples with Different Pre-oxidized Temperatures in Secondary Oxidation Process

The paper used thermogravimetric experiments to study the spontaneous combustion characteristics of coal samples with different pre-oxidized temperatures during the secondary oxidation process and focused on the calculation of kinetic parameters during the oxygen-absorbing and weight-increasing stage. The results showed that the total reaction course of spontaneous combustion of raw coal and pre-oxidized coal were similar; the difference in pre-oxidized temperature only had a greater impact on the critical temperature and dry cracking temperature of the coal sample, and then had a greater impact on the water evaporation and desorption stage and the oxygen-absorbing and weight-increasing stage. And the oxygen-absorbing and weight-increasing stage had a more violent reaction than the water evaporation and desorption stage. In the oxygen-absorbing and weight-increasing stage, the difference of pre-oxidized temperature had little effect on the reaction mechanism of each coal sample. The reaction functions all followed the Jander equation, and the mechanism was three-dimensional diffusion. The energy of activation of pre-oxidized coal samples was smaller than that of raw coal, and decreased with the rise of pre-oxidized temperature. When the pre-oxidized temperature was less than 160°C, the pre-factor of the pre-oxidized coal was larger than that of the raw coal, and when the pre-oxidized temperature was greater than 160°C, the pre-exponential factor of the pre-oxidized coal was smaller than that of the raw coal. The research results can lay a foundation for the subsequent prediction of coal spontaneous combustion reaction process, determination of critical spontaneous combustion conditions and evaluation of inhibitory effect. At the same time, it can also be used as a reference and supplement for the existing research on coal oxidation kinetic parameters.