The variations of free radical and index gas CO in spontaneous combustion of coal gangue under different oxygen concentrations

Abstract

SummaryIn order to study the effect of oxygen concentrations on the change of active groups in the oxidation process of coal gangue, the airflows of different oxygen concentrations were prepared to simulate the oxidation and heating process of coal gangue under oxygen concentrations of 0%, 5%, 10%, 15%, and 21%. During the oxidation and heating process, the free radical parameters were measured at different temperatures in real time. The results show that in the early stage of coal gangue oxidation, the g factor remains at a lower level and do not start to increase until certain temperatures are reached. Besides, the higher the oxygen concentration is, the lower the temperature at which the g factor begins to increase. When the oxygen concentrations are 0%, 5%, 10%, 15%, and 21%, the corresponding temperatures are 225, 200, 150, 150, and 125°C, respectively. Furthermore, with the increase of oxidation temperature, the free radical concentrations experience four stages, namely, the slow increase stage, the rapid increase stage, the stagnant increase stage, and the final increase stage. And the higher the oxygen concentration is, the shorter the free radical stagnant increase stage is. During the oxidation of coal gangue, the line widths decrease slowly before 150°C, and then start to plunge and finally stabilize near the minimum at 350°C. Moreover, the higher the oxygen concentration is, the smaller the minimum values of line widths are. In the oxidation process of coal gangue, the gas product CO amounts are first at a lower level, and then begin to increase rapidly after 150°C. At the same temperature, the increased rates of CO production in coal gangue under the oxygen concentrations of 10%, 15%, and 21% are significantly higher than those under the oxygen concentrations of 0% and 5%. Based on the variation law of free radical parameters in coal gangue under different oxygen concentrations, the actual spontaneous combustion of gangue hills was analyzed and the free radical reaction mechanism of spontaneous combustion of gangue hills was discussed. The research results are of guiding significance for the treatment of spontaneous combustion of coal gangue.