Weight Loss Behavior of Coal under Varying Gas Environments

To investigate the weight-change characteristics of coal under varying gas environments, a programmed temperature weight loss experiment is performed on bituminous coal (long-flame coal) under dry air, pure O₂, and pure N₂ conditions. The study analyzed and compared the temperature evolution patterns, weight loss behaviors, gas product properties, kinetic models of coal-oxygen composite reactions, and activation energies (E _a) across the three environments. The experimental results indicate that the coal sample in an O₂ environment exhibits the highest heating rate, which is significantly greater than those in air and N₂ environments. The weight loss rate of coal samples in the air environment is consistently higher than that in the O₂ environment. In the N₂ environment, pyrolysis led to a gradual increase in the weight loss rate, which became predominant after the coal temperature exceeded 90 °C. The time required for coal samples to achieve the maximum weight loss rate is the shortest in the O₂ environment. Within the same time frame, the weight loss rates of coal samples in air and the O₂ environments are significantly higher than those in the N₂ environment. The concentration of carbon monoxide gas generated from coal combustion in a pure O₂ environment shows a marked increase after 150 °C, reaching concentrations 3-4 times higher than those observed in an ambient air environment. Meanwhile, in the N₂ atmosphere, a minor quantity of carbon-oxygen gases is released from the coal sample as a result of functional group pyrolysis during thermal treatment. The kinetic model describing the O₂ consumption reaction of coal samples in an air environment can be represented by the Avrami-Erofee complex multidimensional homogeneous nucleation model with n = 4. During the low-temperature stage (40-140 °C), the E _a required for CO₂ generation is significantly lower than that for CO generation. Consequently, the coal sample exhibits a greater tendency to produce CO₂ in this temperature range. The research elucidates the dual inhibitory and promoting effects of O₂ concentration on coal oxidation-induced weight loss, as well as the pyrolysis characteristics in a N₂ atmosphere. These findings offer valuable theoretical insights for the precise prevention and control of the spontaneous combustion (SC) of residual coal in goaf areas.