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 (Ea) 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 Ea 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.