Oxidation reaction constants for coal spontaneous combustion under inert gas environments: An experimental investigation

Coal spontaneous combustion (CSC) is a complex physicochemical dynamic evolutionary process. Oxygen consumption rate is commonly used to estimate the intensity of coal-oxygen reactions, but is easily disturbed due to derivation from the volumetric flow rate. To address this issue, a new estimation parameter, called the oxidation reaction constant, was proposed, and modeled using mass flow rate. Its correctness was verified through experiments on the oxidation of coal samples in two inert gas environments (i.e., N2–O2 and CO2–O2), respectively. The ability of N2 or CO2 to inhibit the CSC was also quantitatively evaluated using the oxidation reaction constant. The results show that the oxidation reaction constant is related to the coal's own properties and temperature, but almost independent of the oxygen concentration, which is more appropriate for estimating the oxidation properties of coal. The oxidation reaction constants in CO2–O2 environments are only 40%–85% of those in N2–O2 environments, indicating that CO2 has a stronger inhibitory effect. Furthermore, the stronger the physical adsorption properties of the coal sample to oxygen, the larger its oxidation reaction constant, and the more likely it is to spontaneously combust. This work provides more reasonable characterization parameters for investigating the low-temperature oxidation process of coal.