Numerical investigation on the effects of axial-stress loads on the temperature-programmed oxidation characteristics of loose broken coal

This work innovatively explored the qualitative and quantitative effect of axial stress loads on the low-temperature oxidation behaviors of loose broken coal using a multi-field coupled numerical simulation. To achieve this purpose, a global numerical model for simulating the multi-field coupling temperature-programmed oxidation behavior of coal subjected to axial stress was established. We first acquired the evolution of the temperature, gas concentrations, axial-deformation behaviors, and seepage-heat transfer parameters of coal oxidation under axial stress loads based on the numerical model validation. Subsequently, the influence of various axial stress loads on the temperature-programmed oxidation behaviors was qualitatively and quantitatively evaluated. Results indicate that the numerical model exhibited excellent reliability. In addition, the entire oxidation process comprised temperature-dominated, temperature- and oxygen-dominated, and oxygen-consumption-dominated stages. Moreover, under axial stress conditions, both the porosity and permeability of coal samples decreased, whereas the heat conductivity coefficient increased, indicating an intensifying trend in oxidation reactions. Additionally, there was a critical stress that promoted the coal oxidation process; both the permeability and temperature of the coal demonstrated significant differences as the axial stress reached this critical point. The axial stress affected the oxidation behavior by changing the permeability and heat-transfer characteristics of the coal. This study is significant for predicting, preventing, and mitigating spontaneous fire disasters of stress-loaded coal.