Quantitative characterisation of the influence of different environmental factors on coal spontaneous combustion

Abstract

Coal spontaneous combustion (CSC) events pose hazards to miners, infrastructure, and the environment. To mitigate some of the risk of CSC, this study explored the influence of airflow rate (AFR), oxygen concentration (OxyC), and heating rate (HR) on CSC. A temperature programmed experiment was used to examine a coal sample under different AFRs, OxyCs, and HRs. The characteristic temperature was determined using index gas growth rate analysis, and the characteristic parameters were shown. The apparent activation energy (E_a) of the sample was computed by the Arrhenius equation, and variance analysis was employed to quantitatively characterise the impact of different environmental factors on the characteristic parameters of the coal samples. The experimental results show that the critical temperature of the coal samples ranges between 65 and 75 °C, and the cracking temperature ranges between 115 and 130 °C, dividing the low-temperature oxidation process of coal into three stages: before the critical temperature, between the critical temperature and the cracking temperature, and after the cracking temperature. An AFR of 120 mL min⁻¹ was identified as the optimal level; exceeding or falling below this value inhibits the coal-oxygen reaction. Increasing OxyC and reducing HR improves coal oxidation. Compared to the same samples under AFR and HR conditions, the E_a of coal under oxygen conditions is lower, ranging between 20 and 35 kJ mol⁻¹, while under AFR and HR conditions, the E_a is not less than 30 kJ mol⁻¹, indicating a stronger tendency for spontaneous combustion under oxygen conditions. AFR substantially affects the oxygen consumption rate, CH₄, and exothermic intensity at all stages, with a partial η² of 0.6. Before the critical temperature, OxyC has the greatest impact on CO₂; between the critical temperature and the cracking temperature, OxyC has the greatest impact on CO; and after the cracking temperature, OxyC has the greatest impact on CO, CO₂, C₂H₄, and C₂H₆, with partial η² values of 0.51, 0.59, 0.278, and 0.45, respectively.