Flame behaviors, pressure evolution, and molecular reaction mechanism of methane/pulverized bituminous coal hybrid deflagrations

Abstract

The deflagration of methane/powdered coal hybrids poses a serious risk to the production safety and personnel health for underground coal mines. In this study, we firstly performed 21 sets of deflagration experiments to investigate the pressure variation and flame behaviors of methane/pulverized bituminous coal mixtures. The experimental results revealed that the explosive power attains its maximum at 9.5 vol% methane and 100 g/m³ of pulverized coal, whereas the maximum flame propagation speed was recorded at 35.08 m/s with 9.5 vol% methane and 50 g/m³ of pulverized coal. The gas-phase reaction predominantly governs the deflagration characteristics of the mixtures, with methane concentration significantly exerting a more significant influence on these characteristics than powdered coal concentration. Then, reactive field molecular dynamics (ReaxFF-MD) simulations were conducted to explore the microscopic mechanism of methane/pulverized bituminous coal hybrid deflagrations. The simulation results indicated that bituminous coal molecules undergo successive repeated pyrolysis, generating a substantial number of active intermediates and gaseous products. These volatile species contribute to the gas-phase deflagration reaction, thereby intensifying the overall deflagration process. The primary pathway of the gas-phase deflagration reaction involves the following radical reactions: CH₄ → ·CH₃ → ·CH₃O → CH₂O → ·CHO → CO+H₂ → CO₂+H₂O. This study would provide scientific guidance for efficient prediction, control, and reduction of methane/pulverized bituminous coal hybrid deflagration accidents.