Numerical simulation study of the effect of coal dust on gas explosion overpressure

A numerical simulation study was conducted using Ansys Fluent 2023 R1 simulation software to investigate the influence of coal dust on the overpressure of gas explosion. The results demonstrated that the reliability of the selected mathematical model was validated through comparisons across three data sources: (1) experimental data from a gas and coal dust explosion propagation test system, (2) experimental results from full-scale mine roadway tests reported in the literature, and (3) the current numerical simulation outcomes. Based on elemental and industrial analyses, the stoichiometric concentration for various coal dust explosions was determined, and a formula was established to calculate the actual mass concentration of coal dust participating in the explosion process. A conversion relationship between the equivalent ratio and the mass concentration of coal dust was developed for different coal types. The equivalent ratio is defined as the ratio of the stoichiometric air-fuel ratio to the actual air-fuel ratio, used to quantify whether reactants are in excess or deficiency. When the equivalence ratio Φ equals 1, the methane volume concentration is 9.5%. If the methane volume concentration is below this stoichiometric level, the addition of a small amount of coal dust enhances the explosion intensity. Conversely, when the methane concentration is equal to or exceeds the stoichiometric value, coal dust exerts an inhibitory effect on the gas explosion. When varying concentrations of fat coal dust were introduced into explosions with 7.5% methane, the maximum explosion pressure occurred at a coal dust concentration of 200 g/m³. At Φ = 1, the stoichiometric mass concentration of fat coal dust was calculated as 107.2 g/m³; however, the actual amount of coal dust involved in the reaction did not reach this theoretical value, indicating that the equivalent ratio-based concentration exceeded the stoichiometric concentration. When 7.5% methane reacted with oxygen, the residual oxygen could only support combustion corresponding to a stoichiometric coal dust concentration of approximately 29.7 g/m³, meaning that only about 29.7 g/m³ of the 200 g/m³ fat coal dust participated in the explosion. Under conditions of 7.5% gas concentration and 200 g/m³ coal dust concentration, smaller coal dust particle sizes resulted in higher explosion pressures. Furthermore, under identical experimental conditions, as the degree of coal metamorphism decreased-from lean coal to coking coal, fat coal, gas coal, and finally lignite-the peak overpressure of the gas-coal dust coupled explosion increased sequentially, indicating a negative correlation between explosion overpressure and the degree of coal metamorphism.