Comparative study on the flame retardancy of CO2 and N2 during coal adiabatic oxidation process

To test the effectiveness of N₂ and CO₂ in preventing coal from spontaneously combusting, researchers used an adiabatic oxidation apparatus to conduct an experiment with different temperature starting points. Non-adsorbed helium (He) was used as a reference gas, and coal and oxygen concentration temperature variations were analyzed after inerting. The results showed that He had the best cooling effect, N₂ was second, and CO₂ was the worst. At 70℃ and 110℃, the impact of different gases on reducing oxygen concentration and the cooling effect was the same. However, at the starting temperature of 150℃, CO₂ was less effective in lowering oxygen concentration at the later stage than He and N₂. N₂ and CO₂ can prolong the flame retardation time of inert gas and reduce oxygen displacement with an initial temperature increase. When the starting temperature is the same, N₂ injection cools coal samples and replaces oxygen more effectively than CO₂ injection. The flame retardancy of inert gas is the combined result of the cooling effect of inert gas and the replacement of oxygen. These findings are essential for using inert flame retardant technology in the goaf.