Study on CO formation and pore structure development during low-temperature oxidation of coal in CO2-N2 environment

Abstract

Inert gases prevent coal spontaneous combustion (CSC) through heat transfer inhibition and oxygen restriction, while the development of coal pores reflects the intensity of CSC. To study the impact of inert gases on coal low-temperature oxidation, temperature programming, and nuclear magnetic resonance techniques were used to investigate the changes in CO concentration, pore size distribution, and porosity under different inert gas atmospheres. The results indicate that below 200 °C, the CO concentration follows the order C_N2>C_N2+CO2>C_CO2, while above 200 °C, the order shifts to C_N2>C_CO2>C_N2+CO2. The mixed gas atmosphere delays the inflection point of the CO concentration growth rate. The coal pore size distribution in N₂, C_O2, and mixed gas atmospheres follows three-peak, two-peak, and single-peak distributions, respectively. The pore throat size in the N₂ atmosphere is larger than in the other 2 atm. In the mesopore and macropore ranges, coal porosity is highest in the N₂ atmosphere and lowest in the mixed gas atmosphere. As temperature increases, the peak value of the pore size distribution follows the order: D_N2>D_CO2>D_N2+CO2, indicating that the mixed gas atmosphere is more effective than a single inert gas in inhibiting coal spontaneous combustion at high temperatures. These findings provide a theoretical basis for applying inert gases in preventing spontaneous combustion in coal mine goaf.