Adsorption Behavior Analysis of Index Gases in Coal Molecules of Different Ranks and Establishment of PAR

Index gas monitoring is a commonly used method in coal mines to judge the spontaneous combustion of goafs. Based on the simulation analysis of the adsorption behavior of index gases on coal molecules of different coal ranks, the characteristics of the adsorption sites of index gases on coal molecules were obtained. Combining with their generation laws, an indicator for optimizing index gases for different coal mines, namely the Production – Adsorption Ratio (PAR), was proposed. The results show that the adsorption positions of C2H2, C2H4 and CO are concentrated, and some of them have special adsorption sites on coal molecules, affected by the different molecular diameters and molecular polarities. In the adsorption simulation process of CO2, all adsorption sites in coal molecules can be occupied. Among the five ranks of coal molecules, the adsorption capacity of CO2 is absolutely dominant compared with other index gases. It is found that the PAR of C2H4 in Yangmei No. 5 Mine and Gaojialiang Mine are relatively low, and the loss in the goaf flow field is large. Therefore, C2H4 is not suitable as an index gas for monitoring the goaf status of the corresponding coal mines.