Study on competitive adsorption characteristics of CO/CO2/CH4 multi-component low concentration gases in coal

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ABSTRACT Coal spontaneous combustion indicator gases are one of the important indicators to judge coal spontaneous combustion, but coal spontaneous combustion is not the only source of these gases, the coal will also absorb these gases. Therefore, the study of gas adsorption characteristics in coal is of great significance for the prevention of coal fire. In this work, the adsorption characteristics of the low concentrations of carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4) in coal were studied and the competitive adsorption relationships among these three gases were identified by sorption isotherms. Experiments were performed on two coal samples from the Linnancang Coal Mine (LNC coal sample, named after the first word of the mine name) and Xixizhuang Coal Mine (XXZ coal sample, same as above), which were submitted to different gas atmosphere. A mathematical approach for calculating the adsorptive volume of each gas component under four experimental conditions was proposed, and the relationship between the adsorption capacities of CO, CO2 and CH4 and pressure was obtained during the adsorption and desorption. The results show that for the XXZ coal sample, the adsorption volume of CO under the maximum pressure conditions during the standard gas adsorption and desorption process is 7.7×10−2 mL/g, while the comparable values in gas-He, gas-CH4 and gas-CO2 are 3.5×10−2 mL/g, 1.9×10−2 mL/g, and 1.2×10−2 mL/g, respectively. The adsorption volumes of CO, CO2 and CH4 decrease with increasing pressure, but the decreasing trend is lower than that of standard gas adsorption under low-concentration conditions. The adsorption capacity of the desorption process under the same pressure conditions is greater than that of the adsorption process. In the adsorption state composed of CO, CO2, and CH4 gases, there are mutual constraints and influences between the gases, showing competitive adsorption behavior. Both CO2 and CH4 have obvious inhibitory effects on CO, while He does not inhibit CO adsorption.