Desorption Characteristics of CH-CH Mixed Gas in Heavy Hydrocarbon-Rich Coal Seams.

The gas desorption characteristics of coal are closely related to the gas content of the coal seam. The gas in heavy hydrocarbon-rich coal seams contains CH and CH heavy hydrocarbons. However, most current research on the gas desorption characteristics of coal seams focuses on CH analysis, ignoring the influence of the CH heavy hydrocarbon gas. To accurately determine the gas content of a heavy hydrocarbon-rich coal seam, methods based on CH analysis are inadequate and the desorption characteristics of CH-CH mixed gas must be clarified. This work experimentally and theoretically studies the desorption characteristics of single-component gas and CH-CH mixed gas from coal samples. The results show that increasing the adsorption-equilibrium pressure was found to increase the desorption quantity and desorption speed of single-component gas and increase the desorption quantity, desorption ratio, and diffusion coefficient of mixed gas. Under the same adsorption-equilibrium pressure, the desorption quantity and rate of single-component CH gas exceeded those of CH. The quantity and speed of mixed gas desorption increased with rising CH concentration and decreased with rising CH concentration. The change in the mixed gas concentration during desorption reflects the distribution characteristics of light hydrocarbon components on the outer surface and heavy hydrocarbon components on the inner surface of coal. From the desorption characteristics of mixed gas, desorption models of mixed gas were obtained at different concentrations, laying a theoretical foundation for accurate determinations of gas contents in heavy hydrocarbon-rich coal seams.