Gas Desorption Characteristics of Ultrafine Coal Particles and Their Influence on Gas Content Determination

In order to explore the gas desorption law of ultrafine coal particles (<0.1 mm) in a coal mine and establish a rapid determination method of gas content, four kinds of coal samples were taken as the research object, and experiments were carried out by using self-developed equipment. The desorption characteristics were analyzed by a diffusion model and compared with the traditional method. The results show that the desorption curves of different particle sizes of four coal samples are characterized by "a rapid increase first and then stabilization" and "a rapid decrease in the desorption rate first and then a slow decrease to zero". The gas desorption amount of the mixed particle size sample increases with the increase of the proportion of ultrafine particles, and the Booth mathematical model can accurately describe the dynamic process. When the coal type is determined as gas-fertilizer coal and the proportion of ultrafine particles ω exceeds 27%, the loss deviation in gas content measurement exceeds the national standard. It is necessary to control ω to be less than or equal to 27% through screening with a 150-mesh (0.1 mm) sieve so that the loss deviation in gas content measurement meets the specified standard. Ultrafine coal particles can achieve full release of desorbable gas in 50 min, which significantly improves the accuracy of gas content determination. Based on this, the CWH180 gas content rapid tester is developed to determine two optimal schemes of continuous crushing for 20 min and intermittent crushing (crushing for 1 min every 2 min). The measurement deviation is controlled within ±1%, taking into account the efficiency and accuracy, which can meet the needs of engineering measurement and scientific research analysis. Users can choose flexibly according to actual needs.