Temperature-pressure coupling effect on gas desorption test in soft and hard stratified coal from the Qianxi mining area

Abstract

The gas desorption characteristics in coal seams play a significant role in understanding gas emission patterns in mines and in coalbed methane development. Variations in coal seam temperature and pressure significantly control gas desorption in coal seams with soft and hard coal stratification. Most of the coal seams in the Qianxi mining area of Guizhou Province have high gas content, closely spaced layers, and are prone to outbursts, with a combination of soft and hard layers and low permeability. To further clarify the gas desorption characteristics of these coal seams, the study focused on coal from layers with soft and hard stratification in the Xiaotun and Qinglong coal mines, which are typical in the Qianxi mining area. Gas desorption experiments under varying temperatures and pressures were conducted using an HCA high-pressure volumetric gas adsorption device. The impact of temperature-pressure coupling on gas desorption characteristics of coal samples from layers with soft and hard stratification was comparatively analyzed. The results showed that for the same coal sample, higher temperature and pressure led to a greater initial gas desorption rate. Within 0-120 s of initial desorption, gas pressure played a less dominant role. The initial gas desorption rate of coal in soft layers was higher than that of hard layers, while the cumulative gas desorption amount of coal samples in hard layers exceeded that of soft layers. The cumulative desorption amount of samples in hard layers surpassed that of soft layers within 540 s. The most significant changes in gas desorption occurred within the first 60 s of coal exposure, with coal in soft layers exhibiting a higher proportion of desorbed gas during this period, making it more "active" in desorption. The gas desorption rate increased with pressure and could be divided into three stages: explosion stage (0-60 s), leap stage (60-1 500 s), and stabilization stage (1 500-7 200 s). The median desorption time of coal samples in soft layers was more significantly influenced by temperature and pressure compared to samples in hard layers, with gas desorption in soft layers occurring primarily within the first 1 800 s after coal exposure.

Keywords

• tectonic coal
• soft and hard layer stratification
• gas desorption rate
• gas desorption amount
• temperature-pressure coupling effect