Comparison of the initial gas desorption and gas-release energy characteristics from tectonically-deformed and primary-undeformed coal

Coal and gas outbursts (hereinafter, collectively referred to as 'outbursts') often last for just a few tens of seconds and occur mostly in gas-bearing tectonically-deformed (TD) coal. It has been proved that, in comparison to primary-undeformed (PU) coal, TD coal is more susceptible to outbursts due to its lower mechanical strength, stronger gas-adsorption capability, and faster gas-desorption rate. M the same time, the energy required for the outburst process is mainly provided by the gas. However, the characteristics of the gas-desorption behavior and gas-release energy in TD and PU coal during the first dozen seconds or so have rarely been studied. In this study, gas desorption experiments were carried out on TD and PU coal at different gas pressures using self-assembled desorption equipment. The experiments focus on roughly the first 13 s. The results show that the drop rate of gas pressure is lower with TD coal compared to PU coal, while the gas desorption rate is higher for TD coal compared to PU coal. Most of the gas is released from the two types of coal in the first few seconds. For both TD and PU coal, the time taken to release 90% of the total gas expansion energy (TGEE) is shorter than that to release 90% of the total gas energy (TGE). At the different gas pressures used, the TGEE of the two types of coal accounts for about 14-16% of the TGE. The higher the gas pressure is, the greater the TGEE released by the coal samples gets, and thus the larger the TGEE: TGE ratio becomes. Although the TGEE released from the TD coal is about 3 times that released from the PU coal, it accounts for a slightly smaller proportion of the TGE compared to that in the PU coal samples.