Mining high-gas coal seams in China has the characteristics mining of deep, high storage and low permeability, and low drainage efficiency, which seriously restrict the efficient prevention and control of mine gas disasters. Based on the characteristics of low viscosity and permeability, phase change pressurization, and strong adsorption potential energy of liquid CO₂, the technology system of liquid CO₂ displacement for high-gas and low-permeability coal seam was developed, and field industrial of low-pressure (0.52.5MPa) and medium-pressure (2.515.0MPa) combined injection test was carried out. In this test, the mode of injection followed by drainage was adopted, and the gas drainage effect was investigated for 30 days. The test results show that the effective influence radius of CO₂ in this test is 20m, and the liquid seepage radius is 5 to 7m. After the injection of liquid CO₂ into coal seam, the average gas drainage concentration and drainage purity of all drainage holes were increased by 3.2 and 3.4 times, respectively, and the gas promotion effect was significant. Taking the liquid CO₂ low-medium-pressure displacement gas test area as the calculation unit, from the comprehensive benefit analysis, compared with the original drainage mode, the liquid CO₂-combined pressure injection process can save 34.7 of the engineering cost and shorten the gas drainage standard time by 45.9. Therefore, the application of this technology has important technical support and reference significance for the efficient management of gas in the same type of mine.

Spontaneous combustion of coal is a phenomenon that exists in all coal mining countries. The characteristics of CO production during the spontaneous combustion of coal are the focus of attention of researchers. A novel programmed oxidation heating simulation system with a small-sample size was developed to study the combustion characteristics. The device was used to study the characteristics of CO generation during low-temperature coal oxidation under different conditions (three coal ranks, six particle sizes, four air volumes, and four oxygen concentrations). The microscopic characteristics of the coal structure were tested through Fourier-transform infrared spectroscopy (FTIR), and three types of active functional groups were observed. Ten factors affecting gas production in the low-temperature oxidation stage were analyzed by gray correlation. This study found that moisture in coal had the greatest effect on CO generation, followed by O-containing functional groups. Aliphatic hydrocarbons had the least correlation with CO generation. Further, the CO concentration increased exponentially during the heating process in low-temperature oxidation. In the low-temperature stage, carboxyl, carbonyl, and side-chain C–O bonds of the benzene ring were the main sources of CO generation.

High-temperature poisonous smoke produced by coal mine roadway fire seriously affects miners' lives and safety. Studying the development law of high-temperature smoke in the process of mine roadway fire and then exploring the danger of roadway are of great significance to personnel safety and post-disaster rescue. In order to study this problem, the CFD numerical simulation method is used to establish a fire calculation model based on ANSYS Fluent software in the development stage of mine fire. The high-temperature flue gas flow in the roadway during the development stage of mine fire is simulated, and the variation law of temperature field and gas concentration field with time and space position under different levels of roadway in the development stage of fire is revealed. The variation rules of environmental parameters, such as temperature, CO, and CO₂, are obtained by numerical calculation. Based on these, the danger zones of smoke spread in fire development stage are divided by the critical values of high-temperature smoke and toxicity evaluation index, and the mathematical fitting analysis of the evolution of the dangerous area with time is carried out. The research results have certain theoretical guiding significance for reducing underground environmental pollution and ensuring the personal safety of workers and rescuers.

Coal mine gas disasters have severely restricted production safety. Improving gas extraction efficiency can effectively reduce disasters. Scholars have confirmed that CO₂ successfully displaces coal seam CH₄. This study conducted displacement and in situ experiments and compared gas drainage under different injection pressures. The displacement experiments indicated that CH₄ production rates increased under increased pressures while the displacement ratios decreased. The pressure had a positive effect on sweep efficiency. The in situ experiment showed that CH₄ and CO₂ concentration trends in the inspection hole remained consistent. Through observing the data of the original and inspection holes, the average gas drainage concentration during low- and medium-pressure injections increased by 0.61 times and 1.17 times, respectively. The low-pressure average gas drainage scalar was increased by 1.08 times. During the medium-pressure injection, the average gas drainage purity increased by 1.94 times. The diffusion ranges of CO₂ under low- and medium-pressure injections were 20–25 m and 25–30 m, respectively. The sweep efficiency of medium-pressure injection was 26% better than that of the low-pressure injection, with average pressures of 2.8 MPa and 1.4 MPa, respectively, for sweep efficiency. This study proposes an effective method for improving coal mine gas drainage efficiency.