Spontaneous coal combustion adversely affects coal mine safety and restricts safe, efficient, and green coal mining. Inert gas fire prevention and extinguishing technology is a widely used fire prevention and extinguishing method in coal mines. CO₂ is often used as the primary raw material for inert gas fire prevention and extinguishing, owing to its good inerting and cooling characteristics. However, the lack of data on the physical and chemical properties and fire extinguishing mechanism of CO₂ by field personnel has limited the efficient application of CO₂ in coal mine fire prevention and extinguishing. To explore the practical application effects of CO₂ fire prevention and extinguishing technology on coal mine sites, this paper summarised and analysed the research and development status of CO₂ fire prevention and extinguishing technology and expounded the physical and chemical properties, phase characteristics, and fire prevention and extinguishing mechanisms of CO₂. The CO₂ pipeline, CO₂ pipeline intelligent monitoring and control system, CO₂ inerting mechanism, and comprehensive gas fire prevention and extinguishing technology are summarised and discussed. This study provides a systematic theoretical basis for the field application of CO₂ fire prevention and extinguishing technology.

The oxidation characteristic parameters of residual coal in working face change with the advance of coal seam. To explore the influence of dynamic oxygen-consuming environments, we examined the influence of reducing the oxygen concentration on the formation characteristics and characteristic parameters of coal oxidation products, conducted with temperature-programmed experiments under staged oxygen consumption. The correlation between the characteristic oxidation parameters was determined, and the critical oxygen concentration that determined the gas yield was obtained. The results show that after staged oxygen-consumption, the oxidation of coal is stronger than that under constant low oxygen, the oxidation products are greatly affected, and the influence of pyrolysis gas is small. The oxidation characteristic parameters such as gas product volume fraction, production rate, and heat release intensity are positively correlated with the oxygen-consumed temperature. We found that the oxidation reaction heat of coal is 180~330 kJ·mol⁻¹, and the maximum and minimum exothermic intensities are significantly linearly correlated with the oxygen consumption rate. Finally, the critical oxygen concentrations for gas production rate under oxygen-consumed conditions were 17, 9, and 5%. These results have practical significance for strengthening the prevention and control of spontaneous combustion disasters in goafs.

Taking a composite goaf in goaf-side entry retaining as our research focus, a kilogram-level spontaneous combustion experiment was carried out, and limit parameters for coal spontaneous combustion characteristics were assessed. Combined with the key parameters of the site, a numerical model of a multi-area composite goaf was constructed, and the distribution features of the dangerous area for coal spontaneous combustion in the lower layer of in goaf-side entry retaining were determined by means of the upper and lower layer composite superposition division method. The results show that at a floating coal thickness in the goaf of 1.9 m, the lower limit of oxygen concentration C_min, upper limit of air leakage intensity, and corresponding seepage velocity are 6%, 0.282 cm⁻³·s⁻¹·cm⁻², and 11.28 × 10⁻³ m/s respectively. The dangerous area regarding residual coal on the intake side is 23~38 m away from the working face, while that on the return air side is concentrated amid the goaf at 23~75 m, and that on the flexible formwork wall is concentrated at 0~121 m. The research results are of crucial practical importance for the prevention and control of coal spontaneous combustion within a composite goaf.

During narrow coal pillar mining, a high-temperature point can easily form inside the coal pillar, leading to CSC. This study aims to investigate the effect of key layout parameters of a bending heat pipe on the heat transfer from a coal pillar oxidation heat source. The bending heat pipe (Tianjin Xinhua Energy Equipment Technology Co., Ltd., Tianjin, China) heat transfer model was constructed using the Fluent software 2021 R1; meanwhile, the effects of heat transfer of non-uniform and uniform temperature fields under different spacings (30 cm, 40 cm, 50 cm) of a single heat pipe and multiple heat pipes were studied. According to our findings, the maximum temperature error between the simulated and experimental temperature fields in the bent heat pipe under identical operating conditions is 3.8 °C, which verifies the model’s feasibility. The temperature field in each section of the coal pillar exhibits a “wave-like” change trend in the heat pipe, with the heat transfer effect diminishing markedly as the spacing increases. Considering the thermal effect and on-site operation feasibility, the optimal spacing of the two bending heat pipes is determined to be 30–40 cm. These research results can offer a theoretical foundation for the application of bending heat pipes in the advanced prevention of the hidden danger of CSC in narrow coal pillar mining.