Pan Shu

Performing stability studies of waterproof coal pillars is one of the key measures for preventing mine water disasters. As some areas of the coal pillar were affected by goaf water in the Nanhu Second Mine, the coal pillar and surrounding roadway were somewhat deformed. To investigate whether the pillar can ensure safe production in the mine, the source of goaf water and the direction of water infiltration were analyzed using exploration holes, and it was concluded that the goaf water originated from the V₃ aquifer and was static. Thus, a theoretical analysis was carried out to determine the relationship between the mechanical parameters of the coal and rock structures affected by water. On this basis, a numerical simulation was employed to examine the key changes in the coal pillar and roadway affected by goaf water. The simulation results showed that the plastic area was 6–11 m and the elastic area in the middle was 6–8 m after excavating the working faces on both sides of the coal pillar, and the water flow vector of the aquifer could not pass through the pillar. Finally, in situ monitoring using ground-penetrating radar, deformation measurement, and loosening circle detection revealed that the development degree of internal cracks in the coal pillar was relatively light; thus, the pillar could effectively prevent water damage. These monitoring and analysis methods comprehensively evaluate the stability of the coal pillar and provide a guarantee for the safe mining of the working face.

To investigate the influence of moisture on the exothermic properties of coal oxidation, this study investigated the variation in thermal effect and radical parameters in the oxidation process of coal under different moisture content. This was achieved through thermogravimetric–differential thermal experiments and electron spin resonance experiments. Additionally, the study analyzed the impact of free radicals on the characteristics of the thermal effect of coal at different oxidation stages using the product–moment correlation method. The results indicate that the moisture content of 8% is a critical point for promoting or inhibiting the oxidation reaction of coal. Below this threshold, it promotes the oxidation reaction, while above it, it plays an inhibitory role. The most significant promotional effect was observed at 8% moisture content, which increased both the weight loss and heat release by 8.61% and 1567.04 J/g, respectively, while also significantly enhancing free radical species and complexity. Conversely, when the moisture content of coal reached 20%, there was a notable inhibition effect, with a reduced weight loss and exothermic capacity by 4.94% and 2705.03 J/g, respectively, along with decreased free radical species and complexity. The free radical species and heat effect parameters in coal showed a strong correlation at all stages of low-temperature oxidation, thus indicating that g-factor can characterize the coal oxidation process to some extent.

To solve the problem of unclear targeted inhibition of key free radicals by antioxidants, this paper took the hydroxyl radical with the highest oxidation activity of coal as the inhibition target and selected five antioxidants such as ethylene diamine tetraacetic acid, tea polyphenol, citric acid, vitamin C, and proanthocyanidins. Based on the theory of quantum chemistry, the characteristics and oxidation pathway of antioxidants inhibiting coal oxidation of hydroxyl radical were analyzed. Analyze the influence characteristics of antioxidants on the evolution of free radicals in coal through an electron paramagnetic resonance experiment (ESR). The results showed that the electron density of antioxidants was mainly distributed in the functional groups of carboxyl and hydroxyl, which played a key inhibitory role, and the vicinity of carboxyl and hydroxyl and other functional groups was positive potential, which was the active site of inhibiting hydroxyl radical. The order of inhibitory capacity of the five antioxidants was determined as GTP > PC > EDTA > CA > VC. It is concluded that the energy barrier of hydroxyl radical inhibition by citric acid is much lower than that of EDTA. For the hydrogen extraction reaction, VC inhibited the hydroxyl radical pathway with a higher energy barrier than the other three antioxidants. The mechanism of five antioxidants inhibiting •OH reaction was comprehensively analyzed. It was found that tea polyphenols have more active sites that can react with •OH to quench it, so the inhibition of tea polyphenols should be the most significant. When antioxidants inhibit coal spontaneous combustion, the type, complexity, concentration, and linewidth of free radicals in coal molecules are lower than those in raw coal, with GTP antioxidants having the best inhibitory effect. The research results have important theoretical and practical significance for revealing the mechanism of coal spontaneous combustion inhibition and developing directional coal spontaneous combustion inhibition technology.

To study the oxidation characteristics of coal under different conditions of mixed particle sizes, a C80 microcalorimeter and ESR spectrometer were used to study the heat release characteristics and laws of free radical parameter changes for coal samples with different mixed particle sizes. Research indicates that a smaller average particle size in the mixed coal sample results in stronger low-temperature oxidation and greater heat release from coal and a smaller apparent activation energy and initial heat release temperature. The concentration of free radicals in coals increases with decreasing average particle size in the mixed coal samples. When the average particle size in the mixed coal sample increased from 0.09 mm to 0.246 mm, the cumulative heat release of the GJW coal sample and the YHP coal sample decreased by 36.67% and 20.13%, and the free radical concentration decreased by 4.34 × 10¹⁷/g and 3.66 × 10¹⁷/g. In addition, In the mixed coal samples, the mean particle size mutation value was 0.126, which makes the heat release characteristics of coal at this particle size opposite to the overall trend. Further analysis established the relationship model between the heat of different mixed particle sizes and the free radical concentration of different mixed particle sizes as follows: y = ax³+ bx²+ cx+d.

Ammonium polyphosphate (APP) is a type of fire-fighting material that has excellent performance; however, it also has the disadvantage of facile deliquescence. Microcapsule technology is therefore employed in this study to use melamine resin as encasing material in the preparation of melamine–formaldehyde resin-microencapsulated APP. The performance of prepared microcapsules is characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric experiments. The experimental results show that the same APP characteristic peaks (e.g., N-H stretching vibration peaks) and characteristic absorption peaks of melamine-formaldehyde (MF) resin (e.g., vibration peak of MF ring) are exhibited by the microcapsules. Furthermore, the coated microcapsule surface is rough because of the adsorption of solid particles, indicating that the wall material successfully covers the core material. Thermogravimetric analysis shows that the microcapsules can effectively increase and decrease the maximum weight loss rate temperature and maximum weight loss rate, respectively. When the microcapsule content constitutes 15% of the total sample mass, the maximum weight loss rate and coal temperature decrease and increase by 0.58%/min and 13°C, respectively. This significantly inhibits the composite coal-oxygen process, indicating the improved fire-fighting performance afforded by microcapsules. The Research provides a new direction for the development of fire-fighting materials.