Search

To study the multi-field coupling mechanism of gas and coal spontaneous combustion, low-temperature nitrogen adsorption and SEM were applied to carry out microstructure testing experiments on oxidation of gas-bearing coal in this paper. And a pore fractal calculation model incorporating pore size distribution was established. The effects of low-temperature oxidation and gas ad/de-sorption on the change of coal pore structure were investigated. The results showed that the pore volume and specific surface area of JJK and YJL with different pretreatment conditions were similar in trend, adsorption–desorption process further attenuates the ability of the coal pore to resist the thermal damage, V1 and V2 of JJK-3 and YJL-3 decreased by 0.199, 0.212 and 1.88, 4.214 × 10–3 cm3·g−1, respectively. The pore fractal model based on pore size distribution characteristics was found, and the Dfb of JJK-3 and YJL-3 was 2.23 and 2.33, respectively, which were higher than that of JJK-2 (2.20) and YJL-2 (2.05). The coupling effect of desorption of gas and oxidation was stronger than the effect of oxidation on pore modification. The gas storage state of gas-bearing coal and the distribution of desorbed gas in goaf were affected by change of pore structure, so that the oxidation of gas-bearing coal can be weakened and the risk of spontaneous combustion of gas-bearing coal can be declined, which can provide a theoretical basis for the judgment of the risk of spontaneous combustion of gas-bearing coal in goaf. [ABSTRACT FROM AUTHOR]

Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant. [ABSTRACT FROM AUTHOR]

This study aimed to explore the stress distribution and variation of reverse fault-affected mined coal body. A mechanical analysis model of the coal body in the reverse fault area was first established, then the coal body stress characterization equation was derived, and the stress distribution pattern on the coal body was calculated. Subsequently, applying the Mohr–Coulomb strength criterion revealed the following relationship: the closer is the distance to the reverse fault, the worse is the stability of the coal body, and that the coal body strength influences the stress concentration of the coal body in front of the working face. Moreover, simulation with FLAC3D was carried out to verify the coal body stress calculated by the mechanical model as well as the fluctuation of the coal body stress concentration. It could be concluded that while mining the hanging wall of the reverse fault, the stress concentration of mined coal body decreases with the increase of reverse fault dip angle, but increases with the increase of reverse fault throw; the stress concentration magnitude generated during footwall mining is lesser than that during hanging-wall mining. In other words, the magnitude of coal body stress concentration can be affected by the hanging wall and footwall mining, as well as parameters of the reverse fault. Finally, intrinsically safe GZY25 borehole stress sensors were used to monitor the coal body stresses in the reverse fault area under the influence of mining in Xinchun Coal Mine and ZuoQiuka Coal Mine. It was found that the coal body stress concentration in front of the working face either increased gradually or increased first before decreasing. It can be concluded that with the decrease of the distance between the working face and reverse fault, the vertical stress of the coal body increases, and the vertical stress of the coal body begins to increase obviously at a certain position. At this point, the vertical stress of the coal body can be generalized to 1.02–1.39 times of the initial vertical stress. Furthermore, the stress concentration coefficient of coal body is related to the distance from the reverse fault, and two changes occur: ① if the coal-bearing capacity does not exceed its strength, the coal stress in front of the working face increases gradually, and the stress concentration factor increases gradually; ② the stress concentration coefficient of mining coal body increases first, such that when the coal body bearing capacity exceeds its strength, the coal body fails and loses all its effective bearing capacity, followed by the decrease in coal body stress concentration coefficient. [ABSTRACT FROM AUTHOR]