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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]

Atmospheric dustfall is solid air pollutant, has a major impact on the environment and human health. The objective of this study was to investigate the microscopic characteristics and sources of atmospheric dustfall in open-pit mining coal resource-based city in the arid desert area of Northwest China. The characteristics of size and shape factors, variation of shape factors with size distribution, types of individual particles, and sources of atmospheric dustfall, which were collected in the open-pit mining area and surrounding areas, were analyzed by X-ray diffraction (XRD) and scanning electron microscopy coupled with an energy dispersive spectrometer (SEM–EDS) combined with graphical method and shape factors. The results showed that the atmospheric dustfall in all functional areas was dominated by coarse-grained particles. The shape of the atmospheric dustfall deviated from spherical shape, and with decreasing particle size, the difference in shape factors increased in each functional area. The EDS and XRD analyses indicated the presence of 13 types of particles. The sources were mainly local and included soil dust from each functional area; industrial dust, construction dust, biogenic impurities, fossil fuel combustion, wear products of motor vehicle parts, motor vehicle exhaust emissions, and emission and excreta from biological activities in each functional area except the desert area; emissions from a steel plant in the industrial area; coal-associated ore, coal dust, coal gangue emissions, and emissions from the spontaneous combustion of coal gangue in the open-pit mining area; secondary chemical crystallization products in the industrial area and the open-pit mining area; dust generated by vehicles abrading the surface of the off-mine coal road and in the open-pit mining area. [ABSTRACT FROM AUTHOR]

Aiming at the problem of spontaneous combustion of coal relics caused by the overburden fracture network penetrating the upper and lower coal seams in the process of shallow-buried and short-distance coal seam mining, the 31114 working face of Lijiahao coal mine was used as the research background to study the characteristics of overburden transport and fracture development in shallow-buried and short-distance coal seam mining by using physical similar simulation test; the fractal dimension and image processing techniques were used to quantify the overburden fractures; the classical mechanical models of "solid support beam" and "masonry beam" were combined to analyze the causes of fracture dynamic evolution. The results show that: (1) Before the key seam fracture, the stress in the upper rock seam only changes in a small amount, and the stress in the lower rock seam evolves similarly to the single coal seam mining; when the key seam fracture is broken, the stress in the upper and lower rock seams will change by jumps. (2) The fractal dimension of the fissures rised from 1.4 to 1.5, the total area of fissures is increased from 16,638 pixels to 17,707 pixels, and the total length is increased from 2217 to 3071 pixels; after the main key layer of the overlying rock is broken, the fractal dimension of the fissures is reduced from 1.56 to 1.5, and the total area of fissures is reduced from 31,451 pixels to 29,089 pixels, the total length has increased from 5657 to 6619 pixels. (3) Before the key layer between the coal seams is broken, it will be suspended to form a "fixed beam". After the first break, the broken rock above it will settle synchronously until the rock blocks form a hinged structure and then collapse. After the fall stops, the key layer periodically breaks to form a "masonry beam" structure, and the overlying stratum settles synchronously. [ABSTRACT FROM AUTHOR]

In the process of deep mining of coal resources, coal seams with better geological conditions are gradually mined preferentially, and the safe and efficient mining of working face in complex and heterogeneous spaces of residual coal seams is an urgent problem to be solved.. Based on the Kuangou Coal Mine as the background, using microseismic monitoring instruments and pressure sensor monitoring systems, the rock pressure appearance and microseismic energy characteristics accompanying the evolution of the overburden strata structure in the mining of solid coal and the lower working face of the gob are analyzed. Research on the precursory characteristics and early warning of micro-earthquakes. The research results show that: (1) The period of the W1123 working face mining under solid coal is relatively frequent, and the energy of microseismic events is higher than that under the mined-out area. However, the overlying rock structure under the gob is loose, broken and easy to move, showing obvious "high frequency-low energy" characteristics. (2) Extremely low values of the number and energy of microseismic events occurrs in the first 3 to 5 days of the rockburst event in the working face, and the locations of the rockburst disaster in the mine were generally distributed at the edge of the low-density area of the microseismic event. The accuracy of rockburst prediction is effectively improved through multi-parameter comprehensive early warning. (3) Roof deep hole blasting and roof cutting pressure relief weaken the roof energy accumulation and the concentrated release of rock formation energy, reduce the roof activity intensity in the microseismic event gathering area, and reduce the occurrence of large-energy events, which will easily induce large shock hazards. The energy event weakens into a slow release of multiple small energy events. This research provides a reference for the safe and efficient mining of working faces in complex space environment. [ABSTRACT FROM AUTHOR]

It is necessary to change the air supply rate of the working face during the withdrawal of fully mechanized mining, making it important to study the oxidation characteristics of coal samples under different air supply rates. Through a self-made temperature-programmed experimental device, our focus was on studying the change laws of indicator gases released during the low-temperature (303.15–473.15 K) oxidation stage when the air supply rates of the coal samples were 0.67, 1.33, 2, 2.67, and 3.33 mL/s. The experimental results showed that the air supply increased, the concentrations of CO, C2H6, C3H8, C2H4, and C2H2 generated by the coal sample at the same temperature decreased, and the oxidation process decelerated. The initial temperatures of the four hydrocarbon gases were delayed to varying degrees with the increase in the air volume, and C2H4 was found to be more suitable as a hydrocarbon gas for the early warning of coal spontaneous combustion. Surface fitting was applied to analyze the change law of the CO generation rate under the combined effect of temperature and air supply; the change was divided into three stages. The CO concentration model at the upper corner of the working face during the withdrawal period was deduced, and comprehensive safety measures were put forward to prevent coal spontaneous combustion during the withdrawal period. [ABSTRACT FROM AUTHOR]