Construction and optimization of macromolecular structure model of Tiebei lignite.

Mastering the molecular structure of coal is important for the effective utilization of coal. For a detailed study of the microstructural characteristics of Tiebei lignite, its molecular structure was characterized by elemental analysis, solid 13C nuclear magnetic resonance (13C NMR), Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The results showed that the aromatic carbon content of Tiebei lignite was 51.98%, the aromatic carbon structure was mainly composed of benzene and naphthalene, and the ratio of aromatic bridgehead carbon to surrounding carbon Xbp was 0.14. Oxygen existed in phenol, ether, carbonyl, and carboxyl; nitrogen-containing structures mainly existed in the form of pyrrole and pyridine; sulfur mainly existed in thiophene sulfur; and aromatic substitution was mainly in the form of trisubstitution. The molecular formula of the macromolecular structure model of Tiebei lignite was C190H161O57N2, and the 13C NMR spectrum of the model was in good agreement with the experimental results, which fully verified the accuracy of the macromolecular structure model of Tiebei lignite. The construction of a macromolecular structure model of Tiebei lignite is essential to intuitively understand the molecular structure characteristics of Tiebei lignite and to provide theoretical support and guidance for the micromechanism research and prevention of lignite spontaneous combustion and other disasters.

Prediction of the Penetration Radius of Cumulative Blasting.

To improve the efficiency of coal seam gas extraction, the influence characteristics of different factors on the penetration effect of cumulative blasting were determined and the hole spacing was effectively predicted; in this work, we used ANSYS/LS-DYNA numerical simulation software to establish the penetration model of cumulative blasting. Combined with an orthogonal design scheme, the crack radius prediction of cumulative blasting was studied. A prediction model for predicting the fracture radius of cumulative blasting based on three groups of different factors was established. The results showed that the primary and secondary order of factors that affected the fracture radius of cumulative blasting was as follows: ground stress > gas pressure > coal firmness coefficient. The penetration effect decreased with increasing ground stress and decreased with an increase in the gas pressure and coal firmness coefficient. The industrial field test was carried out. The gas extraction concentration increased by 73.4% after cumulative blasting, and the effective crack radius of cumulative blasting was approximately 5.5-6 m. The maximum error of the numerical simulation was 1.2%, and the maximum error of the industrial field test was 6.22%, which proved that the crack radius prediction model of cumulative blasting was correct.

Study on the Occurrence Difference of Functional Groups in Coals with Different Metamorphic Degrees.

In order to quantitatively study the difference in occurrence content of functional groups in coals with different metamorphic degrees, the samples of long flame coal, coking coal, and anthracite of three different coal ranks were characterized by FTIR and the relative content of various functional groups in different coal ranks was obtained. The semi-quantitative structural parameters were calculated, and the evolution law of the chemical structure of the coal body was given. The results show that with the increase in the metamorphic degree, the substitution degree of hydrogen atoms on the benzene ring in the aromatic group increases with the increase in the vitrinite reflectance. With the increase in coal rank, the content of phenolic hydroxyl, carboxyl, carbonyl, and other active oxygen-containing groups gradually decreased, and the content of ether bonds gradually increased. Methyl content increased rapidly first and then increased slowly, methylene content increased slowly first and then decreased rapidly, and methylene content decreased first and then increased. With the increase in vitrinite reflectance, the OH-π hydrogen bond gradually increases, the content of hydroxyl self-association hydrogen bond first increases and then decreases, the oxygen-hydrogen bond of hydroxyl ether gradually increases, and the ring hydrogen bond first significantly decreases and then slowly increases. The content of the OH-N hydrogen bond is in direct proportion to the content of nitrogen in coal molecules. It can be seen from the semi-quantitative structural parameters that with the increase in coal rank, the aromatic carbon ratio fa, aromatic degree AR and condensation degree DOC increase gradually. With the increase in coal rank, A(CH2)/A(CH3) first decreases and then increases, hydrocarbon generation potential 'A' first increases and then decreases, maturity 'C' first decreases rapidly and then decreases slowly, and factor D gradually decreases. This paper is valuable for analyzing the occurrence form of functional groups in different coal ranks and clarifying the evolution process of structure in China.

Study on smoke blocking and thermal radiation attenuation by water curtain in tunnel fire.

A 1:10 scale model tunnel with a length, height and width of 9 m, 0.6 m and 0.8 m, respectively, was set up in this paper. A water curtain system was installed in the model to investigate the effect of water curtain systems on smoke flow and heat propagation. A reduced-scale experimental and theoretical study was carried out by varying the heat release rate of the fire source, the water curtain pressure, and the number of water curtain rows. A series of tests were carried out for various setups to quantify each mechanism of interaction between the water mist and hot smoke, to propose a method for qualitatively analysing water curtain systems blocking the propagation of heat radiation and the flow of smoke from combustion, and to propose a method for predicting heat fluxes. The study found that the pressure of the water curtain, the number of rows, and the heat release rate of the fire source all had an effect on the smoke blocking effect of the water curtain system. This effect decreased as the heat release rate of the fire source increased and increased significantly with the pressure of the water curtain and the number of rows. The smoke blocking effect was quantified using conservation of momentum by establishing a dimensionless parameter R to represent the ratio of water curtain momentum to smoke momentum, as well as the ratio of heat flux before and after the water curtain to represent the smoke blocking capacity [Formula: see text] of the water curtain. The smoke blockage rate [Formula: see text] ranges between 40 and 75%, and the smoke blockage rate increases as the momentum R increases. Finally, in tunnel fires, a predictive model for the attenuation of heat radiation by water curtains has been developed, providing theoretical support for the quantitative study of the smoke and thermal blockage effects of water curtains, which is beneficial to the protection of human life in confined spaces.

Study on prediction of blasting cracking radius of liquid CO2 in coal.

In this study, we sought to improve the efficiency of coal seam gas extraction, master the characteristics of different factors on the liquid carbon dioxide (CO2) phase change blasting cracking radius, and effectively predict the hole spacing. In this study, we used ANSYS/LS-DYNA numerical simulation software to predict the crack radius of liquid CO2 phase change blasting combined with orthogonal design scheme. The results showed that the primary and secondary factors affecting the fracture radius of liquid CO2 phase change blasting were in ground stress, gas pressure, coal firmness coefficient, and gas content. The fracture radius decreased with the increase of in ground stress and decreased with the increase of gas pressure, coal firmness coefficient, and gas content, which was linear. A prediction model for predicting the cracking radius of liquid CO2 phase change blasting based on four groups of different factors was established. Through the double verification of numerical simulation and field industrial test, the cracking radius of liquid CO2 phase change blasting ranged from 2 m to 2.5 m. The maximum error of numerical simulation was 2.8%, and the maximum error of field industrial test was 5.93%.

Molecular structure characterization analysis and molecular model construction of anthracite.

Coal is the largest non-renewable energy as well as an important basic energy and industrial raw material. Thus, correctly understanding the molecular structure characteristics of coal has important theoretical value for realizing carbon neutralization. In this work, we clarified the molecular structure characteristics of anthracite, where the organic matter in anthracite was characterized and analyzed by industrial/elemental analysis, FTIR, XPS, XRD and solid 13C NMR. The ratio of bridge carbon to the perimeter carbon of anthracite was 0.38, and the degree of condensation in the aromatic structure was high. Nitrogen in coal primarily exists in the form of pyridine and pyrrole. Based on the information on functional group composition, the carbon skeleton structure, and surface element composition, a molecular structure model of Yangquan anthracite could be constructed, where the molecular formula was C208H162O12N4. This study may serve as a reference for researchers in this field to consult and refer to the construction ideas and methods of molecular structure models of different coal samples.

Optimization of mine ventilation network feature graph.

A ventilation network feature graph can directly and quantitatively represent the features of a ventilation network. To ensure the stability of airflow in a mine and improve ventilation system analysis, we propose a new algorithm to draw ventilation network feature graphs. The independent path method serves as the algorithm's main frame, and an improved adaptive genetic algorithm is embedded so that the graph may be drawn better. A mathematical model based on the node adjacency matrix method for unidirectional circuit discrimination is constructed as the drawing algorithm may not be valid in such cases. By modifying the edge-seeking strategy, the improved depth-first search algorithm can be used to determine all of the paths in the ventilation network with unidirectional circuits, and the equivalent transformation method of network topology relations is used to draw the ventilation network feature graph. Through the analysis of the topological relation of a ventilation network, a simplified mathematical model is constructed, and network simplification technology makes the drawing concise and hierarchical. The rapid and intuitive drawing of the ventilation network feature graphs is significant for optimization of the ventilation system and day-to-day management.