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In order to solve the problem of coal dust pollution at the transfer point, a three-dimensional numerical model of wind flow-coal dust at the loading point of underground rubber run was established by computational fluid dynamics (CFD) discrete particle model and finite element method and k-ε turbulence model, and the coal dust diffusion pollution phenomenon caused by the coal flow transfer under the intersection of wind flow in the cross tunnel was studied. Based on the simulation results of wind flow velocity contour, pressure contour and isochronous flow vector distribution, the influence mechanism of wind flow and coal dust characteristics on the distribution of wind flow and coal dust diffusion in the roadway is analysed, and a dust control and reduction system and treatment scheme with new pneumatic screw spray technology as the core is proposed to suppress coal dust pollution at the reloading point. The results of the study show that the wind flow distribution is mainly influenced by the intersection of tape traction and cross-roadway wind flow, showing a complex multi-layer distribution along the roadway and in the normal direction; the diffusion of coal dust of different particle sizes is influenced by the roadway wind flow, and coal dust with particle sizes in the range of 10μm~20μm is more easily diffused, and the dust with particle sizes in the range of 20μm~45μm is mainly collected and suspended near the vortex wind flow at the cross-roadway. The coal dust in the range of 20 μm~45 μm is more likely to gather in the vortex; the treatment system effectively controls the coal dust inside the dust cover, and the spiral-shaped transported droplet particle group formed by the pneumatic spiral spray combines with it efficiently, which verifies the dust control and reduction effect of the pneumatic spiral spray system at the transfer point, and the dust removal efficiency reaches 89.35%~93.06%, which provides relevant theoretical support for the treatment of dust pollution at the coal transfer point in underground coal mines It provides the theoretical support and means to control dust pollution at underground coal transfer points., Competing Interests: The author declares that there are no competing interests.

The distribution of multiscale pores and fractures in coal and rock is an important basis for reflecting the capacity of fluid flow in coal seam seepage passages. Accurate extraction and qualitative and quantitative analysis of pore-fracture structures are helpful in revealing the flow characteristics of fluid in seepage channels. The relationship between pore and fracture connectivity can provide a scientific reference for optimizing coal seam water injection parameters. Therefore, to analyse the change in permeability caused by the variability in the coal pore-fracture network structure, a CT scanning technique was used to scan coal samples from the Leijia District, Fuxin. A total of 720 sets of original images were collected, a median filter was used to filter out the noise in the obtained images, and to form the basis of a model, the reconstruction and analysis of the three-dimensional pore-fracture morphology of coal samples were carried out. A pore-fracture network model of the coal body was extracted at different scales. Using the maximum sphere algorithm combined with the coordination number, the effect of different quantitative relationships between pore size and pore throat channel permeability was studied. Avizo software was used to simulate the flow path of fluid in the seepage channels. The change trend of the fluid velocity between different seepage channels was discussed. The results of the pore-fracture network models at different scales show that the pore-fracture structure is nonuniform and vertically connected, and the pores are connected at connecting points. The pore size distribution ranges from 104 μm to 9425 μm. The pore throat channel length distribution ranges from 4206 μm to 48073 μm. The size of the coordination number determines the connectivity and thus the porosity of the coal seam. The more connected pore channels there are, the larger the pore diameters and the stronger the percolation ability. During flow in the seepage channels of the coal, the velocity range is divided into a low-speed region, medium-speed region and high-speed region. The fluid seepage in the coal seam is driven by the following factors: pore connectivity > pore and pore throat dimensions > pore and pore throat structure distribution. Ultimately, the pore radius and pore connectivity directly affect the permeability of the coal seam., Competing Interests: The authors have declared that no competing interests exist.

In order to efficiently and accurately control coal dust pollution in coal mining faces, this study addresses the insufficient research on the dust generation mechanism during cutting. Firstly, a similar experimental platform for simulating coal wall cutting with a drum cutter was used to investigate the changes in coal wall fragmentation and dust generation at drum speeds of 35 r/min, 50 r/min, 65 r/min, and 80 r/min. The experimental results revealed that the degree of coal wall fragmentation and dust generation increased with the increase in rotational speed, leading to a wider range of particle size distribution and an increase in the generation of fine dust particles. A 1:1 scale discrete element simulation of coal wall cutting with a drum cutter was conducted based on the experiments. The results indicated that, under the four rotational speeds, the cracks generated during coal wall fracture were predominantly tensile cracks, accounting for over 76% of the total crack count. The total number of cracks increased from 10,600 to 11,200, the number of free single particles increased from 2555 to 2728, and the fragmentation volume increased from 0.021607 to 0.023024 m3. The range and degree of coal wall fragmentation increased with the increase in drum speed. [ABSTRACT FROM AUTHOR]

In order to effectively control high temperatures inside coal gangue hills, gravity heat pipes with specific spacings are vertically installed in coal gangue hills. Heat extracted from these heat pipes can be utilized for power generation through energy conversion. In this study, an equivalent model of gravity heat pipes in coal gangue hills was established and, in a laboratory setting, experimental research and optimization were conducted on power generation per unit area using the temperature difference of gravity heat pipes for electricity generation. To facilitate real-time testing of different heat pipe parameters and to display the experimental results, a multi-parameter measurement system was designed and constructed. This study systematically investigated the effects of various structural parameters such as inclination angle, heating temperature, initial absolute pressure, and working fluid height. Through single-factor experiments, it was determined that the inclination angle had no significant impact. The range of values for heating temperature, initial absolute pressure, and working fluid height were confirmed based on six sets of experiments. To maximize the performance of the thermoelectric generator, a response surface analysis experiment was conducted using the Design-Expert software. The optimal conditions were determined to be a working fluid height of 200.001 mm, an initial absolute pressure of 0.002 MPa, and a heating temperature of 413.15 K. Under these conditions, the power generation per unit area of the thermoelectric generator reached 0.122981 W/(m2·K). The accuracy of the theoretical experiments was verified through on-site industrial experiments. By calculations, it was determined that the maximum temperature difference power generation capacity per gravity heat pipe was 42.39 W. This provides a new solution for the management of coal mine gangue hills and the secondary utilization of waste energy. [ABSTRACT FROM AUTHOR]

Coalbed methane mining, suppression of coal dust, and elimination of dynamic disasters are closely related to the expansion of coal body cracks and internal damage. Understanding the expansion mechanism of pore-cracks is critical to investigate coal body damage. In this study, research from 2016 to 2021 conducted on the coal damage mechanism in China was sorted and the progress in this field was analysed to systematically investigate coal body damage. Critical topics of research in this field in recent years were identified, and load types were classified into static and dynamic loads. Dynamic loads with obvious characteristics and considerable damage-increasing effects were classified into impacting, cyclic, pulsating, and other dynamic load types. The current load-generating devices, various detection techniques and methods, research results, and the future research directions under various load types were discussed. The current coal damage research is primarily based on macrocharacteristic analysis and the stage characteristics of characterisation variables. The use of scanning electron microscopy, computerised tomography three-dimensional reconstruction technology, and acoustic emission technology can reveal the pore propagation mechanism at the micro level. [ABSTRACT FROM AUTHOR]

The adsorption of dodecyl trimethyl ammonium bromide (DTAB) on coal can affect the wettability of coal and change the water absorption of coal. After DTAB treatment, the change in the CH4 adsorption capacity of coal is worth further study. To reveal the microscopic mechanism of the influence of DTAB on the CH4 adsorption capacity of coal, we employed the density functional theory (DFT) with the 6-311 G (d, p) basis set. DFT-based computations interpreted the adsorption process of CH4 and DTAB on coal molecules and determined the stable structure, adsorption distance, Mulliken overlapping populations, and adsorption energies of the two adsorption configurations. The results showed that the adsorption energies of CH4 and DTAB on the molecular model of coal were 2.15 and 42.69 kJ/mol and the adsorption stability distances were 0.261 and 0.238 nm, respectively. The DTAB–coal configuration was more stable than the CH4–coal configuration. When there was competitive adsorption between DTAB and CH4 on coal, the coal molecules preferentially adsorb the DTAB. Infrared spectroscopy and adsorption experiments were also carried out, and the calculation results of quantum chemistry are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hygroscopicity of coal powders with different ranks was compared and investigated. • Reasons behind varying hygroscopicity of coal powders were analyzed and explained. • Variation of hygroscopicity of coal powder with particle size was studied. • Effects of ambient temperature and humidity on the hygroscopicity were examined. The hygroscopicity of coal powder is one of the crucial factors that determine its moisture content, which significantly affects its adhesion, flowability, charge properties, and combustion behavior. In this study, the effects of coal particle size, ambient temperature, and relative humidity on the hygroscopicity of coal powders with different ranks were investigated through experimental methods. The results indicated that an increase in coal particle size resulted in a moderate reduction in the maximum moisture adsorption capacity and a substantial increase in the effective moisture adsorption time of the coal powder. As the coal particle size increased from 19 to 21 μm to 6310–6941 μm, the maximum moisture adsorption capacities of the coal powders decreased by 0.28–0.54 times, while their effective moisture adsorption times increased by 1.47–1.68 times. The maximum moisture adsorption capacities of the coal powders increased dramatically with increasing ambient relative humidity, whereas the impact of temperature on their maximum moisture adsorption capacities was not significant. The hygroscopicity of coal powders varied significantly among different ranks. Low-rank coal such as lignite and subbituminous showed strong moisture adsorption ability, while high-rank coal such as anthracite exhibited moderate moisture adsorption ability, and middle-rank coal such as medium volatile bituminous showed the weakest moisture adsorption ability. FTIR spectra analysis and pore testing results revealed that the content of oxygen-containing functional groups and the distribution characteristics of internal pores were critical factors causing the difference in hygroscopicity of the coal powders. The practical value of this study lies in its potential to determine the moisture adsorption rate and the maximum moisture adsorption capacity of coal powder under specific environmental conditions, which is essential for evaluating the moisture status, transportation efficiency and combustion performance of coal powder. [ABSTRACT FROM AUTHOR]

• Ionic liquids can enhance the wettability of coal. [HOEtMIm][NTf 2 ] has the best wetting effect, [AMIm][BF 4 ] the second, [HOEtMIm][BF 4 ] the worst. • NMR results show that the ionic liquid treatment will partially dissolve the hydrophobic groups in coal and increase the hydrophilic groups in coal. • f a C , f al H , and f al O are positively correlated with wettability, while f ; a , f al ∗ , and f a H negatively correlated with wettability. As the degree of coal mine mechanization increases, the dust concentration underground increases significantly, and the effective reduction of dust concentration can guarantee the safe production in the mine. Wet dust removal method is the main means to suppress coal dust, and wettability is its theoretical basis. To study the effect of functional ionic liquids on the microstructure of coal and the effect of coal microstructure on wettability, [AMIm][BF 4 ], [HOEtMIm][BF 4 ], and [HOEtMIm][NTf 2 ] were selected to treat lignite and anthracite with different metamorphic degrees. Firstly, the effects of ionic liquids on the wettability of coal surface were investigated by surface tension and contact angle experiments. Secondly, the carbon structure skeleton of coal was analyzed by nuclear magnetic resonance (NMR) experiments. Finally, the correlation between the structural parameters obtained by NMR and the contact angle was analyzed by origin software. The results show that [HOEtMIm][NTf 2 ] has the most obvious wetting effect on coal, and different ions have different effects. The ionic liquid treatment will partially dissolve the functional groups in coal. As f a H (protonated aromatic carbon) decreases, f a C (carbonyl carbon) and f al O (oxygen-bonded aliphatic carbon) increase, the hydrophilicity of coal increases, and as f a ′ (aromatic ring carbon) and f al ∗ (methyl carbon) decrease, f al H (methylene carbon and quaternary carbon) increases, the hydrophobicity of coal decreases. The results of this paper can provide basic theoretical support for improving the hydrophilicity of coal surface to improve the efficiency of mine dust reduction. [ABSTRACT FROM AUTHOR]

• The contact angle of [Bmim][BF 4 ]/[Emim][BF 4 ] with the mixture ratio of 1:5 on the coal surface reached the min value of 34.483°. • [Bmim][BF 4 ]/[Bmim][Cl] and [Bmim][BF 4 ]/[Emim][BF 4 ] composite solutions can not only increase the content of hydrophilic functional groups, but also decrease the content of hydrophobic functional groups. • C O was the primary functional group affecting contact angle. –OH and C O C were the main functional groups affecting moisture content. • [Bmim][BF 4 ]/[Bmim][Cl] with a compounding proportion of 1:5 had the best water retention performance. To investigate the effect of different ionic liquid composite solutions on the wettability and chemical structure of coal dust, 14 ionic liquid compound solutions with various composite ratios were selected to act on long flame coal. Through the contact angle measuring instrument, 14 ionic liquid compound solutions were optimized, and 4 ionic liquid compound solutions with the same anion/cation were selected. The wetting agent with good water retention performance in the 4 kinds of composite solutions was selected by the water retention experiment. FTIR was used to research the change of functional group content in the coal treated by the 4 kinds of composite solutions. The results displayed that the contact angle of [Bmim][BF 4 ]/[Emim][BF 4 ] solution with the mixture ratio of 1:5 on the coal surface reached the min value of 34.483°. The [Bmim][BF 4 ]/[Bmim][Cl] solution with a compounding proportion of 1:5 had the best water retention performance. The hydrophilic and hydrophobic functional groups of long flame coal treated by ionic liquid composite solutions had changed significantly. The [Bmim][BF 4 ]/[Emim][BF 4 ] composite solutions with the compounding proportion of 2:4 and 1:5 and the [Bmim][BF 4 ]/[Bmim][Cl] composite solutions with the compounding proportion of 2:4 and 1:5 can not only increase the content of hydrophilic functional groups OH⋯O, Si–O–Si, C O C, C O, and C O, but also decrease the content of hydrophobic functional groups CH 2 and 2H. By analyzing the relationship between coal wettability and functional groups, it was discovered that the hydrophilic functional group C O was the primary functional group affecting the contact angle, and –OH and C O C were the primary functional groups affecting the moisture content of coal samples. In this essay, the novel composite wetting agent type was prepared by compounding ionic liquid solutions with the same anion/cation in pairs, which has certain guiding significance for further using the novel composite moistening agent to improve the wettability of coal and preventing and control mine dust. [ABSTRACT FROM AUTHOR]

• Different ionic liquids affected the change of functional group content in four functional group intervals in coal. • The anions and cations of different ionic liquids can increase the content of hydrophilic groups in coal dust with different metamorphisms and destroy the hydrophobic groups in the dissolved coal structure. • C O and OH···O had a significant correlation with the contact angle. • 2% [Emim][BF 4 ] had the strongest wettability to coal. Three imidazole ionic liquid solutions were selected to handle coal with distinct degrees of metamorphism to research the influences of cation and anion ions in ionic liquids on functional groups and the relationship between functional groups and coal wettability. The chemical framework of coal was researched by FTIR and the wetting peculiarity of the coal was researched by contact angle meter. FTIR analysis showed that the cation and anion ions in ionic liquids significantly altered the framework of the coal. The contact angle measurement results demonstrated that compared with coal using pure water, the coal handled with ionic liquids showed a smaller contact angle. Finally, the relationship between contact angle and functional group content was analyzed. The results showed that the anions and cations of different ionic liquids can increase the content of hydrophilic groups in coal dust with different metamorphisms, such as OH···O, C O, and C O, and destroy the hydrophobic groups in the dissolved coal structure, such as CH 2 , CH and the benzene ring 3 substitutions. And 2 % [Emim][BF 4 ] can effectively reduce the coal contact angle and improve the wettability of coal dust. The content of C O and OH···O groups had the greatest correlation with the contact angle, which were 0.845 and 0.754, respectively. By studying the influence of anions and cations in ionic liquids on the content of functional groups in coal, the effect of specific anions and cations on coal structure was further discovered, which provides a theoretical basis for the development of new ionic liquids with specific functions, and provides guiding significance for ionic liquid solutions to improve the wettability of coal and reduce the dust concentration. [ABSTRACT FROM AUTHOR]