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To effectively improve the dust reduction rate of fine dust and prevent the occurrence of secondary dust, surfactant-charged water mist dust reduction technology is proposed. First, the water mist induction-charged atomization mechanism was perfected by an induction-charged spray experiment and the optimal atomization-charged voltage was determined to be 10 kV. Second, by surface tension and spray experiments on AEO-9-charged solutions, the lower the surface tension and viscosity of the solution, the better the atomization effect; the best atomization solution was 10 kV and 0.02% AEO-9. Finally, according to an electrostatic adsorption experiment, it was identified that there was an electrostatic interaction between coal dust and charged droplets. The contact angle experiment showed that the contact angle of the AEO-9 droplets decreased by 68.44% compared with water after 3 s of contact with coal dust. The wetting effect of bituminous coal was significantly improved by adding AEO-9 to water. A molecular simulation was used to study the molecular interaction mechanism among the H2O, AEO-9, and bituminous coal molecules. The simulation results showed that AEO-9 was more active than water, it easily interacted with bituminous coal, and the hydrophilic group covered the surface of the bituminous coal molecules, which increased the electrostatic interaction between the water molecules and bituminous coal surface molecules. After adding AEO-9 to H2O, the intermolecular interaction energy of the H2O/AEO-9/bituminous coal system was enhanced more than that of the H2O/bituminous coal system. This study provides the basis for the application of surfactant-charged water mist dust reduction technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • APG12/active water can achieve efficient atomization and dust removal. • The weakened attraction between H 2 O molecules in the APG12/active droplets. • APG12/active droplets enhance the interactions between H 2 O and anthracite molecules. • The simulation provides guidance for the development of new dust suppressants. Coal mining processes produce large amounts of dust particles that seriously pollute the environment and threaten health. Spraying technology is a primary technique for dust removal. To date, experimental methods are mainly applied to study the atomization and dust removal properties of water droplets, but the intermolecular mechanism involved is unclear. First, a test platform was assembled to evaluate the atomization and dust removal performance of APG12/active water. Then, APG12 droplet and APG12 droplet/anthracite molecular models were constructed, and the underlying mechanism was elucidated through molecular simulation. The experimental results showed that the droplet diameter of the APG12/active water spray decreased by 14.15%, and the dust removal efficiencies of total dust and respirable dust increased by 39.55% and 61.51%, respectively. The simulation results indicated that APG12 molecules and H 2 O molecules exhibited attractive interactions. This interaction weakened the electrostatic attraction between the H 2 O molecules in the APG12/active water droplets. Moreover, the interaction enhanced the repulsive van der Waals interactions, reduced the number of hydrogen bonds, and increased the diffusion coefficient of H 2 O molecules. As a result, the droplets were relatively easy to break. In addition, APG12 molecules covered the surfaces of anthracite molecules, thus increasing the surface oxygen content and the electrostatic attraction, van der Waals forces and hydrogen bonding between H 2 O and coal molecules. This enhancement, in turn, improved the wettability of coal dust. Herein, the molecular mechanism of dust removal from APG12/active water was analysed, providing guidance for the development of new dust suppressants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Corona-charged water mist has a significant capture effect on coal dust. • Proposing the corona spray charging technology of Red Copper Barbed Ring electrode. • Corona charging effectively reduces droplet particle diameter. • The charging effect of corona-charged water mist is highly improved. Water-mist charging technology, as an innovative form of wet dust capture technology, is designed to capture fine coal dust using electrostatic force. With advancements in the charging process, materials, and design of the electrodes utilized in traditional water-mist charging technology, the present study introduced the corona water-mist charging technology utilizing a red copper barbed ring electrode. Initially, the variation in voltage of self-sustained corona discharge and the characteristics of electric field distribution with varying electrode parameters were examined through simulation. This was aimed at identifying the electrode parameters that yield the most effective charging. Subsequently, the charging and dust reduction effects of the corona water-mist charging technology employing a red copper barbed ring electrode were explored experimentally. Findings indicate that this technology significantly reduces the droplet particle size, enhances their charge, and improves the efficiency of settling on coal dust. This research offers a new method and practical advice for the efficient capture of coal dust. [ABSTRACT FROM AUTHOR]

To effectively control the dust generated by coal mining operations, a new type of cyclonic pneumatic mist curtain dust control device was developed. Using CFD software, numerical simulations were conducted on the internal airflow velocity field, the exit velocity of the cyclonic pneumatic mist curtain, and the mist droplet particle field of the curtain. Experiments were carried out to measure the spray coverage, droplet size, and the dust control performance of the model device. The results indicate that when the water pump supply pressure is 8 MPa, the fan supply wind speed is 12 m/s, and the nozzle installation angle is 75 degrees, the cyclonic pneumatic mist curtain dust control device model operates under optimal conditions. The effective coverage of the cyclonic mist curtain is 380 × 3300 mm, fully suppressing dust generation on one side of the curtain. An optimal dust removal distance of about 90 cm was determined. After installing the cyclonic pneumatic mist curtain dust control device, the average dust reduction efficiency for respirable dust reached 91.07%, and the overall dust reduction efficiency achieved 93.34%. [ABSTRACT FROM AUTHOR]

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 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]

To evaluate the granularity distribution pattern for multi-nozzle interference spray, the two-phase flow state inside the nozzle and the fragmentation process of the droplet particles in the eddy current field is studied, and the atomization characteristics of the multi-nozzle spray interference process is simulated based on CFD technology. The results indicate that the braking distance in the atomization field decreases with the increase of atomization pressure, and the decreasing speed is slower, in contrast, the atomizing angle increases with the rise in atomization pressure and the decrease of nozzle diameter. Compared with the single nozzle atomization field, the multi-nozzle atomization field has a more uniform distribution of droplet particles through collision, polymerization and rupture, which can achieve a better dust removal effect. By increasing the atomization pressure, the multi-nozzle interference atomization area can be formed faster, the droplet size is more refined, and the distribution is more uniform. Under the optimal parameters, practical testing indicates that the multi-nozzle air-operated atomization system makes the total dust and respirable dust concentrations at the various measuring points decrease rapidly, and the maximum suppression rates reach 95.52% and 96.84%, respectively. [Display omitted] • The two-phase flow state inside the nozzle and the droplet fragmentation process in the eddy current field was discovered. • The atomization characteristics of the multi-nozzle spray interference process was revealed. • The main atomization parameters of air-operated spraying system were discovered. [ABSTRACT FROM AUTHOR]

In order to accurately characterize and evaluate dust particle diffusion in the dynamic tunneling process of a boring machine, this study considers the 31,116 main transport chute heaving face of the Lijiahao coal mine as a case study. A dynamic tunneling model is developed considering the real dynamic tunneling state of the header, to carry out an in-depth analysis of the spatial and temporal evolution of wind flow and dust dispersion in the tunnel under dynamic excavation. In addition, the results were compared against the calculations of a static standard excavation model of a conventional header. Employing CFD analysis accompanied by field measurements, it was highlighted that the dynamic tunneling of the header leads to an increase in the pressure difference and the turbulent kinetic energy at the working face. Moreover, an increase in the number of vortices was reported, and a higher concentration of dust spreads more quickly along the return wind side wall to the return flow area. On the other hand, the high concentration of dust under the standard tunneling model was found to accumulate a lot on the return wind side. Simultaneously, as the distance between the pressurized air outlet and the working face increases, the average wind speed in the vortex-type wind flow area at the front of the tunnel decreases. When t = 60 s, the return flow area expands to a space of 8 m~24 m from the head, and the dust accumulated above the header spreads to the back of the header to form a high concentration dust region of more than 500 mg/m³. It was shown that the range of high-concentration dust clouds in the breathing zone decreases compared to the results of the standard tunneling model. Moreover, the dust concentration in the breathing zone of the driver is significantly lower than that reported by the standard tunneling model. Based on the results of the field test, the average error between the simulated and measured data of the dynamic tunneling model was calculated to be around 6.46%, thus demonstrating the model's capability in describing the real working conditions of the heave tunnel. [ABSTRACT FROM AUTHOR]

To solve the problem of the inability of traditional spray dust removal technology to efficiently restrain dust diffusion at the heading face, a multilayer spiral fog curtain dust control method based on spirally arranged pneumatic nozzles is proposed. In this paper, the k-ɛ turbulence model and K-H droplet breakage model are used. First, different airflow fields are analyzed by simulating the simultaneous injection of different numbers of nozzles, and the motion law of airflow interaction is obtained. Taking the two-layer fog curtain as an example, a multiphysical field coupling numerical simulation of the two-layer spiral fog curtain applied in the field is carried out, and the variation law of its velocity field distribution and particle motion characteristics is analyzed. A similar experimental platform is established to verify the effectiveness of the simulation results and the feasibility of the dust removal scheme. The simulation results show that the double helix arrangement will form a rotating airflow with the cutting arm as the axis to cover the whole roadway section and produce a double-layer spiral fog curtain. The water mist is fragmented into smaller fog droplets under the action of rotating airflow, which improves the dust catching effect of the fog curtain. Experiments show that the dust removal rate and efficiency of multilayer spiral fog curtains are obviously stronger than those of natural dust reduction and traditional spray. After 3 minutes, a dust concentration of approximately 470 mg/m3 can be reduced to less than 4 mg/m3. The average dust removal rates of total dust and exhaled dust were 2.600 mg/(m3.s) and 0.189 mg/(m3.s), respectively, and the dust removal efficiencies were 97.01% and 94.32%. [ABSTRACT FROM AUTHOR]

The excavation of coal mines generates substantial dust, posing environmental and health risks for underground coal mine workers. To address the dust issue, a novel Vortex Air Flow Negative Pressure Entrainment Dedusting Device was developed. Through numerical simulations and a comprehensive experiment, factors influencing dust removal efficiency, such as the number of air ducts, wind speed, and pressure duct layout angle, were analysed. The result showed that the number of air ducts had the most significant effect on the suppression efficiency, while the pressure duct layout angle had the least significant impact. Six ducts with 25 m/s air velocity and 30° pressure duct angle were determined as the optimum operational parameters for dust removal. Field tests with the optimum setting were also conducted. The results demonstrated the best dust control performance compared to other settings, which resulted in a 90% reduction in coal dust concentrations. The developed device provides underground coal mines with an effective method to control coal dust efficiently during the excavation. [ABSTRACT FROM AUTHOR]

The dust removal efficiency of the existing dust control technologies for coal yards involving multiple dust production spots is low and cannot satisfy the requirements stipulated by the existing standards. This paper proposes a new type of vortex blowing suction dust control technology. The principle of dust control was examined through numerical simulations. The dust control efficiency of the single suction and vortex blowing suction methods was compared experimentally. The results indicated that most of the dust particles were collected by the vortex, and they moved in a spiral from the bottom to the top. The highest vortex airflow performance corresponded to an optimal blowing ratio of 4.814. The experimental comparison indicated that the dust removal performance of the vortex blowing suction technique was better. Specifically, for the formal and latter techniques, dust removal efficiency was 93.25% and 41.19%, and dust escape rate was 6.31% and 46.60%, respectively. [Display omitted] • Solve the problem of dust production in coal yard. • Solve the problem of complicated pipelines and dust deposits in the pipeline. • Combines the principle of vortex generation with dust removal technology. • The best blowing and sucking ratio of the vortex blowing and sucking device is 4.814. • Prevent the dust from escaping and depositing effectively. [ABSTRACT FROM AUTHOR]

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. [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]

A numerical model of single-particle fog-dust collision coupling in a high-speed airflow based on three-phase flow theory. The effect of the fog-to-dust particle size ratio, relative velocity between the fog and dust particles, collision angle and contact angle at the wetting humidity function of dust particles is investigated. Different particle size ratios are determined for achieving the optimal wetting humidity for the interaction of high-velocity aerosols with dust particles of different sizes, for differ, that is, kPM2.5 = 2:1, kPM10 = 3.5:1 and kPM20 = 1.5:1. The optimal humidity increases with the relative velocity U between the fog and dust particles in the high-speed airflow. The larger the collision angle is, the lower the wetting rate is.The smaller the contact angle between the solid and liquid is, the better droplet wetting on dust is. The fine kinetic mechanism of single-particle fog-dust collision-coupling in a high-speed airflow is elucidated in this study. [ABSTRACT FROM AUTHOR]

To effectively solve the problem of high dust concentration during coal cutting and frame shifting in fully mechanized mining faces, based on the theory of gas–solid two-phase flow, a geometric model of a fully mechanized mining face was established by using COMSOL numerical simulation software. Simulations were performed for the movement characteristics of wind flow and the law of dust diffusion. Results show that the air flow at the junction of the working face, the air inlet, the hydraulic support moving area, and the vicinity of the shearer has accelerated movement, and the maximum wind speed zone of about 3 m/s can be formed. Under the influence of wind flow, dust particles above 35 μm settle faster, while dust particles below 35 μm are very vulnerable to the influence of wind flow, and the settling speed is slower. Using a custom experimental platform, the atomization characteristics and wind resistance of a pressure fan nozzle, a supersonic nozzle, and an ultrasonic nozzle were tested, and the nozzle that was suitable for the scheme was selected and applied in the field. Comparing the dust concentration before and after the application of the dust removal scheme at the sampling point, results show that the dust removal efficiency of the proposed scheme exceeds 85%, and the treatment effect is good. [ABSTRACT FROM AUTHOR]

In order to solve the problems of insufficient filtration performance of bag dust collector in coal mine and improper selection of filter materials, the performance parameters of seven kinds of filter materials were compared and analyzed. The results showed that with the increase of filtration time, the resistance of different filter materials showed an upward trend, the resistance of ordinary filter material increased rapidly, while the resistance of membrane filter material increased more gently. The time required for ordinary filter material to reach the cleaning cycle is relatively short, the cleaning cycle of polyester filter material is 80s, and the amount of dust accumulated on the surface of membrane filter material is always in a rising state. When the dust particle size is between 6.5 μm and 23 μm, the dust removal efficiency of PTFE filter material increases with the increase of filtering wind speed; The field practice shows that after the LFD-45 horizontal film-coated flat bag precipitator with pre-installed PTFE filter material is installed on the tail guide trough of 106belt conveyor, the dust reduction rates of total dust concentration and respirable dust concentration are 98.57% and 98.95% respectively. [ABSTRACT FROM AUTHOR]

For the problem of coal dust pollution in the return air lane of the comprehensive mining working face of soft rock mines.Based on the principle of supersonic siphon pneumatic atomization dust control, mobile vehicle-mounted pneumatic spraying combined with full-section fog curtain dust control technology is proposed to address the coal dust pollution problem in the return air tunnel of the comprehensive mining working face of soft rock mines. This technology has a wider spraying range, stronger wind resistance and lower energy consumption.Using the k-ε turbulence module and the fluid flow particle tracking module of COMSOL simulation software, a three-dimensional numerical model of the return air tunnel was established. The effect of wind flow characteristics on the diffusion range of coal dust and fog droplets was analysed, and the dust transport pattern and dust control effect of the new technology were obtained for different cross-sectional return airways. The results show that the velocity of the wind flow is continuously decayed by the slope, and the dust of different particle sizes is distributed differently by the inertial force. Coal dust with particle sizes larger than 6.5 μm accumulates below the structure at a lower velocity, and coal dust with particle sizes smaller than 4.5 μm is mostly suspended above the structure at a higher velocity. The device effectively stops the transport of dust and covers the whole section of the roadway, and the dust removal efficiency reaches 96.53%~97.93%, which provides relevant theoretical support and treatment means for the control of dust pollution in the return airway of coal mines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The sonic boom atomization mechanism was applied to design a nozzle based on the Laval aerodynamics principle. The designed nozzle was simulated on the Fluent platform and the performance of the nozzles was evaluated on a test platform. The different parameters, including the flow characteristics, atomization characteristics, and dust reduction efficiency of the nozzle were analyzed under different air-water conditions. The obtained results show that under the same air and water pressure conditions, the size probability distribution peak, particle size distribution range, and median diameter of the droplet are smaller than those of an internal mixing nozzle. The sonic boom atomization nozzle consumes less water compared to traditional nozzles. After the installation of the sonic boom fog screen dust reduction system in the return air channel, the average values of total dust concentration and respiratory dust concentration were reduced by 91.26% and 90.16%, respectively. The obtained results indicate that sonic boom atomization nozzles can realize water saving and efficient dust reduction in underground coal mines. [Display omitted] • Application of Laval aerodynamic principle to coal mine dust reduction and development of corresponding nozzles. • Proposed sonic boom atomization technology based on Laval aerodynamics and produced the corresponding nozzle. • Using simulation and experimentation to test the various properties of sonic boom atomization nozzles. • Comparing the advantages and disadvantages of sonic boom atomising nozzles and conventional internal mixing nozzles in terms of performance. • Field proven sonic boom atomization nozzles significantly improve dust reduction. [ABSTRACT FROM AUTHOR]

To solve the problem of dust pollution, a new type of ultrafine spiral atomization nozzle with a small droplet size and strong dust reduction ability was developed according to the principle of air-water spray and the generation law of vortex airflow. Numerical simulation software is used to simulate the velocity and streamline distribution of the air flow field inside the air flow director under different parameters, and the best spiral effect parameters of the air flow director for the directional air flow are obtained. Set up an experimental platform to determine the performance parameters of the ultrafine spiral atomization nozzle and compare the dust suppression performance of the ultrasonic dry mist to study its dust suppression performance. The results show that when the angle between the spiral trough and the tapered wall is α = 30° and the ratio of the diameter of the top surface of the air flow director to the height d = 1.25, the air flow director has the best directional air flow spiral effect. When the air supply pressure of the supersonic nozzle and spiral groove is 0.4 MPa, the atomization angle of the supersonic spiral atomizer is the largest, the D 90 of the droplet group is 19.7 μm, and the comprehensive atomization performance is the best. At this time, the total dust reduction efficiency is 92.18%, which is better than the ultrasonic dry mist for dust suppression and dust reduction. The efficiency is 81.97%. When the full-section spiral pneumatic dust control system with an ultrafine spiral atomization nozzle as the core is applied to the 06 return airway of the Mindong No. 1 Mine, the dust reduction efficiency of the respirable dust is 88.8% ~ 91.58%. [Display omitted] • The supersonic spiral fog screen can improve the spray effect. • Device Design proportion to improve Air flow Spiral effect. • When the air supply pressure is 0.4 MPa, the atomization performance is the best. • Supersonic spiral spray has better dust reduction ability than traditional spray. • The device has been applied in the field. [ABSTRACT FROM AUTHOR]

To examine the diffusion characteristics of airflow and dust particles, a multi-factor and multi-level physical self-developed testing system is established. In this study, bunker height, chute angle, feeding speed, coal granularity, and belt speed are selected as independent variables, and airflow velocity and dust concentration are the response variables. The two-factor interactive model is established to analyze the primary and secondary relationship between the independent variables and the response variables. The results demonstrate a denser contour distribution of three-dimensional curved surfaces, suggesting an obvious interaction between the factors. The bunker height increases from 0.75 m to 1.15 m, the maximum increment of the induced airflow velocity at the outlet of the guide chute is observed to be 0.35 m/s, meanwhile, and with the increase in the feed speed from 2t/h to 8t/h, the increment of the induced airflow velocity at the outlet of the guide chute is recorded to be 51%. The coal granularity and bunker height depicted the highest influence on induced air velocity and dust concentration, and the feeding speed proved to be the secondary parameter. This two-factor interactive model can accurately forecast the actual values with a deviation of the calculated values limited to 9%. These research results support the existing research and provide a theoretical foundation to guide the dust control at belt conveyor transfer stations. [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]

• 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]

• [Emim][BF 4 ] formed the highest number of hydrogen bonds, [Bmim][BF 4 ] followed, and [Bmim][Cl] formed the least number of hydrogen bonds in an aqueous environment. • The addition of ionic liquids increased the adsorption thickness along the Z-axis between the water/coal system and promoted the adsorption of water molecules on the lignite surface. • The addition of ionic liquids made water molecules more active, intensified the diffusion of water molecules to the coal surface, and increased the negative interaction energy between water-modified lignite. In order to study the wetting mechanism of imidazole ionic liquids on lignite surfaces, molecular dynamics simulations combined with quantum chemistry were used to analyze the molecular level of 1-butyl-3-methylimidazolium chloride salt ([Bmim][Cl]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF 4 ]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF 4 ]) adsorption and wetting processes on the surface of lignite molecules. The electrostatic potentials and frontline orbital energy levels of [Bmim][Cl], [Bmim][BF 4 ], and [Emim][BF 4 ] and coal molecular models were analyzed to determine their nucleophilic and electrophilic regions based on the density flooding theory (DFT) in Gaussian 09 program. The water-coal system and ionic liquid–water-coal system were constructed from a microscopic perspective by dynamics simulations, and the relative concentration distribution of each system in the z-axis direction, the diffusion coefficients of water molecules in each system, and the non-bonding interactions of each system were analyzed. The results showed that [Emim][BF 4 ] has the largest front-line orbital energy polarity and the best wettability for coal. [Emim][BF 4 ] was more likely to interact with water molecules to form hydrogen bonds and had the highest number of hydrogen bonds with water molecules. The molecular dynamics simulations revealed that the adsorption of ionic liquids on the surface of lignite increased the adsorption thickness between water-coal systems, which led to a more extensive diffusion of water molecules, which increased the negative interaction energy between water-modified lignite and further improved the hydrophilicity of lignite, with [Emim][BF 4 ] molecules having the strongest ability to improve the hydrophilicity of lignite. These results further demonstrated that [Bmim][Cl], [Bmim][BF 4 ], and [Emim][BF 4 ] can significantly improve the wettability of coal dust, which was important for improving the effect of coal seam water injection and reducing the dust concentration. [ABSTRACT FROM AUTHOR]

To better solve the problem of dust pollution at the coal transshipment point, the particle tracking calculation method based on the discrete phase model was adopted to study the dynamic three-dimensional flow field of falling dust during coal transshipment. The induced airflow field characteristics and the dust particles migration law at different times and sections were simulated, and the power function relation between the initial falling velocity, falling height, and the induced airflow rate was deduced. The results showed that in the process of coal falling onto the belt, the induced airflow continuously sucked fresh air to form a vortex due to the reduction of vertical static pressure in the vertical direction and self-generated turbulence. The direction of induced airflow at the coal dropping point was different, and the horizontal airflow velocity could reach 1.4 m/s. The spiral migration path of dust particles was formed by the influence of the eddy current. At the same time, under the effect of the negative pressure caused by the induced airflow, the dust particles carried by the coal were emitted from the outlet of the guide trough, and the dust mass concentration was as high as 540 mg/m3. Meanwhile, the induced airflow velocity of falling point increased with the increase of initial falling velocity and coal material falling height, which matched to power function exponents were 1.01 and 0.41 respectively. With the increase of the falling height, more negative pressure air was absorbed into the blanking pipe, which lead to the increase of dust mass concentration in position after the feeding point. The maximum dust mass concentration was 715 mg/m3. [ABSTRACT FROM AUTHOR]

To solve the problem of dust pollution in the heading face, a new type of external pneumatic vortex fog curtain dust removal device suitable for a fully mechanized excavation face is designed in this paper. Firstly, dust migration laws at different times are simulated and analyzed by COMSOL software, and the functional relationship of dust concentration distribution above 50 mg/m3 at different heights and different wind speed is derived. Aiming at the dust migration laws of the heading face, a new dust removal device was proposed, and the atomization performance of the new type of external pneumatic vortex fog curtain dust removal device under different jet wind speed, different atomization pressure, and different nozzle working angle is explored through atomization performance experiment. It is found that when jet wind speed is 30 m/s, atomization pressure is 4 MPa, and nozzle working angle is 75°, the atomization performance of the new type of external pneumatic vortex fog curtain dust removal device is the best. Through the simulation of COMSOL software, the influence of air volume on the new type of external pneumatic vortex fog curtain dust removal device is analyzed. It is found that the new type of external pneumatic vortex fog curtain dust removal device is relatively stable when the air volume at the pressure outlet is less than 400 m3/min. The dust-reduction efficiency of the new type of external pneumatic vortex fog curtain dust removal device was investigated through the dust-reduction experiment, and it is found that the new type of external pneumatic vortex fog curtain dust removal device had better dust removal performance under the condition that the ventilation conditions did not interfere with the integrity of the vortex fog curtain. [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]