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To better understand the dust dispersion and pollution laws in coal-oil shale fully mechanized mining faces, the airflow distribution and coal and oil shale mixed dust emission law was simulated, and the simulation results are analyzed and verified in combination with the field measured data. The research results showed that in the area 0-10 m on the leeward side of the front drum, most of the coal dust particles with a large particle size stay near the roof of the hydraulic support and the height of the breathing zone, while most of the oil shale dust particles with a large particle size stay in the area below the height of the breathing zone. In the height of the breathing belt, oil shale and coal dust particles seriously polluted the 0-6-m and 0-13-m areas on the leeward side of the front drum of the shearer, respectively. According to the different distribution of coal dust and oil shale dust, a wet dust collector and multi-nozzle atomization set are designed to remove dust. The field test results show that the dust removal rates of the two kinds of dust reach 83.4% and 87.5% respectively after the dust removal device is opened., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Aiming at the problems of the influencing factors of coal mine dust wettability not being clear and the identification process being complicated, this study proposed a coal mine dust wettability identification method based on a back propagation (BP) neural network optimized by a genetic algorithm (GA). Firstly, 13 parameters of the physical and chemical properties of coal dust, which affect the wettability of coal dust, were determined, and on this basis, the initial weight and threshold of the BP neural network were optimized by combining the parallelism and robustness of the genetic algorithm, etc., and an adaptive GA−BP model, which could reasonably identify the wettability of coal dust was constructed. The extreme learning machine (ELM) algorithm is a single hidden layer neural network, and the training speed is faster than traditional neural networks. The particle swarm optimization (PSO) algorithm optimizes the weight and threshold of the ELM, so PSO−ELM could also realize the identification of coal dust wettability. The results showed that by comparing the four different models, the accuracy of coal dust wettability identification was ranked as GA−BP > PSO−ELM > ELM > BP. When the maximum iteration times and population size of the PSO algorithm and the GA algorithm were the same, the running time of the different models was also different, and the time consumption was ranked as ELM < BP < PSO−ELM < GA−BP. The GA−BP model had the highest discrimination accuracy for coal mine dust wettability with an accuracy of 96.6%. This study enriched the theory and method of coal mine dust wettability identification and has important significance for the efficient prevention and control of coal mine dust as well as occupational safety and health development.

In this work, the high‐pressure methane adsorption/desorption tests were conducted in four coal samples (from low‐rank bituminous coal to anthracite) under different temperature and pressure conditions to reveal the mechanism of desorption hysteresis effect in the deep‐buried coal seams. The experimental and fitting results show that the presence of free methane molecules in the adsorption phase results in an obvious difference between the measured methane adsorption amount with the actual adsorption capacity. The Langmuir, Langmuir–Freundlich (L–F) and Dubinin–Astakhov (D–A) models have their own advantages and disadvantages in fitting the experimental adsorption/desorption data. As residual adsorption capacity C fitted by the D–A model would be negative at high temperatures and lose the meaning of the constant, the Langmuir model is more suitable to describe methane desorption process. The residual adsorption capacity fitted by Langmuir model tended to decrease as the temperature increased until it is almost completely desorbed at 373 K. Meanwhile, because the adsorption sites with lower energy are gradually occupied by methane molecules in the high‐pressure stage, intermolecular forces increased and methane molecules are more easily desorbed. Therefore, the desorption hysteresis coefficient trends to increase exponentially with the decrease of pressure and temperature, which indicated that the original gas content of the coal seams may decrease with the increase of the burial depth, but the risk of coal and gas outburst accidents may increase. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Injecting surfactants into coal seams is an effective means to improve coal wettability. Previous studies have shown that nanofluids provided excellent drag reduction and wetting. Therefore, this manuscript investigates the synergies of AOS (Sodium alpha-olefin sulfonate)-modified SiO 2 nanofluid on the wettability of coal. Contact angle experiments were performed to examine the effects of deionized water on the wettability of coal treated with different solutions. The results demonstrated that 0.01 wt% nanofluid containing with 0.2 wt% AOS as the significantly increased the wettability. At the micro level, molecular dynamics simulations were employed to analyze the relative concentration distribution and MSD (mean square displacement) of water molecules in different systems. The simulation outcomes revealed that water molecules formed the thickest adsorption layer, and the diffusion range was more expansive, in the H 2 O/AOS-modified SiO 2 /Coal system. This was attributed to the amphiphilic structure of AOS-modified SiO 2 , which bent and folded on the coal surface, where hydrophobic sites were masked and hydrophilic sites were increased. Therefore, water molecules were attracted to the coal, the potential for collision was increased, and the wettability of the coal was enhanced. These findings provide a crucial foundation for modifying nanoparticles with surfactants and using them in coal seam water injection. • Experimental and simulation research methods were used to explain wetting effects. • Constructed the H 2 O/AOS-modified SiO 2 /Coal simulation system. • The effect of AOS-modified SiO 2 on the wettability of coal was studied. • Provide ideas for the application of nanofluids in coal seam water injection. [ABSTRACT FROM AUTHOR]

Coal is the primary fossil fuel in China's energy sector. As the amount of mining continues to increase, the high concentration of dust generated poses a severe threat to equipment and frontline workers. The coupling influence of HCl and temperature on the structure and wettability of coal were conducted by experiments. The phenomenon indicates that the contact angle between coal treated with HCl of different temperatures and water is reduced, the settling distance in an aqueous solution is longer, and the effect is significant with the increase of temperature, demonstrating the acid-thermal coupling solution improves the wettability of coal. Secondly, detailed analysis of coal functional groups and surface element, shows that the percentage of hydrophilic groups increased, such as OH⋯O, free –OH, and hydrophobic groups were destroyed, such as the asymmetric deformation vibration of adjacent H. The L, 'C' , and DOC show an increasing trend, while I first increase and then decrease by analyzing the trends of IR indices of coal. The conclusions prove that the degree of coal deterioration changed after treatment with acid-thermal coupling conditions. The influence mechanism of acid-thermal coupling solution on coal was explored to provide ideas for improving the wettability of coal from the source. • The effect of acid-thermal coupling on the wettability of coal was studied. • The influence of acid-thermal coupling on functional groups in coal was analyzed. • Acid-thermal coupling has an impact on the degree of coal metamorphism. • As The temperature increases, the acid-thermal coupling effect is significant. [ABSTRACT FROM AUTHOR]

In order to scientifically and reasonably assess the risk of water inrush from the coal seam floor, considering the influence of natural environmental factors such as hydrogeology, mining, and human intervention, the PSR model of ecosystem health evaluation was introduced, and the risk evaluation indicator system of water inrush from the coal seam floor was established. In order to solve the randomness and fuzziness of water inrush event evaluation, the evaluation model is constructed based on extension cloud theory and is applied in the 12123 working face of Pan Er coal mine of Huainan Mining Group. The application results show that the evaluation results are basically consistent with the actual situation, which shows that the model can be used in the actual evaluation work and is scientific. [ABSTRACT FROM AUTHOR]

It is wise to investigate the influence of ionic liquids (ILs) on reducing hydrophobicity and dust pollution of coal from the perspective of side chain groups. In this study, two ILs ([Emim][Cl] and [HOEmim][Cl]), were selected and applied to bituminous coal. The density functional theory results showed that [HOEmim][Cl] containing the –OH group had an energy gap of 5.2895 eV, which was lower than the 5.3873 eV of [Emim][Cl] containing only the -CH3 group. A higher chemical activity of [HOEmim][Cl] was demonstrated due to the presence of the –OH group. A molecular dynamics-based contact angle system was constructed to investigate the wetting properties of coal samples treated with different ILs at the molecular level. The simulation results indicated that, compared to untreated coal, [HOEmim][Cl] exhibited a greater ability than [Emim][Cl] to improve the wetting properties of coal. Contact angle experiments demonstrated that treatment with [Emim][Cl] and [HOEmim][Cl] resulted in a decrease in contact angle by 22.67° and 25.04°, respectively, compared to deionized water, providing validation for the accuracy of molecular simulations. Lastly, the structural changes of coal samples induced by different ILs were observed by FITR, which explained the differences in wetting effects. [Display omitted] • A molecular simulation system for coal treatment with ionic liquids was established. • The effect of ionic liquids on coal wettability was analyzed at the molecular level. • The experimental contact angle verified the rationality of the simulated system. • [HOEmim][Cl] showed better improvement in the wettability of bituminous coal. • The structure change of bituminous coal after ionic liquid treatment was analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pectin-modified dust suppressants with different methoxy levels were prepared. • Comprehensive studies of wetting performance, structural properties and dust suppression performance experiments were carried out. • For the first time, the dust suppression properties of LAT and HAT were compared at the molecular level. • LAT effectively enhances the hydrophilicity of coal and has a significant effect on wetting and agglomeration of coal. Low methoxy level pectin (LM-PC) and high methoxy level pectin (HM-PC) were utilized as materials to produce environmentally friendly dust suppressants, and the impact of pectin modification with different methoxy levels on wetting and agglomeration of coal was investigated. The results of contact angle and settling experiments reveal that the low methoxy level pectin-modified dust suppressant (LAT) can effectively wet coal, and the optimum modification conditions are determined. FTIR spectra of coal samples treated with LAT and high methoxy level pectin-modified dust suppressant (HAT) demonstrate that the absorption peak area ratios of hydrophilic functional groups increase by 4.00 % and 2.61 % compared to the original coal. XPS spectra indicate that the increases in carboxyl and hydroxyl functional groups are the reason for the improvement of wettability in bituminous coal. Compared to the coal samples treated with HAT, the increase of hydrophilic functional groups is higher in LAT treated coal samples. Through the dust suppression performance characterization experiments, it is concluded that LAT is more effective than HAT in reducing coal dust. The mechanism of dust suppressants on the wetting properties of coal was revealed at the molecular level. Experimental and mechanistic analyses show that LAT can effectively wet and agglomerate coal dust while remaining environmentally friendly and economical. [ABSTRACT FROM AUTHOR]

• A three-dimensional molecular model of middle-rank bituminous coal is carefully constructed. • The reliability of the model was verified by FTIR, NMR, density and MEP methods. • The energy level orbital and electrostatic potential of the model is investigated. A suitable model can reflect the properties of coal well. In this study, the properties of HongLiuLin (HLL) coal were studied through industrial analysis, XPS, 13C NMR and FTIR. The results show the coal has middle-rank bituminous coal characteristics, and the ratio of aromatic bridge carbon to aromatic peripheral carbon is 0.16. Benzene and naphthalene ring are the main components of the aromatic structure. N and S exist in pyrrole nitrogen and fatty sulfur, respectively. The hypothesis method was used to deduce the molecular formula C 130 H 73 O 21 NS of the coal model. The stability of the carbon skeleton was improved through the Van Der Waals (VDW) forces in non-bonding energy. Verification of NMR, FTIR and density was completed based on quantum chemistry and molecular mechanics. The coal model energy level orbitals analysis shows that the LUMO and HOMO orbitals are located in the aromatic functional groups. This work provides a reference for further research on the nature of coal in north Shaanxi and improving the utilization rate of coal. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new multifunctional dust suppressant was synthesized by IDS and SDS. • The wetting effect of the suppressant is obviously better than traditional surfactants. • Improving coal wettability by dissolving minerals through IDS molecules. • The synergistic wetting mechanism of SDS and IDS is explained. • Dust reduction effect is characterized by gravity drop hammer dust production. To further enhance the impact of water injection and dust reduction in the deep mining process of the coal mine, an efficient dust suppressant for water injection was synthesized by coupling a chelating agent and a surfactant. The optimal composition solution was determined by surface tension, pre-treatment settling time and contact angle. The experimental results display that the composite solution (0.20 wt%) of Tetrasodium iminodisuccinate (IDS) and Sodium dodecyl sulfate surfactant (SDS) has the best wetting influence on the coal. Under this condition, the surface tension, contact angle and settling time are 23.69 mN/m, 25.72° and 48 s, respectively. FTIR tests exhibit that the proportion of hydrophilic functional groups in the coal sample treated by IDS and SDS composite solution is the highest, reaching 94.23 %. The results of particle size distribution tests show that IDS and SDS composite solution effectively reduces the dust production capacity of the coal body. In addition, the synergistic mechanism of IDS and SDS molecules is discussed from two aspects: Enhancing the pore fluidity and improving the hydrophilicity of coal. In this study, the wetting effect of the dust suppressant is better than traditional surfactants, and the results have important reference significance for improving the water injection effect. [ABSTRACT FROM AUTHOR]

Mining interaction among adjacent coal seams delivers benefits in realizing coal permeability enhancement and mining safety. Despite large amount of studies on interaction phenomenon from several perspectives of stress redistribution, strata movement and permeability change, few investigations focuses on sensitivity analysis, particularly, impacts of interburden parameters on interaction characteristics. A coupled permeability model was established including coal damage effect for better permeability-estimation accuracy. Meanwhile, a numerical simulation model was developed according to targeted coalmine parameters. Weibull statistical distribution is used for setting model property heterogeneity. Effects of interburden Young's modulus (E) on interaction among adjacent coal seams were investigated, mainly the permeability variations in relieved coal seam corresponding to six Weibull shape parameters of E distribution (4, 8, 12, 16, 20 and No Weibull case) and seven Young's modulus combinations of interburden sublayers (HHH, HHS, HSH, SHH, HSS, SHS and SSS combination). Results indicate that: 1) Caused by first mining activities, permeability in underlying relieved seam rises over 950 times near interburden floor. When being farther away the floor, permeability increase ratio first experiences quick decline, then comparatively slight decrease. 2) Permeability value of relieved seam is negatively related to Weibull shape parameter of E , and average permeability increase ratio (P R A v e ) gets the smallest value when Weibull distribution being not included. 3) For seven interburden-sublayer combinations, permeability increase ratio in relieved seam is positively correlated with soft sublayer's number. Meanwhile, P R A v e of HSH combination is larger than that of HHS and smaller than that of SHH. Above results could be beneficial in helping mining researchers and engineers recognize intense-interaction coal seam group (i.e. more soft sublayers and small Weibull shape parameter). Thus, they could make use of seam interaction effect for improving relieved seam permeability and achieve efficient drainage practice through first mining an appropriate coal seam. • Damage-based permeability model is established for good model prediction accuracy. • Weibull statistical distribution is used for setting model-property heterogeneity. • Interaction is intense with more soft sublayers and small m value of interburden. • Coal seam interaction is beneficial for improving permeability and gas drainage. [ABSTRACT FROM AUTHOR]

Faults are one of the important factors influencing coal and gas outburst in outburst coal seams. In this paper, 3# and 8# coal seams in Xinjing Coal Mine were taken as the research objects in the hope of revealing the mechanism of how faults affect coal seam. The pore structure and its resultant change on gas emission of coal samples at different distances from the faults were studied by means of scanning electron microscope, nuclear magnetic resonance and adsorption/desorption experiments. The results show that the fault significantly influences the pore structure. The coal sample closer to the fault has a greater number of well-developed macropores and fractures as well as better connectivity between pores and fractures. Besides, compared with 8# coal seam, 3# coal seam which is more notably impacted by the fault possesses a more developed pore structure at the micron scale. As the distance from the fault increases, the gas adsorption volume declines while the desorption hysteresis coefficient grows on the whole. The coal sample closer to the fault adsorbs a larger volume of gas and meanwhile desorbs gas more easily, so it is more prone to coal and gas outburst. The initial velocity of gas emission falls gradually as the distance from the fault increases. The desorption hysteresis coefficient generally drops with the rise of the initial velocity of gas emission. Judged by the influence scope of the fault, 3# coal seam possesses a much higher outburst risk than 8# coal seam. The research results reveal the mechanism of how faults affect coal pore structure and gas sorption characteristics, which can provide a basis for the prevention and control of gas dynamic disasters in fault-containing coal seams. • The pore structure of coal at different distances from the fault was studied. • The effect of fault on gas adsorption and desorption of coal was analyzed. • The influence scope of the fault on coal seams were discussed. • The interaction between Δp and desorption hysteresis coefficients were discussed. [ABSTRACT FROM AUTHOR]

To further investigate the physicochemical properties and wettability changes of surfactant-modified coal after oxidation, the contact angle, industrial composition, and functional groups of the surfactant-modified coal were measured. The experimental data were analyzed using a ridge regression prediction model to explore the relationship between the physicochemical properties and the wettability. The results indicate that the oxidated-modified coal has a worse wettability at room temperature. The adsorption of SL and CDEA surfactants effectively impedes the increase in the contact angle of the oxidized coal. The hydrophilic functional group (2#C O, C–O–C, RHC CH 2) in coal demonstrates higher sensitivity to surfactants, while the hydrophobic functional group (2# Free OH, 1#C C) exhibits greater reactivity. There is a strong correlation between the industrial composition, structural parameters, and the contact angle. The quantitative influence of the parameters on the contact angle is as follows: FC ad > V ad > P 1 ≥ P 4 ≥ M ad ≥ P 3 ≥ P 2. A coal wetting model is established that considers the combined action of surfactants and coal quality. These findings suggest that wettability is determined by multiple parameters, providing a basis for discovering new reagents that significantly enhance coal wettability and reduce coal oxidation activity. • Investigated functional groups exhibiting robust reactivity towards surfactants. • Examined the effects of surfactants on the oxidation and wettability of modified coal. • Developed a coal wetting model utilizing a more practical ridge regression model. • Ranked the relative importance of indicators influencing the contact angle. [ABSTRACT FROM AUTHOR]

• Electrostatic repulsion reduction between ions in CTAB caused by HCl. • HCl has a great influence on CTAB, and the surface tension is reduced by 10 ∼ 30 mN/m. • Coal surface roughness becomes smaller after treated with acid fracturing fluid. • HCl and CTAB have synergistic effect on the improvement of coal wettability. With the continuous improvement of mechanized mining intensity, dust has seriously threatened the safety of mine production and the health of underground workers. Coal seam water injection is one of the effective means to moisten the primary coal dust in the coal body. Through testing by the surface tension tester, contact angle meter, FTIR, low-temperature liquid nitrogen adsorption, and SEM, the impact of acid fracturing fluid which can be used for coal seam water injection on the wettability and pore structure of coal was studyed. The results showed that HCl and CTAB had good synergistic acidification effect, which can effectively reduce the surface tension of CTAB by 10 ∼ 30 mN/m. Also the contact angle between the solution and the coal sample is significantly affected by the acidity of the solution. However, the impact of the acid fracturing fluid varies for coal with differing levels of metamorphism and mineral content. For low rank bituminous coal, the contact angle decreased by 39.55° after contact with the sample surface for 1 s, and the solution was completely immersed in the coal body after 5 s. The absorbance of hydrophilic functional groups of coal becomes stronger after treatment with acid fracturing fluid, which is conducive to upgrading the wettability of coal. Meanwhile, the acid fracturing fluid increases coal's connectivity and average pore diameter, which in turn influences the wettability of coal. Exploring the influence of acid-based fracturing fluid on coal can provide guidance for improving the wettability of coal, reducing dust concentration and optimizing the underground working environment. [ABSTRACT FROM AUTHOR]

Waterflooding of coal seam is an effective method for dust control and gas outburst control. This work utilized a visual coal waterflooding device to investigate the macroscopic water diffusion in coal matrix and the influence of coal wettability, coal fracture size, and gravity on water diffusion and wetting. The results showed that water diffusion front in coal was flat and steadily advancing when coal was hydrophobic. The diffusion front of small fracture coal was more stable than that of large fracture coal. Water diffused faster in hydrophilic coal than in hydrophobic coal. Water diffused faster in large fracture coal than in small fracture coal. The influence of fracture size on water diffusion was more obvious in hydrophobic coal than in hydrophilic coal. Gravity scarcely affected water diffusion in hydrophilic and hydrophobic coal. The research results have significant reference value for guiding coal seam waterflooding for dust control. [Display omitted] [ABSTRACT FROM AUTHOR]

• Coal chemical components and structures affected by acidification and THF are studied. • Effect of successive treatments of acidification and THF on pore fractal features is analyzed. • Relationship between SSA, average pore size and fractal parameters are discussed. • Successive treatments of acidification and THF could well improve pore development. Chemical solvents could change coal components and effectively enhance conductivity of coal reservoir, which is beneficial to efficient methane extraction. Relationship between coal chemical structure parameters and main functional groups variations affected by acidification and tetrahydrofuran (THF) is investigated through infrared spectroscopy tests and curve peak fitting. Meanwhile, variations in fractal dimensionality and pore structure characteristics are studied by adopting low-temperature nitrogen adsorption tests and Frenkel-Halsey-Hill (FHH) fractal model. Main results are: (1) After extracting raw coal and acidified coal using THF with varying concentrations, absorbance of aromatic hydrocarbon –CH surface and aromatic methyl bond become weaker. While the proportion of substituted aromatic hydrocarbons increases in acidified coal than in raw coal. Acidification treatment could reduce strength of C-O-C absorption peak. Proportion of CH 2 and CH 3 in raw coal decreases with increasing THF concentration, indicating that THF could react with aliphatic structure to reduce CH 2 and CH 3 content. Extraction with THF dissolves aromatic structure, lowering C = C content in coal to different degrees. (2) Acidification pretreatment could produce more micropores in coal samples. Micropore contents of acidified coal after THF extraction are all lower than coal sample S, while transition pores and mesopores contents are both higher than those in coal sample S. (3) Fractal dimension D 1 of raw coal indicates a relatively linear relationship with specific surface area, while the D 1 of acidified coal is less correlated with specific surface area. The factor D 2 shows a linear relationship with average pore size. After treatment of THF, average pore size of raw coal increases with D 2 , while that of acidified coal varies in different degrees with uneven distribution of pore sizes. [ABSTRACT FROM AUTHOR]

• Pore structural characteristics affected by chemical solvents are experimentally studied. • Changes in fractal dimensions of pore surface and pore structure are calculated based on FHH model. • Isothermal adsorption-desorption curves of solvent-treated coal show hysteresis phenomenon. • Relationship between pore volume, average diameter, SSA and fractal dimensions are established. • Results could provide theoretical references for chemical solvents effects on pore properties. Chemical solvent treatment is one of the most effective means to improve pore structure of low-permeability coal and increase production of coalbed methane. Low-temperature liquid nitrogen adsorption method, X-ray diffraction (XRD) mineral analysis and fractal theory were adopted to study variations in coal pore structural parameters and fractal characteristics affected by hydrochloric acid (HCl), tetrahydrofuran (THF) and carbon disulfide (CS 2). Liquid nitrogen adsorption results of coal samples were analyzed using density functional theory (DFT), Brunauer-Emmett-Teller (BET) equation and Barrett-Johner-Halenda (BJH) model. Meanwhile, changes in fractal dimensions of pore surface (D 1) and pore structure (D 2) were calculated based on Frenkel-Halsey-Hill (FHH) model. Relationship between pore volume, average pore diameter, specific surface area and two fractal dimensions were established. Results show that: (1) Hysteresis lines exist in all isothermal adsorption-desorption processes of coal. Pores of raw coal are mainly semi-open pores with poor connectivity. The types of pores do not change significantly after THF and CS 2 treatment, while the number of pores rise. In contrast, affected by HCl treatment, ink-bottle pores and open pores increase and pore fracture network connectivity becomes better. (2) Pore sizes of treated coal mainly distribute in range of 0–10 nm. After HCl treatment, many closed pores are opened, with growth in proportion of micropores. Meanwhile, specific surface area (SSA) of pores increases by 55.21% and 31.36%, respectively. THF extraction results in an increase in pore volume and SSA. After CS 2 extraction, dissolution of organic material increases pore size and further improve volume of transition pores and mesopores. (3) HCl treatment causes decrease in D 1 value of pores. However, in organic-solvent-treatment cases, solvent residues retain on coal pores, resulting in growth in D 1 value and pore surface becoming rougher. Proportion of total pore volume of transition pores and mesopores of acidized coal decreases and D 2 value rises. Pore distribution is more uneven. Relevant results could provide theoretical references for revealing mechanism of chemical solvents effects on gas flow in coal. [ABSTRACT FROM AUTHOR]

Coal seam gas drainage has manifold benefits including ensuring mining safety and efficiency, reducing greenhouse gas emissions and generating clean gas resource. Gas drainage performance is primarily determined by coal permeability. Permeability is a result of the competitive effect of mechanical properties and matrix shrinkage. Aiming to summarize extensive investigations on coupled permeability models and provide both fresh researchers and mining engineers with references on current understanding and future directions of permeability models, coal structures (matrix, cleats and pores) are first discussed in this work, as those structures providing a physical basis for permeability-model establishment. Then coupled permeability models are categorized and reviewed from viewpoints of stress/sorption-based permeability models, stress and sorption-based permeability models, damage-based permeability models and anisotropic permeability models, including model-development theoretical basis, boundary conditions and applications. Current research gap and future work directions in permeability study are identified. Results show that theoretical assumptions of constant vertical stress and uniaxial strain are mainly adopted in permeability models. Meanwhile, the effects of gas desorption/adsorption and stress variation are always incorporated in models compared with coal anisotropy and damage. Future studies on permeability variation during underground coal mining are expected to be conducted with coupling effects of coal damage, coal anisotropy, water and coal fines, for increasing permeability-evaluation accuracy and providing better guidance for gas drainage design. [ABSTRACT FROM AUTHOR]