Guorui Feng

Coal wetting-acidification is a promising method to enhance the coal dust control and gas permeability. To elucidate the internal transformation process of coal wetting-dissolution, this study employs contact angle measurements, low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray diffraction to investigate the wetting characteristics and pore structure changes of coal before and after treatment with acid and surfactant composite reagents. The interaction mechanisms between mineral dissolution and wetting-dissolution characteristics are explored. Results indicate that surfactant-assisted acidification reduces the coal contact angle by approximately 60%, significantly enhancing coal wettability. Post-treatment with the composite reagent alters the pore structure of coal through chemical reactions, increasing the total pore volume and average pore diameter by factors of 2.0 and 1.5, respectively. Fractal theory analysis shows reductions in the fractal dimensions D₁ and D₂ by 24.1% and 10.3%, respectively, compared to raw coal, indicating decreased surface roughness and improved pore connectivity. The addition of [BMIM]BF₄ ionic liquid inhibits surfactant activity, leading to an increased contact angle and decreased coal wettability, which in turn reduce the average pore size. A positive correlation is observed between coal wettability and dissolution; as wettability increases, acid solution facilitates the dissolution of more mineral impurities, thereby increasing the total pore volume and average pore size. The findings on wetting-dissolution transformation and ionic liquid inhibition align with experimental results on contact angle and average pore size, elucidating the microscopic mechanism of coal wetting-dissolution.

A variety of dust control methods are often applied in coal mines, among which the application of wet scrubbers has proven to be an efficient technology for the removal of dust in airstreams, rather than diluting or confining the dust. In this paper, a wet scrubber design was developed. Based on a self-designed experimental test platform, the total dust concentration, respirable dust concentration, air volume, and average pressure drops of wet scrubbers with 12, 16, 20, and 24 blades were measured under different water intake conditions. The results show that the different water intake levels have only minimal effects on the air volume of the wet scrubbers. However, increased water intake had improved the dust removal efficiency of the wet scrubbers with the same number of blades. The wet scrubber with 16 blades was found to have the best dust removal efficiency at a water intake level of 1.35 m³/h. Its total dust and respirable dust removal efficiency reached 96.81% and 95.59%, respectively. The air volume was 200.4 m³/min, and the average pressure drop was determined to be 169.4 Pa. In addition, when the wet scrubber with 16 blades was applied in a coal preparation plant in China’s Shanxi Province, it was observed that the total dust concentration had fallen below 8.1 mg/m³, and the respirable dust concentration had fallen below 5.9 mg/m³. Therefore, the results obtained in this research investigation provide important references for the use of wet scrubbers to improve coal production environmental conditions.

Large numbers of gobs are produced as a result of underground longwall mining, and a large amount of these gobs is known to contain methane gas reserves. The efficient drainage of these methane resources is directly dependent on accurately determining the methane enrichment zone (MEZ) in longwall mining gobs. In this study, a method for accurately determining the MEZ within the zone of interconnected fractures, which utilized a surface directional borehole (SDB) technique, was proposed. The SDB was designed and implemented in a longwall gob located in the Sihe Coal Mine in China’s Shanxi Province. The trajectory of the SDB constantly varied in the different overlying stratum layers and locations above the gob. The methane flow rate and concentration from the SDB, along with the methane concentration in the upper corner of the longwall face, were monitored and obtained as the longwall face advanced. Then, by analyzing the acquired data of the different horizontal and vertical positions of the SDB, the accurate locations of the MEZ within the zone of interconnected fractures were determined. There were the methane decrease zone (MDZ) and methane shortage zone (MSZ) below and above the MEZ, respectively. The results showed that in the MEZ, both the methane flow rate and concentration displayed slight decreasing trends and maintained high levels as the distance from the roof of the coal seam increased. In the MDZ, a sharp decline was observed in the methane flow rate. However, a relatively high methane concentration had still been maintained. In the MSZ, both the methane flow rate and concentration displayed dramatic fluctuation and relatively low levels. The average methane flow rates in the MEZ were determined to be 1.3 and 1.6 times higher than those in the MDZ and MSZ, respectively.