Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines. Based on the internal structure, the pressure nozzle can be divided into the following types: spiral channel nozzle, tangential flow-guided nozzle and X-swirl nozzle. In order to provide better guidance on the selection of nozzles for the coal mine dust-reduction systems by spraying, we designed comparing experiments to study the atomization characteristics and dust-reduction performance of four commonly used nozzles in the coal mine underground with different internal structures. From the experimental results on the atomization characteristics, both the tangential flow-guided nozzle and the X-swirl nozzle have high flow coefficients. The atomization angle is the largest in the spiral non-porous nozzle, and smallest in both the X-swirl nozzle and the spiral porous nozzle. The spraying range and the droplet velocity are inversely proportional to the atomization angle. When the water pressure is low, the atomization performance of the spiral non-porous nozzle is the best among the four types of nozzles. The atomization performance of the X-swirl nozzle is superior to other types when the water pressure is high. Under the high water pressure, the particle size of the atomized droplets is smallest in the X-swirl nozzle. Through the experiments on the dust-reduction performance of the four types of nozzles and the comprehensive analysis, the X-swirl nozzle is recommended for the coal mine application site with low water pressure in the dust-reduction system, while at the sites with high water pressure, the spiral non-porous nozzle is recommended, which has the lowest water consumption and obvious economic advantages.

Surfactants can improve the wetting performance of the dust‐reduction spraying water, thus improving the dust‐reduction effect by spray. In this study, the performance of surfactant solution in wetting coal dust was investigated through experiments. In addition, the effects of surfactant type, mass fraction, metamorphic degree of coal, particle size, and additives were investigated. According to the results of surface tension experiments, the surface tension of the solution decreased with the increase of the concentration of surfactant. However, after reaching CMC, the surface tension did not have significantly decrease. SDBS and OP‐10 had higher efficiency in decreasing the surface tension than the other two types of surfactants. The addition of sodium sulfate additives can further reduce the surface tension of the surfactant solution by a limited range. The coal dust wetting experiment showed that with the increase in the concentration of the surfactant, the contact angle of the droplets on the coal dust tablet was continuously reduced, and the wettability of the solution was continuously improved. The wettability of the OP‐10 solution was optimal. At the same concentration, the minimum contact angle can be obtained in the OP‐10 solution. As the contact angle of the coal dust increased, the growth rate in the coal dust reverse osmosis moisture absorption of the surfactant solution relative to the pure water increased. After the addition of sodium sulfate, the reverse osmosis moisture absorption of coal dust increased to varying degrees. In addition, as the concentration of additives increased, the moisture absorption of coal dust increased.

Coking coal dust is extremely hydrophobic; therefore, combination with droplets in the air is difficult and dust suppression is challenging. Here, a dust suppressant spray for coking coal dust was studied in order to improve of the combination of droplets and coking coal dust. Based on monomer optimization and compounding analysis, two surfactant monomers, fatty alcohol ether sodium sulfate (AES) and sodium dodecyl benzene sulfonate (SDBS) were selected as the surfactant components of the dust suppressant. The surfactant monomers were combined with four inorganic salts and the reverse osmosis moisture absorption of each solution was determined. By combining the reverse osmosis moisture absorption values with the water retention experimental results, CaCl₂ was identified as the optimal inorganic salt additive for the dust suppressant. Finally, the optimal concentration of each component was obtained using orthogonal experimental design i.e., AES (0.03%), SDBS (0.05%), and CaCl₂ (0.4%). The dust suppressant solution formulated using this method had a high moisture absorption capacity and excellent performance. Graphic

Coalbed water injection is the most basic and effective dust‐proof technology in the coal mining face. To understand the influence of coalbed water injection process parameters and coalbed characteristic parameters on coal wetting radius, this paper uses Fluent computational fluid dynamics software to systematically study the seepage process of coalbed water injection under different process parameters and coalbed characteristic parameters, calculation results of which are applied to engineering practice. The results show that the numerical simulation can help to predict the wetness range of coalbed water injection, and the results can provide guidance for the onsite design of coalbed water injection process parameters. The effect of dust reduction applied to onsite coalbed water injection is significant, with the average dust reduction rates during coal cutting and support moving being 67.85% and 46.07%, respectively, which effectively reduces the dust concentration on the working face and improves the working environment.

Wall-mounted swirling ventilation is a new type of system in mechanized excavation faces with a dust suppression performance that is closely related to the blowing-to-suction flow ratio. Physical and simulation models were developed according to the No. C103 mechanized excavation face in the Nahe Coal Mine of the Baise Mining Bureau, Guangxi Province to optimize the blowing-to-suction flow ratio for wall-mounted swirling ventilation. Both the k-ε turbulence model and the discrete phase model were utilized to simulate airflow field structures and dust concentration distribution patterns at various blowing-to-suction flow ratios. The results suggest that higher blowing-to-suction flow ratios increase the airflow field disturbance around the working face and weaken the intensity of the axial air curtain. On the other hand, both the intensity of the radial air curtain and the dust suppression effect are enhanced. At a blowing-to-suction flow ratio of 0.8, the wall-mounted swirling ventilation system achieved the most favorable dust suppression performance. Both the total dust and respirable dust had their lowest concentrations with maximum efficiencies of reducing both types at 90.33% and 87.16%, respectively.

Currently, spraying is a main means for dust prevention and control in underground coal mines. The dust‐suppression efficiency via spraying is highly correlated with the wettability of coal dusts. There are many factors affecting the wettability of coal dust, among which coal’s metamorphic degree has great influence. In order to gain in‐depth knowledge of the effects of coal metamorphic degree on coal dust wettability and the dust‐suppression efficiency via spraying, 6 coal dust samples with different metamorphic degrees were collected and used in the study. In the experiments, the microproperties, wetting performance, and dust‐suppression efficiency via spraying were measured. According to the experimental results of coal’s microproperties, with the improvement of metamorphic degree, the content of hydrophilic oxygen‐containing functional groups on the surface, the surface roughness, the specific surface area, and the interpore diameter all decreased. In addition, as coal’s metamorphic degree was enhanced from lignite to meager‐lean coal, the wettability of the coal dust dropped. On the other hand, as the metamorphic degree of coal quality continued to be improved to anthracite, the wettability of the coal dust increased instead. The measured results revealed that the dust‐suppression efficiency via spraying was highly correlated with the wettability of coal dust. The coal dust with better wettability exhibited higher dust‐suppression efficiency via spraying. With the increase of water‐supply pressure, the effect of coal dust wettability on the dust‐suppression efficiency via spraying was weakened, and the difference of dust‐suppression efficiency among different coal dust samples was narrowed.