Aiming at the respirable dust hazards caused by restricted space, dense equipment layout, and high dust generation intensity during rapid excavation in low-seam coal mines with a seam height below 2.85 m, this study investigated the cross-scale coupled evolution mechanism of airflow and dust in low-height excavation roadways. An onboard integrated dust control and removal technology combining “source suction purification” and “airflow diffusion control” was proposed. A full-scale three-dimensional model of the 11,207 excavation face at Yuandatan Coal Mine was established using the CFD-DPM method and validated against underground measured airflow velocities, with errors controlled within 6%. The results show that, under the original forced ventilation condition, obvious recirculation zones and low-velocity stagnant zones formed within 0–40 m from the heading face due to jet reflection at the face and equipment obstruction, while the dust concentration in the breathing zone remained above 800 mg/m3. After introducing the onboard integrated system, the local airflow field was reconstructed. The optimization results indicate that, at an extraction airflow rate of 450 m3/min, the system achieves a balance between dust capture efficiency and ventilation stability, confining dust within 2 m of the heading face. Field tests show that the dust concentration near the heading face decreased from 976.78 to 58.05 mg/m3, with an average dust reduction efficiency of 94.1%. This study provides technical support for efficient dust control during rapid excavation in low-height roadways.

Cryogenic freezing technology can both reduce the energy storage of coal–rock mass and enhance its strength, showing broad application prospects for outburst prevention in deep outburst-prone coal seams. However, studies on the effects of moisture content and temperature on the mechanical strength and energy response characteristics of gas-bearing coal after freezing remain relatively scarce. In this study, briquette coal specimens and pulverized coal samples were subjected to quantitative water injection and cryogenic freezing after adsorption equilibrium. Uniaxial compression tests and gas desorption experiments were conducted to analyze the variations in mechanical properties, desorption characteristics, and gas expansion energy of coal samples before and after freezing. The results show that the uniaxial compressive strength and elastic modulus of frozen coal samples first increase and then decrease with increasing moisture content, peaking at 4.5%, and both increase continuously with decreasing freezing temperature. Total gas desorption decreases with increasing moisture content and decreasing freezing temperature, whereas the initial desorption rate increases again due to the newly formed macropores and fractures induced by frost heave. Compared with room-temperature conditions, both the increase in compressive strength and the decrease in gas expansion energy of frozen coal samples exhibit a unimodal trend with increasing moisture content, with the optimal values occurring at 4.5%. At a freezing temperature of −30 °C and 4.5% moisture content, the compressive strength increases by 292.23% and the gas expansion energy decreases by 62.78% compared with room-temperature conditions. When the temperature is further reduced to −40 °C, these two values reach 310.88% and 72.56%, respectively, though the growth rates of both enhancements tend to slow down. The outburst-prevention effect of cryogenic freezing is governed by the combined control of moisture content and freezing temperature, and an optimal parameter range exists. The findings provide a theoretical basis for the engineering application of cryogenic freezing technology in deep outburst-prone coal seams.

Effective dust control after coal mine blasting is vital for air quality and safety. This study integrates pressure ventilation with air amplifiers, evaluating performance via numerical simulation and PIV validation in a three-centered-arch roadway model. Results show air amplifiers boost airflow, accelerate dust dilution, and reduce high-concentration duration. A dynamic mixed-effects model identifies an optimal setup of 30 m placement and 0.5 MPa pressure, balancing rapid settling and minimal resuspension. The findings offer technical guidance for underground coal mine dust mitigation.

To enhance the understanding of dust diffusion laws in tunnel blasting operations of metal mines and determine optimal ventilation dust removal times, a scaled physical model of a metal mine tunneling face under the China Zijin Mining Group was established based on field measurements. Numerical simulation was employed to investigate airflow movement and dust migration in the tunneling roadway, and the fundamental features of airflow field and dust diffusion laws after tunnel blasting operations in the fully mechanized excavation face were revealed. The effects of three main factors included airflow rate (Q), ventilation distance (S), and tunnel length (L) on the dust removal time after tunnel blasting operations were investigated based on the orthogonal design method. Results indicated that reducing the dust concentration in the roadway to 10 mg/m3 required 53 min. The primary factors influencing dust removal time, in order of significance, were determined to be L, Q, and S. The lowest dust concentration occurs when the ventilation distance was 25 m. A predictive model for dust removal time after tunnel blasting operations was developed, establishing the relationship between dust removal time and the three factors as T = 20.7Q−0.73S0.19L0.86. Subsequent on-site validation confirmed the high accuracy of the predictive model, demonstrating its efficacy for practical applications. This study contributes a novel integration of orthogonal experimental design and validated CFD modeling to predict ventilation dust removal time, offering a practical and theoretically grounded approach for tunnel ventilation optimization.

To optimize spray-based dust capture efficiency at coal mine working face, a novel micro-nano bubble enhanced ultrasonic dry fog dust suppression approach was developed. The characteristics of micro nano bubbles water were studied through wettability experiments and the dust suppression effect of micro nano bubbles water and tap water was compared by using the custom-designed spray dust suppression experimental platform. Experimental results indicate that micro-nano bubble water increases the concentration of negative ions around the spray area compared to tap water. Additionally, the surface tension of micro-nano bubble water is 9.3 mN/m lower than that of tap water and the contact angle of micro-nano bubble water with coal particles is 5.76 degrees smaller than that of tap water. Application findings of tunnel working face confirm that the micro-nano bubble ultrasonic dry fog purification system achieving average suppression efficiencies of 60.43 % for total dust and 44.84 % for respirable dust, representing a relative improvement of over 30 % compared to the conventional purification system. Moreover, the micro-nano airflow dry fog purification system consumes water at an average rate of 5.13 L/min, which is 2.43 L/min lower than the conventional water curtain purification system, indicating a relative reduction in water usage by more than 30 %. Evidently, the micro-nano bubble ultrasonic dry fog purification system delivers effective dust control and reduce water consumption.

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.

As a new type of nozzle, the internal mixing air atomizing nozzle has been widely used in the field of dust reduction via spraying. In this study, the effect of water supply pressure on the atomization characteristics and dust-reduction efficiency of the internal mixing air atomizing nozzle was investigated. Firstly, the FLUENT software was used to simulate the flow field inside and outside the nozzle under different water supply pressures. The numerical simulation results showed that as the water supply pressure increased, the internal pressure and water flow velocity in the mixing chamber of the nozzle increased while the air flow rate decreased sharply, resulting the continuous decrease in the relative velocity between gas and liquid. Meanwhile, as the water supply pressure increased, the fragmentation scale of the liquid jet at the outlet of the nozzle was prolonged and the atomization of the liquid was limited. Secondly, based on the custom-developed dust reduction experimental system via spraying, the atomization characteristics of the nozzle were investigated. According to the experimental results, when the water supply pressure increased, the water flow rate and air flow rate of the nozzle had exponential increase and decrease, respectively. As the water supply pressure increased, the range, droplet volume fraction, droplet size, and velocity all increased, while the atomization angle first increased and then decreased. Finally, the dust reduction experiment via spraying was performed under different water supply pressures. The results showed that with the increase of water supply pressure, the dust-reduction efficiency for both the total dust and the respirable dust first increased and then decreased. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

For the purpose of mastering the influence of the strip-shaped air-out slits’ width in the fully mechanized working face under wallattached swirling ventilation condition, By using fluent software, numerical simulation of airflow field and dust diffusion in fully mechanized working face under different strip-shaped air-out slits’ width conditions was carried out. The results show that the wall-attached swirling ventilation can effectively control the dust diffusion in the fully mechanized working face, improve the dust collecting effect of the bag precipitator fan, and reduce the particle mass concentration at the driver and the rear of the tunnel; Increasing the air volume of the strip-shaped airout slits can improve the control effect of the swirling air curtain on the dust, appropriate air volume can make the swirling air curtain control the dusty airflow and push it to the end of the heading surface to control, block and propel the dust; When the width of the strip-shaped air-out slits is 0.06 m, the dust collecting effect of the exhaust air cylinder on the dust and the effect of the wall-attached swirling on the plugging of the dust are best.

为了掌握内混式空气雾化喷嘴喷雾特性及降尘性能,借助自主研发的喷雾降尘实验平台,对内混式空气雾化喷嘴与X旋流型压力喷嘴流量、雾化角、射程、雾滴体积分数、雾滴粒径、雾滴速度等喷雾特性参数及降尘效率进行了实测,并对实验结果作对比分析.结果 表明:随着供水压力的增加,内混式空气雾化喷嘴水流量和气流量分别呈指数形式递增和递减,气液质量流量比不断下降;压力喷嘴水流量随着供水压力的增大而增大,水流量与供水压力的1/2次方成正比.随着供水压力的增加,2种喷嘴的雾化射程、雾滴体积分数及雾滴速度均增大.X旋流型压力喷嘴雾化角明显大于空气雾化喷嘴,其喷雾作用范围更宽;随着供水压力的不断提高,空气雾化喷嘴雾化角呈现先增大后减小的变化规律,而压力喷嘴则一直以较小的幅度不断减小.空气雾化喷嘴由于有压缩空气作为助力,在供水压力较低时能获得较为理想雾滴粒径,且随着供水压力的增大,雾滴粒径不断增大;普通压力喷嘴的雾化粒径随着供水压力的提高而减小,且需在较高的供水压力下才能获得理想的雾滴粒径.在相同的供水压力下,空气雾化喷嘴雾滴粒径和水流量均小于压力喷嘴,而雾滴体积分数、雾滴速度及降尘效率均高于压力喷雾.气水喷雾较压力喷雾具有明显的优势,获得相同的降尘效率,气水喷雾耗水量仅约为压力喷雾的一半.

Wall-attached swirling ventilation is a new type of ventilation for the mechanized excavation face. The dust control effect of the wall-attached swirling ventilation is affected by the forced-to-exhaust air volume ratio. In order to investigate the influence of the air volume ratio on the dust control effect of mechanized excavation face, art experimental model of the wall-attachment swirling ventilation for mechanized excavation face was developed as a reduced scale representation of the D04 mechanized excavation face in Dong Huai Coal Mine of Guangxi Baise Baikuang Group Co., Ltd. Based on this model, the airflow field and dust control of mechanized excavation face at different forced-to-exhaust ratios was analyzed using the study equipment including particle image velocimetry (PIV) system, FCC-25 explosion-proof dust sampler, LS 13320 laser diffraction particle size analyzer, and etc. The analysis results showed that the air velocity at the front end of air supply tube in the wall-attached swirling ventilation was small, the disturbance to the dust production at the heading end by the air flow was weak, and the dust dispersion ability was weak at the front end. In the wall-attached swirling ventilation, both radial air curtain and axial air curtain were generated and pointing to heading end. The cooperation effect of both air curtains controlled dust in the heading area. Thus the operating area for the driver was kept clean and fresh when wall-attached swirling ventilation was running, which ensured a healthy working environment for the roadheader driver. The dust control effect of wall swirling ventilation depended on not only axial air curtain but also radial air curtain. If the forced-to-exhaust ratio was increased, on one hand, the disturbance on the flow field was larger and the intensity of the axial air curtain in the heading end area was weaker; on the other hand, the intensity of the radial air curtain and the dust separation ability were enhanced. When the forced-to-exhaust ratio was 0.8, the wall-attached swirling showed the best dust control effect, the concentration of both the full dust and the respiratory dust around the driver was the lowest, and the separation efficiencies for the full dust and respiratory dust were the highest, which were 93.64% and 98.18%, respectively.

为了确定合理压抽流量比β,采用长压短抽式通风对综掘面进行有效控尘,利用Fluent计算流体力学(CFD)软件,对不同压抽流量比β下综掘面风流流场及粉尘扩散分布进行讨论研究.结果 表明:随着增大与掘进面之间的距离,粉尘浓度逐渐下降,到距离掘进面18,20 m时,粉尘平均浓度只有20 mg/m3.由此可见,长压短抽式通风能够有效对巷道进行降尘.当压抽流量比小于0.8时,能够较好地将粉尘控制在产尘面前端5m范围内,阻止粉尘向司机工作区域及其后方扩散;当压抽流量比控制在1.0～1.2之间时,控尘效果最佳.

As a air-liquid two-phase flow nozzle, the internal-mixing air-assisted atomizer nozzle has been widely used in the field of spray technology for dust reduction. Structural parameters are important factors to influence the atomization characteristics and dust-reducing performance of the atomizing nozzle. However, the mechanism of the influences of the structural parameters is not clear. In this study, the customized experimental spraying platform for dust control was used to study the atomization characteristics and dust reduction performance of the nozzles under different structural parameters. Based on the experimental results, when the parameters such as water pressure and air pressure were constant, the dust reduction efficiency for both the total dust and the respiratory dust first increased then decreased with the increase of the diameter of the water-injection hole in the liquid cap and the number of air-injections holes. The dust reduction efficiency was optimal when the diameter of the water-injection hole in the liquid cap was 1.5 mm and the number of air-injections holes was 4. As the diameter of the air cap outlet increased, the dust reduction efficiency for both the total dust and the respiratory dust was improved; however, the improvement was limited. Based on the comprehensive consideration of the factors including the dust reduction efficiency of the nozzle, the water flow rate, and the air flow rate, the diameter of the air cap outlet should be in the range of 2.0 (3) over tilde .0 mm. When an internal mixing air atomizing nozzle was used for dust reduction in industrial production sites, it is recommended have the diameter of the water-injection hole to be 1.5 mm, the number of air-injection holes to be 4, and the diameter of the air cap outlet to be 2.0 (3) over tilde .0 mm. Under these recommended structural parameters, the dust reduction performance of the nozzle is good while the water consumption and air consumption remain relatively low. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.

Spiral channel pressure nozzles are commonly used pressure nozzles in practical workplaces. In this paper, two kinds of spiral channel type pressure nozzles, namely, spiral hole type and spiral non-porous type, the atomization characteristics and dust reduction efficiency under different spray pressures are discussed and compared. Based on the experimental method, based on the self-designed spray dust-reducing roadway experimental platform, the macro-atomization characteristics of the two nozzles, namely the flow rate, the atomization angle, the range, and the droplet size, were measured. The following conclusions were drawn: (1) The flow rates of both nozzles increase with increasing spray pressure, and the flow coefficient of the spiral non-porous nozzle is small. (2) The change of the atomization angle of the two nozzles first increases and then decreases with the increase of the spray pressure, and the atomization angle of the spiral non-porous nozzle is larger. At the same time, the range of the two nozzles gradually increases as the spray pressure increases, and the range of the spiral perforated nozzle is always larger than that of the spiral non-porous nozzle. (3) When the spray pressure is gradually increased, the droplet size of the two nozzles selected in the experiment is gradually reduced, and the droplet size of the spiral perforated nozzle is always larger than that of the spiral non-porous nozzle before 5 MPa, and then gradually Become smaller. The main reason why the droplet size decreases with the increase of the spray pressure is that the increase of the spray pressure leads to an increase in the spray speed of the water droplets, so that the water droplets are completely split when they are ejected from the nozzle, resulting in a smaller droplet size. In summary, when the spray pressure required in the actual working environment is low, the use of a spiral non-porous nozzle is more conducive to dust reduction.

Spraying is a main technique means for the prevention and control of coal dust in coal mines. The dust suppression efficiency by spraying is highly correlated with the wettability of coal dust. There are many influencing factors for the wettability of coal dust, among which the particle diameter of dust is one of the most significant factors. In order to analyze the influence of particle diameter on the wettability of coal dusts and the dust suppression efficiency via spraying, 18 different samples with 3 different types of coal samples and 6 different particle diameters were selected in this study. A series of experiments were designed and performed to evaluate the micro-properties, the wettability, and the dust suppression performance via spraying of coal dust. According to experimental results on the micro-properties, the amount of hydrophilic oxygen-containing functional groups gradually dropped with the decrease of the particle diameter. As the particle diameter decreased, the specific surface area of coal dust gradually increased while the average diameter of the internal pores decreased. Based on the experimental results on the wettability of coal dust, the wettability of the dust with the same property dropped with the decrease of particle diameter. Finally, based on the experimental results on the dust suppression efficiency via spraying, the dust suppression efficiency via spraying was determined by both the wettability of coal dusts and the value of AD 50 (the absolute value of the difference between the droplet diameter and the dust particle diameter). As the particle diameter of coal dust increased, the dust suppression efficiency via spraying first increased and then decreased. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

The dust and gas control effect of the wall-mounted swirling ventilation method is closely related to the axial-to-radial flow ratio of the forced air. In order to determine the optimal axial-to-radial flow ratio, a scaled physical model of the wall-mounted swirling ventilation was developed based on the prototype of the fully mechanized excavation face, C103, in Nahe Coal Mine, Baise City Mining Bureau, Guangxi. The airflow field, dust diffusion pattern, and gas concentration distribution under different axial-to-radial flow ratios were investigated using numerical simulation based on k-ε turbulence model, discrete phase model (DPM), and component transport model. The results showed that the axial-to-radial flow ratio of 2:8 was reasonable for the fully mechanized excavation face in this study. Under this axial-to-radial flow ratio, the gas concentration of the working face can be controlled within the safety limit, while a desirable dust-control effect can be achieved.

为了得到综掘工作面附壁旋流通风的最佳控尘效果,对附壁旋流通风的流场进行数值模拟.首先在附壁旋流通风方式下,对不同的吹吸流量比进行数值模拟,再改变压风筒轴向和径向的风量比进行数值模拟,得到不同的吹吸流量比和不同轴径风量比下的气流特性以及粉尘浓度分布规律.结果表明:在不同的吹吸流量比下,若吹风量太小,虽然对掘进面的扰动也小,但附壁旋流径向风幕太弱,对粉尘的封堵效果不好.若吹风量太大对掘进面的扰动太大会导致粉尘向巷道后方运动,不利于径向风幕对掘进面粉尘的封堵.在不同的轴径风量比下,随着轴径风量比的减小,径向风幕的强度增强,对掘进面粉尘的封堵效果也增强.当吹吸流量比为0.8和轴径风量比在1︰9以下时可获得较为理想的控尘效果,能够有效的把粉尘控制在掘进面前端由吸风筒排出,使掘进机司机处粉尘浓度得到有效控制.