CFD investigation on dust dispersion pollution of down/upwind coal cutting and relevant countermeasures for spraying dustfall in fully mechanized mining face

To explore the effects of downwind and upwind coal cutting on dust pollution in a fully mechanized mining face, the airflow-dust migration was simulated by using ANSYS-FLUENT software, and the follow-up spraying dust control method was optimized according to the differences in dust concentration distribution during downwind and upwind coal cutting. The results show that during downwind and upwind coal cutting, the average airflow velocity of the fully mechanized mining face is about 1.053 m/s. During downwind coal cutting, the dust generated by the shearer mainly pollutes the mining area and the area within 0–50 m on its downwind side, while the dust generated by the advancing support mainly pollutes the mining area and the sidewalk area within 0–20 m on the downwind side of shearer. During upwind coal cutting, the dust generated by the shearer mainly pollutes the vicinity of the drum and the area within 0–45 m on its downwind side, while the dust generated by the advancing support mainly pollutes the sidewalk area within 0–30 m on the downwind side of shearer. In view of the differences in dust concentration during downwind and upwind coal cutting, the dust concentration in the working face was divided into four areas and the follow-up spraying dust control method was optimized. The field measurement results indicate that compared with the original spraying facility, the optimized opening mode raises the average dust removal rates of total dust and respirable dust in the working face by 52.1% and 43.8% during downwind coal cutting and by 53.6% and 42.3% during upward coal cutting.     

Investigation on the atomization characteristics of a solid-cone spray for dust reduction at low and medium pressures

Water spray is the most widely used means of wet dust reduction, and its atomization parameters are directly related to the effect of dust reduction. In order to obtain the atomization properties of solid-cone spray for dust reduction, the paper used droplet velocity and particle size to characterize its atomization characteristics. The Phase Doppler Particle Analyzer (PDPA) was used to precisely measure droplet sizes and velocities of a solid-cone spray at distances of 15?cm, 25?cm and 45?cm horizontally from the nozzle outlet, using low and medium spray pressures. The results show that the droplet size was fluctuant before spray pressure increasing to 2.0?MPa and then decreased gradually with the increasing of spray pressure. The droplet velocity increased with the raising spray pressure and the velocity at 45?cm is the minimum. The droplet size measurements taken 45?cm from the nozzle exhibited more complex slope changes in particle size curve that were not existed at the closer distances spray of 15?cm or 25?cm, which implies that the near-field spray is more stable than far-field spray. This study is of important significance for further understanding the characteristics of solid-cone spray and guiding its application in dust reduction.     

Research on mine dust suppression by spraying: Development of an air-assisted PM10 control device based on CFD technology

In order to solve the serious pollution problem of PM10 in a fully mechanized mining face, focusing on the drum cutting process which produces the most dust, a new type of shearer sprayer is developed in the paper. At present, it is difficult for a single spray device to meet the dust control demands of a mine. Therefore, in combination with the airflow-carrying-droplet mechanism, a fan is added to the shearer’s spray device to develop an air-assisted PM10 control device. A No. III nozzle is optimally chosen following the spray experiments, and CFD software is used for a numerical simulation of the 4307 fully mechanized mining face of the Bailu Coal Mine. According to the airflow and spraying field distribution, it is observed that when the spray device’s pressure is 8 MPa, the spraying field’s microscopic parameters are more conducive to the settling of PM10 by the mist droplets. The PM10 data measured at 1^#-3^# measuring points of the 4307 fully mechanized mining face of the Bailu Coal Mine have shown that the best PM10 settling effect is at a spraying pressure of 8 MPa. The PM10 concentrations at 1#-3# measure points were reduced to 0.987 mg/m³, 0.405 mg/m³ and 0.262 mg/m³ respectively, with the dust control rate being above 90%. Thus the serious PM10 pollution problem in a fully mechanized mining face has been solved effectively.     

Research on wet-type swirl dust collection technology and its application in underground excavation tunnels

Wet-type dust collectors are widely used in underground excavation tunnels to control dust pollution. Nozzles and filter screens easily blocked by deposited scale and sticky dust, however, are usually a challenging problem for traditional wet-type dust collectors. This increases the cleaning workload and reduces the service life of the equipment. To address this issue, a wet-type swirl dust collection method without using spray nozzles and filter screens is proposed, and a novel wet-type swirl dust collector is designed. Experiments and field application of the wet-type swirl dust collector were carried out. Experimental results showed that the optimum water intake of the dust collector was 1.0 m³/h at 1480 r/min^?1 impeller speed; the dust suppression efficiency of the dust with particles size less than 75 μm was 93%, and that of dust with particles size of 180–250 μm was 95.2%. The field application in China's Tongqing Mine indicated that the respirable dust at the roadheader driver was reduced to 6.9 mg/m³, with a dust removal rate of 92.0%. The wet-type swirl dust collector effectively improves the dust collection efficiency and makes up for the problem of nozzles and filter screens being easily blocked in underground excavation tunnels by the traditional methods.     

无人机静电喷雾治理开放性粉尘的数值模拟

将静电喷雾技术与无人机技术相结合用于治理开放性粉尘,使用Fluent对粉尘的扩散模型进行数值模拟.模拟得出无人机工作高7m,喷雾压力为0.2MPa时,无人机静电喷雾的平均降尘效率能达到85.87％,并在自然风速为1m/s、空气相对湿度为70％时,局部区域的降尘效率高达95.93％.本文提出的无人机静电喷雾控制开放性粉尘...     

Application and research of dry-type filtration dust collection technology in large tunnel construction

Large amounts of rock dust are produced in the process of constructing large tunnels. It then accumulates in the tunnel where, because it is difficult to disperse, it is a serious threat to workers’ health; more than 90% of dust is respirable. Traditional methods to reduce rock dust concentrations, such as a water spray, ventilation, and foam are not effective. Therefore, a new dry-type filtration dust collection method is put forward to use in the construction of large tunnels, and a dry-type filtration dust collection device is designed. Experiments and field application of the dry-type filtration dust collection device were carried out. Experimental results showed that the total dust suppression efficiency reached 98.41% and the leakage rate was 7.86% with the dry-type filtration dust collector. The field application in the Chaoyang tunnel indicated that the efficiency of the dry-type dust collector in suppressing total and respirable dust was 98.13% and 97.86%, respectively. During lining trolley shotcreting operations, the total dust concentration decreased from 253.41?mg/m³ to 29.97?mg/m³ and the respirable dust concentration dropped from 226.73?mg/m³ to 28.85?mg/m³. The dust collection system also reached the optimal dust removal efficiency in two other tunnel construction operations and made an obvious improvement in the environment behind the dust collection system in the large tunnel. The dry-type filtration dust collector effectively improves the rock dust collection efficiency and makes up for the problem of inadequate treatment of respirable dust by the traditional methods.     

Droplet breakup in electrostatic spray based on multiple physical fields

A droplet breakup model was proposed for simulating electrostatic spray in multiple physical fields. The static electricity, laminar flow and droplet atomization in COMSOL Multiphysics were coupled completely, and a two-dimensional simulation model was established. The process of droplet breakup and movement of electrostatic spray was revealed under the action of electric field, gravity field and air field. The electric field distribution under the needle ring electrode configuration was studied. The effects of different electrostatic voltage, needle ring distance and ring electrode diameter on droplet breakup characteristics, distribution uniformity and charge characteristics were analyzed. When the electrostatic voltage is -6 ～ -7 kV, the needle ring distance is 4 mm, and the ring electrode diameter is 30 mm, the electrostatic spray effect is better, and the density standard deviation is as low as 0.04528 /mm², 0.0559 /mm² and 0.06016 /mm², respectively. Electrostatic spray has the characteristics of refining droplets, improving the uniformity of droplets distribution and controlling spray morphology, which provides a strong basis for the application of electrostatic spray in surface film preparation, dust removal, fuel injection and other practical engineering fields.     

Study of high-pressure air curtain and combined dedusting of gas water spray in multilevel ore pass based on CFD-DEM

In order to solve the problem of dust pollution caused by ore unloading in ore pass, this paper, taking Li Lou Mining as a case study, conducted the wind speed variation law in the fluid domain and the impact of the collision between the ore in the unloading process on the fluid to determine the key dust control point based on the CFD-DEM coupling software. By Fluent software, the air curtain dust-proof efficiency under the action of unloading airflow is analyzed, and the relationship between the dust-control wind speed and the impinging airflow is known. And an experimental model of gas water spray is established to analyze the effect of spray dust removal. By analyzing the impact airflow and dust migration caused by ore unloading and the effect of air curtain dust control through numerical simulation, it can be seen that when the ore discharging quantity M_o = 4000 kg, the dust production is mainly concentrated in the fourth middle section. By high-pressure air shield assisting dust removal, dust diffusion can be better controlled when the ratio of impact wind speed of ore pass wellhead (denoted as λ) to high-pressure air curtain wind speed (denoted as ζ) is at least 1:8. When the dust removal effect is optimal, the ratio δ of the water supply amount q_l and the gas supply amount Q_g is determined by the gas water spray dust control experimental platform.     

Development of Venturi negative-pressure secondary dedust device and application of local spray closure technique

In order to enhance the spray for dust suppression performance in a fully-mechanized mining face, based on orthogonal test, comparison test, numerical simulation and field application, the Venturi negative-pressure secondary dedust device was developed. Meanwhile, the local spray closure technique was proposed, which can not only effectively prevent the escape of coal dust from entering the footway space, but also remove coal dust around the respiratory zone from the footway space successfully. The results demonstrated that, under spray pressure of 6?MPa, the Sauter mean droplet size, negative pressure suction flow rate and effective spray distance of the novel dedust device with a throat-to-nozzle distance and throat diameter of 20?mm and 65?mm were 47.37?µm, 11.21?m³/min and 5.4?m respectively. Moreover, the novel dedust device produced droplets to a smaller scale than a single-nozzle. Additionally, the negative pressure and airflow velocity in the negative pressure suction inlet of novel dedust device were within the range from ?0.97?Pa to ?541.04?Pa and from 2.96?m/s to 27.29?m/s respectively. Finally, compared with the original dust suppression measures, the local spray closure technique can enhance the removal ratio of respiratory dust by an average of 44.3%.     

基于CFD技术的螺旋桨风机气流速度场数值模拟研究

为了检测帐篷结构的抗风能力,需建立相应的吹风试验系统。采用标准湍流模型对拟建立吹风试验系统中螺旋桨风机的气流速度场进行了三维实尺度数值模拟。分析了单风机和不同轴心间距时双风机的气流速度分布规律。结果表明单风机气流速度峰值位于风机轴心线上,风速沿流向逐渐减小。双风机气流速度关于通过风机轴心连线中点的垂面呈对称分布,气流速度叠加范围沿流向逐渐增大,距风机出口越远,风速分布越均匀。在通过风机轴心的垂面之间,风速沿流向逐渐增大,至距风机出口13~15m远处开始下降。双风机形成的气流速度在距风机12.2m远处的4m×7m矩形区域上分布均匀,风速值均大于20m/s。风机轴心间距为4m时,4m×7m矩形区域角点处均风速值较大。     

露天台阶爆破水雾降尘技术及效果评价

根据露天台阶爆破粉尘的产生和扩散机制,提出了适用于大型露天台阶爆破的水雾和泡沫降尘技术。通过现场试验,完善了水雾和泡沫发生装置,获得了爆炸成雾合理的爆炸能及延期时间等参数。该技术在缅甸莱比塘矿山大规模露天爆破中得到应用,测得露天台阶爆破粉尘的质量浓度降低了43.0%~49.5%,炮烟体积降低了50%,露天矿台阶爆破降尘效果非常明显。这对减少爆破雾霾、降低环境污染具有重要的作用。     

基于二值化灰度图像的大豆蛋白液喷雾相对雾化程度的研究

目的 为了更直观的评估大豆蛋白液喷雾雾化程度,辅助筛选出有效扇形面积更大、缺陷更少的喷雾,有助于研究喷雾场的雾化均匀性,以期得到均匀一致的大豆蛋白膜。方法 选取合适的阈值后,对粒子图像速度场仪（Particle Image Velocimetry,PIV）拍摄的图像进行二值化处理,划定喷涂有效区域,利用二值化图像计算喷涂雾化场区域在喷涂有效区域内的点位数占比,将数值定义为相对雾化程度,改变稠度系数、喷涂参数,研究相对雾化程度的变化趋势。结果 低稠度系数的大豆蛋白液喷雾相对雾化程度受喷涂参数的影响较小,并保持在90%以上;中高稠度系数的大豆蛋白液喷雾相对雾化程度随着喷涂流量的增加而减小,随着液压、气压的增大有增大的趋势,随着气液比的增加先增大后减小。结论 基于二值化的PIV图像处理可以有效地辅助评估大豆蛋白液喷雾场的均匀性。     

双介质喷嘴雾化特性数值模拟研究

目的 双介质喷嘴雾化效果直接影响烟卷加料工艺的进一步提升，通过对雾化过程进行数值模拟，方便对雾化特性进行透彻的分析，提升雾化效果。方法 采用数值模拟方法构建两相流连续相流场与DPM离散态双向耦合的数值模型，研究蒸汽压力、液体流量以及双介质喷嘴结构对喷嘴雾化特性的影响。结果 适当增加蒸汽压力，可以在不影响最大流速、颗粒粒径均匀度及颗粒中值粒径的情况下，减小雾化扩散角，小幅度地增加喷射距离，雾化细度变好，进而提高雾化效果。随着有机液流量的增加，雾化扩散角增大，喷射距离增加，雾化粒径均匀度变好，从而使雾化效果变好。液体路通流面积越大喷雾的贯穿距离越小，气路通流面积越大喷雾的雾化扩散角度越大。若需要得到较好的雾化效果，需要保证较小的蒸汽路通流面积，与此同时液路侧保持正常开度。结论 适当地提高有机液流量或者蒸汽压力，以及采用较小蒸汽路通流面积，同时液路侧保持正常开度的结构，有利于提高料液喷洒的均匀性，减少了料液的浪费，提高了烟丝制备的工艺水平。     

大豆蛋白喷涂液雾化粒子场实验

目的研究大豆蛋白喷涂液雾化场的粒度分布,及喷涂过程中喷涂参数对大豆蛋白液雾化液滴粒径的影响,从而在蔬菜复合纸覆膜成型过程中选择最优喷涂参数。方法利用激光粒度仪测量不同喷涂参数下大豆蛋白液喷涂雾化场的粒度分布,并通过数据分析软件Origin研究喷涂参数对大豆蛋白液喷涂雾化粒度的影响。结果喷涂参数相同时,喷涂雾化场中随着轴向距离的增加,大豆蛋白液液滴粒径先显著减小后趋于稳定;喷涂雾化场中同一轴向位置随着径向距离的增加,大豆蛋白液液滴粒径呈减小趋势。在喷涂雾化场同一测量点,随着喷涂气压的增大,大豆蛋白液液滴粒径逐渐减小;喷涂液压对大豆蛋白液液滴粒径没有显著影响。结论喷涂气压为0.2 MPa,喷涂液压为0.16 MPa,喷涂雾化场轴向30 cm平面内,大豆蛋白液雾化液滴粒径较小且均匀。     

基于CFD的新型风幕控尘装置的模拟研究及其应用

针对传统风幕控尘装置设备多、空间小、掘进机移动不便等诸多不足之处,⌒进行了优化设计。为确保新型风幕控尘装置的实际应用效果,指导现场防尘系统设计,确定抽出式风机风筒安设位置,依(山西某矿掘进巷道工作面1:1建立了物理几何模型,并利用计算流体动力学(CFD)进行模拟。根(湍流模型特性及流体运动特点,选取拉格朗日法离散相模型对掘进巷道粉尘浓度分布进行了模拟分析并进行现场实践。结果显示,所选物理几何模型参数设置合理,拟合精度达到预测要求;加装新型风幕控尘装置前后,粉尘浓度下降对比明显;距底板2.1 m处安设抽出式风机风筒时,系统降尘效果显著。     

Effect of water supply pressure on atomization characteristics and dust-reduction efficiency of internal mixing air atomizing nozzle

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.     

多联式空调换热器自动清洁功能研究

为研究空调的除尘和杀菌能力,使空调提供品质优良的空气,本文设计了基于变制冷剂流量型多联式空调系统换热器的自动清洁功能。首先通过换热器产生凝结水实现室内机除尘清洗,然后通过换热器产生高温实现室内机杀菌。通过选用空调中常见的翅片管式换热器,以室内机的凝结水量和盘管表面温度为指标,实验分析了室内风机转速、压缩机频率、室外温度、运行时长等对换热器除尘和杀菌能力的影响。结果表明:在除尘阶段,随着室内风机转速的增加,凝结水量先增加后降低,在相同的条件下运行20 min,室内风机转速为350 r/min时凝结水量达到最优值186 g,可以达到最优的清洁效果,增加运行时长、提高压缩机运行频率可提高凝结水量;在杀菌阶段,降低室内风机转速可提高换热器的盘管温度,转速为200 r/min时盘管温度达58.6℃,提高室外温度有利于提升杀菌阶段的盘管温度,但会降低除尘阶段的凝结水量。     

Urease producing microorganisms for coal dust suppression isolated from coal: Characterization and comparative study

In order to promote the biomineralization technology application to the field of coal dust inhibition, two strains of urease producing bacteria from coal were screened in this study. They are X3 with extracellular enzyme and X4 with intracellular enzyme. The ITS and 16S rDNA sequencing showed that the strains X3 and X4 were highly similar to Aspergillus sydowii and Bacillus DB-6. Strains X3 and X4 had their maximum urease activity at the initial 0.5 M urea concentration and slightly alkaline (pH 8) and neutral (pH 7) initial pH, respectively. Their mineralized products have a spherical structure and conform to the elemental composition of calcium carbonate. The dust suppression effect showed that both X3 and X4 bacteria liquid can effectively bind coal dust to form coal dust consolidation bodies containing calcite and vaterite type calcium carbonate. Interestingly, the coal dust consolidation body treated with the strain X4 is more resistant to wind and rain. The screening, mineralization and dust suppression potential analysis of the two strains of urease bacteria provided empirical support for the application of microbial induced calcium carbonate precipitation technology in the coal dust suppression.     

Preparation of microbial dust suppressant and its application in coal dust suppression

To promote the application of microbially induced carbonate precipitation (MICP) technology for coal dust suppression, two urease-producing bacteria (SZS1-3 and SZS1-5) in a coal mine soil were screened. 16 s rDNA sequencing of these bacteria indicated sequences similar to those of Acinetobacter guillouiae CIP 63.46 and Staphylococcus caprae ATCC 35538, respectively. Strains SZS1-3 and SZS1-5 had their largest urease activity at the initial urea concentration of 0.5 mol/L, under slightly alkaline (pH = 9) and neutral (pH = 7) initial pH levels, respectively. Their final mineralized products were vaterite-type and calcite-type calcium carbonate. Although dust suppression results indicated that both bacteria can effectively bind coal dust particles, consolidated coal dust treated with SZS1-5 had a stronger resistance to wind and rain. The screening, mineralization and dust suppression potential analysis of these two urease-producing bacteria can provide reference for the application of MICP technology in coal dust suppression.     

Effects of injection pressure difference on droplet size distribution and spray cone angle in spray cooling of liquid nitrogen

Spray cooling with liquid nitrogen as the working fluid has been widely employed in a plenty of fields requiring cooling at cryogenic temperature, such as the cryogenic wind tunnels and cooling super-conducting magnets. In this study, we built a liquid nitrogen spray system and experimentally investigated the influence of injection pressure difference on the droplet size distribution and the spray cone angle. The measurements using particle size analyser show increasing the injection pressure difference improves the atomization, as indicated by the homogenization and reduction of the droplet size. The initial spray cone angle is insensitive to the injection pressure difference. However, the far-field spray cone angle decreases dramatically with increasing the injection pressure difference. The results could enrich our knowledge of spray cooling of cryogenic fluids and benefit the design of cryogenic spray cooling systems.