Numerical simulation study on atomization rule and dust removal effect of surface-active dust suppressants.

Spray dust reduction is a common dust control process in coal mines. However, the actual efficiency of spray dust reduction in a coal mine is low due to poor coal wettability. We select four surfactants that can greatly improve the surface activity of a dust suppressant solution. The wettability of the surfactant solution on coal dust is investigated in terms of two aspects: surface tension and contact angle. The effects of the type of surface-active dust suppressant and its concentration in the spray solution on the wetting of the coal dust and curing effects were analyzed. Numerical simulations were used to simulate spray atomization and to deduce how different types and concentrations of dust suppressant solutions affect the spray. The technical approach of the spray dust reduction method was further optimized by comprehensive analysis and numerical simulations, which could provide guidance for the application of spray dust reduction in coal mines.

Numerically simulated behavior of diesel particulate matter emitted by hydraulic support transporters.

WC55-Y hydraulic support transporters allow an efficient transport of support equipment in fully mechanized mining faces. However, the diesel particulate matter (DPM) emitted by these transporters seriously pollutes the air environment along mine roadways, endangering the health of coal mine workers. In this paper, we simulated the diffusion dispersion of DPM during the functioning of a WC55-Y hydraulic support transporter (emitting high amounts of exhaust pollutants) by computational fluid dynamics, identifying high DPM concentration zones. While the transporter was driven along a coal auxiliary transportation roadway, the diffusion-dispersion characteristics of DPM changed: DPM reached a long horizontal diffusion distance and a high concentration. We found that to avoid the inhalation of DPM and reduce its potential harm, coal mine workers should keep a distance of at least 21.27 m from the hydraulic support transporter while the vehicle runs along the roadway. Moreover, according to our simulation, the operators responsible for disassembling the hydraulic support transporter should wear protective equipment with good filterability while unloading it. Overall, the findings of this study can be applied to outline new work practice guidelines and design new optimum auxiliary ventilation for reducing underground miner exposure to DPM.

Study on the optimal parameter range of droplet-wrapped respirable dust in spray dustfall by mesoscopic method.

Coal miners on the fringes of cities are often exposed to respirable dust hazards. Spray is one of the most effective dust reduction measures. When studying the coupling and collision behavior of droplets and dust particles, it is helpful to optimize the parameter range of the droplets to capture dust particles at the mesoscopic level, to determine the effect of the spray field on the dust particles at the macroscopic level. In this study, the volume of fluid (VOF) method was used to track the interface of multiphase flow. A numerical simulation of 13 working conditions was carried out using the control variable method. Based on the numerical simulation results, we obtained the optimal parameter range for dust to be encapsulated by droplets. To confirm the reliability of the simulation, we independently developed an experimental system and conducted experiments. The simulation results obtained were measured using the experimental system, and an optimal droplet parameter range of 7 µm to settle dust in a coal mining face was determined. Numerical simulation using a mesoscopic method to study dust-spray coupling produced reliable results, which can be used in the practical application of spray dust reduction and has wider relevance for practical engineering.

Research on air curtain dust control technology for environmental protection at fully mechanized working faces.

The development of coal industry is restricted by dust pollution. Air curtain dust control technology was proposed as a solution to the serious problem of pollution. A mixture of numerical modeling and field tests has been used to study this technology. Numerical simulation is used to analyze the dust control effect of this technology under different dust generation conditions. Field measurements are used to verify the effectiveness of this technology. The results show that following the application of this technology, the fan-shaped air curtain generated by the fans forms a trapezoidal protective area between the coal cutter and the sidewalk. This protective area prevents dust from entering the coal-cutter driver's workspace. The average dust concentrations where the coal-cutter driver works were 1590 and 466 mg/m3, severally, before and after the implementation of this technology. The dust control rate in this space is approximately 70.69%. This research provides useful data for dust control technology in fully mechanized mining faces, and will contribute to the stable development of coal fuel.

Research on environmental dust pollution: ventilation and dust space-time evolution law of a fully mechanized mining face with 7-m mining height.

To investigate the influence of dust produced by multi-dust sources at a fully mechanized mining face with a large mining height on the safety conditions in a coal mine, the No. 22305 fully mechanized mining face of the Bulianta coal mine was considered as the research object in this study, and the space-time evolution of dust was analyzed with computational fluid dynamics (CFD). The wind flow simulation results show that the distribution law of wind flow is mainly affected by the structure of the roadway, and the speed and direction of the wind flow change greatly while passing by corners and through large-scale equipment. The dust generation and pollution diffusion laws with respect to time and space were investigated based on simulations of dust production due to 5-s, 30-s, and 60-s coal cutting, continuous coal cutting, and hydraulic support shifting. The space-time evolution law under different dust-producing times shows the transportation and diffusion procedure of dust under the wind flow; the dust-generated via coal mining and shifting were superposed on the downwind side and a 36-m-long dust belt was formed, which filled the coal mining space; the dust concentration in the breathing zone 120 m downwind the front drum had a dust concentration higher than 1700 mg/m3, this was the crucial dust-proof area, and effective dust reduction methods should be addressed.

Effect of spraying on coal dust diffusion in a coal mine based on a numerical simulation.

Aimed at effectively controlling coal dust pollution in the mining face of a coal mine, this study first conducted a theoretical analysis and then combined a spraying experiment and a numerical simulation to perform an in-depth examination of the atomizing characteristics and dust suppression performance of a coal cutter external spraying device. Based on the experimental spraying results, the optimal nozzle was determined to be a pressure round-mouth nozzle with an X-shaped core. The characteristics of the spray fields from nozzles of different calibers (1.6, 2.0 and 2.4 mm) at different spraying pressures (2, 4, 6 and 8 MPa) were then analyzed. It was found that the droplet concentration in the spray field increased with increasing spraying pressure and nozzle caliber. The droplet diameter was mainly dependent on the spraying pressure and varied more slowly with increased spraying pressure. At a spraying pressure of 8 MPa, the spray field formed could achieve effective dust suppression; specifically, the droplet concentration in the spray field was mostly more than 15 g/m3, and the droplet size was mainly distributed in the range of 30-100 µm. When using a 2.4 mm caliber nozzle, the dust concentration measured around the coal cutter operator was reduced to 87.21 mg/m3 under a spraying pressure of 8 MPa, suggesting adequate dust suppression.

Spray dedusting scheme under hybrid ventilation at a fully mechanized excavation face.

In order to evaluate the dust suppression performance with a spraying system at the fully mechanized excavation face, an airflow-droplet-dust multiphase coupling model was established based on the Eulerian-Lagrangian method. Subsequently, the model's accuracy was validated experimentally using a self-developed system for measuring dust suppression efficiency. For the pressure/exhaust hybrid ventilation condition, the following conclusions can be drawn: with an increase of airflow migration distance, the number of vortices gradually decreased, and dust-capturing probability caused by collision with wall decreased gradually along the axial direction of the roadway. Jointly driven by the rebounded airflow, the entrainment effect of high-velocity jets around the pressure inlet, and the transverse vortex field near the cutting face, three high-concentration dust particle clusters, denoted as particle flows I, II, and III, were formed, and the distribution patterns of dust particle clusters after the implementation of different spray schemes were determined. By analyzing the droplet field distribution surrounding the coal cutting head and comparing the dust suppression performance, the study proposed two optimal spray schemes: with gravity-driven supply of water, the spray scheme K2.0-4 MPa delivered optimum dust suppression performance, and the mean dust concentrations at specific fixed operating points dropped to 130 mg/m3; after utilizing a booster pump, the P2.0-8 MPa spray scheme delivered optimum dust suppression performance, with a mean dust concentration at fixed operating points dropping to 65 mg/m3. After applying the K2.0-4 MPa and P2.0-8 MPa schemes, the dust suppression performance was better for the dust with bigger size. The dust suppression efficiencies for the respirable dust were less than 60.7 and 72.5%, respectively. Other dust prevention measures should be taken to further reduce the dust hazard.

Development of a novel wind-assisted centralized spraying dedusting device for dust suppression in a fully mechanized mining face.

Aiming at addressing serious pollution in the No. 30106 fully mechanized coal mining face of Shiquan Coal Mine during coal cutting process, the spraying device between hydraulic supports was improved through the combination of experimental analysis, numerical simulation, and field measurement, and a novel wind-assisted centralized spraying dedusting device was developed. The newly developed device could make the formed spraying field more concentrated on the dust-producing source around the coal shearer's drum, and thus significantly enhanced the spraying performance. According to numerical simulation results, the spraying performance reached the optimum at a hydraulic pressure of 8 MPa for the spraying device and an air pressure of 1 MPa for the pneumatic motor; under these optimal conditions, the droplet concentration in the spraying field around the coal cutter drum was as high as 24.85 g/m3, and the formed high-concentration spraying field could basically cover the whole section in the spraying field from coal wall to the support pillar. Field measured results revealed that, at a hydraulic pressure of 8 MPa and an air pressure of 1 MPa, the dust suppression rate around coal cutter driver reached up to 87.96%, suggesting that the developed wind-assisted centralized spraying dedusting device had remarkable dust suppression performance and could effectively improve the operating environment in the fully mechanized mining face. Graphical Abstract In this paper, we have designed a novel wind-assisted centralized spraying dedusting device and studied the optimal spray parameters. Firstly, the nozzles were selected according to the multi-factor experimental platform for measuring the spraying field's atomization characteristics. Secondly, we had a numerical simulation of the fully mechanized mining face. And the third, we tested the effect of dust removal.

Micro-scale pollution mechanism of dust diffusion in a blasting driving face based on CFD-DEM coupled model.

In order to investigate the diffuse pollution mechanisms of high-concentration dusts in the blasting driving face, the airflow-dust coupled model was constructed based on CFD-DEM coupled model; the diffusion rules of the dusts with different diameters at microscopic scale were analyzed in combination with the field measured results. The simulation results demonstrate that single-exhaust ventilation exhibited more favorable dust suppression performance than single-forced ventilation. Under single-exhaust ventilation condition, the motion trajectories of the dusts with the diameter smaller than 20 µm were close to the airflow streamline and these dusts were mainly distributed near the footway walls; by contrast, under single-forced ventilation condition, the motion trajectories of the dust particles with a diameter range of 20~40 µm were close to the airflow streamlines, and a large number of dusts with the diameter smaller than 20 µm accumulated in the regions 5 m and 17~25 m away from the head-on section. Moreover, under the single-exhaust ventilation, the relationship between dust diameter D and negative-pressured-induced dust emission ratio P can be expressed as P = - 25.03ln(D) + 110.39, and the dust emission ratio was up to 74.36% for 7-µm dusts, and the path-dependent settling behaviors of the dusts mainly occurred around the head-on section; under single-forced ventilation condition, the z value of the dusts with the diameter over 20 µm decreased and the dusts with a diameter smaller than 7 µm are particularly harmful to human health, but their settling ratios were below 22.36%. Graphical abstract The airflow-dust CFD-DEM coupling model was established. The numerical simulation results were verified. The migration laws of airflow field were obtained in a blasting driving face. The diffusion laws of dusts were obtained after blasting.