Article

Improved dust management at a longwall top coal caving (LTCC) face – A CFD modelling approach

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Abstract

Dust management at longwall faces has always been a concern for mine operators. Recent respirable dust monitoring at a longwall top coal caving (LTCC) face indicated that extremely high dust exposure levels have been experienced at the face. Dust contamination from intake ventilation and the incorrect use of ventilation arrangements (i.e. curtains) at maingate (MG) area were identified as the main cause of this issue. Computational Fluid Dynamics (CFD) modelling studies were therefore conducted to investigate the impact of different ventilation arrangements on the dispersion behaviour of respirable dust at the LTCC face, with a special focus on the airflow patterns and the aerodynamics of fugitive dust at the intersection of MG and face. Field investigation was first carried out to observe the dust issue and obtain essential data for the development and validation of base model. Then parametric studies were conducted to evaluate the effectiveness of two different curtain configurations at MG considering the worst scenario of intake dust contamination to face (dust from travel road and beam stage loader (BSL) discharge point flows towards face) with the shearer cutting into the MG. Model results demonstrate that the occurrence of flow separation and incorrect use of curtains account for the main reasons of high dust exposure level at the intersection of MG and face, especially when the shearer is cutting into the MG. Ventilation arrangements at the MG and face entry are critical to minimise the impact of flow separation on the dust flow patterns at the intersection. Based on model results, new ventilation arrangements at the MG and face entry have been proposed and evaluated through which significant dust mitigation effect can be achieved at face entry, contributing to the overall reduction of dust exposure levels along the face.

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... The mathematical model in this study consists of the Navier-Stokes equation (NS; the Eulerian method) in polar coordinates 23 . For turbulent flow, the standard k-ε two-equation model was used. ...
... When the working face inclination is 0° and 20°, the air velocity is small and the wind flow is influenced by the hydraulic pillar, which leads to a smaller angle of wind deflection, and the tendency of the dust carried by the moving frame to enter the sidewalk is small. The dust produced by the front roller of the coal mining machine is at the height of the breathing zone, which is a serious hazard, and is influenced by the cut-off turbulent wind flowing to the sidewalk and unexploited zone at an incidence angle of 25° to 34°, so the wind curtains No. 21,22,23,24,25 and 26 are turned on, and a wind curtain of + 5° is formed in the running direction of the coal mining machine to adjust the direction of the wind flow, and at the same time, the air velocity sensor is combined to adjust the wind curtain speed is adjusted in combination with the air velocity sensor to change the trend of dust transport to the sidewalk and improve the working environment at the working face. 2. When the working face inclination angle is 40°, the tendency of the dust carried by the wind flow into the sidewalk increases obviously, and the dust carried by the dust is concentrated in the vicinity of the roof, and the diffusion range increases due to the effect of the updraft. ...
... When a wide range of www.nature.com/scientificreports/ highly congested dust clouds are formed, air curtains 21,22,23,24,25,26,27,28,29, and 30 are switched on and a curtain of + 15° in the direction of the shearer's operation is formed to regulate the direction of the wind flow, while the speed of the curtain is adjusted in conjunction with the air velocity sensor to control the dust transport trend and improve the working environment at the working face. ...
Article
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Based on the gas–solid two-phase flow theory, numerical simulation of the dust dispersion law of fully mechanized mining work under different inclination angles and comparative analysis of field-measured data show that with the increase of working face inclination, the inclination of airflow into the unmined zone increases from 25° to 50° and the maximum wind speed increases from 2.16 to 2.25 m/s after the mixing of cutting turbulent wind and system ventilation. Meanwhile, the range of high-concentration dust clusters, suspension time, lateral migration intensity, and deposition zone increase to varying degrees; dust clusters increases from 62.02 to 202.46 m3. When X < 53.96 m, the dust concentration in the sidewalk-breathing zone shows a sine function with the length of the working face, and when X ≥ 53.96 m, it satisfies the exponential decay function. Based on this, the tracking closed dust control technology is proposed. Combining the offset angle of the airflow and t the gathering position of dust mass, the wind curtain angle and air velocity are automatically controlled to ensure that the dust is restricted to one side of the cable trough.
... The presence of hazards in underground mining is related to the ongoing exploitation activity and results from the disruption of the initial balance in the intact rock mass. One of such hazards that poses a significant threat to the life and health of mine workers is harmful dust [2][3][4][5][6]. It results from the widespread presence of coal and stone dust in mine headings (as a mixture of silica, aluminosilicates and other elements, including trace metals), which is generated in the mining and transportation of the excavated coal material [2][3][4]6]. ...
... One of such hazards that poses a significant threat to the life and health of mine workers is harmful dust [2][3][4][5][6]. It results from the widespread presence of coal and stone dust in mine headings (as a mixture of silica, aluminosilicates and other elements, including trace metals), which is generated in the mining and transportation of the excavated coal material [2][3][4]6]. ...
... The issues related to the dust hazard appear in numerous publications [2][3][4][5][6][7]11,12,15,16,23,[30][31][32][33], but they mainly concern the methods for measuring dust levels in mine headings [2,4,11,30], the analysis of average dust values occurring in underground mining or for the particular groups of working positions [31][32][33]. As a result, the publications mostly provide a general analysis of the dust content in all the mine headings, without account being taken of the type of these headings (longwall or dog headings) and the specificity of the particular working positions. ...
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The mining production process is exposed to a series of different hazards. One of them is the accumulation of dust which can pose a serious threat to the life and health of mine workers. The analysis of dust hazard in hard coal mining should include two aspects. One is the risk of coal dust explosions, which poses a direct risk of injury or even loss of life, the second is the risk of harmful dust, associated with the possibility of negative health effects as a result of long-term exposure to dust in the worker’s body. The technologies currently applied in underground mining produce large amounts of coal and stone dust. Long-term exposure to dust and crystalline silica may cause chronic respiratory disease. The article presents the results of tests on the dust levels in the area of a fully-powered longwall. The tests were conducted for five longwalls from different hard coal mines. In each of them, the average values of inhalable and respirable dust as well as the percentage content of free silica in the dust were determined in ten selected working positions. Additionally, for the longwall with the highest dust concentration, the levels of dust were determined for the basic activities related to the phases of the technological cycle. The comparative analysis conducted and the results obtained demonstrate large variations in the dust levels in the different areas. The permissible values were significantly exceeded in a number of cases. This poses a great threat to the health of Polish miners. The results obtained indicate that it is necessary to undertake more effective measures in order to improve the working environment of the crew in hard coal mines.
... Longwall faces and development panels are two major dust-producing places in underground collieries. Prolonged exposure to the underground working environment where high levels of respirable and inhalable dust exist can pose significant threats to the health of coal mine workers, potentially causing them to develop irreversible, life-threatening respiratory diseases, such as coal workers' pneumoconiosis (CWP), silicosis, mixed dust pneumoconiosis, chronic obstructive pulmonary diseases, occupational asthma, bronchitis symptoms, and even progressive massive fibrosis (PMF) which is regarded as the most severe form of CWP (Baur et al., 2019;Joy et al., 2012;McBean et al., 2018;Ren et al., 2018;Wang et al., 2020;Wang and Ren, 2013). As a result of improvements implemented to adhere to legislative requirements such as technological advances in dust management and control, better personal protective equipment (PPE) available for coal workers, and routine medical surveillance and screening, it had been approximately 30 years since a case of miners diagnosed with CWP had been formally reported in Australia (Coal Workers' Pneumoconiosis Select Committee, 2017;Zosky et al., 2016). ...
... The movement of airflow and dust within the heading face complies with conservation equations of mass and momentum and gas-solid twophase flow theory. Given that the volume fraction of respirable dust particles within the CM-tunneled development headings is less than 10 %, the Euler-Lagrange approach is more appropriate than Euler-Euler for an investigation into the motion of dust (Ren et al., 2018;Zhang et al., 2022). Regarding the Euler-Lagrange approach, dust particles are regarded as a discrete phase, while airflow is treated as a continuous phase. ...
... Yao et al. [15] studied the influence of different parameters on the dust flow law of a fully mechanized caving face and the dust generation law of different working procedures in steeply inclined fully mechanized caving face. Ren et al. [16] focused on airflow and coal dust dynamics at the intersection between the fully mechanized caving face and the air intake lane and proposed an optimal layout of air curtain at the entrance of air intake lane and working face based on the results of numerical simulation. ...
... Substituting formula (16) into (15), then, ...
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The dust concentration changing regularities are the basis to take dust depression measures, which is greatly influenced by the airflow. In the software of FLUENT, the value of ventilation velocity is set as a constant, which cannot express the real ventilation. According to the flow characteristics of the sublayer and data from Nicholas’ experiment, the ventilation velocity distribution formula of sublayer in the inlet section of fully mechanized caving coal face is deduced. The boundary condition of velocity is given by UDF. Taking the 3top1110 fully mechanized caving coal face as an example, the dust distribution in the process of coal mining and hydraulic support shifting was studied. According to the dust-spray coupling experiment, three types of nozzle are chosen based on the efficiency of dust suppression. Combining the dust migration rule and the characteristics of nozzles, the negative pressure-secondary dust suppression devices of spray were developed and applied. And the above measures have lowered the dust concentration effectively.
... In this study, the airflow is incompressible (Kurnia et al., 2014a;Ren et al., 2018;Wang et al., 2018); no heat-transfer is considered, the temperature is assumed as 288 K; and the gravity is 9.81 m/s 2 . The standard k − ε model is one of the most widely used turbulent models in the simulation of air flow in underground mines due to its accuracy and efficiency Toraño et al., 2011Toraño et al., , 2009Wang and Ren, 2013;Xu et al., 2015). ...
... According to the above reasons, only drag force and gravity are considered in this study. (Hu et al., 2019;Ren et al., 2018;Xia et al., 2016). The governing equation is given by: ...
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Diesel particulate matter (DPM) is carcinogenic to humans. DPM concentrations in underground mines are much higher than other working environments, thus pose substantial health threats to miners due to overexposure. Computational fluid dynamics is commonly used to study the DPM dispersion and assess the concentration distribution in various working environments. However, most such studies for underground mines treated DPM as a continuous phase (gas phase) in the model. DPM is a solid discrete phase, and its behaviours could be quite different from that of gaseous contaminants. This study compared DPM concentration distributions by using three modelling methods: the Eulerian-Lagrangian method and the Eulerian-Eulerian method that treats DPM as discrete phase particles, and the species transport method that treats DPM as a continuous phase gas. The model was based on a typical underground mine development face with a forcing auxiliary ventilation setup. It was found that the general DPM concentration distribution for the three numerical methods was similar for simple geometry with more uniform flow regions. However, large discrepancies existed in the development heading with complex geometry and flow features. The findings suggest that when simulating DPM, although the species transport method can provide relatively accurate results with much less computational time, the parameters of the modelled gas need to be carefully calibrated to get a better simulation result. For key areas where the diesel machinery and miners are usually located, the Eulerian-Lagrangian method should be used for more accurate analysis.
... Long-term exposure to dust particles, particularly respirable coal dust and respirable crystalline silica dust, increasingly poses considerable threats to the occupational health and safety of workers in underground space (Wang and Ren, 2013). Workers exposed to elevated dust levels are more likely to develop a range of occupational lung diseases, including but not limited to Coal Workers' Pneumoconiosis (CWP) or 'Black lung', mixed dust pneumoconiosis, silicosis, progressive massive fibrosis (PMF), chronic obstructive pulmonary disease (COPD) and, in the worst case, lung cancer (Doney et al., 2019;Ren et al., 2018;Wang et al., 2019;Zosky et al., 2016). In consideration of the resurgence and rising incidences of dust-related diseases and in an effort to better protect coal mine workers (CMWs) from adverse health effects induced by breathing excessive amounts of coal and silica dust, statutory workplace exposure standards (WES) for respirable coal dust (RCD) and respirable crystalline silica dust (RCSD) have been set at 1.5 mg/m 3 and 0.05 mg/ m 3 , respectively, both in New South Wales (NSW) and Queensland. ...
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Long-term exposure to respirable coal and silica dust during underground tunnelling operations has gained increasing attention in recent years. The solution to effective mitigation of dust exposure depends not only on higher-order engineering controls, but also on administrative controls for frontline workers. However, there is a disconnect between knowledge gathered in the field of dust exposure monitoring and the frontline worker, resulting in important learnings being overlooked in underground tunnelling operations. To remedy this discrepancy, an immersive educational tool was developed to visualise computational fluid dynamics (CFD) modelling datasets of ventilation and respirable dust flow characteristics in the tunnel face in a virtual reality (VR) environment. An algorithm was developed for processing the large and complex CFD datasets into a form that can be processed and visualised using standalone VR headsets with limited processing power. The VR-CFD system was assessed by an industry expert and via many industry showcases, where regular feedback was received for making significant improvements in this education tool. This tool has been developed as a training platform to allow frontline workers to better understand the results of decisions made during tunnelling operations and the best practices for dust controls. A number of key technological achievements were made that can be used in the future to quickly translate real-world particulate readings collected from underground space into a VR visualiser. This VR-CFD digital technology can readily be extended to mining, construction and other tunnelling operations in the underground space, thus improving health and safety.
... For the inhalation of the respirable dust, it must be clear that the particle characteristics of mixed dust and the amount inhaled by the coal miners, which are related to the surrounding distribution characteristics and the spatiotemporal evolution of the coal-quartz dust mixture. Numerous efforts have been made to the diffusion and distribution of coal dust in underground coal mines Ren et al. 2018;Chang et al. 2019;Cai et al. 2019;. However, it is still unclear how quartz dust will affect coal dust distribution and its changes in limited spaces, ultimately affecting the mixture distribution. ...
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Dust exposures during mining activity can result in lung diseases such as coal workers’ pneumoconiosis (CWP) and silicosis, and it is closely related to quartz dust. In the present study, coal-quartz dust mixture were investigated considering the particle size and the specific constituents. Multiple numerical techniques, including computational fluid dynamics and discrete element method (CFD-DEM), hard sphere model, and direct Monte Carlo simulation (DSMC), were presented, and the dust diffusion processes were investigated. According to the validation of the numerical method, the suspension characteristics of the polydisperse mixed dust were analyzed in detail. The results show that PM10 responds quickly, has a large diffusion range, and is easily affected by the reflux. The particle size increases gradually from top to bottom. When the air velocity is low, the percentage of coal dust in the breathing zone tends to be 50%. The results provide theoretical guidance for the comprehensive prevention of the mixed dust in underground coal mines.
... Long-term exposure to respirable coal dust and respirable silica dust in underground mines continues to present an occupational health and safety hazard to mine workers in underground coal mines (Wang et al., 2019, Ren et al., 2018, Zosky et al., 2016. Airborne dust monitoring data collected by Coal Services (CS) show that Development/Continuous Miner (CM) operators have the second highest workplace exposures next to longwall (LW) workers when compared to the workplace exposure standards (WES) (Boyne, 2022). ...
... Therefore, dust suppression is necessary, and it aims to control or reduce the number of fine particulates, which are airborne or suspended in the air (Cai et al. 2019;Fabiano et al. 2014;Geng et al. 2019). Dust particle size mainly varies from nanometer to millimeter level, and it is reported that approximately 60~77% (±14) of the coal dust is less than 212 μm Liu et al. 2018;Ren et al. 2018;Yuk et al. 2021). The particulate matter has posed a significant threat to human health, and PM 2.5 has been regarded as the criminal chieftain for numerous adverse health effects (Chu et al. 2019;Liu et al. 2020;Qian et al. 2014). ...
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The present study investigates dust generated from the unloading process in a high-rise building for the mine hoist system and analyzes dust dispersion with the moving conveyance in the building. First, the gas-solid two-phase flow in the building was investigated based on the CFD-DPM method. In particular, the moving conveyance was considered in detail and treated via the dynamic mesh technology. Then, the airflow and dust distribution were investigated in the building. The airflow and the dust concentration at selected points show good agreement with the relative results of field measurements by ourselves. It is found that the descending conveyance significantly influences the surrounding flow field and the spatial and temporal distribution of dust. Dust concentration before the dust source (2 m × 2 m) is high, which extends downward with the conveyance. Dust concentration of the lower floors increases obviously when compared with that of the condition without the movement of the conveyance. The descending velocity of the conveyance also affects the amount of PM2.5 discharged from the return air outlet. The fitting functions are provided to predict PM2.5 emissions to the surrounding atmosphere. The research results are of great significance for the improvement of the dust control system for cleaner production technology. Graphical Abstract
... The solid phase of dust was discrete and relatively dilute and was treated as the discrete phase (Geng et al. 2017;Gui et al. 2021). The Euler-Lagrange method was adopted in the present study based on the following assumptions: the dust was assumed to consist of spherical particles with different sizes; the airflow at room temperature was used as the operation gas, and heat and mass transfer were ignored during the dust dispersion process Ren et al. 2018;Wang et al. 2015;Yin et al. 2019;Zhang et al. 2020). The dispersion process of dust pollutants with the airflow in the dust collector was simulated via the Euler-Lagrange model. ...
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... In hard coal mines, this hazard results from the common occurrence of coal and hard dust in mining excavations (including a mixture of silica, aluminosilicates and other components, such as trace metals). The dust is produced in the process of mining and transporting the mine output [1][2][3]. The main reason for the formation of large amounts of dust in this process is current machining-based technology used for mining the rock mass. ...
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Dust is one of the most burdensome hazards found in the environment. It is composed of crushed solids that pose a threat to the health and life of people, machines and machine components. At high concentration levels, it can reduce visibility. All of these negative phenomena occur during the process of underground mining, where dust hazards are common. The negative impact of dust on the efficacy of the mining process prompts research in this area. The following study presents a method developed for model studies of dust dispersion in driven dog headings. This issue is immensely important due to the fact that these dog headings belong to a group of unidi-rectional excavations (including tunnelling). This paper presents the results of model studies on dust dispersion in driven dog headings. The main focus is on the analysis of the distribution of dust concentration along a dog heading during the mining process. In order to achieve this goal, a model test method based on the finite volume method, which is included in the group of CFD methods, was developed. Analyses were carried out for two different values of dust emission from the face of the excavation for the transient state. The results made it possible to determine areas with the highest potential for dust concentration. The size and location of these areas are mainly dependent on the amount of dust emissions during the mining process. The results can support the process of managing dust prevention and protection of workers during the mining excavation process.
... At present, there are many studies on dust diffusion during the mining process (Chang et al. 2019;Gui et al. 2021;Peng et al. 2019). For example, Ren et al. (2018) employed CFD models to investigate the dust flow behavior above an underground bin, and the mechanism of respirable dust capture under the ventilation system and the water mist dust was investigated by the classical and the two-phase flow theories. Based on the Lagrange method, Toraño et al. (2011) studied the dust migration and the distribution characteristics in the mine roadway under the two common auxiliary ventilation systems. ...
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... However, field measurement in underground coal mines is limited with certain potential dangers due to the special environment and its time-consuming and energyconsuming factors. By contrast, numerical investigation has long been applied to study the aerodynamics of particulates and the dust flow dynamics in the underground environment, which has been validated as a useful tool to further understand the dust flow and the ventilation under the specific mining conditions (Wang et al., 2019b;Ren et al., 2018). Particularly after 2010, Computational Fluid Dynamics (CFD) investigation on the dust flow increases dramatically (Wang et al., 2019a(Wang et al., , 2019bChang et al., 2019). ...
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... Due to the poor effect of drum coal loading, a large amount of floating coal remains in the working face. If the floating coal can not be cleaned in time, it will not only affect the working efficiency of fully mechanized mining equipment, but also cause floating coal flying when the wind speed is too high, which is not conducive to the development of underground dust removal work and seriously endanger the health of workers Reng et al;. Therefore, improving the coal loading performance of coal shearer is of great significance for improving the production efficiency of coal mines and increasing the degree of fully mechanized mining in thin coal seam. ...
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... However, field measurement in underground coal mines is limited with certain potential dangers due to the special environment and its time-consuming and energyconsuming factors. By contrast, numerical investigation has long been applied to study the aerodynamics of particulates and the dust flow dynamics in the underground environment, which has been validated as a useful tool to further understand the dust flow and the ventilation under the specific mining conditions (Wang et al., 2019b;Ren et al., 2018). Particularly after 2010, Computational Fluid Dynamics (CFD) investigation on the dust flow increases dramatically (Wang et al., 2019a(Wang et al., , 2019bChang et al., 2019). ...
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... The region air flow is assumed incompressible, and no heat transfer is considered in the simulation [17], [24], [28][29][30]. Navier-Stokes equations are used to describe the motion of air. The incompressible continuity and momentum equations are [31],: ...
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Diesel particulate matter (DPM) is carcinogenic to humans. Underground miners have a high risk of over-exposure to high concentrations of DPM. To control DPM effectively, it is essential to understand the DPM dispersion characteristics. In this study, the DPM distributions of three key and representative mining activities, shotcreting, charging and loading activity, in an underground development face were studied. A computational model for the mining activities was developed using 3D imagery, onsite data and OpenFOAM. Tracer gas experiments were first conducted in the underground mine for the validation of CFD simulation. The simulations were carried out at a steady-state using the standard k-ε turbulence model, and the transport and dispersion of DPM were modelled using a segregated species transport model. DPM distribution characteristics for each mining activity were analysed, and the regions with high concentration (>0.1 mg/m³) were identified, and the reasons for the high concentrations were also discussed. At last, the efficiency of the current auxiliary ventilation system on DPM dilution was evaluated based on the simulation results. The results show that a broader region with high DPM concentration was identified in the downstream of the loader during the loading activity, and this issue could be solved by simply increasing the ventilation rate. The findings in this paper could be used for optimizing the auxiliary ventilation design for future mining activities in this development face.
... In the construction of a TBM-based tunnel, fresh air passed through the tunnel working area at the top of the tunnel, and the rock-dust generated in the tunnel was sucked into the dust removal fan [27]. Due to the complicated flow process of rock-dust through the supported working area and the air duct, in this study, the fluid dynamics was employed to develop the flow-related characteristic mathematical models, including three-dimensional (3D) steady-state airflow model and the rock-dust flow model [28][29]. ...
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Study on powder behavior is the key to dust pollution prevention and control in tunnel construction environment, using wind energy to control dust diffusion is a common and effective dust control method at present. In this paper, the numerical simulation and field measurement were used to study the powder diffusion in construction of a tunnel boring machine (TBM)-based tunnel, in which the movement and diffusion properties of the powder in the tunnel were achieved and analyzed. By adjusting the height of the exhaust vent and the secondary blowing distance (L P ), the quality of air in the tunnel was optimized. The accuracy of the simulation results was also verified by the field measurements. The results showed that when the height of the dusty return airflow (H W ) is close to that of the exhaust vent (H E ), the rock-dust concentration in the tunnel could be reduced to a certain extent. When L P < 50 m, the primary and secondary blowing airflows could form a coupled wind field in the middle of the tunnel to limit the further backward diffusion of the rock-dust. When L P > 50 m, the dust-control air-curtain could be formed within 18.83 m away from the heading. When L P = 60 m, the rock-dust in the tunnel was effectively controlled, and the diffusion distance of the rock-dust was less than 16.4m as well.
... Especially for the health-related field, a number of literatures investigated the coal dust dispersion and distribution characteristics by using simulation modeling technique. Ren et al. (Ren, Wang, and Cooper 2014;Ren, Wang, and Zhang 2018;Wang and Ren 2013) conducted a number of studies to investigate the coal dust distribution in different scenarios; related coal dust management method was provided according to the simulation results. Hu et al. (Hu et al. 2016;Hu, Wang, and Feng 2015) studied the distribution characteristics of the coal dust after blasting in an underground development face by CFD modeling and the results were validated by the onsite measurement data. ...
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Coal dust is one of the most serious hazards on mine sites. Water spray with surfactant added is an effective way to control the coal dust. In this study, wind tunnel experiments were designed to evaluate the surfactant on coal dust suppression efficiency. A CFD modeling was first constructed in to investigate the coal dust particles movement characteristics, and the stimulation results were provided for the wind tunnel design. The CFD results indicated that the location of the nozzle placement and the time for the water spraying start time. The coal dust suppression efficiency was then evaluated in the presence of different surfactants. The experiment results suggest that the anionic and non-ionic surfactants are helpful to improve the suppression efficiency while the cationic surfactant failed to increase it. For the SDBS at various concentrations, the highest suppression efficiency is achieved when at 0.20%. Compared with the larger coal dust particles, the finer ones are more difficult to capture for both water and SDBS surfactant solution. The results also demonstrate the potential application of this surfactant on coal mine industries.
... The k-e equation can be written as [35][36][37]: ...
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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 Mo = 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 ql and the gas supply amount Qg is determined by the gas water spray dust control experimental platform.
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Dust exposures during mining activity can result in lung diseases such as Coal workers' pneumoconiosis (CWP) and silicosis, which are closely related to quartz dust. In the present study, coal-quartz dust mixture were investigated considering the particle size and the specific constituents. Multiple numerical techniques, including Computational Fluid Dynamics and Discrete Element Method (CFD-DEM), hard sphere model and direct monte carlo simulation (DSMC) were presented, and the dust diffusion process was investigated. According to the validation of the numerical model, the suspension characteristics of the polydisperse mixed dust were analyzed in detail. The results show that PM10 responds quickly with good following performance with the air flow. The particle size increases gradually from top to bottom. When the air velocity is low, the percentage of coal dust in the breathing zone tends to be 50%. The results provide theoretical guidance for the comprehensive prevention of the mixed dust in underground coal mines.
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Controlling the isolation of different tobacco odors in the tobacco workshop is of great significance to the air quality regulation in the workshop. For the isolation of odor, the existing literature mainly adopts the method of controlling the diffusion source with mechanical device, but this method is not suitable for the tobacco workshop where the diffusion source is widely distributed and complex. This paper proposed the alternative idea of flexible isolation of two types of storage cabinets using air curtains. Numerical simulations were performed to study the effects of the airflow collection device width (H), the inlet and extraction air velocities (Vs and Vc) on the air curtain airflow path and collection, and the odor isolation efficiency. At small airflow collection device width, the air curtain airflow path was split into three sections leading to the two types of storage cabinets and inside the airflow collection device, respectively. As inlet air velocities increased and the extraction air velocities decreased, the pressure difference at the entrance of the airflow collection device dropped, the airflow turbulence effect intensified, in contrast to the coupling effect between the air curtain airflow and the extraction airflow. This expanded the vortex area, deteriorating the air curtain airflow collection efficiency. At high the inlet and extraction air velocities the thickness and range of the air curtain increased, improving the odor isolation efficiency. The optimal parameters provided the air curtain airflow collection efficiency of 99.01%, the odor isolation efficiency of 94.6%. This economical and simple scheme allows for efficient odor isolation and partial odor capture.
Chapter
Although the future of coal mining lies belowground, the present status of Indian underground (UG) mining and, in particular, thick seam mining is not inspiring. Thick seams share about 40% of the proven Indian coal reserves. However, several consistent efforts were made, no method could sustain effective extraction, and it remained an ever-posing technical challenge to the Indian mining engineers. The longwall-based top coal caving methods (LTCC) are developed and excelled in China for their production, productivity, and conservation advantages over other thick seam mining methods. In this perspective, a study into the feasibility of the application of LTCC in Indian geo-mining conditions is taken up. The present paper reviews the LTCC mechanism, safety issues, and the global experiences for implementation in the Indian geo- mining conditions. This study contributes to evolving a bulk-producing underground mining method with conservation and safety in India. KeywordsThick seam mining technologiesLongwall top coal cavingRisksIndian geo-mining conditions
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Bioneutralization of alkaline bauxite residues (BR) may be achieved through in situ organic acids produced from fermentative decomposition of carbohydrates-rich organic matters (e.g., plant residues), which are driven by organophilic and heterotrophic prokaryotes tolerant of extremely saline and alkaline conditions. The present study investigated if the resilience of tolerant prokaryotes in soil microbial inoculums could be improved by pre-culturing them in carbohydrate-rich plant residues, leading to enhanced bioneutralization efficacy in strongly alkaline BR. In a 2-week microcosm experiment with BR (pH ~ 10.5), it was found that the resilience of prokaryotic communities and their functional modules and bioneutralization efficacy were significantly boosted in BR admixed with plant residues (i.e., SM: sugarcane mulch, LH: Lucerne hay) pre-cultured with soil microbial inoculum. The results showed that 10-20% of the initially inoculated soil prokaryotic features were recovered in treatments with pre-cultured plant residues. Besides, the enriched diverse prokaryotes formed highly clustered networks in the amended BR. These modules actively drove C and N mineralization and sustained 0.8-2.0 units of pH reduction, despite the buffering effects of alkaline minerals in BR solid phase. In contrast, soil microbial inoculation cultured in the growth medium lost >99% of the original prokaryotic features in soil inoculums, resulting in merely 0.2-0.7 unit pH reduction in the treated BR. Therefore, pre-culturing soil inoculum in plant residues would be preferred as an integral system to treat BR for effective bioneutralization.
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Pressure swirl nozzles are widely applied in various mineral industries, and their excellent spray performances have been found to be directly related to dust removal results. In this study, in order to examine the influencing effects of the swirl intensity levels of pressure swirl nozzles on atomization characteristics and dust-reduction efficiency, five spiral guide grooves were added for the purpose of improving the quality of the atomization and dust control. The swirl intensities of pressure swirl nozzles were first theoretically investigated using the established models. The effects of the swirl intensities on the atomization angles and distributions of the atomization sizes were comparatively studied using theoretical calculations, numerical simulations, and experimental methods. A dynamic wind tunnel was built in order to conduct dust-reduction experiments with different swirl intensities. The proximate and ultimate analysis results and the sizes of the coal samples were characterized, and the mechanism of the dust reduction was summarized. The results demonstrated that the applications of spiral guide grooves improved the atomization angles and coverage areas by up to 98.8° and 73%, respectively. At the same time, the enhancements of the swirl intensities were observed to reduce the uniformity index of the distribution sizes,` which significantly decreased the Sauter mean diameter (SMD) from 101.3 μm to 22.1 μm. The atomization results revealed that the increasing of the stagger angles benefited the larger atomization angles and smaller SMD. In addition, the proposed theoretical model had achieved better prediction accuracy. Also, the high atomization quality had obviously improved the dust-reduction ability of the pressure swirl nozzles, with the efficiency of total dust and respirable dust removeable increased by approximately 11.23% and 9.33%, respectively.
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The safety of the coal production process, which in the coming years will continue to be one of the basic energy resources in many countries worldwide, has a significant impact on its efficiency. The random character of many hazardous phenomena accompanying this process requires the application of both modern and safe methods to study these phenomena. Model studies based on the Computational Fluid Dynamics (CFD) method are known to have such features. They enable the analysis of very complex and hazardous phenomena, which are hard or even impossible to investigate with the use of other methods. Therefore, this article focuses on the analysis of the state of the art in terms of the Computational Fluid Dynamics application in research on ventilation safety during underground hard coal mining. It was assumed that CFD-based studies may significantly improve the safety of the mining production process. For this purpose, a systematic literature review was carried out, which – according to the adopted methodology – involved four research questions. The review included scientific publications (articles) contained in the two most prestigious databases, i.e., the Web of Science and the Scopus. In accordance with the adopted search criteria, articles that used the Computational Fluid Dynamics method and focused on ventilation safety during underground coal mining were selected. The meta-analysis of these data made it possible to identify seven thematic areas undertaken in these publications. The following paper presents a list of articles assigned to these groups with selected items being discussed. On the basis of the conducted research, comprehensive answers to the research questions were provided. The results systematize the knowledge of CFD application in research on ventilation safety in mining. Also, they are a valuable source of information for future researchers and engineers concerned with the safety of the mining production process. Moreover, potential directions of further research in the field of possible Computational Fluid Dynamics applications were indicated to improve the safety of the process in question.
Article
In order to investigate the effects of turbulent airflow from coal cutting (TACC) on the pollution characteristics of coal dust, the pollution behaviors of coal dust under the action of system ventilation airflow (SVA) only (Condition 1) and the addition of TACC disturbance (Condition 2) were respectively simulated and verified through a comparison with the field measurement data. The results show that the effects of TACC on the pollution characteristics of coal dust cannot be ignored on the operation site. TACC could not only enhance the turbulent intensity in the flow field, but also induce the positive deviation of airflow. The airflow with a velocity of about 1.0∼1.75 m/s in the footway space moved from the region X=0.3∼36.8 m, Y=4.1∼4.5 m under Condition 1 to the region X=-5.1∼26.5 m, Y=3.8∼4.5 m under Condition 2. After the addition of TACC disturbance, the absolute value of positively-deviated airflow velocity component in the operational range of rear drum driver rose from 0∼0.8 m/s to 0.2∼1.8 m/s. Meanwhile, the flow field under Condition 2 could effectively cause lateral dispersion of coal dust to the footway space, which led to an increase in the lateral dispersion scale of coal dust. Under Condition 2, the region polluted by cutting-induced coal dust moved forward by 11.3 m along the negative direction of X-axis, and the peak coal dust concentration along the footway space was approximately doubled.
Article
When tunnel boring machines (TBMs) are used to construct tunnels, large quantities of rock dust are produced, affecting the working environment of construction personnel. To explore ways to improve the air quality in tunnels, this study employed a numerical simulation to investigate controlling rock dust via tunnel ventilation systems. The results showed that when the secondary compressed airflow rate (Q2) was set to 4–11 m3/s, the rock dust produced could be controlled within a range of 77.2 m from the tunnel face. When Q2 = 8 m3/s, the rock dust diffusion distance (LD) reached a minimum of 42.7 m, and the rock dust concentration around the operating region (CW) was approximately 30.1 mg/m3. To explore the further enhancement of dust suppression performance in a tunnel, a numerical simulation was conducted on rock dust diffusion in the tunnel when Q2 was fixed but the exhaust airflow rate (QC) was set to different values. According to the numerical simulation results, when QC = 15 m3/s, the rock dust produced could be effectively controlled at the front of the tunnel with a length of 14.6 m, i.e., the rock dust could be most effectively suppressed.
Article
An air curtain dust control technology for a fully mechanized mining face was developed, using a method that combined numerical simulations with field measurements in this paper. The results show that a triangular air curtain was formed between the shearer and the footway by the high velocity airflow field generated at the outlets of two fans after the technology was applied, which can effectively prevent dust from entering the driver's working area. Before the dust control technology was applied, the dust concentration of the shearer driver's working area exceeded 2000 mg/m³. However, after the dust control technology was applied, the dust concentration of the shearer driver's working area was reduced to 300 mg/m³. After verification through field measurements, the dust control rate of each measuring point, apart from the advancing support, exceeded 40%, and that of the shearer driver's working area was over 90%.
Article
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Dust control in underground coal mines has long been of great concern to mine operators, and the use of an auxiliary ventilation system is essential to address dust pollution. The present study focuses on analysing gas-solid two-phase flow in a typical coal roadway with a fully mechanized heading face in the presence of an auxiliary ventilation system with an air curtain. The two-phase flow was simulated by the Euler-Lagrange method. The dust particles were simulated via the discrete phase model (DPM) based on certain sample particles in the form of parcels. To control dust more effectively, the air curtain generator was optimized based on a recently proposed structure. It was found that the air curtain and the improved form have obvious effects on the air flow field, the dust distribution and the amount of particulate matter (PM2.5) in the front part of the roadway (within approximately 15 m of the heading face). PM2.5 around the driver is substantially reduced after the improvement but is limited when the initial supply air velocity is increased. Selected simulation results were verified by relative field measurements. The results obtained in this study provide useful information on auxiliary ventilation design for use in mining activities.
Article
The ventilations of pressure cylinders is a widely used practice in coal mine roadways in China. It has been determined that the velocities of the ventilations will directly affect the diffusion of the dust particles which reduce the visibility of road-header drivers, and also tend to slowdown operating efficiency. In this study, a CFD-DPM method was adopted in order to examine the airflow flow and dust pollution behaviors in coal mine roadways under various ventilation velocities. The results showed that airflow fields could be divided into disordered regions of airflow flow fast and chaos; recirculation regions, where there were dust backflow; and stable regions, from the heading faces to the exits of the coal mine roadways. The airflow were observed to carry the dust particles along the roadway wall away from the pressure cylinders from the disordered regions into the recirculation regions due to the blocks caused by the road-headers. It was observed that the dust migration had slowed down in the areas behind the road-headers due to the sudden decreases in the airflow velocities. Then, major amounts of dust particles were carried by airflow into the stable regions. The remaining dust was carried to the exits of the pressure cylinders as a result of the dust backflow. As a result, areas of approximately 5 m behind of the road-headers, as well as the areas near the exits of the pressure cylinders, contained high dust concentrations. The dust concentrations near the exits of the pressure cylinders into which the dust particles had been attracted due to the strong entrainment effects, were found to increase with increasing of the ventilation velocities. However, this had only occurred when ventilation velocities had exceeded 17 m/s.
Article
Self-heating of coal mass has been a long-standing thermal dynamic hazard and also an environmental concern during coal mining, processing, and storage. Especially self-heating of coal in longwall goaf poses a great danger to underground working crew and goaf inertisation is often practiced to combat the hazard. To investigate goaf inertisation with more insights regarding two different philosophies (i.e. proactive and reactive), a three-dimensional non-equilibrium thermal CFD model was developed to study heating evolution and a range of inertisation plans in a modern longwall. The theoretical model mainly incorporated a set of governing equations (e.g. energy conservation, continuity, and momentum balance) and coal oxidation kinetics which are determined by an adiabatic coal heating test. A comprehensive inertisation plan is developed. At initial stage of mining, a proactive inertisation plan is recommended because a heating in start-up area can develop to a fire incident if precautions are not implemented. While a reactive inertisation is suggested after longwall advancing a certain distance as the heating behind longwall face can be left in the fully suffocated zone before escalating to an advanced stage.
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