Influence of Recirculation Flow on the Dispersion Pattern of Blasting Dust in Deep Open-Pit Mines.

The recirculation within a deep open-pit mine is a significant factor contributing to the deterioration of the atmospheric environment. However, the underlying mechanisms of how recirculation influences the dispersion pattern of dust clouds within the deep open-pit mine have not been clearly elucidated. In this research, the dispersion patterns of blast dust clouds were investigated in a deep open-pit mine located in northern China. This research initially conducted a similar experiment to verify the existence of recirculation flow in the experimental mine, which can cause dust particles to aggregate toward the upwind slope. In response to the dust pollution issue in deep open-pit mine blasting operations, this study conducted a numerical simulation analysis based on on-site measurement data to investigate the effects of varying natural wind velocity, natural wind direction, and blast location on the diffusion pattern of blasting dust. The results indicate that natural wind velocity (v), natural wind direction (α), and blast location (d) affect the distance between the blast location and the recirculation center point (Drecir), subsequently influencing the diffusion pattern of blasting dust. The recirculation flow effect influences the diffusion of dust toward the upwind slope under smaller Drecir values, leading to widespread and long-term pollution within the mine. Under larger Drecir values, dust diffuses toward the downwind slope with the straight flow of wind, resulting in less pollution within the mine. Through orthogonal experiments, the equation Drecir = -120.61v2 + 237.27v + 0.82d - 0.07α2+ 6.75α + 151.08 was established in this deep open-pit mine, which provides a basis for predicting the diffusion pattern of blasting dust and control strategy in this deep open-pit mine.

Influence of vehicle and pavement characteristics on dust resuspension from soil pavement of open-pit mine.

It is essential to explore the distribution characteristics of dust concentration distribution near the surface of soil pavement in open-pit mines to develop effective dust control measures. Therefore, in this study, the dust resuspension process of soil pavement was analyzed by building the dust resuspension experimental system of open-pit mine, and the change rules of dust concentration under different factors were investigated. The results showed that under the action of wheel rolling, the dust moved around the wheel along the vertical direction, and the diffusion trajectory in the horizontal direction was approximately parabolic. After re-suspension of the open-pit mine soil pavement, the area of high dust concentration behind the wheel is roughly triangular. The relationship between the average dust concentration (Total dust, Respirable dust and PM2.5) and the vehicle speed and weight were fit to a power function, while the relationship with silt content and water content were quadratic. Vehicle speed and water content had significant effect on the total dust, respirable dust (RESP) and PM2.5 average concentration, while vehicle weight and silt content had little effect on the respirable dust and PM2.5 average concentration. When the water content of mine soil pavement reached 3 %, the average dust concentration could be reduced to <10 mg/m3, and the vehicle speed should be reduced as much as possible under the mine production permitting conditions.

Research on the Influencing Factors and Prediction Model of Impact Airflow in the Process of Unloading of an Ore Pass Based on a Coupled Computational Fluid Dynamics and Discrete Element Method.

In this paper, a coupled computational fluid dynamics and discrete element method (CFD-DEM) is used to numerically simulate the energy transfer of the ore falling process and the change law of impact airflow velocity under different influencing factors. The results are as follows: the total drag force is an important factor that determines the impact airflow velocity. The greater the total drag force, the greater the impact airflow velocity. The impact airflow velocity increases with the increase of mass flow rate and discharge height and decreases with the increase of ore size, and it is found that the discharge height has the greatest impact on the impact airflow velocity, the ore size is the second, and the mass flow rate is the smallest. Therefore, in the allowable range of mine production, the discharge height should be appropriately reduced. The mathematical model of the impact airflow velocity is obtained by multivariate nonlinear regression on the experimental results of orthogonal experiments.

Research on Control of Ore Pass Dust by Unloading Time Interval and Foam Control Technology.

To control the dust pollution caused by the unloading of a multilevel ore pass, numerical simulation and similar experiments were carried out to study the airflow and dust migration influenced by the unloading quantity and the continuous unloading at different time intervals in the ore pass. From this research, the following conclusions are drawn: when the first level of the ore pass is unloaded, the third and fourth levels are the main dust-producing positions, and the concentrations of dust in the breathing zone can reach 85 and 325 mg/m3, respectively. Increasing the unloading interval and reducing the total single unloading quantity can prevent the superposition of dust production. The foam dust removal technology can reduce the secondary dust generation caused by the backlash of the airflow in the ore pass, and the dust emission rate can reach 60% at the fourth level.

Study on Parameters of a New Gas-Water Spray in Ore Pass Dedusting Based on Experiment and Numerical Simulation.

To solve the problem of ore unloading dust in ore pass crosscuts, the atomization characteristics of a new gas-water spray and the effect of the ore discharge airflow on the spray effect were studied by experiments, and the installation position of the spray nozzle in the crosscut was determined by numerical simulation. The results show that when the gas-water flow ratio is 100-150, the atomization effect is the best. In this situation, the droplet size can be less than 28 µm. The impact airflow induced by ore unloading has a great influence on the size of the spray droplets, and the dust-collecting ability of the spray is negatively correlated with the impinging airflow. The best location for the spray is 5 m away from the wellhead. At this position, the impact airflow is less than 1.5 m/s, which can ensure that the total dustfall rate of the gas-water spray is 67% and that of the respiratory dust is 34%.

Study on Gas Diffusion in Fire Working Areas of Oil and Gas Pipelines Based on Temperature Difference.

When a pipeline is under fire safety work construction, the stack effect of the pipeline will increase the diffusion rate of nitrogen, reduce the oxygen content, and cause asphyxia. To prove the influence of the stack effect of the pipeline on the nitrogen movement in the pipeline and put forward effective ventilation control measures, the formation mechanism, gas diffusion law, and ventilation parameters of the stack effect of the oil and gas pipelines are studied through theoretical derivation and numerical simulation. The results show that the nitrogen concentration at the height of the breathing zone in the hot zone first increases and then decreases along the axial distance. The larger the temperature difference, the faster the diffusion speed of nitrogen in the fire safety work area, and the lower the oxygen concentration. When the temperature difference increases to 30 °C, the maximum oxygen concentration in the work area is 0.177; to control the problem of low oxygen content caused by the stack effect, three ventilation schemes are put forward. Through the analysis that installing fans symmetrically on both sides, 4 m away from the pipe opening, can effectively reduce the stack effect intensity when the optimal working wind speed of the fan is 4 m/s. The findings of this study can help in better understanding the causes of the chimney effect during pipeline fire safety work and provide theoretical basis for controlling personnel suffocation caused by the chimney effect.