Study of gas–liquid two-phase flow patterns of self-excited dust scrubbers

Effects of press-in airflow rate and the distance between the pressure duct and the side wall on ventilation dust suppression performance in an excavating tunnel

The efficiency of mine excavation has been significantly enhanced by continuing improvements in tunneling capabilities; however, this has also resulted in serious environmental pollution and greater safety risks for workers. To ensure safe production, the focus of this study is on the effect of varying the air pressure and the distance between the air pressure cylinder and the side wall settings on dust dispersion behavior and dust control in excavated tunnels. We also investigated temporal-spatial dust diffusion rules in tunnels by combining numerical simulation data with field measurement results. Through further analysis, when the pressure air volume and the exhaust air volume are both equal to 250 m³/min, the dust diffusion distance could be fitted as: [Formula: see text]. When the exhaust air volume is equal to 250 m³/min, dust control effects were improved as the pressure air volume decreased, becoming optimal when the pressure air volume dropped to 150 m³/min. Under these conditions, areas of high dust pollution were contained within 16 m of the cutting face, and the dust diffusion distance satisfied the formula: [Formula: see text]. When the pressure air volume is fixed, the change of the distance between the pressure air cylinder and the side wall has little effect on the dust diffusion. When the distance is 1.5 m, the dust control effect is the best, and the high dust pollution area is controlled within 14 m of the cutting surface. This alleviated dust pollution to a certain degree, thereby enhancing the air quality and ensuring safer production. This study provides a new understanding of the environmentally sustainable development of tunnels and is of great significance for clean production.

Multiscale dynamic distribution characteristics of dust collectors in wet scrubber based on image fields

In order to reveal multiscale dynamic distribution characteristics of dust collectors in a wet scrubber, a method for scale decomposition of dust collectors based on Wigner-Ville distribution (WVD), empirical mode decomposition (EMD) and Hurst analysis of grayscale signals is reported. The WVD features of grayscale signals were used to observe the energy distribution details of dust collectors at different frequency bands and time periods. Then, the scale decomposition of dust collectors based on EMD and Hurst analysis of the grayscale signals was carried out. These analysis results showed that the motion behaviors of micro-, meso- and macro-scale subsets of dust collectors were determined: specifically, the single fractal features of micro-scale subsets conform to the motion characteristics of individual dust collectors. The dual fractal characteristics of meso-scale subsets denote the interactions among dust collector aggregations. Additionally, the fractal features of the macro-scale subsets reflect persistent liquid surface fluctuation behavior in wet scrubbers. Finally, the relative contribution of dust collectors at different scales to the effectiveness of dust removal was represented. This is not only an important innovation in the study of micro mechanism of wet dust removal but provides powerful theoretical support for technological innovations in wet scrubbers. Implications: The multiscale dynamic distribution characteristics of dust collectors in wet dust scrubber were explored, using a method for scale decomposition of dust collectors based on Wigner-Ville distribution, empirical mode decomposition and Hurst analysis of grayscale signals. The fractal characteristics of different scales of dust collectors are determined. Besides, the contribution of different scales of dust collectors to the effect of dust removal is quantized. Therefore, this research is very meaningful, which not only has important innovation in the study of micro mechanism of wet dust collectors but provides a powerful theoretical support for technological innovation of wet dust scrubbers.

Analysis of the spatial distribution of collectors in dust scrubber based on image processing

The spatial distribution of the collectors in dust scrubber is key in determining the effectiveness of the dust removal process. In the present study, a high-speed camera was used to capture images of the distribution of the collectors. Some of the image information was extracted by image processing, such as the gray mean (GM), the angular second moment (ASM), and the entropy (ENT) from the gray-level co-occurrence matrix of the image. Subsequently, the spatial distribution rules of the collectors were studied by analyzing the spatial proportion, dispersion area, and uniformity and intensiveness of the collectors. It is an intuitive approach and a novel analysis method for the operating state of dust scrubber. The results show that the spatial distribution of the collectors could be better reflected by image processing methods. The dispersion area of the collectors expanded with an increase in the airflow velocity. When the initial liquid level (ILL) was higher, the collectors expanded in an approximate circular shape, and when the ILL was lower the collectors expanded in an approximate sector shape. In general, the variation trend in the spatial proportion enhanced with an increase in ILL and airflow velocity, which is consistent with the uniformity of collectors. When the liquid level was 0-20 mm and the airflow velocity was greater than 6.5 m/sec, the spatial proportion and uniformity of the collectors reached the highest degree. However, the growth rate of the spatial proportion and uniformity of the collectors slowed down and even led to negative growth when the ILL was lower and the airflow velocity was higher. The intensiveness of the collectors was great when the ILL was higher, which was free from the apparent influence of the airflow velocity and the ILL. However, when the ILL was lower, the intensiveness of the collectors was poor, intensifying as the airflow velocity and ILL increased. When the liquid level was -5-10 mm and the airflow velocity was greater than 8 m/sec, the intensiveness of the collectors reached the highest degree, indicating that a liquid level greater than 0 mm and a higher airflow velocity improved the spatial distribution of the collectors. Implications: This paper focuses on the spatial distribution of the collectors in dust scrubber. Some of the image information was extracted by image processing, such as the gray mean of the image, the angular second moment, and the entropy from the gray-level co-occurrence matrix of the image. The spatial distribution rules of the collectors were studied by analyzing the spatial proportion, the dispersion area, and the uniformity and intensiveness of the collectors.

Mesoscale behavior study of collector aggregations in a wet dust scrubber

In order to address the bottleneck problem of low fine-particle removal efficiency of self-excited dust scrubbers, this paper is focused on the influence of the intermittent gas-liquid two-phase flow on the mesoscale behavior of collector aggregations. The latter is investigated by the application of high-speed dynamic image technology to the self-excited dust scrubber experimental setup. The real-time-scale monitoring of the dust removal process is provided to clarify its operating mechanism at the mesoscale level. The results obtained show that particulate capturing in self-excited dust scrubber is provided by liquid droplets, liquid films/curtains, bubbles, and their aggregations. Complex spatial and temporal structures are intrinsic to each kind of collector morphology, and these are considered as the major factors controlling the dust removal mechanism of self-excited dust scrubbers. For the specific parameters of gas-liquid two-phase flow under study, the evolution patterns of particular collectors reflect the intrinsic, intermittent, and complex characteristics of the temporal structure. The intermittent initiation of the collector and the air hole formation-collapse cyclic processes provide time and space for the fine dust to escape from being trapped by the collectors. The above mesoscale experimental data provide more insight into the factors reducing the dust removal efficiency of self-excited dust scrubbers.

IMPLICATIONS

This paper focuses on the reconsideration of the capturer aggregations of self-excited dust scrubbers from the mesoscale. Complex structures in time and space scales exist in each kind of capturer morphology. With changes of operating parameters, the morphology and spatial distributions of capturers diversely change. The change of the capturer over time presents remarkable, intermittent, and complex characteristics of the temporal structure.