Performance estimation of a Venturi scrubber using a computational model for capturing dust particles with liquid spray

Study on the dust migration law and a spray dust suppression scheme in transportation roadway

To solve the problem of excessive dust concentration in the belt transportation roadway of the mine. Numerical simulations were used to study the dust migration in the belt transportation roadway under 1.5 m/s ventilation conditions. The simulation results show the process of dust ejection from the inflow chute to contamination of the whole belt transportation roadway, and the spatial distribution of dust velocity. A comprehensive dust reduction scheme of "central suppression and bilateral splitting" was designed according to the dust distribution, with simultaneous control of the infeed chute and the roadway. In practical application, pneumatic spraying greatly reduces the amount of dust in the guide chute. The misting screen has a significant effect on dust collection and segregation. The solution effectively controls the dust in the space of 20 m on both sides of the transfer point, and the dust removal efficiency reaches more than 90%.

Numerical Investigation of Fine Particulate Matter Aggregation and Removal by Water Spray Using Swirling Gas Flow

In this paper, a mathematical model based on the two-fluid frame model coupled with the population balance model which considers the aggregation of particles and droplets in detail for cyclonic spray dedusting is proposed. The model is applied to study the characteristics of multiphase flow field and the effects of the gas velocity, spray volume, and particle concentration on the removal efficiency. In addition, the simulation results are verified by the experimental data. The results suggest that the turbulence kinetic energy increases near the wall as the inlet velocity increases, and the spray region increases as the spray volume increases. This is conducive to turbulent mixing of the particles and droplets, and the agglomeration efficiency of the particles is improved, so the particle size increases, and the particle removal efficiency increases to 99.7% by simulation results are within the allowable range of error (about 99-99.5% in dedusting efficiency by experimental data). As the particle concentration increases, the particle removal efficiency initially increases, then decreases and reaches the highest value at 2 g/m³, which is due to the limited adsorption efficiency of the spray droplets. The results are helpful for providing a theoretical basis for spray to promote agglomeration of particles and improving the dust removal efficiency in the swirl field.

Incorporating ash removal unit in local rice parboiling industries for flue gas cleaning and heat recovery

Local rice parboiling industries of Bangladesh are burdened with heavy emission. Despite recent modification in the rice-parboiling boiler, the amount of stack emission (especially particulate matter) from local rice parboiling industry is still considerably high to jeopardize public health and environmental sustainability. There is no provision of flue gas cleaning in these industries since flue gas cleaning often requires significant investment, complicated installation and heavy-maintenance. Therefore, a modified flue gas cleaning system, namely Ash removal unit (ARU) was designed for simultaneously and synergistically removing particulate matter (PM), SO₂, NOx, CO₂ and heat from flue gas of local rice parboiling industries. In this study, ARU was incorporated in a local rice parboiling industry in order to evaluate the co-removal efficiency achieved by the ARU. Installation of ARU eliminated PM from flue gas by 91.8%, while it removed 78.5% SO₂, 78.3% NOx and 23.9% CO₂ respectively from the emitting stack. Other than flue gas cleaning , ARU also facilitates heat exchange between flue gas and boiler feed water. Hence, flue gas temperature was dropped by 42.1%, while boiler feed water temperature was raised by 36% in 30 min. Moreover, adopting ARU also improved the ambient air quality surrounding the industrial area, since it reduced SO₂, NOx, SPM, PM2.5 and PM10 level in ambient air by 81.7%, 78.2%, 21.1%, 22.9% and 43.1% respectively.

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.

Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method

The venturi tube is a special kind of pipe which has been widely applied in many fields. Cavitation is one of the most important research issues for the Venturi tube. Hence, three key structural parameters (contraction angle, diffusion angle and contraction ratio) were selected to investigate the influence of different factors on cavitation characteristics, using the computational fluid dynamics (CFD) method. A series of experiments for measuring the relationship between differential pressure and flow rate were carried out to verify the accuracy of the simulation method. Results showed that the simulation results had a high accuracy and the numerical method was feasible. The average vapor volume fraction of cross-section from the throat in the axial direction increased with increasing contraction angle. The cavity length increased with increasing contraction angle. The average volume fraction in the diffusion section rapidly decreased with increasing diffusion angle. The diffusion angle had no significant effect on the cavitation characteristics in the throat section and had a significant influence in the diffusion section. The average vapor volume fraction increased with decreasing contraction ratio. The contraction ratio had no significant effect on the cavity length under the same differential pressure. The average vapor volume fraction increased with decreasing contraction ratio. However, the variation in the throat section was less than the diffusion section. Under the same inlet and outlet pressure, the cavity lengths for different contraction ratios were basically the same, which indicated that the contraction ratio had no significant effect on the cavity length.

Loss of Smad4 expression inhibits epithelial-mesenchymal transition in SMMC-7721 cells

AIM: To investigate the influence of loss of Smad4 expression on TGF-β1-induced epithelial-mesenchymal transition in the human hepatocellular carcinoma cell line SMMC-7721.

METHODS: The influence of loss of Smad4 expression on the expression of β-catenin and Vimentin mRNAs and proteins was evaluated by RT-PCR and Western blot. Immunofluorescence was used to analyze the location and fluorescence intensity of Smad4, β-catenin, Vimentin in non-transfected SMMC-7721 cells and those transfected with Smad-specific siRNAs (RNAi-Smad4-2 and RNAi-Smad4-12) or unspecific siRNA (RNAi-NC).

RESULTS: Compared to non-transfected SMMC-7721 cells and those tranfected with RNAi-NC, the expression of β-catenin mRNA and protein remarkably increased in SMMC-7721 cells transfected with RNAi-Smad4-2 or RNAi-Smad4-12 (all P < 0.05). Loss of Smad4 expression promoted β-catenin nuclear translocation. Immunofluorescence assay revealed that β-catenin fluorescence was located in the nuclei of non-transfected SMMC-7721 cells and those tranfected with RNAi-NC, but in the cytoplasm of SMMC-7721 cells transfected with RNAi-Smad4-2 or RNAi-Smad4-12. On the other hand, loss of Smad4 expression down-regulated Vimentin protein expression (P < 0.05) and cytoplasmic fluorescence intensity, but had no significant impact on Vimentin mRNA expression in SMMC-7721 cells and those transfected with different siRNAs.

CONCLUSION: Loss of Smad4 expression regulates β-catenin and Vimentin and therefore plays an important role in inhibiting epithelial-mesenchymal transition in SMMC-7721 cells.