Collection Efficiency Of Fine Particles Research Articles

Computational Fluid Dynamics Analysis of Wet Dust Removal in High-Gravity Countercurrent Rotating Packed Bed

High-gravity wet dust removal technology has attracted much attention because of its potential to cut liquid into smaller liquid droplets and lower energy consumption. However, the complex structure and the high-speed rotation of the rotating packed bed do not allow us to analyze the flow field using conventional methods, and thus the capture mechanism of fine particles in a high-gravity environment is poorly understood. In this study, a two-dimensional computational fluid dynamics model was established to investigate the distribution of the gas–liquid two-phase flow field inside of a rotating packed bed. The characteristics of the flow field, such as the liquid form, gas–liquid contact time, and gas flow path, were investigated, and the droplet size distribution and gas–liquid slip velocity were quantitatively analyzed. The inertial capture efficiency was calculated using the Stokes number, and the dust removal efficiency distribution in the rotating packed bed was compared. The reason for the high collection efficiency of fine particles by the high-gravity wet dust removal technology was explained by numerical simulations. Two new structures were designed to improve the total dust removal efficiency.

Effect of arc element diameter on fine particle collection efficiency of the separator

Clean gas without suspended particles is an essential factor for many industries. The paper is concerned with the design of a separation device with rows of the arc elements, in which a wave-like flow pattern is observed. The separation of solid particles from the gas occurs due to inertial and centrifugal forces. A three-dimensional model of the device and its operating principles are presented. The aim of the work is to numerically study the effect of the size of the arc elements of the separation device on the efficiency of particle collection. In the course of the simulation, the diameter of the arc elements varied from 25 to 50 mm. The exit to the stationary solution was estimated by the pressure drop of the separation device. It was found that about 870 iterations were needed. Results have shown that the diameter of the arc elements, at which the maximum efficiency of collecting particles from gas-solid flow occurs, is 40 mm. The separation efficiency of the device with a diameter of the arc elements of 25, 40, and 50 mm averages 81.1, 90.1, and 86.5%, respectively, at an inlet gas velocity of 0.5 to 5.0 m/s. The pressure loss in the separation device ranged from 12.6 to 1924.1 Pa at a gas velocity of 0.5 to 5.0 m/s. It is concluded that it is important to use a separation device to collect fine particles at a dusty gas velocity of less than 3 m/s because its pressure drop is significantly lower compared with other air separators.

Effects of Various Physical and Chemical Disinfection Methods on the Fine Particle Collection Efficiency of N95 Respirators and Surgical Masks.

Several studies have reported on the effectiveness of various disinfection methods for severe acute respiratory syndrome coronavirus 2 and their applicability to the disinfection of N95 respirators and surgical masks. To date, there have been no reports on the decontamination of deep in the intermediate layers of the multilayered structure. In this study, the conditions required for decontamination of such layers were simulated by considering the thickness and shape of N95 respirators or surgical masks (samples). After applying heat (steam, dry heat, or hot water) at 75°C for 60 min or chemical (benzalkonium chloride or laundry detergent) treatment, the collection efficiency of the samples was evaluated. Following the dry heat treatment, the time between the treatment and heat reaching the intermediate layer of the filter fiber was extended by 10 min. A dry heat disinfection method that combines hot water and a closed container was also evaluated, and satisfactory conditions were extended by 60 min. For each heat treatment, there was almost no effect on the collection efficiency, although there were cases where deformation was caused by mechanical stress. In contrast, chemical treatment resulted in a reduction in the collection efficiency of smaller particles.

A novel approach for investigation of collision mechanisms between fine particles in electrostatic precipitator under consideration of Brownian effect

In this paper, a novel approach based on the Lagrangian particle tracking method which adopted the accumulated displacement of particles as judgment standard was proposed to investigate the particle collision mechanism under the influence of non-contact external forces in a typical wire-plate electrostatic precipitator. The accumulated displacement of different diameter particles could reflect the range of particle motion and the collision probability inside the ESP, which was obtained from the calculated trajectory coordinates of particles under the influence of Brownian force and electric force. Results showed that the electric force controlled the particle’s trajectory direction while the Brownian force only made particles fluctuate along with the main track. The binary collision models with the determination of the dominant force were developed, which can be divided into two areas respectively called the electric force dominant region and the Brownian force dominant region. The total accumulated displacement of the submicron particle presented a U-shape curve, which matched well with the grade collection efficiency of fine particles in various experiments and demonstrated the validity of the proposed method. Also, the approach had good expansibility in investigating the role of other external forces in particle collision and could provide references for the design and working condition selection of ESP.

Heterogeneous condensation combined with inner vortex broken cyclone to achieve high collection efficiency of fine particles and low energy consumption

Gas cyclones are widely used for separating particles from gas, while recently various techniques have been developed to improve their performance. One is to use the supersaturated water vapor to increase the sizes of fine particles and hence their collection efficiency and another is to use the vortex-broken wing to decrease the pressure drop. This paper studies the synergistic effect of these two techniques. The supersaturated vapor, the vortex-broken wing and their combination were added to a conventional cyclone respectively and compared to the original cyclone by both experiments and numerical simulations. Through experiments, it was found that the removal efficiency of fine particles in the cyclone with the combined techniques was improved significantly while the pressure drop was reduced at the same time. The mechanism for such improvement was revealed through the computational fluid dynamics simulations. It was observed that the inner vortex can be effectively destroyed by the vortex-broken wing. This not only reduced the pressure drop, but also decreased the turbulence intensity under the vortex finder, which promoted the diffusion of water vapor and made the vapor distributes more uniformly. As demonstrated in the simulation, the improvement of the vapor distribution can enlarge the supersaturated region and enhance the condensational growth of fine particles. This was also testified by the online laser particle size analyzer in experiments. The findings establish a theoretical guidance for this new type cyclone and may provide new idea for the treatment of fine particles.

Cake formation and filtration characteristics of a cyclone-granular bed filter

The dust cake is critical to improve the fine particle collection efficiency in the gas-solid separation process of the granular bed filter (GBF). In this work, the dust cake formation and the corresponding filtration characteristics in a cyclone-granular bed filter (C-GBF) were investigated by experiments under a constant-velocity filtering condition. It was found that cake filtration, deep-bed filtration and the corresponding transitional phenomena could be observed in the C-GBF. A critical porosity was defined to identify the transition from cake filtration to deep-bed filtration. A following parametric study showed that a higher filtration gas velocity could increase the critical porosity and made it more difficult to form a dust cake. It was also demonstrated that the critical porosity was little affected by the dust concentration. However, the time point of the transition of different filtration modes was earlier with a higher dust concentration. The inlet gas velocity ultimately resulted in the different dust concentrations into the GBF. The similar dynamic processes of cake formation were obtained for different granular sizes. These results provided a deeper understanding of the dynamic behaviors of cake formation and filtration mode transition, which played an important role in the design and the scaling-up of the C-GBF filtration systems.

Effect of cylinder vortex stabilizer on separator performance of the Stairmand cyclone

The phenomena of precessing vortex core (PVC), entrainment of particles from the ash hopper, and swing of the vortex end in swirling flow have a negative effect on flow field and separation performance of cyclone. In order to alleviate these negative effects, a strategy to improve flow structure by installing cylinder vortex stabilizer is proposed, and the effects of different size stabilizers on the performance of cyclones are studied by experiment and CFD simulation. The results show that cylinder vortex stabilizer can improve the stability of the vortex in the cyclone, by reducing the impact of PVC, entrainment of particles from the ash hopper, and swing of the vortex end. This improves collection efficiency of fine particles, with an increase of 5.52% for particles whose diameters are smaller than 3 μm. The stabilizer has little effect on the pressure loss of the cyclone, with an increase of only 3.61%.

Numerical study on the effect of the supersaturated vapor on the performance of a gas cyclone

Gas cyclones are widely used to purify waste gases but are not effective in collecting fine particles. The cloud-air-purifying (CAP) technology was recently developed to overcome this deficiency by unitizing the supersaturated vapor in the cyclone. This paper presents a CFD study on the CAP cyclone. The condensational growth of particles is implemented in the CFD model. Its positive effect on the collection efficiency is confirmed and more clearly understood from microscopic investigations. Particles with the same initial size can grow into a narrow size distribution, yet the average growth ratio is increased with the increase of the supersaturation ratio and the decrease of the initial size, resulting in a significant improvement of the collection efficiency for fine particles, particularly in controlling those escaping through the middle-reverse flow. A predictive model is developed to consider the effect of the vapor. These results can help understand and optimize the CAP cyclone.

Enhancement of air purification by unique W-plate structure in two-stage electrostatic precipitator: A novel design for efficient capture of fine particles

In this paper, a novel W-plate two-stage ESP was developed and investigated systematically through the experimental and simulated process. Numerical models and available calculation procedure of solving coupling electrostatic field, fluid field, and particle dynamics were established, whose accuracy was validated by experiments. The relationship among collection efficiency, gas velocity, and particle diameter was studied, and the distribution of electrostatic field, the evolution of EHD flow and fluid field, and particle dynamics, including particle charging, particle trajectory, transverse velocity, and particle concentration, were also investigated thoroughly. Results showed that W-plate two-stage ESP exhibited excellent number-based collection efficiency for fine particles which benefited from the reasonable structure design and the exceeding weak influence of EHD flow. Besides, the particle charging process suggested that the diameter decided the dominant charging mechanism, and the trajectory also played an important role in controlling the charging action. Compared with the behavior of each particle injected at different inlet positions, fine particles injected near the discharge wire got more charging number and quicker capture. Importantly, W-plate structure could exert its crucial role in capturing particles with the help of fluid field and inertial effect when inlet gas velocity increased rapidly. W-plate two-stage ESP had more than 90% number-based collection efficiency for >3 μm diameter particles and more than 75% number-based collection efficiency for 0.3–1 μm diameter submicron particles at 2 m/s gas velocity in both experimental and simulated investigations.

Enhancing the collection efficiency of a gas cyclone with atomization and electrostatic charging

This paper presents a study on the combination of atomization and electrostatic charging to improve the collection efficiency of fine particles in a gas cyclone. A technology combining atomization and cyclones called cloud-air-purifying (CAP) has recently been developed, which utilizes the supersaturated vapor in the cyclone to realize the enlargement of dust particles and improve the collection efficiency. Here, the technology is further improved by charging the particles and droplets. Three different charging schemes are studied, including charging vapor droplets only, charging dust particles only, and charging both of them with opposite polarities. Experimental results indicate that all three charging schemes can significantly improve the collection efficiency. In particular, with charging, the collection efficiency of particles of approximately 2 μm is mostly improved. Consequently, the combination of the CAP technology and electrostatic charging can be a promising novel method to effectively remove PM2.5.

Numerical study on combined cyclone-filter aerosol collector performance

A cyclone was modified by inserting a stainless steel filter to enhance efficiency in collecting fine particles. Velocity and pressure distributions in the combined cyclone-filter were computed by computational fluid dynamics to explain experimental results from a previous study. Two different filter quantities (0.94 g and 1.83 g) were used. The pressure drop was reduced because the filter increased the turbulence intensity, thus reducing of tangential velocity. Insertion of the filter into the annular space of the original cyclone radically hindered the development of a swirl flow. Most of the gas flows axially through the filter. Good agreement between simulation and experimental results was found for the 1.83 g filter (maximum deviation of 5.1%), while for the 0.94 g filter, agreement was acceptable with the maximum deviations - 39.6%. Single-fiber collection efficiencies were calculated. Larger particles (1 µm) were mainly collected by inertial impaction with 65-70% efficiency at 13.3 m/s and 75–79% at 19.9 m/s, whereas, smaller particles (0.3 µm) are mainly removed by diffusion with 92–94% efficiency at the lower and 89–91% at the higher velocity. Therefore, the added filter enhances the fine particle collection efficiency by changing the centrifugal force to diffusion and inertial impaction mechanisms.

Numerical study on electrohydrodynamic flow and fine-particle collection efficiency in a spike electrode-plate electrostatic precipitator

In this work, a numerical study on the electrohydrodynamic secondary flow and transport of fine particles has been carried out based on spike electrode-plate electrostatic precipitator (ESP). The effect of the inlet flow velocity, negatively applied voltage, and position of spike tip on airflow streamlines distribution are analysed in detail. The electrohydrodynamic (EHD) secondary flow patterns and particle collection efficiencies are examined for three different corona discharge electrode configurations, the spike tip locates at i) upstream, ii) downstream and iii) at both sides of the channel. The results show a complex and turbulent flow structure in the ESP with the spiked electrode. A pair of vortices is formed in the vicinity of the spiked electrode with the tip of the upstream-directed spikes, driving the main airflow toward the collecting plates and improving the collection efficiency of particles. Compared to the EHD secondary flow streamlines in the spike-plate type ESP one can deduce that the stronger vortices occur at higher Ehd/Re2 ratios. Furthermore, the distribution of deposited particles with the aforementioned spike tip locations reflected the real condition of particle deposition. The results help to improve the structural optimization of the spike-type ESP.

Corona discharging and particle collection of bipolar transverse plate ESP

To improve the fine particle collection efficiency, a bipolar transverse plate electrostatic precipitation (ESP) technology was developed. In this ESP, there are not only the negative wire electrodes and ground plate electrodes, but also the ground wire electrodes and the negative plate electrodes. It has aroused a special interest about the corona discharging effect of the ground wire electrodes. Therefore, the corona currents of the negative wire-ground plate, the ground wire-negative plate, as well as the bipolar wire-plate electrodes have been investigated experimentally. In the experiments, the RS barbed wire and the C-plate are used as the electrodes for the purpose of the industrial application. The experimental results have shown that, when the wire-plate spacing is 200 mm, the corona current of the wire in the smooth side of the ground C-plate is 15% higher than that of curved side, however the corona current of the ground wire is about 30% less than that of the negative wires regardless of the wire is located at different sides of the industrial plate electrode. Moreover, the corona current of bipolar wire-plate electrodes is 30% less than that of the traditional wire-plate electrodes, and an important phenomenon had been discovered from this experimental work that, for the bipolar wire-plate electrodes, whenever the front side of the C-plate faces to the gas flow or not, the VI characteristics curve keeps almost no change at given wire-plate spacing. Last, an experimental setup was established for comparison of collection efficiency. When the negative polarity is applied to the bipolar transverse plate ESP, the collection efficiency increases sharply from 69.1% to 99.1%. Since both electrical forces and inertial forces play important roles in the bipolar transverse plate ESP, the penetration of the bipolar transverse plate ESP is 0.9%, which is substantially less than the penetration of 4.2% of the conventional ESP. The advantage of bipolar transverse plate ESP unit has been proved by successful operation in sintering flue control in China.

Purification characteristics of fine particulate matter treated by a self-flushing wet electrostatic precipitator equipped with a flexible electrode

ABSTRACTA self-flushing wet electrostatic precipitator was developed to investigate the removal performance for fine particles. Flexible material (polypropylene, 840A) and carbon steel in the form of a spiked band were adopted as the collection plate and discharge electrode, respectively. The particle concentration, morphology, and trace-element content were measured by electric low-pressure impactor, scanning electron microscope, and energy-dispersive x-ray spectroscopy, respectively, before and after the electrostatic precipitator. With increasing gas velocity, the collection efficiency of fine particles (up to 0.8 μm in diameter) increased, while it decreased for particles with diameters larger than 0.8 μm. Increasing the dust inlet concentration increased the collection efficiency up to a point, from which it then declined gradually with further increases in the inlet concentration. The particulate matter after the wet electrostatic precipitator showed different degrees of agglomeration. The collection efficiency of trace elements within PM10 was less than that of the PM10 itself. Notably, the water consumption in the current setup was significantly lower than for other treatment processes of comparable collection efficiencies.Implications: Wet electrostatic precipitators, as fine filtration equipment, were generally applicable to coal-fired plants to reduce PM2.5 emissions in China. However, high energy consumption and unstable operation, such as water usage and spray washing directly in the electric field, seriously restricted the further development. The utilization of self-flushing wet electrostatic precipitator can solve these problems to some extent.

Numerical investigation on non-steady-state filtration of elliptical fibers for submicron particles in the ‘‘Greenfield gap’’ range

While noncircular fibers (especially elliptical fibers) have demonstrated significant advantage of high collection efficiency for fine particles, only a few investigations have yet been conducted to study the non-steady-state filtration performance of noncircular fibers during the particle deposition process. In this work, we utilize a lattice Boltzmann-cellular automata (LB-CA) probabilistic model to investigate the growing process of particle dendrites on elliptical fibers. The transient pressure drop and collection efficiency are analyzed. For the deposition of sub-micron particles (0.3–0.5µm in the “Greenfield gap’’ range) which are dominated by the diffusion and interception mechanism, the captured particles distribute relatively uniformly around elliptical fibers (the equivalent diameter df of 22.8µm and the packing density of 5% in this work) at the initial stage of loading process. The deposited particle leads to the formation of complicated dendrites, expanding the filtration area and thereby altering the flow field. Then particles will mostly deposit on the windward of the elliptical fibers (especially on the both ends of the elliptical long axis) at the complete dendrites capture stage. Various operation conditions (inlet flow velocity of 0.1–0.3m/s, particle diameter of 0.3–0.5µm, aspect ratio of elliptical fibers of 2–4, orientation angle of 30°~60°) are simulated. It is found that the pressure drop of dust loaded elliptical fibers normalized by the corresponding pressure drop of clean elliptical fibers increases almost exponentially with the mass of captured particles; and the normalized collection efficiency of elliptical fibers is approximately a linear function of the deposit mass when the increase rate of the normalized efficiency is stabilized.

電気集塵装置微粒子分離性能大幅改善に向けた気流制御

電気集塵装置微粒子分離性能大幅改善に向けた気流制御

정전분무 방전극을 이용한 습식 전기집진장치의 미세먼지 집진효율 평가

Abstract The wet electrostatic precipitator(wet ESP) is an effective control device which removes submicron particles re-entrained in a collection plate and water soluble gas. However, its collection efficiency decreases, as its operation is subject to water-induced distortion of the collection electrode. In order to make up for the limitation, we modified the wet ESP system by installing electrosprayed discharge electrodes. The modified wet ESP system can wash both the collection plate and discharge electrode.As a result, we were able to fabricate a compact wet ESP with a small specific collecting area(0.18m 2 (m 3 /min)) that can accomplish a high collection efficiency of fine particles(97.1%). In addition, the device obtained a rela-tively low specific corona power of approximately 10W/(m 3 /min). Key words : Fine particle, Wet ESP, Electrosprayed discharge electrode, Specific collecting area, Specific corona power *Corresponding author. Tel : +82-(0)41-660-1431, E-mail : kimjh@hanseo.ac.kr

Effects of simultaneous acoustic and electric fields on removal of fine particles emitted from coal combustion

Traditional electrostatic precipitation has a relatively low collection efficiency of fine particles emitted from coal combustion due to insufficient particle charging. This paper establishes an experimental system combining travelling sound waves with wire-duct electrostatic precipitation in order to measure the separated and simultaneous effects of an electric and acoustic field on fine particle penetration efficiency. The ranges of the main physical parameters are as follows: discharge voltage, V=8–12kV; acoustic frequency, ƒ=800–2400Hz; sound pressure level (SPL), SPL=130–148dB; residence time, t=2–6s; initial fine particle concentration, N0=6.5×105–4.99×106/cm3. The application of acoustic waves in an electric field is proven as an advisable method to remove fine particles with the lowest total penetration efficiency of 4.4%. Although the sound does not change the current–voltage curves of negative corona, it can distort the motion trajectory of the particles leading to a positive result for fine particle removal. The effectiveness of sound on the improvement of fine particle removal diminishes as the voltage increases. For a given discharge voltage, there exists an optimal frequency and SPL. The optimal frequency slightly increases, while the optimal SPL decreases as the applied voltage increases. The influence of residence time and initial fine particle concentration in combined fields are also studied.

Experimental Study on the Enhancement of Particle Removal Efficiency in Spray Tower Scrubber Using Electrospray

There have been a lot of efforts to keep permissible emission standards and to reduce the amount of emitted air pollutants. There are several air pollution control equipments, however, wet scrubber is used to remove particulate matters and gaseous pollutants simultaneously, even if it has low collection efficiency in the particle size less than 5.0 μm. To overcome this problem, we introduced a spray tower scrubber with an electrospray system which a high voltage was indirectly applied. We found that collection efficiency of fine particles in the electrospray system was improved by increasing electrical field strength and the ratio of liquid-gas flow rate (from 41% to 84% for 0.3 μm particles). In addition, a number of small droplets generated from an electrospray system led high collection efficiency, resulting from electrostatic attraction between droplets and particles and higher collision frequency. Therefore, we can conclude that the introduction of an electrospray system is quite effective to increase the particle removal efficiency of a spray tower scrubber.

Effect of the EHD flow on the collection efficiency of fine particles in wire-plate electrostatic precipitators

This paper focuses on the low collection efficiency of fine particles in air pollutant. Based on analyzing the collection rate of fine particles in electrostatic precipitator (ESP), a two-dimensional model of wire-plate discharge was established. The CFD code FLUENT was used to simulate the ionic winds at typical voltages 25, 40, and 45 kV, respectively. In the process of simulating, the ionic wind was replaced by the dynamic wind. According to the state graphs of ionic winds, the abnormal manifestation of the fine particles collection appeared in 40 kV voltage was explained. This work will provide a theoretical support for optimizing electrodes matching.