Particle Collection Efficiency Research Articles

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.

Experimental study on the removal of fine particles using hole-slotted collectors in wet electrostatic precipitators

ABSTRACT The fine particles are considered a significant environmental pollution problem. The wet electrostatic precipitators (ESPs) are now used most widely among the advanced fine particle removal technologies. The rigid glass fiber reinforced plastics (FRP) collectors modified with hole-slotted structures were used to enhance the water film distribution over their surfaces. This paper experimentally investigated the effects of the hole-slot patterns and the operating parameters on the particle removal performance in wet ESPs using the hole-slot-structured collector. The voltage-current characteristics and the energy consumption among the different pattern collectors were discussed. Besides, the effects of the water film on the particle number concentration classification and the effects of the applied voltage and the specific collecting electrode areas (SCA) on the relative collection efficiency (RCE) were investigated and discussed. The experiment results show that the corona current of three hole-slot structured FRP collectors was higher than that of the conventional rigid collectors (CRC) at the same voltage. Using the FRP collectors with circular holes and horizontal slots could decrease the energy consumption and using the FRP collectors with vertical slots increases the energy consumption compared with the CRC when the collection efficiency was lower than 92.5%. The water film could increase the collection efficiency of the fine particles and prevent the fine particles cross through the holes and the slots. The hole-slot-structured FRP collectors were appropriate for the working conditions of high SCA and long residence time. When the water film in the hole and slotted structures was incomplete, the fine particles could pass through the collector plate to form secondary back-mixing. Implications: The wet ESPs are used most widely among the advanced treatment technologies of the fine particles’ removal. The rigid glass fiber reinforced plastics (FRP) collectors modified with hole-slotted structures were used to enhance the water film distribution over their surfaces. The hole-slot-structured FRP collectors were appropriate for the working conditions of high SCA and long residence time. When the water film in the hole and slotted structures was incomplete, the fine particles could pass through the collector plate to form secondary back-mixing.

Experimental study of a string-based counterflow wet electrostatic precipitator for collection of fine and ultrafine particles

ABSTRACT Wet electrostatic precipitators (WESP) have been widely studied for collecting fine and ultrafine particles, such as diesel particulate matter (DPM), which have deleterious effects on human health. Here, we report an experimental and numerical simulation study on a novel string-based two-stage WESP. Our new design incorporates grounded vertically aligned polymer strings, along which thin films of water flow down. The water beads, generated by intrinsic flow instability, travel down the strings and collect charged particles in the counterflowing gas stream. We performed experiments using two different geometric configurations of WESP: rectangular and cylindrical. We examined the effects of the WESP electrode bias voltage, air stream velocity, and water flow rate on the number-based fractional collection efficiency for particles of diameters ranging from 10 nm to 2.5 μm. The collection efficiency improves with increasing bias voltages or decreasing airflow rates. At liquid-to-gas (L/G) as low as approximately 0.0066, our design delivers a collection efficiency over 70% even for fine and ultrafine particles. The rectangular and cylindrical configurations exhibit similar collection efficiencies under nominally identical experimental conditions. We also compare the water-to-air mass flow rate ratio, air flow rate per unit collector volume, and collection efficiency of our string-based design with those of previously reported WESPs. The present work demonstrates a promising design for a highly efficient, compact, and scalable two-stage WESPs with minimal water consumption. Implications: Wet Electrostatic Precipitators (WESPs) are highly effective for collecting fine particles in exhaust air streams from various sources such as diesel engines, power plants, and oil refineries. However, their large-scale adoption has been limited by high water usage and reduced collection efficiencies for ultrafine particles. We perform experimental and numerical investigation to characterize the collection efficiency and water flow rate-dependence of a new design of WESP. The string-based counterflow WESP reported in this study offers number-based collection efficiencies >70% at air flow rates per collector volume as high as 4.36 (m3/s)/m3 for particles of diameters ranging from 10 nm – 2.5 μm, while significantly reducing water usage. Our work provides a basis for the design of more compact and water-efficient WESPs.

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.

Developing a Compact Particle Collector by Integrating a Wet Electrostatic Precipitator and an Inertia Mist Eliminator

ABSTRACT Wet electrostatic precipitator (WESP) is a reliable alternative to realize the ultra-low emission of particulate matter from coal-fired power plants. This work proposes to develop a compact particle collector by integrating a WESP and an inertia mist eliminator (IME). The particle collection efficiency and charging characteristics of the WESP were analyzed to determine the potential for compact design. Results show that the WESP was easy to achieve a collection efficiency of 95% for both pin and wire electrodes. Particle charging can still be guaranteed with short WESP length and high voltage, indicating the particle charging was sensitive to electrical parameters. Charges carried by the escaping particles acted as a bridge between the WESP and the IME. The collision enhanced by particle charging can lead to an improvement in overall efficiency and charge loss. The particle charge loss of the particle sized 7.29 μm was 22.6% and 29.4% for the one and two stage IME, which coincided with the efficiency enhancement of WESP. The collection efficiency significantly decreased as the WESP size decreased, but the collection efficiency can be enhanced by the combination with IME. The 6-wire WESP enhanced by one-stage IME can be considered the optimal combination because the WESP size can be shorten by 40% while maintaining a similar efficiency. The research findings are beneficial for the retrofit of air pollution control devices in limited space.

Bipolar Precharger for Hybrid Electrostatic Filtration Systems

ABSTRACT Both hybrid electrostatic filtration and agglomeration technologies can effectively improve the efficiency of fine particle collection. A hybrid electrostatic filtration system with a wire-tube bipolar precharger was developed on the basis of bipolar transverse plate electrostatic precipitation technology. Theoretical analyses of electric field and flow field distribution showed that a uniform electric field and high turbulence intensity improve ion migration and particle agglomeration in the novel wire-tube bipolar precharger. The influence of unipolar and bipolar prechargers on dust removal was investigated. In the hybrid electrostatic filtration system with the bipolar precharger, the corona current was 30% higher, the particles deposited on the surface of the filter bag were 19% larger, and the pressure drop was 30% smaller than a filtration system with a unipolar precharger. When silicon powder with a median diameter of 1.7 µm was used, the mean penetration of the experimental device with the bipolar precharger was 45% lower than that of the experimental device with the unipolar precharger.

Numerical evaluation of particle collection efficiency of circular cylinders in cruciform arrangement

Numerical evaluation of particle collection efficiency of circular cylinders in cruciform arrangement

Effect of barbed tubular electrode corona discharge EHD flow on submicron particle collection in a wide-type ESP

In an electrostatic precipitator (ESP), the electrohydrodynamic (EHD) flow induced by the corona discharge is formed from the coupling of ionic wind and primary flow. This kind of non-laminar flow has a notable impact on submicron particle collection. The barbed tubular electrode is commonly used in industrial dust removal due to its high corona discharge intensity and fine particle collection efficiency, as well as its low inception voltage. However, the specific EHD flow functionary mechanism induced by the ESP's corona discharge for the purpose of submicron particle movement and collection has yet to be evaluated. In this work, a Particle Image Velocimetry (PIV) system was used to investigate EHD flow characteristics under this type of corona discharge. The experimental variables included barb tip orientation (in observation planes), primary flow velocity, and applied voltage. Based on the submicron particles' force and the entire flow field's velocity distribution within the ESP, we proposed two mechanisms for this type of corona discharge—“vacuum vortex obstruction” and “high-speed flow driven deposition,” and determined that submicron particle re-entrainment is closely related to both phenomenon.

Evaluation of a Catalyst Packed-bed Nonthermal Plasma Reactor for VOC and PM Removal

Volatile organic compounds (VOCs) and particulate matter (PM) emitted from factories in the painting and printing industries, and various exhaust gas regulations have been implemented. VOCs are the cause of photochemical oxidants and suspended PM such as PM2.5, which has become a global environmental problem. As one of the solution technologies, catalysis nonthermal plasma (NTP) techniques have been studied as VOCs control methods. In this study, in order to extend the application to the treatment of water-soluble VOCs, a wet-type catalysis plasma reactor is proposed. As an initial step to evaluate proposed technique, the simultaneous removal of nanoparticles and toluene or typical VOCs, are performed at relatively high gas flow rates of 10 L/min. As catalyst pellets, α-alumina spheres are filled in the NTP reactor, and a MnO2 catalytic reactor is installed after the plasma reactor for ozone removal. Simultaneous removal of toluene and nanoparticles using dry and wet-type catalytic NTP reactors showed that the results used the wet-type reactor were superior in particle collection efficiency of 99%. As for the toluene removal efficiency, the dry-type was 91% and the wet-type was 73%, with the dry-type showing better results. However, the proposed wet-type catalysis NTP reactor could efficiently treat water-soluble VOCs, such as acetaldehyde and acetic acid.

Experimental investigation of a one-level eight-channel cyclone-separator incorporating quarter-rings

The main aim of this investigation was an experimental analysis of the air cleaning efficiency in a mock-up next-generation air cleaning device - one-level 8-channel industrial cyclone-separator with quarter-rings - while changing parameters of the inner structure and the assessment of the effects of dispersion of particulate matter. Therefore, the research was carried out in two stages: the first stage covered the analysis of the efficiency of the multi-channel cyclone with particulate matter of <20 and <50 ?m. During the second stage, a cascade impactor was used to measure the particle collection efficiency in the multi-channel cyclone by fractions: PM1, PM2.5 and PM10. Results of the tests with using the cascade impactor were compared to show changes in the PM composition before and after the multi-channel cyclone-separator. According to the obtained experimental data, the one-level 8-channel cyclone-separator collects 70 to 80 % of PM up to 10 ?m in size, 45 to 60 % of PM up to 2.5 ?m in size and 21 to 25 % of PM up to 1 ?m in size.

Experimental investigation of the effect of collection length in a two-stage electrostatic precipitator for removal of PM2.5

• The effect of collection length in a two-stage ESP was investigated in detail under consideration of various factors. • The collection efficiency of sub-micron particles could reach up to be more than 95% at 4 m/s gas velocity. • The sequence of the influence degree of main parameters in governing ozone concentration was obtained. In this work, a laboratory-scale charger, with a single wire electrode of one charging unit for effective ozone control, and collector with a 300 mm length and 5 mm plate-plate distance extremely short for high-efficient capture of noxious particles, was designed and assembled as a two-stage ESP to study the effect of collection length for removal of PM2.5, in particular to these sub-micron particles which had the highest penetration rate during the electrostatic capture process. The influence factors, including the current density of charger, the electric field strength of collector, and gas velocity, were investigated in detail. Multiple channels of the collector were chosen to thoroughly compare the performance difference by detecting the particle concentration in the electric field directly. Besides, the ozone concentration test was carried out in various parameters to explore the influence degree simultaneously. Experimental results showed that the collection efficiency based on the number concentration could reach up to be 92.9%, 96.7%, and 97.7% for 0.25 μm, 0.35 μm, and 0.45 μm diameter particles at 4 m/s gas velocity, respectively, which benefited from the advantages of long collection plate and short migration distance. Compared with the influence factors of charger current density and gas velocity, electric field strength occupied the middle position in effecting the collection efficiency, whose most massive index factor was about 18 at a collection length of 30 cm. While the maximum index factor of current density was 3.7 at a collection length of 15 cm and of gas velocity was 27.5 at a collection length of 10 cm. The ozone concentration test suggested that charger current, gas velocity, collection length, and electric field strength could affect the ozone concentration from strong to weak in sequence.

Mist Removal Performance of a Novel Electrostatic Precipitation Type Mist Eliminator, With a Narrow Gap and High Gas Velocity, for Use in Coal-Fired Power Plants

To remove fine particles from a wet flue gas desulfurization (FGD) system in a coal-fired power plant, we develop a flat-plate type wet electrostatic mist eliminator (EME), with a narrower gap and higher gas velocity than that of a conventional electrostatic precipitator. Particle collection and pressure drop performance tests are conducted at the laboratory scale for the EME with a single-channel geometry and collection area of 0.5 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at various gas velocities and applied voltages. The results are compared to those achieved for a chevron-type mist eliminator. The pilot EME, which is designed based on the laboratory-scale device, has a collection area of 4.6 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and tested at a fixed velocity of 4 m/s, with and without the chevron-type ME. Its long-term performance is evaluated for approximately 400 min. Mists smaller than 10 μm are generated, including CaCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles, and an optical particle counter and United States Environmental Protection Agency M5 method are used to measure the particle collection efficiency. The collection efficiency of the laboratory-scale EME at 4 m/s is approximately three times higher than that of the chevron-type ME, whereas the pressure drop is only 8% of that of the chevron-type ME. The particle emission from the pilot scale EME with multiple channels is 2 mg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which decreased to 1.4 mg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> when it is combined with the chevron-type ME. Although the initial particle collection efficiency of the pilot scale EME (71.2%) decreases to 60.5%, the efficiency recovered to almost the initial state after 10 min of water cleaning at 43.5 L/min.

CFD simulation design and optimization of a novel zigzag wave-plate mist eliminator with perforated plate

A zigzag wave-plate mist eliminator with an internally improved structure of perforated plate was proposed in this work, which applied in particle removal process for lime-stone wet flue desulfurization (WFGD) system. Its performance was evaluated by Computational Fluid Dynamics (CFD) methods with three criteria, overall collection efficiency, system pressure drop, and impact factor. The realizable k-ε turbulence model and Eulerian-Lagrangian methodology were adopted to describe the motion of the continuous phase and dispersed phase. The CFD results showed that the main factors affecting the performance of perforated plate mist eliminator are the number of perforated plates N, the perforated plate interval spacing I, the hole diameter d1, the distance between two holes d2, porosity ε, installation angle α, and the height of the perforated plate h. Compared with the wave-plate mist eliminator with porous foam layers, the mist eliminator with perforated plate is found to have better performance in particle removal. The overall particle collection efficiency is increased by more than 2.3%, the pressure drop is reduced by more than 27.4% while the porosity of the perforated plate is small. When ε is large, the particle collection efficiency of the porous plate with large porosity decreased by 0.3–1.2%, the pressure drop was reduced by more than 34.7%. Besides, it has a simple structure and can be processed by integrated technology. All these advantages make the perforated plate mist eliminator a promising candidate for fine particle removal in the WFGD system.

Bio-inspired patterned surface for submicron particle deposition in a fully developed turbulent duct

Arrays of surface ribs have been reported to significantly enhance particle collection efficiency in particle removal devices. However, the surface ribs also cause a higher pressure drop. Therefore, the overall performance needs to take into consideration the above factors. In this study, different forms of surface ribs inspired by nature were designed and parametric studies were performed to enhance deposition efficiency. Our parametric studies comprised three different aspects: geometry of the patterned surface, pitch-to-height ratio, and particle size. The flow field around patterned surfaces was simulated in a two-dimensional channel flow by using the Reynolds stress model, corrected by turbulence velocity fluctuation in the wall-normal direction. The particle trajectory was solved by using Lagrangian particle tracking. When the overall efficiency ratio was considered, a semi-circular pattern had the best overall efficiency with 1137 times increase when compared to the case without patterns. Although the open-circular pattern has the minimum particle deposition enhancement, the overall efficiency of the open-circular pattern has 862 times increase compared to the case without patterns. Surface ribs (semi-circular, triangular and rectangular) can achieve a higher particle deposition velocity, but a higher flow resistance is generated compared with applying the open-circular surface ribs. The deposition location was then investigated for different surface ribs at different pitch-to-height ratios (p/e). This study shows that the semi-circular surface pattern should be recommended to enhance the overall performance of particle removal devices, especially for submicron particles.

Investigation of bubble-particle attachment, detachment and collection efficiencies in a mechanical flotation cell

The paper presents the effect of impeller speed and superficial gas velocity on bubble-particle attachment, detachment and collection efficiencies using pure quartz particles in a mechanical flotation cell. Detachment and collection efficiencies in different parts of cell were calculated by local turbulent energy dissipation rate measurements using high speed stereoscopic particle image velocimetry technique. In addition to high detachment efficiency, low attachment efficiency is also one of the reasons for low collection efficiency for coarse particles. The flotation rate constant increased with an increase in superficial gas velocity. However, the effect of superficial gas velocity on collection efficiency was negligible. This means that any effect of superficial gas velocity on flotation rate constant was due to changes in the number of bubbles and collision frequency. The flotation rate constant, collision frequency, and the number of bubbles increased with increasing impeller speed. However, collection efficiency decreased with increasing impeller speed.

CFD Modeling of Hydrocyclones—A Study of Efficiency of Hydrodynamic Reservoirs

The dynamics of hydrocyclones is complex, because it is a multiphase flow problem that involves interaction between a discrete phase and multiple continuum phases. The performance of hydrocyclones is evaluated by using Computational Fluid Dynamics (CFD), and it is characterized by the pressure drop, split water ratio, and particle collection efficiency. In this paper, a computational model to improve and evaluate hydrocyclone performance is proposed. Four known computational turbulence models (renormalization group (RNG) k- ε , Reynolds stress model (RSM), and large-eddy simulation (LES)) are implemented, and the accuracy of each for predicting the hydrocyclone behavior is assessed. Four hydrocyclone configurations were analyzed using the RSM model. By analyzing the streamlines resulting from those simulations, it was found that the formation of some vortices and saddle points affect the separation efficiency. Furthermore, the effects of inlet width, cone length, and vortex finder diameter were found to be significant. The cut-size diameter was decreased by 33% compared to the Hsieh experimental hydrocyclone. An increase in the pressure drop leads to high values of cut-size and classification sharpness. If the pressure drop increases to twice its original value, the cut-size and the sharpness of classification are reduced to less than 63% and 55% of their initial values, respectively.

Prediction of Particle-Collection Efficiency for Vacuum-Blowing Cleaning System Based on Operational Conditions

The dust-collection system, as the core of a sweeper vehicle, directly inhales dust particles on the pavement. The influence of variable operational conditions on particle-separation performance was investigated using computational fluid dynamics (CFD) Euler–Lagrange multiphase model. The particle-separation performance efficiency and retention time were used to evaluate the dust-collection efficiency. The uniform design (UD) and multiple regression analysis (MRA) methods were employed to predict and optimize the effects of reverse-blowing flow rate, pressure drop, and traveling speed on separation efficiency. The results indicated that the dust-collection performance initially increased and then decreased with increasing reverse-blowing flow rate. As the pressure drop increased, there was an increase in total dust-collection efficiency. However, the efficiency decreased with increasing traveling speed. The regression model showed that the proposed approach was able to predict the particle collection efficiency accurately. In addition, the optimum operational conditions were obtained, namely a reverse-blowing flow rate of 2100 m3/h, a traveling speed of 5 km/h, and a pressure drop of 2400 Pa. The maximum particle-separation efficiency was 99.10%, which showed good agreement with the experimental results.

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.

Deposition of Aerosol Nanoparticles in Screen Diffusion Batteries

The deposition of aerosol particles in diffusion batteries composed of model screens oriented perpendicularly to a Stokes flow has been considered. The particle collection efficiencies have been calculated as depending on screens parameters and the Peclet diffusion number. It has been shown that, at large Peclet numbers, the particle penetration through dense screens is independent of the interscreen distance and coincides with the penetration calculated by the empirical equation used for screen diffusion batteries.

Enhanced Capture of Aerosol Particles on Resonator-Based PM Mass Sensors Using Staggered Arrays of Micro-Pillars

This work presents the effect of addition of micro-pillars with different array configurations on the particle collection efficiency (CE) of resonators for gravimetric airborne particulate matter (PM) sensors. Inline and radially staggered arrays of micro-pillars with rectangular and circular cross sections were 3D-printed on a surface of fused silica glass using 2-photon stereolithography and the particle collection efficiency of these pillar-covered surfaces due to impaction was evaluated. The experimental results show that in some cases the CE is highly dependent on the angle of incidence and array configuration of the pillars. The CE of inline array of rectangular micro-pillars (60%) was similar to the CE of the bare surface with no pillar. However, the radially staggered arrangement of the same pillar size and geometry improved CE by 25% on average. The presented result shows the strong significance of the incident angle, array configuration, and pillar shape on particle capture behavior of the pillared-enhanced impaction surfaces. The results pave the way for highly sensitive real-time gravimetric PM mass sensors. [2020-0124].