Two-stage Electrostatic Precipitator Research Articles

Retrofitting of an Air Handling Unit by a Two-Stage Electrostatic Precipitator

Retrofitting of an Air Handling Unit by a Two-Stage Electrostatic Precipitator

Study of the multi-physics field-coupled model of the two-stage electrostatic precipitator

Study of the multi-physics field-coupled model of the two-stage electrostatic precipitator

Analysis of electrostatic filter to mitigate ash diffusion into engine

Between March and June 2010 a series of volcanic events at Eyjafjallajökull in Iceland caused enormous disruption to air travel across Western Europe. The disruptions started over an initial period of six days in April 2010. About 20 countries closed their airspace to commercial jet traffic and it affected approximately 10 million travelers. Volcanic ash has been caused grounding of many aircraft as a source of possible damage to aircraft engines. The projected technical strategy, an electrostatic precipitator (ESP), was tailored for the high bypass turbofan engine model PW4000 in this study. It was based on the standard two-stage ESP but designed with the PW4000 engine. The innovative ESP prototype is primarily made up of a hexagram structure of six discharge electrode plates and three circular collecting electrode rings. An aerodynamic verification was conducted through computational fluid design (CFD). It built a 20-meter wind tunnel and placed the engine with ESP in the centre of it. A particle-laden atmosphere was created in the simulation using a discrete phase model (DPM) to replicate volcanic ash injection into clean air. From the results, it has a clear aerodynamic impact near the engine's intake, although the effect is small and may be ignored after the engine fans. Additionally, a CFD electrostatic verification was generated with a voltage of 20000 V, and the contour of the electric potential is perfect distributed, suggesting that an electric field can be adequately given by this ESP configuration design. Therefore, the simulation results of the new ESP layout would have allowed drawing conclusions about the electrostatic filter's ability to reduce volcanic ash intake in an engine with high aerodynamic performance.

Electrostatic precipitation (ESP) index driven bio-aerosol collection for a high biological viability sampling

In this work, a two-stage electrostatic precipitator as the integration of a pre-charger and an electrostatic collector is proposed for airborne bio-aerosol sampling, where a pre-charger was applied for collection efficiencies enhancement and the following parallel-plate collector captured bio-aerosols with high biological viabilities. And the effects of operation parameters, including applied voltages, flow rates and collection area, on both the physical collection efficiency and biological viability are investigated. Specifically, the electric field strength of 4.3 kV/cm keeps the best balance between sampling efficiency and microorganism survival. For general designs and applications of present two-stage sampler, the modified ESP index and Pre-charger index are defined based on the charging characteristics of two typical bio-aerosols as Escherichia Coli and Candida albicans for predicting physical collection efficiency, biological viability and their ratio. A porotype with 2 × 1012 s V2 m−3 and 1.5 × 1014 s V2 m−5 for ESP and Pre-charging Index, respectively, obtains collection performance 3–5 times higher than conventional AGI-30 sampler during an on-site sampling, proving its feasibility for bio-aerosol collection.

Electrostatic Precipitator Design Optimization for the Removal of Aerosol and Airborne Viruses

In the midst of the COVID-19 pandemic, new requirements for clean air supply are introduced for heating, ventilation, and air conditioning (HVAC) systems. One way for HVAC systems to efficiently remove airborne viruses is by filtering them. Unlike disposable filters that require repeated purchases of consumables, the electrostatic precipitator (ESP) is an alternative option without the drawback of reduced dust collection efficiency in high-efficiency particulate air (HEPA) filters due to dust buildup. The majority of viruses have a diameter ranging from 0.1 μm to 5 μm. This study proposed a two-stage ESP, which charged airborne viruses and particles via positive electrode ionization wire and collected them on a collecting plate with high voltage. Numerical simulations were conducted and revealed a continuous decrease in collection efficiencies between 0.1 μm and 0.5 μm, followed by a consistent increase from 0.5 μm to 1 μm. For particles larger than 1 μm, collection efficiencies exceeding 90% were easily achieved with the equipment used in this study. Previous studies have demonstrated that the collection efficiency of suspended particles is influenced by both the ESP voltage and turbulent flow at this stage. To improve the collection efficiency of aerosols ranging from 0.1 μm to 1 μm, this study used a multi-objective genetic algorithm (MOGA) in combination with numerical simulations to obtain the optimal parameter combination of ionization voltage and flow speed. The particle collection performance of the ESP was examined under the Japan Electrical Manufacturers’ Association (JEMA) standards and showed consistent collection performance throughout the experiment. Moreover, after its design was optimized, the precipitator collected aerosols ranging from 0.1 μm to 3 μm, demonstrating an efficiency of over 95%. With such high collection efficiency, the proposed ESP can effectively filter airborne particles as efficiently as an N95 respirator, eliminating the need to wear a mask in a building and preventing the spread of droplet infectious diseases such as COVID-19 (0.08 μm–0.16 μm).

Gas Absorption and Particle Removal Performance of Wet Parallel-Membrane Array System

In this study, the gas absorption and particle removal performance of wet parallel-membrane array systems were investigated. SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and oil mist were used as the target gas and particles, respectively. To evaluate the gas absorption performance of the wet membrane, we compared it with a packed-bed scrubber at the same flow rate. Unlike a typical packed-bed scrubber, the membrane scrubber has a high absorption rate and easily absorbs water so that the liquid flows dynamically across the entire membrane. Therefore, the membrane exhibited a higher mass transfer rate than the packed bed. Additionally, the pressure drop was extremely low because the flow was not blocked. We evaluated the particle removal performance of a wet two-stage electrostatic precipitator (ESP) with a wet parallel-membrane array collection stage. A PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> removal efficiency higher than 90% at a flow velocity of 1 m/s was achieved using the proposed system. In addition, the wet-membrane-based two-stage ESP was easy to design according to the existing ESP design theory, Cochet's charging theory, and Deutsch equation. Also, our new wet-membrane-based two-stage ESP can remove acid gas and particles simultaneously. Therefore, this membrane can be a promising material for air pollution control devices, such as scrubbers and ESPs.

Electrostatic precipitator with Surface Dielectric Barrier Discharge ionizer

The performance of a two-stage electrostatic precipitator (ESP) with an ionizer with Surface Dielectric Barrier Discharge (SDBD), where the ionizer both generates the free charges and forces the airflow via the electrohydrodynamic (EHD) effect, was experimentally studied. The Particle Image Velocimetry Method (PIV) measurements revealed the airflow patterns and showed that the total flow rate generated by the ionizer (with both flat edge and saw-like high-voltage electrodes) increases with the applied discharge voltage up to a maximum of 73 l/min for 24 kV. These measurements, supported by Computational Fluid Dynamics (CFD) simulations, suggested that changing the airflow pattern with a flow guide would improve the filtration efficiency. This has been experimentally confirmed using an optical particle analyzer, and we recorded a maximum total mass filtration efficiency of 98% for the ionizer with a flat electrode and a flow guide with 3 mm inlet gap. We found that the filtration efficiency increases with the applied voltage up to about 14 kV, then decreases with the voltage due to a reduction in the particle charging rate caused by the high flow velocity of the particles through the discharge region. We also determined that, taking into account both flow rate and filtration efficiency, the ESP works optimally with an applied voltage of 18 kV–20 kV, achieving a filtration efficiency of 77% and simultaneously a flow rate of 63 l/min for the ionizer with the saw-like electrode and respectively 89% and 28 l/min for the ionizer with the flat electrode.

Development and experimental investigation of the narrow-gap coated electrostatic precipitator with a shield pre-charger for indoor air cleaning

We designed and evaluated a two-stage electrostatic precipitator with a shield pre-charger and a narrow precipitator for indoor air cleaning. Unlike the conventional ESP-type air cleaner, the ion generation and particle charging regions were separated by a perforated plate with bias voltage. The electrical energization was achieved by connecting a large resistor in series with the shield electrode. A narrow-gap plate-plate precipitator was placed after the pre-charger for a strong electric field and a high specific collection area. The performance of the shield pre-charger, the narrow precipitator and their integration in lab-scale of 62 m3/h and pilot-scale of 500 m3/h were evaluated. The overall collection efficiency was 98.6 % and 75.5 % for gas flow velocities of 0.4 m/s and 1.2 m/s, respectively. The ozone concentration was around 0.2 ppm for a 24 h continuous operation. Our study showed a close relationship between particle charging and shield voltage with charging current, and a relatively stable performance under high gas flow velocity. The particle collection efficiency was 2.5 times higher than that of a conventional ESP-type air cleaner of similar size at a gas velocity of 1.2 m/s.

A Study on the Particle Removal Efficiency and Durability According to the Material of the Ionizer of the Fiber Brush Type Electric Precipitator

In this study, we investigated the particulate matter (PM) removal efficiency and durability of the two-stage electrostatic precipitator (ESP) different materials of brush-typed ionizers (non-metal: carbon fiber/metal: stainless steel (SUS) fiber). The PM removal efficiency was reduced when the average diameter and number of fibers of the brush-typed ionizer increased due to thin and multi-edge in a large number of fibers, which decreased the average electric field, resulting in lower PM removal efficiencies. In contrast with the carbon fiber ionizer, when the SUS fiber ionizer was used, the PM removal efficiency was maintained for a long time, due to its lower electrical resistivity (∼6.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> Ω * m) of the SUS fiber compared with the carbon fiber (∼5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> Ω * m), which prevents the positive ions to be stacked on the fiber. Therefore, the present research showed the potential use to apply SUS fiber ionizers as two-stage ESPs for a future air pollution control technology with high PM removal efficiency and durability without ozone emission and additional maintenance.

Experimental research of capture enhancement mechanism of submicron particles by designing two-stage electrostatic precipitators with various ratios of charger and collector units

In this paper, six kinds of two-stage ESPs with various ratios of charger and collector units are designed to research the capture enhancement mechanism of submicron particles. The working conditions are optimized by studying the influence of gas velocity, charger current, and electric field strength of collector. Results show that the electrostatic field characteristics of the two-stage ESP with Ra = 1/6 is beneficial to improve the collection efficiency while slightly less stable. The indicator factor of particle charging enhancement effect of two-stage ESP with Ra = 6/1 fluctuates between 0.06 and 0.1, which suggests that the two-stage ESP with a higher proportion of charger units cannot achieve the satisfying performance for the limitation of ionic wind effect. Under comprehensive consideration of ionic wind effect and ozone emission, the two-stage ESP with Ra = 2/5 is selected at the first priority by exerting the advantages of fully particle charging and enough collection space, which has a strong potential in both particle charging enhancement and electric field enhancement. However, for improving the collection efficiency of submicron particle with a size ranging from 0.2 to 0.5 µm which suffers from both of weak particle charging and agglomeration effect, the two-stage ESP with Ra = 4/3 is not recommended.

Improvement of an In-Duct Two-Stage Electrostatic Precipitator via Diffusion Charging.

An in-duct two-stage electrostatic precipitator (ESP) improved by ion diffusion effect was studied. We increased the collection efficiency of a two-stage electrostatic precipitator without additional energy input by adjusting the space arrangement of the charger and the collector, which increased the particle diffusion charging time. The collection efficiency and the particle charge were systematically investigated according to the occurrence of diffusion charging and electric field charging in the charger as generated by the negative ions. The collection efficiency of the separated two-stage ESP was 39% higher, on average, than the theoretical efficiency at the same power consumption. Through simulation, it was verified that the ions generated in the carbon fiber ionizer penetrated the charger. We proposed a modified charging mechanism assuming that the penetrated ions cause additional particle charge. The optimal separation distance between the charger and the collector, which showed the maximum collection efficiency, was derived through the modified charging model. Therefore, the in-duct two-stage ESP developed in this study is a promising energy-efficient and cost-saving design for indoor air management.

Comprehensive control of PM 2.5 capture and ozone emission in two-stage electrostatic precipitators

Indoor air purification is extremely urgent to eliminate the health threat of PM 2.5, VOCs and microbial aerosol for exposing people, for which ESPs enjoy exceptional advantage for its special high-voltage characteristic. However, the secondary air pollutant of ozone is produced to possibly cause potential risk. In this work, six kinds of two-stage ESPs containing various charger and collector units, whose structure and size design are determined according to the indoor application, are developed to investigate the comprehensive control of PM 2.5 capture and ozone emission. Responsive surface methodology is employed to explore the relationship among ozone concentration, wire number, charger current and airflow velocity, and obtain regression model for predicting ozone emission. The comprehensive evaluation standard considering efficiency-ozone double factors is proposed to optimize structure design and working conditions of two-stage ESPs. Experimental results show that two-stage ESPs with a unit ratio of >3/4 can keep relatively good stable state, whose current reduction is in around 10 μA, for preventing particle charging function of charger from basically affecting. For the two-stage ESP with Ra = 2/5, it finds the optimization of working conditions of collector can bring rapid improvement of collection efficiency for 0.25 μm particles, which reaches up to be >60 %, while the optimization of that of the charger can only result in an enhancement of <30 %. RSM analysis exhibits a strong connection between the interactive effect of charger current and airflow velocity for presenting a steep response surface. Based on comprehensive control of PM 2.5 and ozone pollutants, it suggests the two-stage ESP with Ra = 2/5 is selected at the first priority and then that with Ra = 1/6, while two-stage ESP with Ra = 4/3 is not recommended for unsatisfied consequence of both of PM 2.5 capture and ozone emission.

Development of On-Demand Antiviral Electrostatic Precipitators with Electrothermal-Based Antiviral Surfaces against Airborne Virus Particles.

Particulate matter, including airborne pathogens, is of particular concern because it can cause the spread of diseases through aerosol transmission. In this study, a new concept is proposed: on-demand antiviral electrostatic precipitators (ESPs) with electrothermal-based antiviral surfaces. We applied electrothermal-based antiviral surfaces to air-purifying applications and demonstrated that the proposed method is effective with regard to collecting airborne virus particles on collection plates in a two-stage ESP. With alternating current power, MS2 bacteriophage and H1N1 viruses were completely deactivated after exposure to 50 °C for 30 min. This remarkable antiviral performance via electrothermal effects indicates that on-demand platforms for self-antiviral surfaces can perform sterilization immediately without generating secondary pollutants, thus effectively preventing the spread of infectious microorganisms in public places. We believe that the results of this study can provide useful guidelines for the design and realization of practical and wearable devices for antiviral air-purifying applications.

Removal of ultrafine particles in a full-scale two-stage electrostatic precipitator employing a carbon-brush ionizer for residential use

Despite recent advances in the area of industrial electrostatic precipitators (ESPs), their residential use remains uncertain owing to the concern about ozone emissions when the removal efficiency of fine and ultrafine particles is increased. In this study, we propose a comprehensive numerical simulation of a full-scale two-stage ESP equipped with a carbon-brush ionizer that is capable of efficiently removing ultrafine particles with minimal ozone emissions. We calculated the spatial distributions of the electric potential and ionic charge density, the turbulent gas flow field coupled with ionic currents, and charge states and behavior of ultrafine particles in the entire region of the ESP. However, we did not investigate the ozone emission from the ionizer. In addition, we built an identical system to measure the profile of the local ionic current at the bottom of the discharging zone as well as the particle-collection efficiency. We clarified the effects of the orientation of the carbon brush tip and gas flow on the behavior of the ions and explored the behavior of charged particles in the collection unit with the insertion of a dielectric separator, thereby preventing air breakdown and increasing collection efficiency. All the simulation results were found to be consistent with experiments. We determined that a single carbon-brush electrode was sufficient to remove ultrafine particles at an efficiency of approximately 100% at 225 m3/h.

Evaluation of collection efficiency and automatic cleaning using a two-stage electrostatic precipitator for reduction of ultrafine particles in subway stations

Evaluation of collection efficiency and automatic cleaning using a two-stage electrostatic precipitator for reduction of ultrafine particles in subway stations

Removal of Mist Particles by a Two-Stage Electrostatic Precipitator Featuring Plastic Plate Electrodes

To reduce corrosion, cost, and weight, we developed a nonmetallic, two-stage electrostatic precipitator (ESP) using electrodes fabricated from carbon ink and polyethylene terephthalate (a plastic), rather than expensive corrosion-resistant metals. Five collection modules were manufactured; we varied the materials used to fabricate the high-voltage and ground electrodes. The plate-type electrodes of the collection module were made of stainless steel, carbon-coated plastic (CPC), or plastic-coated carbon (PCP). Particle removal performance was investigated by the voltages of the precharger and collection modules, the particle diameter, the airflow rate, and the particle collection area. The particles were an oil mist. The electrode material had little effect on particle removal performance. The experimental performances of two-stage ESPs featuring plastic and carbon plate electrodes met the theoretical efficiencies predicted by the Deutsch equation and Cochet charging theory. Although fluttering developed when the flow velocity exceeded 2 m&#x002F;s over CPC electrodes, the use of PCP electrodes (the rigidity of which was reinforced by the plastic coatings) eliminated fluttering. Moreover, in an extremely humid condition where the water vapor continuously condensed into water droplets, the polyethylene terephthalate film of the PCP electrode ensured stable operation without spark regardless of humidity or water droplets on the surface. In summary, plastic electrodes were light and economical, while affording high removal efficiencies similar to the removal efficiencies of metals. Moreover, the PCP electrode plastic coating protected the carbon ink from abrasion and corrosion.

Exploring the potential of electrostatic precipitation as an alternative particulate matter filtration system in aircraft cabins.

On most modern airliners, cabin air pressurization, heating, and renewal are mainly achieved using air supplied from the gas turbine engines during flight. This air intake impairs the motors yield and needs to be conditioned, leading to energy overconsumption. Recent advances in thermal management enable aircraft manufacturers to reduce further the intake airflow needed to maintain cabin temperature at high altitude. Nevertheless, for lower air renewal rates, an appropriate air filtration system will be needed to maintain acceptable air quality in the cabin. In this context, Clean Sky 2 Joint Undertaking (CS2JU) project EC2S (Environment Control Secondary System) aims at developing an integrated filtration system to be implemented in existing cabin air management systems (so-called environmental control system-ECS). The EC2S unit will include three filtration units addressing separately volatile organic compounds (VOCs), CO2 , and particulate matter (PM). Circulated air in the ECS is conventionally filtered on pleated HEPA filters that generate substantial pressure drop. Since the EC2S VOCs and CO2 filtration units would generate additional pressure drop in the ECS system, electrostatic precipitation is foreseen as a low flow resistance alternative for PM removal. This paper reports the development and performance assessment of a two-stage electrostatic precipitator (ESP) designed for aircraft recirculated air filtration. The ESP prototype presents high single-pass particle collection rates (i.e., over 90% for airborne particles with an aerodynamic diameter of 0.5μm or larger), low-pressure drop (i.e., 4Pa at nominal flowrate), and a limited ozone generation rate (i.e., below 8mgh-1 ).

Maintaining the PM Removal Efficiency of a Two-Stage ESP With External Ion-Injection Discharge via a Water Film on the Collection Plate and Cleaning of the Ionizer

A two-stage electrostatic precipitator (ESP) with a reduced footprint, external ion-injection discharge, and water film on the collection plate was developed for long-term operation. For optimal particulate matter (PM) removal efficiency, the ionizer of the external ion injection system was fixed at a distance of 5 mm from the bias plate. Under these operating conditions, the 0.3- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m PM (PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> ) removal efficiency was reduced to approximately 70% due to low migration velocity. The application of an additional collection plate extended the residence time of the charged particles in the electric field, which resulted in a removal efficiency exceeding 95%. However, long-term operation (675 min) of the two-stage ESP with external ion-injected discharge resulted in spark generation due to contamination of the ionizer, and the PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> and PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> removal efficiencies decreased linearly from 80.4% to 62.2% and 87.7% to 68.2%, respectively. Changing the ionizer to a pin shape with electrical specifications similar to those of carbon fibers resulted in water film formation on the collection plate. The PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> and PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> removal efficiencies remained at their initial levels for 120 min. The two-stage ESP with external ion-injected discharge operating with a water film is likely suitable for long-term operation in an industrial setting.

Minimizing the Size and Ozone Emission of Electrostatic Precipitators Using Dielectric and Rolled Carbon Film Coatings

Electrostatic precipitators (ESPs) are widely used to control air pollution. However, their applications in portable air cleaners are limited owing to ozone generation during the discharging process. In this article, we developed a compact two-stage ESP that combines corona discharging and particle collection modules. The former generates an extremely small amount of ozone using dielectric film coating, whereas the latter has a large specific surface area. A polypropylene (PP) film is coated as a dielectric material on the ground electrode of the discharging module. The corona current is reduced by the PP film, which in turn reduces the ozone generation. The efficiency of atmospheric particle collection and ozone generation were evaluated by varying the flow rates and applied voltages of the four-channel discharging and roll-type collection modules. Additionally, the specific surface area of 707&#x00A0;m²&#x002F;m³ of the roll-type collection module minimized the size of the device by increasing its integrity. The proposed ESP with PP coating exhibited the tendency of a conventional ESP that follows the Deutsch equation. All particles of size over 1&#x00A0;<i>&#x03BC;</i>m were removed from the atmosphere by the proposed device at a flow rate of 194.4&#x00A0;L&#x002F;min, which is more than three times that of human breathing. Furthermore, our experimental device removed more than 50&#x0025; of the ultrafine particles of size 0.3&#x00A0;<i>&#x03BC;</i>m without ozone generation. Therefore, the proposed device can be potentially used in portable or wearable air-cleaning devices to aid individual healthcare.

Characterization of electrohydrodynamic flow in a plate-plate electrostatic precipitator with a wire-cylinder pre-charger by data-driven vortex and residence time analysis

The two-stage electrostatic precipitator (ESP) is widely used for indoor air cleaning field, while both the Particle Image Velocimetry (PIV) observations and well-characterized quantitative descriptions are probably scarce. In this work, we propose to use vortex analysis, which is the main quantitative method for flow field, and the relative residence time method (RRT) to evaluate the electrohydrodynamic flow (EHD) in a plate-plate ESP. The effects of electrical energization, pre-charger polarity and primary gas flow velocity are studied. Two vortex indexes sort the particle flow as five patterns and increase almost linearly with applied voltage. Four final particle statuses, penetrated, collected, stagnant and back-mixed are clarified by RRT method. The data generated by RRT are utilized to derive the PIV index for further analysis of the ESP performance. The trend, which rises first and drops later, suggests PIV index is expected to pave a new way to clarify the relationship between the ESP flow patterns and particle collection efficiency.