Two-stage Electrostatic Precipitator Research Articles

Investigation of inactivation process for microorganism collected in an electrostatic precipitator

This study is aimed at investigating an inactivation process of microorganisms collected by a two-stage type electrostatic precipitator (ESP). The experimental system consisted of a discharging section and an electrostatic section. A bacterial culture of Staphylococcus aureus, as a model of airborne microorganisms, was put on the surface of grounded plate electrodes in these sections. Negative DC high voltages were applied to these sections. The gas flow velocity in the experimental system was 0.5 m/s. The survival ratio was calculated by the colony counting method, and the amount of 250-nm-absorbing substance, such as protein and minerals, was measured using a spectrophotometer. Living and dead microorganisms were distinguished using a fluorescence microscope, and their forms were observed using a scanning electron microscope (SEM). Reactive oxygen species (ROS) distribution on the surface of the grounded plate electrode was observed using a gel reagent. The collection efficiencies and the ozone concentrations were also measured in a single-stage ESP and the two-stage type ESP.As a result, ROS concentration was the greatest under the wire electrode. The result of the colony count showed that microorganisms were inactivated by the corona discharge. The observation using the fluorescence microscope showed that the amount of dead microorganisms was greater than that of the living microorganisms after the inactivating treatment. The SEM observation revealed that the cell walls were destroyed, and the result obtained with the spectrophotometer showed an increase in the amount of 250-nm-absorbing substance. These results indicated ROS destroys cell walls and causes cell content to flow out, whereby microorganisms collected in an ESP are inactivated. It was also revealed that the collection efficiency can be improved without increasing ozone concentration and energy consumption in the two-stage type ESP.

Two-stage electrostatic precipitator using induction charging

An electrostatic precipitator (ESP) without using corona discharge was investigated herein. The ESP employed a two-stage configuration, consisting of an induction charging-based particle charger and a parallel plate type particle collector. By applying a high voltage of several kV, under which no corona discharge was generated in the charger, particles were charged by induction due to contact with charger electrodes. The amount of charge on the charged particles increased with the applied voltage and turbulent air flow in the charger. Performance of the ESP equipped with the induction charger was investigated using ambient air. The removal efficiency for particles ranging 0.3 µm to 5 µm in diameter increased with applied voltage and turbulence intensity of gas flow in the charger when the applied voltage was sufficiently low not to generate corona discharge. This suggests that induction charging can be used for electrostatic precipitation, which can reduce ozone generation and power consumption significantly.

Electrostatic Precipitation of Submicron Particles with an Enhanced Unipolar Pre-Charger

A two-stage electrostatic precipitator (ESP) has been developed using an enhanced unipolar pre-charger with dielectric coated ground electrodes. The electrical and particle collection performance was evaluated for particles in the submicron range. By varying the voltage applied to the pre-charger, the particle charging characteristics was compared with that calculated by the theoretical model. The experimental results show that with the adoption of the pre-charger, the charging of the particles at submicron range was enhanced. Further results indicate that the collection efficiency can be improved by about 12.1%–15.9%, compared with the results obtained without the pre-charger. Higher particle collection efficiency can be achieved by increasing the voltage applied to the pre-charger. The unipolar pre-charger studied in this paper proves to be a simple and useful device to improve the submicron particle collection efficiency of conventional ESPs.

Two-stage vs. two-field electrostatic precipitator

The paper presents comparison of the collection efficiency of semi-industrial, two-field electrostatic precipitator and two-stage electrostatic precipitator comprising an electrostatic agglomerator. The two-stage electrostatic precipitator was converted from two-field electrostatic precipitator, in which the first field was replaced by unipolar electrostatic agglomerator. The investigated electrostatic precipitator was of parallel-plate type, with spiked-wire discharge electrode between sigma type collection electrodes. In the unipolar agglomerator used in this system, the particles were charged by ion current and forced to oscillate by alternating electric field. The oscillatory motion of particles perpendicular to the gas flow causes the collision between particles and deposition of small particles onto the larger ones. The agglomerated particles were next collected by one-field electrostatic precipitator.The collection efficiency of two-stage electrostatic precipitator for PM2.5 and PM1 particles was 99.1% and 98.8%, compared to 99% and 98.1% of two-field electrostatic precipitator, respectively. The most important result of this research is that the replacement of the first field of electrostatic precipitator by an electrostatic agglomerator does not change the overall collection efficiency of the system but the power consumption of electrostatic agglomerator can be 10–50 times lower than by the replaced field of electrostatic precipitator.

Ultrafine Particle Collection Performance of a Two-Stage ESP With a Novel Mixing-Type Charging Stage Using Different Geometries and Electrical Conditions

We improved the two-stage electrostatic precipitator (ESP) developed for information technology manufacturing with highly corrosive and explosive gases by adding a novel mixing-type charger to generate unipolar ions outside of the gas duct and inject them into the main gas flow using an additional electric field. The charging stage (100 × 100 × 400 mm3) is composed of a brush-type charger located outside of the upper part of the charging stage and two parallel plates with an additional electric field. Downstream of the charging stage is a typical collection stage with parallel plates and a collection area of 0.1 m2 at 50 L/min. Electrical and particle removal characteristics of the ESP were evaluated using ultrafine particles and varying the thickness, hole size, and electrical connections in the charging stage. The total air flow rate in the ESP during tests was approximately 50 L/min, with a 10:1 ratio of the main and mixing flows. Using our novel mixing-type charging stage and electrical connections, a high voltage of −5 kV was applied between the brush charger and the grounded upper plate, and a positive high voltage was applied to the lower plate in the charging stage. Collection efficiency ranged from 20% to 90% of 60 nm particles over a wide range of electrical potentials between the upper and lower plates of 0–15 kV.

Two-stage electrostatic precipitator with dual-corona particle precharger for PM2.5 particles removal

The collection efficiency of lab-scale, two-stage electrostatic precipitator comprising a dual-corona particle precharger and parallel-plate particle collector for the removal of PM2.5 particles was investigated in this paper. In the precharger stage, particles conveyed by a gas were electrically charged by ionic current in corona discharge, and in the collection stage, the charged particles were removed from the gas by DC electric field between two parallel-plate electrodes. For the same electrode geometry, the precharger can operate as unipolar or bipolar precharger and/or agglomerator, depending on the mode of electrode supply. The collection efficiency of the system was determined for various modes of precharger electrodes supply with DC or AC voltage. The measurements have shown that number collection efficiency for PM2.5 particles was higher than 80% for the system with dual-corona unipolar precharger supplied with AC voltage and >90% for supply with DC voltage of negative polarity. For the same system, mass collection efficiency was >90% and >96% for PM2.5 particles when precharger was supplied with AC and DC voltages, respectively.

Enhancement of collection efficiency for fly ash particles (PM2.5) by unipolar agglomerator in two-stage electrostatic precipitator

Abstract Semi industrial-scale, two-stage electrostatic precipitation system comprised of unipolar electrostatic agglomerator and electrostatic precipitator was investigated in this paper. In this type of agglomerator, the process of particle charging and their agglomeration is accomplished in the same device. The particles are charged by ion current in alternating electric field, and agglomerated due to their oscillatory motion in this field, perpendicular to the gas flow. The charged and agglomerated particles are collected in the next stage, which is a conventional electrostatic precipitator with spiked wire discharge electrodes and collection electrodes of the sigma type. Collection efficiency of this system was measured for different gas temperatures, different fly ash concentrations and for various magnitudes of AC voltage applied to the agglomerator. Two-stage electrostatic precipitator allows obtaining higher fractional collection efficiency for PM1 and PM2.5 particles than a one-stage electrostatic precipitator. In this type of two-stage electrostatic precipitator with an agglomerator, the number collection efficiency for fly ash particles in PM10, PM2.5 and PM1 size ranges was about 96%, 96% and 94%, respectively, and mass collection efficiency in same size ranges was 98%, 97% and 95%, respectively.

Two-stage electrostatic precipitator with co- and counter-flow particle prechargers

Lab-scale, two-stage electrostatic precipitation system comprising of precharging stage, in which PM2.5 particles are electrically charged, and collection stage, in which the charged particles are removed from the flowing gas by electric field, was investigated in this paper. Two types of electrostatic particle prechargers were compared with respect to the collection efficiency of the system: (1) co-flow precharger, in which ionic current was generated co-currently with the gas conveying the particles, and (2) counter-flow precharger, in which ionic current was generated oppositely to the flowing gas. In each case, the electrodes of precharger were supplied with DC or AC high-voltage in order to compare the effect of discharge mode on the collection efficiency of two-stage electrostatic precipitator. The collection stage was formed by two parallel-plate electrodes connected to DC high voltage source. Plate electrodes without discharge points (spikes) are corona-free electrodes, which prevent the collection stage from electrical discharges, and reduce the probability of back discharge ignition. The back discharge decreases collection efficiency of conventional electrostatic precipitators.It was concluded that the co-flow electrode configuration of the precharger, supplied with DC high voltage, has the highest total number collection efficiency for PM2.5 particles, higher than 95% and the mass collection efficiency larger than 99%. The counter-flow precharger provided only about 90% number collection efficiency of two-stage electrostatic precipitator. It was also shown that by AC electrode excitation, the collection efficiency of the system is lower than for DC supply. The two-stage electrostatic precipitators allowed obtaining higher fractional collection efficiency for PM2.5 particles than other conventional systems and can be recommended as highly effective devices for gas cleaning in power plants or cement industry.

Performance of Ultrafine Particle Collection of a Two-Stage ESP Using a Novel Mixing Type Carbon Brush Charger and Parallel Collection Plates

A novel two-stage electrostatic precipitator (ESP) for information technology manufacturing industries was developed. It uses a mixing type carbon brush charger located outside of the main gas flow duct to completely prevent contact of the polluted gases with the chargers, and applies an additional electric field between the upper and bottom plates of the charging stage to enhance collisions between ions and particles, thereby increasing the particle charges. The performance of the ESP was evaluated experimentally for ultrafine particles with a mean diameter of 100 nm based on number, and of 200 nm based on surface area by varying the voltages of the chargers and for generating the additional electric field, and by varying the number of the chargers. Finally, the collection efficiencies of the ESP were compared to those obtained from Deutch's collection theory using the average experimental particle charges. The total air flow rate used in the tests was approximately 110 L/min with a 10:1 ratio of the main and mixing flows in the ESP, and the applied voltages of the charger and additional electric field were –10 to –22 kV, and –5 to –10 kV, respectively. Collection efficiencies in the ESP were linearly proportional to the increase in the number of chargers and the increase in the applied voltage to the chargers, which in turn were inversely proportional to the increase in the applied voltage used to generate the additional electric field. A collection efficiency of the ESP of > 90% was obtained at a flow rate of 110 L/min, corresponding to flow speeds of approximately 0.19 m/s through the charging stage and 0.23 m/s through the collection cell based on the total particle number at an applied voltage to the triple chargers of –15 kV and an additional electric field between the upper and bottom plates in the charging stage of –6 kV/100 mm.

Ozone Emission and Electrical Characteristics of Ionizers With Different Electrode Materials, Numbers, and Diameters

We investigated the ozone emission characteristics of ionizers differing in terms of the materials, edge numbers, and diameters of their high-voltage electrodes. Our goal was to determine the low ozone emission performance of a carbon brush ionizer that we developed in our previous research on a two-stage electrostatic precipitator (ESP) for cleaning indoor air and exhaust gases from industry. We measured corona discharge current and ozone concentration from the ionizer with different high-voltage electrodes using a digital voltage and current meter and an ozone monitor, while varying applied voltages from 0 to –12 kV at a constant air flow rate of 100 L/min. The corona currents varied from zero to several hundreds of μA depending on electrode material and geometry, while ozone concentrations varied from zero to several hundreds of ppb. Materials did not significantly affect the relationship between voltage and corona current, or ozone emissions from the ionizers. At the same applied voltage, both corona currents and ozone emissions were lower with higher edge numbers, while corona currents increased but ozone decreased with lower high voltage electrode diameters. We conclude that the low-ozone performance of the carbon brush ionizer is due to the effect of thin and/or multiedged electrodes.

Dust particles precipitation in AC/DC electrostatic precipitator

Submicron and nanoparticles removal from flue or exhaust gases remain still a challenge for engineers. The most effective device used for gas cleaning in power plants or industry is electrostatic precipitator, but its collection efficiency steeply decreases for particles smaller than 1 micron. In this paper, fractional collection efficiency of two-stage electrostatic precipitator comprising of alternating electric field charger and DC supplied parallel-plate collection stage has been investigated. The total number collection efficiency for PM2.5 particles was higher than 95% and mass collection efficiency >99%. Fractional collection efficiency for particles between 300 nm and 1 μm was >95%.

Numerical Modelling of ESP for Design Optimization

Electrostatic precipitators (ESP) are widely used for collection of particulate matters. In the present paper, a Computational Fluid Dynamics (CFD) model, based on Eulerian-Lagrangian framework, is used to simulate the gas-particle flow under electric field. A typical two-stage ESP is chosen as a case study and its collection performance is assessed under a series of modified geometric conditions, including inlet pipework, perforated plate, addition of flow baffles, and spatial extent of electric field. The results show that the collection efficiency for PM2.5 can be increased by 20% after optimization.

The Gillings Sampler – An electrostatic air sampler as an alternative method for aerosol in vitro exposure studies

There is growing interest in studying the toxicity and health risk of exposure to multi-pollutant mixtures found in ambient air, and the U.S. Environmental Protection Agency (EPA) is moving towards setting standards for these types of mixtures. Additionally, the Health Effects Institute’s strategic plan aims to develop and apply next-generation multi-pollutant approaches to understanding the health effects of air pollutants. There’s increasing concern that conventional in vitro exposure methods are not adequate to meet EPA’s strategic plan to demonstrate a direct link between air pollution and health effects. To meet the demand for new in vitro technology that better represents direct air-to-cell inhalation exposures, a new system that exposes cells at the air–liquid interface was developed. This new system, named the Gillings Sampler, is a modified two-stage electrostatic precipitator that provides a viable environment for cultured cells. Polystyrene latex spheres were used to determine deposition efficiencies (38–45%), while microscopy and imaging techniques were used to confirm uniform particle deposition. Negative control A549 cell exposures indicated the sampler can be operated for up to 4h without inducing any significant toxic effects on cells, as measured by lactate dehydrogenase (LDH) and interleukin-8 (IL-8). A novel positive aerosol control exposure method, consisting of a p-tolualdehyde (TOLALD) impregnated mineral oil aerosol (MOA), was developed to test this system. Exposures to the toxic MOA at a 1ng/cm2 dose of TOLALD yielded a reproducible 1.4 and 2-fold increase in LDH and IL-8 mRNA levels over controls. This new system is intended to be used as an alternative research tool for aerosol in vitro exposure studies. While further testing and optimization is still required to produce a “commercially ready” system, it serves as a stepping-stone in the development of cost-effective in vitro technology that can be made accessible to researchers in the near future.

Integration of a nonmetallic electrostatic precipitator and a wet scrubber for improved removal of particles and corrosive gas cleaning in semiconductor manufacturing industries

To remove particles in corrosive gases generated by semiconductor industries, we have developed a novel non-metallic, two-stage electrostatic precipitator (ESP). Carbon brush electrodes and grounded carbon fiber-reinforced polymer (CFRP) form the ionization stage, and polyvinyl chloride collection plates are used in the collection stage of the ESP. The collection performance of the ESP downstream of a wet scrubber was evaluated with KCl, silica, and mist particles (0.01–10 μm), changing design and operation parameters such as the ESP length, voltage, and flow rate. A long-term and regeneration performance (12-hr) test was conducted at the maximum operation conditions of the scrubber and ESP, and the performance was then demonstrated for 1 month with exhaust gases from wet scrubbers at the rooftop of a semiconductor manufacturing plant in Korea. The results showed that the electrical and collection performance of the ESP (16 channels, 400 × 400 mm2) was maintained with different grounded plate materials (stainless steel and CFRP) and different lengths of the ionization stage. The collection efficiency of the ESP at high air velocity was enhanced with increases in applied voltages and collection plate lengths. The ESP (16 channels with 100 mm length, 400 × 400 mm2 × 540 mm with a 10-mm gap) removed more than 90% of silica and mist particles with 10 and 12 kV applied to the ESP at the air velocity of 2 m/s and liquid-to-gas ratio of 3.6 L/m3. Decreased performance after 13 hours of continuous operation was recovered to the initial performance level by 5 min of water washing. Moreover, during the 1-month operation at the demonstration site, the ESP showed average collection efficiencies of 97% based on particle number and 92% based on total particle mass, which were achieved with a much smaller specific corona power of 0.28 W/m3/hr compared with conventional ESPs. Implications: Current electrostatic precipitators (ESPs) for the semiconductor manufacturing industry have economic drawbacks. For example, ESPs with metal components require the use of expensive anticorrosive metallic materials to protect against the corrosive gases produced in the semiconductor industry. This paper evaluates a nonmetallic, two-stage ESP that uses a carbon brush charger, carbon forced resin plate ground channels, and polyvinyl chloride collection plates into which aluminum sheets are inserted. This nonmetallic ESP can be used to remove particles and mists from highly corrosive gases in the semiconductor industry as well as in other industries.

Fine Particle Removal Performance of a Two-Stage Wet Electrostatic Precipitator Using a Nonmetallic Pre-Charger

ABSTRACT A novel two-stage wet electrostatic precipitator (ESP) has been developed using a carbon brush pre-charger and collection plates with a thin water film. The electrical and particle collection performance was evaluated for submicrometer particles smaller than 0.01∼0.5 μm in diameter by varying the voltages applied to the pre-charger and collection plates as well as the polarity of the voltage. The collection efficiency was compared with that calculated by the theoretical models. The long-term performances of the ESP with and without water films were also compared in tests using Japanese Industrial Standards dust. The experimental results show that the carbon brush pre-charger of the two-stage wet ESP had approximately 10% particle capture, while producing ozone concentrations of less than 30 ppb. The produced amounts of ozone are significantly lower than the current limits set by international agencies. The ESP also achieved a high collection rate performance, averaging 90% for ultrafine particles, as based on the particle number concentration at an average velocity of 1 m/sec corresponding to a residence time of 0.17 sec. Higher particle collection efficiency for the ESP can be achieved by increasing the voltages applied to the pre-charger and the collection plates. The decreased collection efficiency that occurred during dust loading without water films was completely avoided by forming a thin water film on the collection plates at a water flow rate of 6.5 L/min/m2. IMPLICATIONS Current two-stage electrostatic precipitators (ESPs) have several technical problems such as a drop in collection efficiencies by small-particle re-entrainment during rapping and corrosion of metallic electrodes of the ESPs by corrosive gases. This paper evaluates a novel two-stage ESP that uses a nonmetallic pre-charger and water film collection plates to avoid the above mentioned problems of other ESPs. This ESP can be used not only for industrial applications but also for residential purposes because it has a high removal performance for fine particles with low ozone generation and maintains its efficiency due to the continuous cleaning of the collection plates with water film.

Deflective Behavior of Charged Particles in a Two-Stage Electrostatic Precipitator

Even if smoke, fumes, mist or dust particles are removed by electrostatic precipitators (ESPs), the occurrence of ozone, which is harmful to human body, has to be severely restricted in the indoor environments of hospitals, offices, and workshops. Therefore, the two-stage ESP generating positive corona at the ionizer is typically used because it creates less ozone than the two-stage ESP generating negative corona at the ionizer.<BR> In order to predict the collection performance and the optimal design of the two-stage ESP applied to positive high-voltage, particle concentration is experimentally investigated in this paper. In addition, particle motion within the collector section is also numerically analyzed.<BR> The positive corona discharge current of the ionizer is found to be affected by the applied voltage in the collector section but less so by the particle concentration. Particle concentration shows a minimum near the high voltage electrode of the collector section. The minimum value of the collection efficiency is almost proportional to gas velocity. When the collector length decreases, the minimum value of the collection efficiency increases. Charged particles entering the collector region are linearly deflected towards the grounded plate by an electric field.<BR> From the above experimental and numerical results, two empirical equations on the concentration ratio and the collection efficiency are derived, and are in good agreement with the experimental data.

Single and two-stage electrostatic demisters for biomass pyrolysis application

Single-stage and two-stage tubular electrostatic precipitators were designed. A nitrogen stream containing very fine droplets of fogging oil was forced through the electrostatic precipitator chamber. It was found that 98.6 wt% of the oil droplets present in the turbulent jet were mechanically collected on the inner walls of the test chamber. When the electrode was energized at 13 kV, 92.37 wt% of the droplets that had not been mechanically separated were collected in single-stage mode. The collection efficiency was increased to 93.18 wt%, when the electrostatic precipitator was operated in two-stage mode. Voltage–current ( V– I) characteristics of the single-stage and two-stage electrostatic precipitators were studied in detail for different test conditions. Nitrogen impurities played a major role in determining the V– I characteristics. They became less relevant with the introduction of mist in the nitrogen stream, presumably due to the presence of water vapor in the gas. The two-stage tubular electrostatic precipitator was scaled up and tested on a fluidized bed pilot plant used for the pyrolysis of biomass. A droplet collection efficiency of 95 wt% was observed. Such demisters will extend, to the product recovery train, the process intensification gains of short residence time processes such as fast pyrolysis.

Collection of submicron particles by an electrostatic precipitator using a dielectric barrier discharge

Although dielectric barrier discharge (DBD) in air has been used to clean hazardous air pollutants (HAPs) because of its high electron density and energy, its potential use as precharging dust aerosol particles is not well known. In this work, we measured the size distributions of bimodal submicron aerosol particles and estimated the collection efficiency of the particles for a hybrid two-stage electrostatic precipitator (ESP) comprised of a DBD charger as the particle charger and an ESP as charged particle collector. Nano-sized particles of NaCl (30–100 nm) and DOS (50–800 nm) were generated by evaporation–condensation and atomization, respectively. Various electrical and flow conditions were applied on the DBD charger: AC applied voltage of 9–11 kV, frequency of 60–120 Hz, and air flow rate of 60 – 180 L min - 1 ( 0.048 – 0.016 s of particle residence time). The particle collection efficiencies increased as the AC applied voltage increased at a fixed frequency–flow rate, whereas the efficiencies decreased as the frequency and flow rate increased at a fixed AC power–flow rate and a fixed AC applied voltage–frequency.

Collection Efficiency of Nanosize Particles in a Two-Stage Electrostatic Precipitator

The collection efficiency of particles in the nanosize range (5−100 nm) in a two stage parallel plate electrostatic precipitator is studied by numerical simulation based on a fundamental model of the process. Specifically, the particle charging process is based on Fuchs' theory. For the collecting stage, the model employs an Eulerian approach for the solid−gas flow and explicitly accounts for Brownian and eddy diffusion, turbulent flow, and electrostatic migration. Calculation results indicate that particles in the nanosize range are not uniformly charged. Ultrafine particles with diameter less than 20 nm seldom acquire more than one unit of elementary charge. Larger particles (20−100 nm) may carry several units of charge, depending on the product of ion concentration and charging time. The simulation results also indicate that there is a local maximum in the collection efficiency in the nanosize range, a finding which is consistent with experimental observations reported in the literature. The simulation also points out that the most efficient way to increase the collection efficiency of particles in the ultrafine size range is to enhance the charging process. For particles with larger size, both the parameters in the charging stage (the product of ion concentration and charging time) and those in the collecting stage (electrostatic intensity and length and width of the collecting cell) have an important effect on the overall collection efficiency.

Electrostatic charging of particulates by ionic current in alternating electric field

Charged liquid droplets or solid particles are widely used in industrial electrostatic processes, such as surface coating or painting, particle separation, scrubbing or two-stage electrostatic precipitation, improving their throughput or saving energy. The efficiency of these electrostatic processes can be further improved by maximizing the charge imparted to the particles and minimizing their loss while charging. This can be accomplished by charging the particles by an ionic current in alternating electric field. The paper deals with the alternating electric field charger in which the particles can be charged close to the theoretical Pauthenier limit. In this type of charger, the particles undergo oscillations and the number of particles precipitated on the electrodes is diminished, which was confirmed by the CCD camera recordings. An alternating electric field charger was constructed and mounted in a channel of cross section of 160×160 mm. Airborne MgO particles of mean diameter of 10 μm were charged in this charger up to 5 fC, and their specific charge was in the range of 1–3 mC/kg.