Development of high collection efficiency ESP by barrier discharge system

Effect of obstructions on the particle collection efficiency in a two-stage electrostatic precipitator

The collection of low resistive particles from diesel engine emission is difficult by the conventional electrostatic precipitators (ESPs). The low resistive diesel engine particles are detached from the collection plate, which causes the dust reentrainment, resulting in poor collection efficiency. The new electrohydrodynamically (EHD) assisted ESP (EHD ESP) was developed to minimize reentrainment. The EHD ESP utilizes the ionic wind, combined with electrostatic force to transport the charged particles into the pocket zone attached to the collection plate effectively. The pocket zones are designed as zero electrostatic field, i.e., no electrostatic repulsion force acting on particles, so that no reentrainment takes place. The electrode position was designed to achieve an optimum electrode location with respect to pocket position, which was determined by observing EHD streamlines and particle collection efficiency. The particle size dependent collection efficiency was obtained using scanning mobility particle sizer (SMPS).

Two-stage vs. two-field electrostatic precipitator

The influence of design parameters on the occurrence of shielding in multi-electrode ESPs and its effect on performance

In this paper, a numerical model was developed to describe the wire-plate electrostatic precipitator, commonly called electronic air cleaners. Electrostatic precipitator have been widely used to control particulate pollutants, which adversely affect human health. In this model, the complex interactions between fluid dynamics, electric fields and particle dynamics are considered. Therefore different approach methods are used in this study for each field, Eulerian reference frame was used for the fluid flow field and the electric field, Lagrangian reference frame used for the particles trajectories. In order to describe corona phenomena around high voltage electrode, electric field and ion current density field in electrostatic precipitator are numerically calculated using the iterative method for corona discharge model suggested by Kim (2010). The most important concept in electrostatic precipitator is the electric force applied to particles through the particle charging phenomena. The charge acquired by the particle in the corona region was obtained by combining the field charge, the diffusion charge and the time available for charging being the residence time of the particle in the corona region. In order to simulate more accurately, the charging model suggested by Lawless (1996) is used for the charging phenomena of particles by corona discharge because this model was designed to predict combination effect of diffusion charge and field charge. The diminution of particle concentration along the collection plate was derived from Deutsch’s theory, and migration velocity of the particle was developed from the condition that the magnitude of Coulomb force is equal to that of Stoke’s resistance force. This model is implemented by UDF in commercial software Fluent and validated with experimental and numerical results from literatures. CFD results had been compared with various experimental data obtained by Penney&Matick, Parasram and Kihm. Our results shows good agreement in terms of distributions of electric potential, current density, electrohydrodynamic flow pattern, and particle trajectories as well as corona current and collection efficiency. From this simulation, the effect of wire arrangement on electrostatic precipitator characteristics and particle charging are investigated. Both inline and staggered arrangements of wire electrode have been considered for fixed values of gas velocity equal to 2m/s. Applied voltage on wire electrode varies 6∼13kV and particle diameter is 4μm. For low voltage condition, staggered arrangement of wire electrode caused the turbulent effect so that collection efficiency increase more than inline arrangement. However, collection efficiency decrease in high voltage condition because electric force applied on particles passing between the wire electrodes is canceled out by both side wire electrodes.

An electrostatic precipitator (ESP) has such advantages as high collection efficiency of high concentration particles and low pressure loss. However, it can cause the re-entrainment phenomenon, and the hole-type ESP is considered to suppress this phenomenon. The authors developed a parallel-plate hole-type ESP after investigating the characteristics of collection efficiency with the hole-type electrode having a double-cylinder. In this study, the authors examined the right conditions for particle collection and electrode configuration. In the case of large particles, the collection efficiency decreased when the discharge current increased. However, with respect to the particle size of 300nm or less, the greater collection efficiency was achieved when the discharge current increased. The collection efficiency was improved by moving the position of the needle electrode toward the ESP outlet. The collection efficiency also reached the highest point when the hole diameter was 5mm.

ABSTRACTThe fine particles are considered a significant pollution problem. The wet electrostatic precipitators (ESPs) have advantages of efficient collection of the fine particles with lower pressure drop and eliminating reentrainment. The wetting properties of the collector surfaces have significantly important effect on wet ESPs’ stable and secure operation. The modified rigid collector (MRC) was modified by coating specific vinyl ester resin composites and loose glass fiber cloth over the conventional carbon steel in a certain way. The rigid collector surfaces before and after modification had been characterized by scanning electron microscopy (SEM) and interface tensiometer. The effect of operating temperatures on the wetting properties of the rigid collector surfaces before and after modification was investigated. The temperature range was 40~90 °C, and the wetting properties contained liquid holdup, surface flow rate, film rate, average film thickness, and critical saturation time. The modified rigid collector surface exhibited excellent wetting properties at the operating temperatures. The fine particles collection performance compared among the MRC, the conventional rigid collector (CRC), and the flexible collector (FC) in the wet ESPs was investigated. The effects of the applied voltage, the water film, corona power, and the specific collecting area on the fine particles collection were evaluated. The modified rigid collector provided high fine particles collection effect with lower energy and water consumption.Implications: To improve the submicron particles collection efficiency and decrease energy and water consumption, the formation of uniform water film over the collector surfaces has been widely studied. The modified rigid collector was modified by coating specific vinyl ester resin composites and loose glass fiber cloth (ERGF) over the conventional carbon steel (CCS) in a certain way. The modified rigid collector surface exhibited excellent wetting properties. The wet ESPs by the modified rigid collector exhibited significantly higher particles collection efficiency than by the conventional rigid collector.

Harmful substances, such as particulate matter (PM), nitrogen oxides, and sulfur compounds in exhaust gas emitted from marine diesel engines have a great impact on the air environment. Among them, especially black carbon in PM has a negative effect on global warming. The exhaust gas from marine diesel engines using fuels containing heavy fuel oil has a high PM concentration and high temperature. Therefore, a commonly used diesel particulate filter is not suitable for collection because it tends to cause clogging and reduce efficiency. Furthermore, it is often the case that ships are at sea for more than one month, so it is difficult to replace the filter, that is, maintenance is difficult. On the other hand, an electrostatic precipitator (ESP) has the advantages of a simpler structure, lower pressure loss, and higher collection efficiency of high concentration particles. This suggests that the ESP is suitable for collecting harmful substances from the marine diesel exhaust gas. At high temperatures, corona discharge is unstable, and a flashover tends to occur at low applied voltage. Therefore, it is necessary to study the stable corona discharge generation range for the stable operation of the ESP. The purpose of this research is to analyze the optimal electrode structure and its corona discharge characteristics under the simulated exhaust gas of a diesel engine in the range of 100 °C – 400 °C using a negative dc power supply.

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.

BackgroundA newly designed electrostatic precipitator (ESP) in tandem with Versatile Aerosol Concentration Enrichment System (VACES) was developed by the University of Southern California to collect ambient aerosols on substrates appropriate for chemical and toxicological analysis. The laboratory evaluation of this sampler is described in a previous paper. The main objective of this study was to evaluate the performance of the new VACES-ESP system in the field by comparing the chemical characteristics of the PM collected in the ESP to those of reference samplers operating in parallel.ResultsThe field campaign was carried out in the period from August, 2007 to March, 2008 in a typical urban environment near downtown Los Angeles. Each sampling set was restricted to 2–3 hours to minimize possible sampling artifacts in the ESP. The results showed that particle penetration increases and ozone concentration decreases with increasing sampling flow rate, with highest particle penetration observed between 100 nm and 300 nm. A reference filter sampler was deployed in parallel to the ESP to collect concentration-enriched aerosols, and a MOUDI sampler was used to collect ambient aerosols. Chemical analysis results showed very good agreement between the ESP and MOUDI samplers in the concentrations of trace elements and inorganic ions. The overall organic compound content of PM collected by the ESP, including polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and alkanes, was in good agreement with that of the reference sampler, with an average ESP -to -reference concentration ratio of 1.07 (± 0.38). While majority of organic compound ratios were close to 1, some of the semi-volatile organic species had slightly deviated ratios from 1, indicating the possibility of some sampling artifacts in the ESP due to reactions of PM with ozone and radicals generated from corona discharge, although positive and negative sampling artifacts in the reference filter sampler cannot be ruled out.ConclusionThe very good overall agreement between ESP and reference samplers makes it an attractive alternative to filters and biosamplers for chemical and toxicological evaluation of PM properties, including the possibility of conducting direct in vitro cell exposures. Moreover, the concentration enrichment of ambient aerosols by the VACES allows for short-term exposure studies, which preserve cell viability and enable studies to PM generated from specific sources and-or formation mechanisms in the atmosphere.

SUMMARYAn electrostatic precipitator (ESP) is a means to collect particulate matter (PM). They are characterized by a high total particle collection efficiency with a low pressure drop. The particle behavior in ESP depends on the particle characteristic, electric field, space charge, and flow pattern. It is important to understand the particle behavior in ESP. Particle image velocimetry (PIV) was used to grasp the particle behavior in ESP. In this paper, results of PIV of the particle flow velocity fields in a wire‐to‐plate type ESP model are presented. The ESP was an acrylic parallelepiped with a wire electrode and plate collecting electrode. The positive and negative dc voltages were applied to the wire electrode, placed at right angles to the main gas flow. The obtained results show that the particle flow velocity was increased with increasing discharge current. This is attributed to increase in ionic wind. The particle velocity right under of the wire electrode was the fastest.

Electrohydrodynamic gas flow in a positive polarity wire-plate electrostatic precipitator and the related dust particle collection efficiency

This paper explores the collection efficiency of Electrostatic precipitator (ESP) of a laboratory scale model which is geometrically similar to the industrial ESP of a local coal based power station. The variable fly ash velocity is used to determine the collection efficiency of an ESP. The applied voltage and current are being kept constant during different field test. Moreover a test run will be conduct to see the collection efficiency without applying high voltage. The experimental result shows that ESP collection efficiency is higher at lower fly ash velocity and suddenly decreases after a range of velocity. To confirm the validity of collection efficiency a mathematical model has been built and verified with experimental data. In addition, a test run is conducted without the high voltage (HV) supply to see the ability of capturing fly ash particles by keeping all other parameter same. The peak efficiency of ESP found in this experiment is 99.87%.

The electrostatic precipitator (ESP) is used all over the world to clean particles from contaminated industrial and domestical air. Recent observations and experiments however are disturbing. These indicate that, when capturing an oil mist or possibly droplets in general, phenomena occur that can cause the ESP to generate rather than remove (sub)micron particles. At spots where the electric field strength is high enough, collected droplets deform into a conical shape, the so-called Taylor cone. At the tip of this cone a jet is formed that breaks up in an enormous number of (sub)micron-sized droplets. In the ESP, this occurs at the charging corona wires and at sharp points on the collector plates. Because a part of the ESP energy is thus being used to spray droplets electrically, less energy can be utilized for ionization to charge incoming particles. Simultaneously, the active field strength between the collector plates decreases. These factors result in a substantial decrease in collection efficiency over the total size range. In addition to this overall decrease in efficiency, particles in the order of 1 μm are generated from the tip of the developed Taylor cones. Most of these generated droplets will be trapped in the ESP, but droplets formed close to the exit of the plates, depending on the configuration of the ESP, will be discharged from the precipitator. Thus, for particles of this size, the ESP is a particle generator rather than a particle remover.

Recent concerns of environmental protection encourage the use of a compact indoor air cleaner and various types of electrostatic precipitators (ESPs) have been manufactured. Although a wide range of airborne particles can be collected effectively with an ordinary ESP using a positive DC corona, it is difficult to remove gaseous compounds such as tobacco smoke which induces submicron particles and an offensive odor. In the present paper, the authors investigated the collection of submicron particles and the decomposition of acetaldehyde (CH/sub 3/CHO) using a commercial ESP and a nonthermal plasma reactor because the offensive odor of tobacco smoke is mainly caused by acetaldehyde molecules. For an ESP, the authors evaluated the particle-size dependent collection efficiency using a monodispersed aerosol because little investigations have been conducted in this area. As for acetaldehyde decomposition, more than 90% of decomposition efficiency was obtained with the use of the nonthermal plasma under dry air. However, the decomposition efficiency was deteriorated under humidified conditions. The higher collection efficiency was achieved for a particle size of 0.6 /spl mu/m than that of 0.3 /spl mu/m although the overall over collection efficiency exceeded more than 99%. The combination of ESP and nonthermal plasma technologies leads to the breakthrough of the conventional indoor electronic air cleaner technology.