A Numerical Simulation of Diffusion Charging Effect on Collection Efficiency in Wire-Plate Electrostatic Precipitators

In this study, a mathematical model was introduced to calculate the collection efficiency of dust particles in a wire-pipe single-stage electrostatic precipitator (ESP). The aerodynamic diameters of these particles are less than 10 m (PM10). The mathematical model, using combined Deutsch-Anderson Equation, considers coupling effects among gas flow field, electric field and particle field. A simplified 2-D ESP model was established using GAMBIT and a software application (FLUENT) was used to investigate the effects of the diffusion charging on PM10 collection efficiency. Furthermore, the effects of different variables such as applied potential, gas velocity and particle distribution on diffusion charging and collection efficiency were also studied. The numerical results indicate that grade efficiency of ESP satisfies U-shape distribution. It was further demonstrated that, for particles with a diameter of less than 10 micrometers, the influence of diffusion charging on PM10 collection efficiency is significant with either decreasing applied potential or increasing gas velocity of the inlet. Moreover, the reduction of size distribution parameter and mean diameter of particles results in the phenomenon that diffusion charging has a more significant effect on PM10 overall efficiency, but there is no guarantee for improving overall collection in the case.

The PM10 collection efficiency of a wire-cylinder electrostatic precipitator (ESP) was studied by means of a developed mathematical model, including the multi-field coupling between the gas flow field, the particle dynamic field and the electric field, and applying the Deutsch–Anderson Equation. The diffusion charging mechanism was considered due to the diameter range of PM10. The investigated variables were the applied potential, the gas velocity and the particle distribution. Numerical results indicate that the diffusion charging has significant influence on PM10 removal performance and the effect is more obvious with the decreasing diameter, and that the PM10 collection efficiency increases with the increasing applied potential and the increment of collection efficiency is more significant at lower voltage. Moreover, as the gas velocity at inlet decreases, collection efficiency of PM10 will increase. Finally, the overall efficiency increases with increasing the mean diameter of particle distribution. The research results can provide theoretical and technical references for the design of novel ESP aiming at economy and environment protection.

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.

The collection efficiency of many electrostatic precipitators (ESPs) must be improved in order to fulfill the particulate emission standard, which has become increasingly rigorous. According to classical collection theory, decreasing the gas velocity for an electric field is one of the most effective methods of enhancing the collection efficiency. Thus, we proposed a side-flow ESP, which, compared to its conventional counterpart, requires a far lower gas velocity for the electric field when the gas flow rate is constant. First, using aerodynamics, a theoretical expression of the collection efficiency and dust re-entrainment lift force was derived for a turbulent flow. The calculations indicated that a greater increase in efficiency was achieved by decreasing the gas velocity, which potentially reduces dust re-entrainment, than by lengthening the electric field. To confirm the advantages of the side-flow ESP, the collection efficiency and dust re-entrainment were measured in comparison experiments with a conventional ESP, in which talc powder with a medium diameter of 11.6 µm was used as the test dust. The dust concentration at the inlet averaged ~1400 mg m–3, and the strength of the electric field ranged approximately from 3 to 4 kV cm–1. The experimental results indicated that the emitted concentration and the dust re-entrainment were 45% and 42% lower, respectively, for the side-flow ESP than for the conventional ESP at the same gas flow rate.

Collection of inertialess particles on elliptical and irregular cylinders with electrical forces and gravitation

In this work, the effect of electrohydrodynamic (EHD) secondary flow on the wire-plate type electrostatic precipitator partial collection efficiencies for submicron and ultrafine dust particles in the range from 0.01 μm to 10 μm have been calculated based on the cross-sectional averaged values of numerically obtained ion density, electric field and gas velocity and coupled together with particle surface charge models based on the modified diffusion and field particle charging rates. The results show that the particle surface charge of particles between 0.01 μm and 1 μm are not significantly influenced by EHD secondary flow, however, EHD flow do perturbing the local surface charge and local particle collection efficiency. The net effect on the partial collection efficiency is not significant for the submicron size particle range.

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.

Since 1995, DOE has supported development of a new concept in particulate control, called the advanced hybrid particulate collector (AHPC). The AHPC combines the best features of electrostatic precipitators (ESPs) and baghouses in a unique configuration, providing major synergism between the two collection methods, both in the particulate collection step and in the transfer of dust to the hopper. The AHPC provides ultrahigh collection efficiency, overcoming the problem of excessive fine-particle emission with conventional ESPs, and it solves the problem of reentrainment and re-collection of dust in conventional baghouses. The AHPC appears to have unique advantages for mercury control over baghouses or ESPs as an excellent gas-solid contactor. The objective of the three-task project is to demonstrate 90% total mercury control in the AHPC at a lower cost than current mercury control estimates. The approach includes bench-scale batch testing that ties the new work to previous results and links results with larger-scale pilot testing with real flue gas on a coal-fired combustion system, pilot-scale testing on a coal-fired combustion system with both a pulse-jet baghouse and an AHPC to prove or disprove the research hypotheses, and field demonstration pilot-scale testing at a utility power plant to prove scaleup and demonstrate longer-term mercury control. This project, if successful, will demonstrate at the pilot-scale level a technology that would provide a cost-effective technique to accomplish control of mercury emissions and, at the same time, greatly enhance fine particulate collection efficiency. The technology can be used to retrofit systems currently employing inefficient ESP technology as well as for new construction, thereby providing a solution to a large segment of the U.S. utility industry as well as other industries requiring mercury control.

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.

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).

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.

Electrostatic precipitators (ESPs) are among the most widely used devices for removing dust, fumes, and aerosols from gas streams. The efficiency of particle collection depends on several interrelated factors, necessitating continuous monitoring and optimization. Among these, particle resistivity plays a key role in determining ESP performance, especially in relation to the behaviour of the dust layer deposited on the collecting electrode. High-resistivity particles, such as PVC, are difficult to charge and tend to retain their charge upon contact with the grounded electrode. This leads to an accumulation of surface potential and the onset of the back corona phenomenon, which significantly reduces collection efficiency. To optimize filtration, it is essential to maintain a high-intensity electric field that enhances particle charging and collection—particularly for high-resistivity materials—without triggering electrical arcing. This study introduces a novel experimental method for controlling a wire–cylinder type ESP. The method is based on the automatic adjustment of the high-voltage supply using a motorized potentiometer (PM), which ensures the discharge current remains at a predefined set point. The proposed approach allows for the in-situ estimation of the surface potential and resistivity of the pollution layer under electrical discharge conditions, across different particle sizes.

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

This study investigated the performance of a novel electrostatic precipitator. This system consists of a charging section and collection section with glass plates that have discharge electrodes on them. Biased alternating current (AC) with high voltage was intermittently applied to the discharge electrodes to build up charges with polarity similar to the bias on the dielectric surface to create a strong electric field between the electrodes and the surface. This electric field attracts the soot charged in the charging section to the glass surface, where plasma can cause the oxidative decomposition of the collected soot. In this system, the intermittent mode of voltage application plays a key role in the collection of particulates. The collection efficiency of the reactor was estimated with an OFF duration in the range of 0–1990 ms and an ON duration of 10 ms. The surface potential distributions of the dielectric substrates used in the reactor were measured with respect to the time duration after the voltage application had been completed. Thus, it was found that the collection efficiency was influenced by the OFF duration, because the surface charges on the glass plates had a certain lifetime.

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.