Theory and application of cyclone impulse electrostatic precipitation

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.

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.

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 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.

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 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).

Current trends observed in air pollution control technology are closely related to the development of new, more efficient hybrid systems, i.e., those, which simultaneously utilize two or more physical mechanisms for dust or gaseous contaminants removal. These systems can operate more economically than conventional devices, especially in the removal of PM2.5 particles. The electrostatic scrubber (electroscrubber), discussed in this paper, is one of such types of devices, which combines advantages of electrostatic precipitators and inertial wet scrubbers, and removes many shortcomings inherent to both of these systems operating independently. The electroscrubber is a device in which Coulomb attraction or repulsion forces between electrically charged scrubbing droplets (collector) and dust particles are utilized for the removal of particles from a gas. Unlike wet electrostatic precipitators in which particles are precipitated only on the collection electrode, in electroscrubbers, the collection of dust particles takes place in the entire precipitator chamber. Compared to inertial scrubbers, the electroscrubbers can operate at lower droplet velocities, but the collection efficiency for a single droplet can be larger than 1. The paper reviews the state-of-the-art of wet electrostatic scrubbing (electroscrubbing) technique used for gas cleaning from dust or smoke particles. Three groups of problems are discussed: (1) The fundamental problems concerning the charged dust particle deposition on a charged collector, usually a drop, with a focus on different models describing the process. (2) The experimental works of fundamental importance to our knowledge referring to the scrubbing process, which can be used for validating the theory. (3) The laboratory demonstrations and industrial tests of different constructions of electroscrubbers designed for effective gas cleaning. The electroscrubber is not designed to replace wet or dry electrostatic precipitators but can be used as a complementary device following the last stage of conventional electrostatic precipitator, which helps to remove submicron particles. It was shown in the paper that a higher collection efficiency of an electroscrubber could be obtained for higher values of Coulomb number (i.e., higher electric charges on the collector and particle), and for a Stokes number lower than5 (i.e., low particle-collector relative velocity).

In this study, two different dust collectors, one based on an inertial separator and the other based on an electrostatic precipitator (ESP), were developed in order to reduce brake wear particulate matter (PM) emissions. Additionally, the collection efficiencies for brake wear particles (BWPs) of the inertial separator and the ESP were evaluated according to brake pad type. In the case of the inertial separator, the BWP collection efficiencies for the low-metallic (LM) and non-asbestos organic (NAO) pads were similar, and the cut-off size at 50% collection efficiency (D50) was 2.2 µm. The ESP was designed without an additional electrostatic charging device because naturally induced electrostatic charging occurred due to the friction between the brake disc and pad. The BWP collection efficiency of the ESP was higher for NAO pad than for LM pad because the BWPs generated from the NAO pad contained a relatively low iron (Fe) component compared to that of the LM pad, thereby generating more frictional electricity. The maximum ESP collection efficiencies of the BWPs generated from the LM and NAO pads were determined to be 60% and 75%, respectively, and the remaining BWPs that were not collected were presumed to be particles that were not frictionally charged.

One of the electrostatic precipitator (ESP) applications is the cleaning in superhighway tunnels. In superhighway tunnels, contaminants in the air are carbon particles, NO/sub x/ etc. The ESP consists of the precharger and collecting section. The ESP can little remove NO/sub x/, when corona discharge is used as a precharger. The autors suggest a barrier discharge-type precharger instead of corona discharge. In this work, experiments were carried out using small two-stage type ESP with barrier discharge. As a result, it was shown that the particle collection efficiency and NO/sub x/ removal rate were high in barrier discharge type ESP.

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.

A new concept of electrostatic precipitator (ESP), named a Staged ESP (an Energy & Environmental Research Center proprietary), was conceived in June 2004. The concept is based on a simple design that can be retrofitted on existing coal-fired power plants to provide high particulate matter (PM) collection efficiency without compromising reliability. A prototype of Staged ESP was designed, fabricated, and tested in two different combustion coal flue gases with different fly ash resistivities. Several design parameters of the Staged ESP were evaluated under various operating conditions to optimize PM collection performance. A set of particulate sampling data, including aerodynamic particle sizer, scanning mobility particle sizer, and U.S. Environmental Protection Agency Method 5 data, was collected to determine PM emissions of the Staged ESP configurations. These data were compared against data collected with a conventional ESP configuration. Compared to PM capture performance in conventional ESPs, an additional 30% to 70% reductions on total PM emissions were achieved for Staged ESPs in flue gas with medium- to high-resistivity fly ashes. Experimental data proved that the Staged ESP concept is capable of achieving higher PM collection efficiency, especially for particles in the submicrometer size range typically thought difficult to capture in an ESP.

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.

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.

The evaluation of drift velocity of charged particulate in a laboratory scale electrostatic precipitator (ESP) will be discussed. The collection efficiency of an ESP depends on a large number of electrohydrodynamic parameters. The main mass transfer parameter in an ESP is the drift velocity of particulate which is determined by gravitational force, Coulomb force, drag force, inertial force of added mass, and lift force. The calculated migration velocity, using the fimdamental motion equations of particles in an electrohydrodynamic field, differs very much from the effective drift velocity obtained experimentally. In the paper we develop a new concept of drift velocity calculation using the theory of dimensional analysis and the experimental data of collection efficiency in a laboratory scale ESP. As a result we obtained a universal relationship between drift velocity and a proposed ESP similarity number.

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.