Field Of Electrostatic Precipitator Research Articles

Effect of Magnetic Field on Corona Discharge Under Airflow

Corona discharge under airflow is extensively researched due to its wide applications in the fields of electrostatic precipitator, flow control, thermal management, and so on. The adjustment of discharge characteristics has been an important research topic in recent years. In this article, a magnetic field is applied as a method to adjust the characteristics of corona discharge under airflow. The experimental result illustrates that the intensity and direction of the magnetic field would influence the turning point of the discharge state under airflow, and the corresponding discharge image and Trichel pulse characteristics, such as amplitude and frequency, would also be changed. The physical mechanism for this phenomenon is analyzed by considering the magnetic force of the corona discharge. With increasing magnetic field intensity, the pressure in the discharge space would change and the airflow state and the discharge process, as the ionization process and the attachment process, would be influenced. The overall characteristics of discharge under airflow would be adjusted by the magnetic field. The results illustrated that the magnetic field is possibly utilized to improve the application of corona discharge under airflow.

Numerical study on the effect of staggered wire electrodes in an electrostatic precipitator

In this paper, a numerical model is developed to describe the wire-plate electrostatic precipitator used in industrial application for air cleaning. The complex interactions between fluid dynamics, electric fields and particle dynamics are considered. Therefore, the combined Eulerian and Lagrangian approach is used in this study. 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 [1]. The charging model suggested by Lawless [2] is used for the charging phenomena of particles by corona discharge because it was designed to predict combination effect of diffusion charge and field charge. The numerical model in this study is implemented by UDF in commercial software FLUENT and validated with experimental and numerical results from literatures. The effects of wire arrangement on electrostatic precipitator characteristics are investigated. Both inline and staggered arrangements of wire electrode have been considered for fixed value of gas velocity equal to 2 m/s. Applied voltage on wire electrode is varied in the range of 6 to 13 kV and particle diameter is 4 µm. For low voltage condition, staggered arrangement of wire electrode caused the turbulent effect so that the collection efficiency increases more than inline arrangement. However, the collection efficiency decreases in high voltage condition because electric force applied on particles passing between the wire electrodes is canceled out by both side wire electrodes.

Nonmonotonous Phenomenon of Corona Discharge Characteristics Under Different Airflow Rates

Corona discharge is extensively researched due to the wide applications in the fields of electrostatic precipitator, flow control, thermal management, and so on. Previous researches observe that the characteristics of the corona discharge, such as the average current in the Trichel pulse regime, could be influenced by the airflow velocity. In this paper, the effect of the airflow rate on the corona discharge is further investigated by using a needle-mesh discharge structure. The experimental results show that the discharge is transferred from a large amplitude, long pulse interval time condition to a small amplitude, short interval time condition when increasing the airflow rate and, at the same time, the discharge region is shrunk toward the centerline of tube channel (i.e., shrinking regime). However, after a stable regime around a certain airflow rate, the above-mentioned parameters are changed toward the opposite direction and the discharge region is expanded, when further increasing the airflow rate (i.e., expanding regime). This nonmonotonous phenomenon has not been observed in literature before, and we further investigate it under different tube channel diameters. It is found that, under a larger tube channel diameter, the transition point (corresponding to the minimum pulse amplitude and interval time) moves toward a larger gas flow rate. The physical mechanisms for this phenomenon are analyzed by considering the transport effect by airflow under different Reynolds numbers. It can be caused by a comprehensive effect of the mass transfer, heat transfer, movement process of particles, and frictional loss in the discharge space. The phenomenon revealed in this paper is possibly utilized to improve the application of corona discharge under airflow.

An experimental investigation on the effect of particle size into the flowability of fly ash

In this paper, physical properties and flow properties of fly ash collected from seven fields of Electro-Static precipitator (ESP) hoppers of a coal fired thermal power plant have been investigated by using Powder Flow Tester operating based on Jenike's methodology. It was experimentally observed that the fly ash from different ESP hoppers have different flow properties. Various powder flow properties, such as cohesion, unconfined yield strength, angle of internal friction and wall friction angle were found to have power law variation with median particle size. Critical particle size, which caused a change in the flow properties of fly ash from cohesive to easy flowing, was experimentally evaluated and validated. Hopper half angle and critical outlet opening trends were determined for different fly ash samples to achieve mass flow condition for discharge. Additionally, two power law models were also developed for estimating hopper half angle and critical outlet openings using powder flow properties.

Modeling flow properties of fine dry powders using particle morphological properties and its effects on geometry of fly ash evacuation hoppers

ABSTRACTThis paper results from an ongoing effort to correlate the physical properties of powders at a fundamental level with their bulk behavior. Cohesion and unconfined yield stress are the measure of inter-particle forces of attraction in the bulk powder. The existing model for cohesion does not include important bulk properties, such as particle size distribution, tapped density, and prevailing applied stress. In the present paper, flow properties of 25 bulk solids (different cement and fly ash samples) have been evaluated using a ring shear tester and the products have been characterized according to their flowabilities. Models for cohesion and unconfined yield strength have been developed in this study by taking into account the effects of particle size distribution, tapped bulk density and pre-shear stress. The newly developed models have provided good fit to the experimental data. The effect of these flow properties on the design of hoppers have been investigated for fly ash samples collected from seven consecutive electrostatic precipitator (ESP) hoppers of a coal fired thermal power station. The results show that fly ash from the rear end ESP hopper would require higher amount of opening size compared to the first or second field of ESP to ensure proper mass flow condition is achieved at all the ESP hoppers.

Finite element method investigation of electrostatic precipitator performance

AbstractThis paper aims at analysis of the monopolar ionized field in electrostatic precipitator. A numerical model for simulating precipitation of particles in electrostatic precipitator is discussed in this paper. It includes all essential phenomena affecting the process.An iterative finite‐element technique is used to solve Poison's equation. We proposed the introduction of a potential corresponding to the critical minimum ionization field directly in the finite element formulation as a Dirichlet condition. The theoretical migration velocity is obtained by balancing the drag force with the Coulomb force or electrostatic force acting on a particle. We used the model introduced by Cochet for predicting a particle charge. The model assumes that a particle of the same size attains an equivalent maximum amount of charge for a charging time equal to infinity. Particles influence the electrical field, flow field, electrical migration velocity, gas discharge, particle charge and collection efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

Changes in trace element contents in ashes of oil shale fueled PF and CFB boilers during operation

Two oil shale combustion technologies, pulverized firing (PF) and circulated fluidized bed (CFB) were compared with respect to partitioning of selected elements (Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Rb, Sb, Sn, Sr, Th, Tl, U, V, and Zn) in the ashes along the flue gas ducts. The ash samples were characterized by high-resolution ICP-MS. The average contents of toxic heavy metals in fly ash samples from the CFB boiler are lower compared to the PF boiler. Main differences in trace element contents between combustion technologies were as follows: Cd content in the fly ash samples of PF boiler was up to 0.9mg/kg while in CFB boiler it remained below 0.1mg/kg in all analyzed ash samples; Hg was observed in the ashes of electrostatic precipitator (ESP) of CFB boiler while in the PF boiler it was close to or below detection limit. In the PF boiler content of Sn was detected only in the ashes of ESPs, while in CFB boiler it was evenly distributed between bottom and fly ash samples. Highest content among heavy metals in ash samples was observed for Pb in the last field of ESP of the PF boiler (142mg/kg).

A Comprehensive Analysis of the Particle Size and Shape of Fly Ash from Different Fields of ESP of a Super Thermal Power Plant

Fly ash samples collected from the hoppers of various electric fields of electrostatic precipitator attached to two different units (1 and 2) of a Super Thermal Power Plant were critically examined in respect of their particle size distribution and shape. Particle size analysis of each of the samples collected over a period of three months from the dust hoppers of seven fields of each unit (unit 1 and 2) reveals that in general ash particles collected from the hoppers of field 1 are coarser and show bimodal distribution. Ashes from hoppers for other fields of electrostatic precipitator are finer. Ashes from unit 2 have a smaller particle size than those of unit 1. The particle size of the ashes decrease along field 1 to field 7 for both units, with field 7 ashes being the finest. Ashes from fields 5–7 of both the units contain significant amounts of ultrafine particles (particle diameter ϕ < 5 μm). Shape analysis reveals that ash particles of fields 1 and 2 are irregular in shape and the rest are spherical. The spherical nature of ash particles increases in the sequence of fields 3–7. Ashes of fields 6 and 7 of each unit are suitable for use as fillers/partial replacement of cement in high performance concrete due to an enhanced “ball bearing effect.”

Leaching characteristics of heavy metals in fly ash from a Chinese coal‐fired power plant

AbstractChina is the largest coal ash producer in the world. Hydraulic ash transport systems are used in most coal‐fired power plants, which lead to serious water pollution due to leaching of trace elements. The investigation on the leaching behavior of trace contaminants from coal ash is critical to environmental risk assessments. Batch leaching tests have been performed on the fly ash collected from each field of the electrostatic precipitator (ESP) of a coal‐fired power plant to study the leaching characteristics of Cd, Cr, Pb and V. Leaching solutions included HCl solution of initial pH = 4 and NaOH solution of pH = 10. The liquid/solid (L/S) ratio was about 4:1 in all leaching tests. Fourteen leaching time intervals were selected, ranging from 15 min to 7 days. The results show that under studied experimental conditions, Cr has a relatively higher leachability in the acid‐leaching solution, while Pb has a higher leachability in the alkaline solution. With the increase of leaching time, the leachability of Cr in each ash sample increases obviously. Within the same time interval, Cr in the ash sample from the last field of ESP has the highest leachability. The concentration of Cd in FA3 is the highest, but the leachability of Cd for FA3 is not the highest among the three ash samples. The concentration of V in FA1 is the highest; no increased trend with leaching time has been found in the experiment. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Laser flow visualization and velocity fields by particle image velocimetry in an electrostatic precipitator model

Although improving electrostatic precipitator (ESP) collection of fine particles (micron and submicron sizes) remains of interest, it is not yet clear whether the turbulent flow patterns caused by the presence of electric field and charge in ESPs advance or deteriorate fine particle precipitation process. In this paper, results of the laser flow visualization and Particle Image Velocimetry (PIV) measurements of the particle flow velocity fields in a wire-to-plate type ESP model with seven wire electrodes are presented. Both experiments were carried out for negative and positive polarity of the wire electrodes. The laser flow visualization and PIV measurements clearly confirmed formation of the secondary flow (velocity of several tens of cm/s) in the ESP model, which interacts with the primary flow. The particle flow pattern changes caused by the strong interaction between the primary and secondary flows are more pronounced for higher operating voltages (higher electrohydrodynamic number NEHD) and lower primary flow velocities (lower Reynolds number Re). The particle flow patterns for the positive voltage polarity of the wire electrodes are more stable and regular than those for the negative voltage polarity due to the nonuniformity of the negative corona along the wire electrodes (tufts).