Wire-duct Electrostatic Precipitators Research Articles

An experimental implementation and testing of the corona discharge in wire-duct electrostatic precipitators affected by velocities of incoming flow gases

This paper is intended to determine the space-charge-free field on the stressed discharge wires’ surface, the corona-onset voltage of wire-duct electrostatic precipitators (ESP) as influenced by the variation of the velocities of the incoming flow gases. The corona current-voltage (I-V) characteristics of wire-duct ESP is calculated under varying velocities of incoming flow gases. The calculation is made using the improvement of Deutsch’s Method. The method is endorsed by an iterative process to determine an estimate for the underlying dissemination of the charge density close to the surface of the stressed discharge wire(s). The electric potential, field, space-charge density in the interelectrode spacing, corona onset voltage and current-voltage characteristics of the precipitator are considered. Besides, the effect of gradually increase of the velocities of incoming flow gases, changing the number of stressed wires and changing the wire radius of wire-duct ESP are investigated. An experimental set-up has made in the Laboratory of High Voltage Engineering, Czech Technical University (CTU) in Prague, Czech Republic to investigate the accuracy of mathematical/simulation analyzed of the corona-onset voltage as well as the validation of the developed Deutsch’s Method in modeling the I-V characteristics of wire-duct ESPs. The experimental results reasonably agree with the theoretical analysis.

Finite Element Solution of the Corona Discharge of Wire-Duct Electrostatic Precipitators at High Temperatures—Numerical Computation and Experimental Verification

Global warming is the greatest challenge faced by humankind, and the only way to reduce or totally eliminate its effects is by minimizing CO2 emissions. Electrostatic precipitators are very useful as a means to reduce emissions from heavy industry factories. This paper aims to examine the performance of wire-duct electrostatic precipitators (WDESP) as affected by high-temperature incoming gases with a varying number of discharge wires while increasing their radius. The precipitator performance is expressed in terms of the corona onset voltage on the stressed wires and the corona current–voltage (I–V) characteristic of the precipitators working with incoming gases at high temperatures. The start of the corona onset voltage on the surface of the discharge wires is calculated for the precipitators under high temperatures based on the standard of the self-repeat of avalanches’ electrons developing on the surface of the stressed wires at high temperatures. For this, calculating the electrostatic field in the precipitators with single- and multi-discharge wires due to the stressed wire with the use of the well-known charge simulation method (CSM) with high-temperature incoming gases is important. The modeling of corona I–V characteristics is adopted using the finite element method (FEM) for single- and multi- (3-, 5-, and 7-) discharge wires of WDESP with high-temperature incoming gases. Additionally, the electrostatic field, potential, and space charge of WDESP are calculated by a simultaneous solution of equations of Poisson, current density, and the continuity current density. A WDESP was set up in the Laboratory of High Voltage Engineering of Czech Technical University (CTU) in Prague, the Czech Republic, to measure the corona onset voltage values and corona I–V characteristics for different WDESP configurations at high temperatures with a varying number of discharge wires while increasing their radius. The calculated values of the corona onset voltage based on CSM and the calculated corona I–V characteristics based on FEM agree reasonably with those measured experimentally with high-temperature WDESP.

Positive direct current corona discharges in single wire-duct electrostatic precipitators

This paper is aimed to study the characteristics of the positive dc corona discharges in single wire-duct electrostatic precipitators. Therefore, the corona discharges were formed inside dry air fed single wire-duct reactor under positive dc voltage at the normal atmospheric conditions. The corona current-voltage characteristics curves have been measured in parallel with the ozone concentration generated inside the reactor under different discharge conditions. The corona current-voltage characteristics curves have agreed with a semi empirical equation derived from the previous studies. The experimental results of the ozone concentration generated inside the reactor were formulated in the form of an empirical equation included the different parameters that were studied experimentally. The obtained equations are valid to expect both the current-voltage characteristics curves and the corresponding ozone concentration that generates with the positive dc corona discharges inside single wire-duct electrostatic precipitators under any operating conditions in the same range of the present study.

Numerical and experimental evaluation of fly ash collection efficiency in electrostatic precipitators

This paper evaluates experimentally and numerically the influence of different geometrical and operating parameters of a single stage wire-duct electrostatic precipitators (WDEP) on its fly ash collection efficiency. The governing equations are solved under dust loading conditions using the finite element method (FEM) and a modified method of characteristics (MMC). In addition, a proto-type design that represents a WDEP was successfully designed and fabricated at the research institute of KFUPM (RI-KFUPM). The experiments were carried out under laboratory conditions where the WDEP was made of Plexiglas with a length of 2m, height of 1m, wire-to-collecting plate spacing of 0.2–0.3m, and an inter-electrode (wire-to-wire) spacing of 0.16–0.21m. Smoke of fired coal was used as a source of seed particles of PM10 category (with 75–80% of particles lying below 10μm). An indication of the effectiveness of the numerical approach was carried out through a comparison of computed results as well as presently and previously obtained experimental data.

Analysis of Collection Efficiency in Wire-Duct Electrostatic Precipitators Subjected to the Applied Magnetic Field

This paper describes a strongly coupled calculation procedure for the particle dynamics in electrostatic precipitators (ESPs) subjected to the applied magnetic field with the statistical particle size distribution taken into account. The turbulent gas flow and the particle motion under external forces are modeled by using the commercial computational fluid dynamics code FLUENT. Numerical calculations for the gas flow are carried out by solving the Reynolds-averaged Navier-Stokes equations, and the turbulence is modeled by using the turbulence model. An additional source term, which is obtained by solving a coupled system of the electromagnetic field and charge transport equations, is added to the gas flow equation to capture the effect of the electromagnetic field. The particle phase is simulated by using a discrete phase model. Different kinds of particles which follow the Rosin-Rammler distribution were simulated under different conditions, and the influence of the magnetic field density on the capture of a fine particle was investigated. In order to show the dust removal effect, the collection efficiency and the escaped particle size distribution were discussed in case of different applied magnetic fields. The particle trajectories inside the ESP were also given under the effect of both aerodynamic and electromagnetic forces. Numerical results in the wire-duct ESP show that the collection efficiency increases with the increase of the applied magnetic field, that the particle trajectory is more visible to the direction of the dust collection duct, and that the collection efficiency varies smoothly when the absolute value of the applied magnetic field trends to a certain size. Furthermore, the average diameter of escaping particles decreases and the dispersion for dust particles in different sizes increases with increasing applied magnetic field, and particle sizes are linearly decreasing with the magnetic field before the particle diameter is up to a certain size.

Simulation and experimental studies of corona power loss in a dust loaded wire-duct electrostatic precipitator

This paper investigates numerically and experimentally the performance of a single stage wire-duct electrostatic precipitators (WDEP) as influenced by different geometrical and operating parameters. To numerically solve the governing equations, namely Poisson’s and the current continuity equations, the finite element method (FEM) and a modified method of characteristics (MMC) were used. One major advantage of the present work over those reported in the literature is that the characteristic lines follow the FE grid pattern which results in fast convergence and reduction of the computational time. To verify the results experimentally, a proto-type WDEP was successfully designed and fabricated at the research institute of KFUPM (RI-KFUPM). The experiments were carried out under laboratory conditions and a smoke of fired coal was used as a source of seed particles of PM10 category (around 78% of particles lying below 10 μm). The results show how different parameters (such as discharging wire radii’s, wire-to-wire spacing and wire-to-plate spacing as well as the fly ash flow speed and applied voltage polarity) influenced the corona power loss and current density profiles. An indication of the effectiveness of this approach was carried out through a comparison of previously computed results and previously as well presently obtained experimental data.

Analysis of a wire–duct electrostatic precipitator under dust loading conditions

A combined finite element based method (FEM) and a modified method of characteristics (MMC) is developed for the analysis and computation of the current density profiles, corona current and hence corona power loss associated with WDEP under particle loading conditions. To test the developed algorithm, comparison with experimental and numerical findings reported in the literature has been made. Comparisons showed high accuracy of the developed algorithm accompanied with a reduction in the number of iterations needed to converge. One major problem reported in the literature, namely, that the characteristic lines never follow the FE grid pattern, is eliminated in the present work. A proto-type design that represents a WDEP, which has been fabricated at the research institute of KFUPM (RI-KFUPM), is used to test the developed algorithm. Smoke of fired coal is used as a source of seed particles of PM10 category (with 75–80% of particles lying below 10 μm). A group of experiments were carried out under laboratory conditions. The results show how different design parameters influenced the corona current and current density profiles.

Simulation of dust loaded V-I characteristics of a commercial thermal power plant precipitator

A new approach based on finite difference method, is proposed for the simulation of electrical conditions in a dc energized wire-duct electrostatic precipitator with and without dust loading. Simulated voltage-current characteristics with and without dust loading were compared with the measured characteristics for analyzing the performance of a precipitator. The simple finite difference method gives sufficiently accurate results with reduced mesh size. The results for dust free simulation were validated with published experimental data. Further measurements were conducted at a thermal power plant in India and the results compares well with the measured ones.

Three-dimensional ionic wind and electrohydrodynamics of tuft/point corona electrostatic precipitator

The two-dimensional flow interaction between the primary flow and the secondary flow (often called an electric wind or ionic wind) in the wire-duct electrostatic precipitator (ESP) has been investigated theoretically and experimentally in the past. However, the analysis was limited to the two-dimensional, which is acceptable only for the positive polarity and small tuft spacing. The negative corona, commonly used for the industrial ESPs, generates tufts along the corona wire and the point coronas on the discharge wire and requires three-dimensional analysis. Three-dimensional electric field and space-charge density distributions, and the flow interaction between the primary flow and secondary flow, i.e., electrohydrodynamics were investigated. The computational results show that the secondary flow distribution consists of a donut-shaped ring from each tuft or corona point, which was predicted by the first author 16 years ago. When the primary flow exists, a pair of spiral rings, like Goertler vortices, is formed in the direction of the primary flow. The flow interaction was described using dimensionless number N/sub EHD/, which is the ratio of the ionic wind velocity to the primary flow velocity. The effects of particle motion in the electrohydrodynamic field in the tuft/point corona ESPs are discussed.

Prediction of pre-breakdown V– I characteristics of an electrostatic precipitator using a combined boundary element-finite difference approach

A new approach is proposed for the simulation of electrical conditions in a DC energized wire-duct electrostatic precipitator under dust free conditions. Voltage–current characteristics under clean air conditions are considered as a reference in analyzing the performance of a precipitator. This paper gives the simultaneous solution for the governing Poisson's and current continuity equations using a combined Boundary Element and Finite Difference Method over a one-quarter section of the precipitator. The solution of the domain integral, which represents the effect of space charges in the Poisson's equation, is also simplified using a numerical technique. The significant features of this paper are, reduced problem domain and hence less memory space and cost, less number of iterations and closer agreement of voltage–current characteristics with published experimental data when compared to other methods. The results are validated against the data obtained from experiments conducted by authors on a laboratory scale precipitator at Bharat Heavy Electricals, Ranipet, India. The distribution of electric field and current density along the plate have also been presented and discussed in this paper.

A combined algorithm based on finite elements and a modified method of characteristics for the analysis of the corona in wire-duct electrostatic precipitators

This paper numerically analyzes corona power loss associated with wire-duct electrostatic precipitators. The finite-element method is used to solve Poisson's equation and a modified method of characteristics is used to satisfy the current continuity condition. The two methods are repeated iteratively to obtain a self-consistent solution of the describing equations. The effectiveness of this approach is tested by comparing the computed results with previously obtained experimental and calculated values. The agreement with experimental results is found to be satisfactory.

Simulation of corona in wire-duct electrostatic precipitator by means of the boundary element method

A new approach for modeling the space density and the electric field distribution in electrostatic precipitators is presented in this paper. Two numerical techniques are used iteratively until a self-consistent solution is obtained: the boundary element method, for evaluation of the electric potential; and the characteristic method, determining the charge distribution. This hybrid approach is applied to simulate the electrical conditions in a wire-duct electrostatic precipitator and obtained results are compared with the experimental data. >

An estimation of the wire-duct electrostatic precipitator efficiency

In this paper, a simple and fast method for estimating the saturated profiles of the field intensity, ions and particles charge density, ions and particles current density, relative precipitated dust and the overall precipitation efficiency of the wire-duct electrostatic precipitators is reported. Both ions and particles in space surrounding the energized wires are taken into consideration. This method is based on simple expression which define the ionized field in the interelectrode spacing surrounding the HV wires of the wire-duct electrostatic precipitator in presence of dust particles and under saturated conditions. The precipitation efficiency of the electrostatic precipitators under saturated conditions is also estimated for cement industry. The effect of some parameters on the precipitation efficiency is also reported. The precipitation efficiency of the wire-duct electrostatic precipitator as influenced by both the applied voltage and the gas flow speed is discussed in this paper. The present findings are correlated to the physics of electrical corona discharge.

Electrical conditions in wire-duct electrostatic precipitators

In this paper, a modified numerical method for calculating the electrical conditions, namely the charge density, the electric field intensity and the current density, in wire-duct electrostatic precipitators is reported. Variation of mobility for both ions and particles in the space surrounding the energized wires is taken into consideration. This method is based on numerically solving the main set of equations, defining the ionized field with presence of dust particles. The space-charge-free field is calculated using the charge simulation technique. This method is checked against published calculated and measured results, showing good agreement. The present findings are correlated to the physics of electrical corona discharge.

Donor cell-finite element descriptions of wire-duct precipitator fields, charges, and efficiencies

Computations of electric field and charge density structures and resultant efficiencies in wire-duct electrostatic precipitators are described. The computational method is based upon the finite-element method as a means for computing the potential and electric field for a known charge distribution and a donor cell method that imposes conservation of charge in integral form as a means for computing charge densities for a known field structure, with iterative convergence to self-consistent solutions. The solution region is discretized by the Delaunay algorithm. This division simultaneously provides the triangles needed for the finite-element method and the Voronoi polygons over which charge conservation is imposed. Thus, a natural geometric interface is established between the finite-element method and the donor cell description. Results are shown in models that include the time-averaged effect of turbulence through a diffusivity coefficient, bipolar ionic species modeling back ionization, and the effects of particulate and ionic space charge. >

The effect of corona wire heating on the downstream ozone concentration profiles in an air-cleaning wire-duct electrostatic precipitator

The effect of corona wire heating on the downstream ozone concentration profiles in an air-cleaning wire-duct electrostatic precipitator was studied experimentally. The results show that ozone concentration profiles depend significantly on the applied voltage and polarity. Significant ozone concentrations were only observed in a narrow region downstream of the corona wire for positive coronas. For the corona wire surface temperature profile measurements made using a real-time IR thermoimage processing system, it was observed that the heat generated by corona discharge alone only increased the surface temperature of the corona wire by a few degrees centigrade. Ozone generated by corona discharges can be significantly decreased by the external heating of the corona wire.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electric field in a wire-duct type electrostatic precipitator

The theoretical calculation of electric and current field in a wire-duct electrostatic precipitator presents special problems because of the non-linear equations that describe the space-charge fields. A new method of solving these equations is presented in this paper. It is based on a method originally developed by Sarma and transforms his integral equations into differential equations. The theoretical values of corona onset voltage, corona voltage-current characteristics, corona current density and electric field distributions on the plate are calculated by the new method and are in good agreement with the measured values. The method is satisfactory for duct-type electrostatic precipitators in which the average electric field is 0.20–0.4 MV/m with plate spacings between 100 and 300 mm, and can also be used to find the distributions of potential, charge density and electric field in the gas space between the discharge wire and plates.

線対平行平板電極形電気集じん装置における流れ場の解析と実験

線対平行平板電極形電気集じん装置における流れ場の解析と実験

Wire-duct precipitator field and charge computation using finite element and characteristics methods

A model is described for computation of charge density and electric field structures in wire-duct electrostatic precipitators. The model employs an iterative technique, wherein the finite element method is used to compute electric potential structure for an assumed charge density distribution, and the method of characteristics is used to compute charge density structure for an assumed electric field distribution. The computed potential values are in excellent agreement with experimental data, including a region which has produced disagreement in prior models.

A mathematical model for calculating effects of back corona in wire-duct electrostatic precipitators

A new mathematical model for the electrical conditions in wire-duct electrostatic precipitators is described. The model is based on the solution of Maxwell’s equations for the electric field components and offers several advantages over numerical solutions of Poisson’s equation. The model is used to calculate the effects of back corona on (1) the voltage-current characteristic, (2) the current-density distribution at the collector plate, and (3) particle collection for five simple mechanisms describing the generation of back corona. Each mechanism is capable of simulating the V-I curves characteristic of precipitators operating in back corona, but two in particular are identified as potential back corona mechanisms on the basis of generating hysteresis in the V-I curves or characteristic current density variations. These mechanisms are consistent with limited experimental data. This method of calculation is useful and can be extended to more complex mechanisms for back corona generation.