Abstract
In this paper, we describe an experimental study of rapping reentrainment with a laboratory – scale Electrostatic Precipitator (ESP).  To observe the particle reentrainment on collecting electrodes, the laser light sheet technique was used.  Reentrained particles were illuminated by a He-Ne laser light sheet, formed from a half cylindrical rens, so that its trajectories were visualized.  The collecting electrodes were rapped under various discharge conditions.  The particle trajectories were recorded by a video camera.  The following observations were made.  A decrease in corona current and applied voltage found that the particle reentrainment occurred on the whole area of collecting electrodes.  While an increase in corona current and applied voltage allotted for particle reentrainment to occur on the small area of collecting electrodes just under and between the discharge electrodes.  Further, reentrained particles were attracted toward the discharge l=electrodes temporarily.  Its trajectories were strongly influenced by the electrohydrodynamic (EHD) field in ESP.  the surface profile and thickness of the dust layer on collecting electrodes were measured by a laser displacement sensor combined with an automatic X-Y stage.  As a result, with the increase in the corona current and applied voltage, it was especially observed at the upstream of collecting electrodes that the surface roughness of dust layer was small and the bulk density was increase on the collecting electrodes

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Abstract
The paper presents results of studies and main characteristics of dust cleaning processes at an alternating polarity power supply (APPS) in comparison with similar data obtained with the use of a unipolar power supply.  The studied dusts have resistivities from 10² to 10⁸ Ohm*m.  the paper considers the effect of APPS operating conditions on dust accumulation at the precipitating electrodes and efficiency of dust catching.  The presented dependence of dust accumulation at APPS regime is affirmed by the presence of a dynamic balance of the dust precipitating at the electrodes and dust pouring off to a bunker.  This shows a possibility of working without mechanical shaking-off systems under self-regeneration of the precipitating electrodes.  With a constant quantity of dust accumulated at the electrode under APPS regime the efficiency is maintained practically stable and its value exceeds that at unipolar power supply by 10%.  The problem of the effect of a rate of wavefront rise when polarities of APPS are changed is also studied.  Research of the process of dust accumulation on electrodes and hence, the efficiency shows an electrostatic precipitator can operate without mechanical shaking-off systems.

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Abstract
The paper presents results of test of power supply sources combining alternating polarity and pulse power supplies for electrostatic precipitators working with dusts having resistivities from 10² ÷ 10⁸ Ohm*m.  Against to an unipolar power supply such combination permits substantially to increase a degree of dust cleaning and save expenses for maintenance.  Field tests at a thermal power station using ash with a resistivity ~a0⁸ Ohm*m showed an increase of dust cleaning efficiency by 1.5 ÷ 1.8 times when operated without shaking off systems of the precipitating electrodes.

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Abstract
Growing concern regarding global atmospheric pollution has led to an increasing interest in reducing the emission of fly ash particles.  Electrostatic precipitator is a flue gas particle collector commonly used in coal-fired power plants.  Since ESP has a relatively low efficiency for the collection of submicronsized particles, electrical agglomeration has been proposed to enhance the collection efficiency for the submicron particles.  In this work, the characteristics of electrical agglomeration of fine particles produced from NaCl resolved solution are investigated with DC corona charging and AC applied electric field.  This study has been initiated for enhancing the agglomeration between unipolar charged particles by using an alternating electric field to increase the relative motion between different sized particles.  Application of AC voltage promotes agglomeration in addition to that caused by Brownian motion.  A particle oscillating amplitude increases as a particle size increases from submicron to micron.  By controlling the concentration of the NaCl solution, it is possible to use the initially different sized particles.  Then each primary particle will become pearl-chain shape. The size of the particle is sampled and observed with SEM photographs.  The results show that the number of agglomerated particles mainly depend on the electrical DC corona field intensity, AC frequency, temperature, and moisture content.

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Abstract
During the past four years the Skew Gas Flow Technology has been successfully implemented by Eskom on 6000MWe of fossil fuel generating plant.  The application of this technology was a result of an extensive research study conducted by Eskom in collaboration with Stothert Engineering Ltd.

The technology has been applied at Matimba, Lethabo, Arnot and Tutuka Power Stations with a reduction in emissions of 53%, 25%, 45% and 42% being quantified respectively.  The studies at Arnot and Tutuka have also included a comparison and quantification of varying the inlet distributions from a top to bottom skew.

Stothert Engineering has been working with PacifiCorp at their Huntington Station in Utah , USA , and have achieved comparable results.  Since minimal, if any, mechanical or electrical repairs were carried out during the application of this technology the measured reduction in emissions can be directly attributed to the modification of the flow distribution.  This paper briefly describes the principle of the skew gas flow model and the methodology which has been applied to establish the skew gas flow technology as a viable and successful option to improve the performance of existing and new electrostatic precipitators.

Abstract
In this paper a new computational model was introduced for ESPs.  The model works with the combination of Boundary Element and Finite Differences Method to simulate the movement of the dust particles in turbulent boundary layer type flow field.  This semi-3 dimensional method takes into account the effect of the inhomogenity of the electric field due to the space charges.

The paper proposes a proper model for determining the transport of dust particles in turbulent flow in ESP channel.  A computer program has been developed with numerical straight forward marching method of finite differential forms.  The turbulent boundary layer type flow for typical case of wire-smooth plate model-precipitator equipment has been calculated by solving numerically the turbulent boundary layer equation.