Abstract
Behaviour of fine particles is still a "hot topic", especially, because of the regulations connecting to PM 2.5. To determine the performance of ESP for fractions 2.5 µm and below is extremely important, because these particles are more dangerous for the human health than larger pollutants.

The present examinations represent further development of our previous ESP model [1,2,3] especially by taking into consideration the change of the supply mode (different types of the time function of the supply voltage and supply current) of the electrostatic precipitators. As a case study, two different supply modes are compared, continuous DC case and supply by impulse voltage. |

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Abstract
The collector efficiency of an ESP is directly related to the applied corona power.    However, this corona power needs to be applied effectively in order to impart the largest benefit possible at the actual  point  of  corona discharge  which  emanates  from  an  element  referred  to  as  a  discharge electrode.

Discharge electrodes have evolved quite ungrammatically over the years and it is still quite common today to be faced with ESPs equipped with such elements which were designed and installed over 30 years  ago. However,  new  demands  for  higher  efficiencies  coupled  with  corresponding  lower maintenance costs, have led to some manufacturers favouring technologies and applications more suitable for today’s general usage.   This implies looking into models which consider not only updated technology  aspects  but  also  manufacturing  process,  reliability  in  the  long  term  as  well  as  easy installation in order to effect cost effective replacements.

Rigid  Discharge  Electrode  (RDE)  technology  has  been  utilised  extensively  in  Europe  and  North America and it has been found that the electrical characteristics of such electrodes have contributed significantly to an improvement in the efficiency of many ESPs. Furthermore, because of greater flexibility  in  geometry  and  configuration  of  the  electrode  units,  RDE  technology  allows  for  such improvements as increases in Specific Collection Area  (SCA), aspect ratio, migration velocity and treatment time.

This  paper  deals  with  an  innovative  type  of  RDE  conceptualised  in  South  Africa,  considered specifically to optimise the practical issues associated with effective corona discharge processes and at the same time improve the expected life cycle of such devices combined with a simple configuration providing for easy replacement of obsolete or faulty units.

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Abstract
The last European directive (2001/80/EEC) for Large Combustion Plants limits the emission of particulate matter in E.U. to 50 mg/Nm³ for ≥ 500 MWth existing coal power plants and to 30 mg/Nm³ for ≥ 100 MWth new facilities. In other hand, it is probable that next European regulations will limit the fractions more difficult to collect: PM10 and PM2.5. These limits can be difficult to reach considering only existing ESPs, particularly for some high resistivity ashes.

In this sense, this paper describes a series of pilot plant tests carried out in order to enhance the ESP efficiency and to prove the new emergent hybrid collector (HyColl) technology applied to flue gases from coal power plants. The ESP tests have been performed with the main objective of studying ESP behaviour when different coals and different filter configurations/energisation methods are used. The primary aim of this study was to reach conclusions about the ESP design and sizing optimisation for high efficiency applications. In the other hand, the HyColl tests have been performed with the objective of comparing the efficiency and costs of this new technology with ESP technology.

A HyColl consists of an ESP followed by a fabric filter (FF) installed in the same casing. The tests have been carried out in an ESP/HyColl pilot plant developed within the HyColl Project (ECSC 7220-PR/079).The pilot plant consists of an ESP with three electric fields followed by a 32 bags FF section, processing 15,000 Nm³ of real flue gases extracted from the flue gas ducts of a power station. The pilot plant is located at Los Barrios P.S. (Spain), but additional evaluation tests have been performed at Dürnhror P.S. (Austria).

Modifications on design and operation parameters of ESP and HyColl have been tested according to the factorial design of experiments in order to obtain their optimisation for collecting particulate matter in coal combustion flow gases.

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Abstract
The objective of this experimental study was to investigate the influence of corona electrode design  on  the  collection  efficiency.  The  experiments  were  carried  out  with  fly  ash  from  lignite combustion in a pulverised-fuel boiler and a fluidized-bed boiler, and with three corona electrodes which  differed  in  design.  Current-voltage  characteristics  and  collection  efficiency  curves  were established.  The  study  was  performed  under  laboratory  conditions  with  a  horizontal  electrostatic precipitator model. The chamber of the experimental setup had a length of 1000 mm, a height of 450 mm and an interelectrode spacing of 400 mm. The results (gathered in tables and plotted in figures) show how the design of the corona electrode and the type of the fly ash affect the collection efficiency under experimental conditions. This finding implies that the optimization of the corona electrode design should include not only the parameters of the electric field, but the physicochemical properties of the fly ash as well.

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Abstract
This investigation presents experimental velocity fields obtained by stereo particle image velocimetry (stereo-PIV) for  3 different pin-electrodes in a laboratory model of a negative corona ESP at low particle loads. Additional data include photographic records of dust patterns, measured distributions of current density and particle size distributions upstream and downstream of the 0.2×0.2 m by 1.0 m long, seven-electrode test section, yielding experimental efficiencies. A computational study of velocity and concentration fields for one type of electrode show encouraging agreement with experiments. Pin electrodes yielding less well-organized secondary flows tend to have higher efficiency, even though the turbulence level is higher. 

More specific topics include measured particle fluxes close to the collector plate, which suggest considerably higher effective drift velocities than those predicted and normally used in the laminar sublayer as boundary condition for concentration fields. Using the measured velocities gives good agreement experimental efficiency. A hypothesis is advanced to explain the differences. Also, the source of turbulence generation is discussed in light of current theories and the present experimental data, which provide estimates of shear production. The possible coupling between fluctuations in electric field variables and gas velocity has been studied experimentally by measuring velocity-current correlations near the collector plate, which yields a production comparable to that due to shear flow.

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