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ICESP IX CONFERENCE PAPER ABSTRACTS A 31-32 SERIES

Held in Kruger Gate, Mpumalanga, South Africa
May
May 17 - 21, 2004

The International Conference on Electrostatic Precipitation (ICESP) is the official conference of the International Society for Electrostatic Precipitation (ISESP).  

The following is a list of the Abstracts for the A 31-32 Series papers from the IX ICESP Conference.  

A31  INFLUENCE OF CORONA QUENCHING ON CHARGINGAND COLLECTION OF NANOPARTICLES
A. Marquard, J. Meyer, G. Kasper

Abstract
The increasing importance of nanoparticles regarding health aspects and new nanoaerosol productionprocesses requires the adoption of reliable particle collection techniques. In these fields, electrostaticprecipitation is an economically promising technique. With respect to nanoaerosol processes electro-static precipitation might be a cost effective competitor to the surface filtration technique - the current state of the art. Due to the demand of economic mass throughputs an efficient application of electrostatic precipitators can be limited by corona quenching phenomena, which are induced by the necessarily high particle concentrations.In this work three issues are addressed: First, the precipitation of two particle systems with diameters below 100 nm within a one-stage lab-scale wire-tube ESP is studied experimentally and theoretically. Whereas the first particle system, spherical DEHS-particles, was chosen because of the ideal particle shape, a SiO2-system was investigated because of itís technical relevance as a system of agglomerate structures. The second aspect focuses on the charging behaviour of these particle systems. Finally, the third case deals with the influence of the aerosol concentration on both the precipitation and the charging behaviour, respectively. For that purpose, the used SiO2-aerosol generator allows for avariation of particle concentration over two orders of magnitude up to some 108 #/cm3.

A Deutsch-similar correlation between measured overall collection efficiencies and migration velocities is found, covering all investigated cases: negative and positive corona, spherical and non-spherical particles, different particle sizes and  - what might be the most important result  - both low and high corona quenching conditions, respectively. It is shown for the given case of electrostatic precipitation of nanoparticles that the particle movement happens to be independent on the charging circumstances. The precipitation correlates only to the charging result (electric particle mobility) in the average electric field, represented by the migration velocity or the non-dimensional Deutsch number.Since the charging physics for particles below 200 nm is dominated by the diffusion charging mechanism, the established Fuchs theory (1963) is used for the comparison with the measured charge values, with ion density calculations based on an analytical solution of the Poisson equation. In the case of negatively charged particles for high N∑t-products a considerable underestimation of the experimental data is observed. In the case of positively charged particles the measured data match the predictions better, but for N∑t > 1014 s/cm3 the measured values also tend to surpass the predicted ones.

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A32  DOES SO3 FLUE GAS CONDITIONING HAVE AN IMPACT ON THE ENVIRONMENT - AN ASSESSMENT
Michael Vukmir & Michael W. Rollock, BS ChE.

Abstract
The impact of SO3 flue gas conditioning on the environment has been a topic that has not received a lot of attention in the past.   This is mainly due to the huge improvements in ESP performance that can be achieved by the utilisation of this technology.   The amount of SO3 being  injected  only  forms  between 2%  and  4%  of  the  total  SOx  (total  SO2  and  SO3) concentration and it was accepted that all the SO3 reacted with the fly ash in order to achieve the improved ESP performance.   SO3 FGC is a very effective way of reducing the particulate emissions and has been effective in doing so at all the Eskom Power Stations where it has been implemented.   There are however some exceptions where SO3 FGC alone will not be able to achieve the low emission levels that will be required by the Chief Air Pollution Control Officer (CAPCO).   These are typically the older power stations with small ESPís that have been  sized  to  achieve  the  emission  required  at  the  time  of  construction  and  are  not acceptable for current requirements.   These power stations normally have to install SO3 FGC and upgrade their existing ESPís to be capable of reliably giving emissions below 50mg.S.m3 or they have to install fabric filters.   SO3 FGC forms an integral part of Eskomís drive in the reduction the particulate emissions and it was therefore decided to evaluate its impact as part of the Eskom Emissions Research Portfolio.    This paper reports on the results obtained during this assessment. 

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