Abstract
Computational Fluid Dynamics (CFD) is a well-established technology to model fluid flow. The incorporation of collection dynamics into the CFD capability could establish CFD as useful tool for electrostatic precipitator (ESP) efficiency predictions.

Eskom has applied CFD extensively for the successful implementation of skew gas flow technology to 8270 Mwe. Present research focuses on the manipulation of the particle distribution, the incorporation of electrostatic field forces and reentrainment. Case studies have been carried out, which demonstrate the working of the model regarding the capability of predicting the efficiency of ESPs.

The paper describes in principle how electrostatic forces and reentrainment have been incorporated into the CFD model.

The ultimate goal of the research is to develop an accurate predictive model, which takes all major collection parameters, including flow dynamics, into account. The model will be used to predict ESP performance and indicate optimal modifications to improve the performance of existing plant, rebuilds and new installations.

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Abstract
The aim of the present study is to investigate the gas flow distribution within a full Electrostatic Precipitators (ESP’s) with special focus on modeling the gas distribution screens present in the inlet and outlet cone sections. The three-dimensional flow distribution and the pressure distribution within an ESP is calculated by standard Computational Fluid Dynamical (CFD) tools giving high resolution of the calculation domain. The gas distribution screens are modeled by a newly developed source term model especially designed for FLS miljo screens. This model is linked to the standard CFD tool package and a principal approach is presented where different screen designs quickly can be evaluated. The ESP geometry studied includes inlet ducting, inlet cone section with gas distribution screens, precipitation section with collecting plates, hopper, outlet cone section with gas distribution screens and outlet ducting. The presented results include validation of the new gas distribution screen model, simulations based on FKS miljo central type ESP inlet design with focus on different screens configurations causing different gas distributions, and investigation of a skew inlet gas distribution versus the traditional uniform distribution. Finally movement of small particles are studied with special focus on re-entrainment in the hopper. The study of different screen configurations clearly demonstrates the flexibility of the FLS miljo screen design making it easy to implement a numerically obtained gas distribution at site. Moreover, calculations with small particles initiated at the bottom of the collecting plates indicates that many of these are re-entrained in the case of a uniform gas distribution and less are re-entrained in the case of a skew distribution with bottom peak velocities at the inlet and top peak velocities at the outlet.

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Abstract
This paper examines dust movement within a precipitator and how it leads to the optimization of gas flow distribution to improve precipitator performance. The information presented is based mainly on experience with precipitators installed in the coal-fired utility industry, some of which was gained recently with the application of Skewed Gas Flow Technology.

The examined utilizes a two-dimensional model of a vertical plane parallel to the gas flow. Analysis of dust movement indicates that it moves horizontally while particles are suspended in the gas flow until it is deposited to form a layer of dust on the precipitator collecting surfaces. When it is dislodged, agglomerated dust falls vertically downward under the influence of gravity until it is dispersed and re-entrained or until it falls below the treatment zone and is truly collected. The downward movement of dust is examined in some detail.

The model, which correctly predicted performance improvement with Skewed Gas Flow Technology, also predicts performance improvement with Precipitator Extraction Technology, which is presented conceptually in this paper.

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