The numerical modelling of a flue gas precipitator

Abstract

Suspended fly-ash particles in industrial emission gasses have a major degrading effect on the whole environment. Electrostatic precipitation is one of the oldest and most effective gas-cleaning processes used today. Electrostatic precipitators use electrostatic forces to clean the flue gas of ash particles. Stricter emission control laws force industries (like SASOL) to improve their electrostatic precipitators. This study consists of a comprehensive literature survey and the development of a numerical fluid flow model. The proper flow of the gas through an electrostatic precipitator is one of the most important factors to ensure high collection efficiencies. The gas flow must be distributed over the whole flow domain in order to utilize the entire collecting area. The three-dimensional numerical model only considers the fluid dynamics of a precipitator. The finite volume method together with the SIMPLE algorithm is used to solve the fluid dynamic equations. The computer resources available are not sufficient to simulate the full detail of the structures inside a full-scale precipitator. Thus the precipitator flow domain was simplified by making certain assumptions and approximations. The distribution plates in the precipitator inlet ensure good gas distribution through the entire precipitator. Porous baffles are used to approximate the distribution plates and the electrical fields are approximated by porous mediums. The effect of the distribution plates and the electrical fields on the gas flow through the precipitator was investigated. The results have shown that the gas flow was expanded over the whole flow domain and the maximum velocity inside the precipitator was significantly reduced because of the effect of the distribution plates. The simulated gas flow velocity profiles are in relative good agreement with measured velocity profiles. The methodology followed in this study can be used to predict gas flow patterns inside a precipitator but further research is necessary.