Analysis of electric conditions and collection efficiency in electrostatic precipitator

Abstract

In experimental and most industrial-scale tests, it has been reported that the effective migration rate increases with plate-spacing, so called wider plate-spacing effect. There are various hypotheses for explaining the wider plate-spacing effect. It is possible to classify the hypotheses as follows. One is the higher electrical field strength in the proximity of collection plate due to the space charge, the other is the back-diffusion of particles near the plate due to the turbulent mixing. It is very difficult to predict the performance of the electrostatic precipitator reliably by using theoretical formulation based upon a simple flow. The particle flow field is related to the turbulent flow field and the electrical field. Moreover, there is a strong interaction between the space charge and the electrical field. The charged particle may interact with the electrical field and similarly the motion of the particles may modify the electrical field. Therefore, calculation of both the space charge and the electrical field is needed to analyze the collection process in the electrostatic precipitator. Although it is accepted that the electrical field, turbulence and particle back-diffusion near the collection plate decisively affect the collection behavior, the quantification of this influence is, even today, scarcely possible. In the present work, simple models for the prediction of the collection efficiency of the electrostatic precipitator are developed to investigate the effects of particulate space charge in a quantitative aspect on the basis of the various theoretical relationships. In the first part, a simplified model taking into account of the effect of the electrical disturbance and particle size distribution are proposed through the moment method. The particle size distribution is assumed to be in a log-normal function. It is not successful so far to elucidate the so-called "non-Deutschian phenomenon", which is generally observed for an electrostatic pre...