The Efficiency of Electrostatic Precipitators Under Conditions of Corona Quenching

Abstract

The suppression of corona by particle space-charge is of considerable importance in electrostatic precipitators dealing with medium to high concentrations of particulates. However, the effect of the dust concentration on collection efficiency has found no direct answer in the literature. In addition to the expected reduction in corona current due to low mobility dust particles, the presence of these charged particles has two other main effects: 1. The electric field in the vicinity of the discharge electrode is weakened and hence the concentration of ions originating in the ionization zone and forming the charging current is decreased. 2. The resulting space-charge build-up causes an increase in the field strength adjacent to the collecting surface of the precipitator. The importance of each of these effects on the collection efficiency will be dependent on the relative decrease in particle charge as compared to the increase in the collection field. Experiments were carried out under both positive and negative corona with aerosol concentrations having specific surfaces in the range 0 to 44 m²/m³. These results showed: 1. For low values of corona current densities, as the specific surface area increases, the efficiency decreases. In this cqse, the charge per particle decreases as the particle concentration increases and becomes far below the normal charge attainable. Here the increase in the collection field is more than counteracted by the jarge reduction in particle charge. 2. For higher values of initial corona current densities, as the particle specific surface area increases, the efficiency either increases slightly or stays constant, in spite of major reductions in the measured corona current. In this case there should also be a reduction in the charge per particle with the increase in particle concentration, however, this is apparently offset by the increase in the collection field strength. Analysis of the results, coupled with an interpretation of existing theories, indicates that a major parameter that must be considered is the ratio of the initial corona current density and the specific surface of the particles.