The behaviour of conductive particles in pulsed corona fields

The efficiency of certain electrostatic technologies (precipitation of dust, removal of gaseous pollutants from flue gases and separation of mixed granular solids) can be improved by using pulsed instead of DC corona discharges. In this work, the behaviour of millimetre-sized conductive spheres and cylinders either in DC or in pulsed corona fields was studied with a three-electrode arrangement, which had the advantage that the space charge density and the electric field strength could be independently controlled. By energizing the upper corona electrode from a square-wave high-voltage generator (30 kV; 250 pulses per second), a space charge density of periodical variation in time was produced in the air gap of 10 to 25 mm between the earthed median metallic grid and the lower static electrode, connected to a DC high-voltage supply. It was found that particle movements in pulsed fields (small-amplitude vertical oscillations on the surface of the lower electrode) were less affected by the space charge than in the case of a DC corona. The results of numerical simulation of particle behaviour in ionized fields were in good agreement with the experimental findings. The observed phenomena can be explained in connection with the process of particle charging in corona fields.