THE BEHAVIOR 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 con ductive spheres and cylinders either in DC or in pulsed corona fields was studied with a three-electrode arrangement, which had the advantag e 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 secon d), a space charge density of periodical variation in time was produce d in the air gap of 10 to 25 mm between the earthed median metallic gr id and the lower static electrode, connected to a DC high-voltage supp ly. It was found that particle movements in pulsed fields (small-ampli tude vertical oscillations on the surface of the lower electrode) were less affected by the space charge than in the case of a DC corona. Th e results of numerical simulation of particle behaviour in ionized fie lds were in good agreement with the experimental findings. The observe d phenomena can be explained in connection with the process of particl e charging in corona fields.