Characterization of dual corona-electrostatic electrodes for electrostatic processes applications

The dual corona-electrostatic electrodes consist of one or several ionizing elements (wires, needles, and blades) attached to a metallic support. This paper analyzes the characteristic features of a particular type of such electrodes and formulates recommendations on their design and utilization. The experiments focused on several models of dual corona-electrostatic electrodes, the ionizing element being the edge of a thin metallic blade. The tested devices had similar cylindrical metallic supports but blades of different sizes. Thus, it was possible to investigate the influence of electrode geometry on corona onset voltage and spark-over threshold in configurations that are specific to industrial electrostatic processes. Most of the experiments were performed by using roll-type electrostatic separators. A special experimental setup was employed for the study of the distribution of corona current density at the surface of a plate collecting electrode. For the model having the blade edge closer to the metallic support, the corona onset voltage was higher, and the corona discharge affected a smaller area at the surface of the collector. These experiments are discussed in relation with the results of the numerical analysis of the electric field generated by the different electrode configurations. At a given voltage and distance between the ionizing element and the collector, the presence of the cylindrical support diminishes the electric field at the edge of the blade and distorts the field lines. These effects were exploited in the design of the electrode system of an electrostatic separator for the recycling industry.