Effect of pipe-end geometry on powder charging and electrostatic discharge in a silo

Abstract

Electrostatic charging of insulating powders during pneumatic conveying can cause hazardous discharges during storage-vessel loading. This study investigated the effect of pipe-end geometry on powder charging and electrostatic discharge behavior during silo loading using tongue-shaped metal electrodes. The electrodes locally enhance the electric field and promote corona discharge. Voltage–current ( U–I ) measurements showed that corona discharge from the tongue electrode started at −3.3 kV. Polypropylene powders were conveyed and loaded into an industrial-scale silo. The specific charge of the loading powder decreased significantly with increasing electrode count, reaching 17% of that without electrodes when four electrodes were used. During silo loading, brush and high-energy super-brush discharges occurred without electrodes, whereas they were eliminated when tongue electrodes were installed. Comparison of the corona current detected at the tongue electrodes during powder loading with the U–I characteristics showed that increasing the number of electrodes decreased the apparent surface potential of the loading powder. This suggests a more uniform charge distribution within the loaded powder, reducing the electrostatic elimination effect of each electrode. When the apparent surface potential falls below the onset voltage, corona discharge ceases. Thus, the number of pipe-end protrusions should be optimized according to the powder charging level.