Measurement of electrostatic charging during pneumatic conveying of powders

The accumulation of static electricity during powder transport is a possible ignition source for explosions and, thus, a hazard for operation safety in process industry. However, due to its high sensitivity to initial and boundary conditions, the process of charge build-up is challenging to study experimentally and many of the underlying mechanisms are still not well understood. Aiming at bridging this gap, in this paper we present the results of our experimental study on the influence of a range of parameters on the triboelectric charging of powders and transport pipes. The experiments were conducted in a recently assembled test-rig that facilitates the control of the ambient conditions to a high degree. According to our measurements, the powder charge increases if the conveying air velocity is increased. However, at a certain velocity the powder experiences a maximum charge whereas for higher velocities the charge subsequently drops. The air velocity that maximized the powder charge depends on the pipe material, diameter and powder loading. Further, a larger pipe diameter showed to enhance the charging process significantly. The results were highly repeatable and in good comparison with theoretical predictions.