Analysis of electrostatic powder charging for fractionation of foods

Electrostatic separation based on different tribo-electric charging behaviours of components has emerged as a novel, sustainable dry fractionation process. This study aims to characterise charging behaviour of single-component particles in nitrogen gas flowing through aluminium tubes. Experiments were carried out with polystyrene (PS) particles and wheat gluten as model particles. Results indicated that specific charge increased linearly with gas velocity up to 28 m/s for both materials. It was found that surface charge densities of different-sized PS particles overlapped for laminar gas flow, whereas for higher stronger gas flow rates, surface charge density of the smallest particles deviated from that of larger particles. Specific charge of PS particles increased linearly with increasing tube length from 125 to 225 mm. Additionally, charging of PS particles was unaffected by relative humidity (RH) of gas; however, specific charge of wheat gluten decreased for RH > 80%. Concluding, these results provide insight in critical parameters affecting charging behaviour, thus facilitating the development of electrostatic separation processes to fractionate food ingredients.