Role of vibration in solid-liquid separation using a vacuum belt filter

Abstract

Modelling and analysis are carried out for stages of de-watering mineral slurry on a vacuum-belt filter, with a patented vibrating roller module called `Viper' situated atop the formed cake. The long-term goal here is to improve the efficacy of the dewatering since enhancements by as little as 1% solid mass fraction have significant economic benefits. We show that Darcy's law accurately models the dewatering process through a clogging filter mat until no more water can be extracted using mere vacuuming, and the predicted solid mass fraction is in accordance with available data. It is shown that after this initial de-watering stage, air fingers are formed in accordance with Saffman--Taylor theory, thereby releasing the hydraulic pressure gradient and de-watering ceases as a result. The Viper units break up these fingers, thus facilitating further de-watering. Estimates of the time span of development of the air fingers are made using extended Saffman--Taylor theory and these are used to determine the optimal spacing of the Viper units. At the vibrational frequencies used in Viper units, the estimated Deborah number is small enough so that liquefaction is expected to occur; this would explain the efficacy of the Viper device.