Preliminary study of delayed cake formation



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This study aims at developing basic information for thin cake filtration using a vacuum drive. In thin cake filtration, an accumulation of cake is eliminated by stirring the slurry at a distance very close to the filter medium for a given pressure difference. The thin cake formed in this process leads to an increase of filtrate flow rate when compared with conventional cake filtration. The new filter represents an innovative technological advance with potentially good pay off in solid-liquid separation. In the present filter, the feed slurry is continuously concentrated instead of producing a cake. Flow of liquid past the particles in the slurry produces a flow resistance in addition to the conventional resistances of the cake and medium. It was found that a linear relationship exists between the reciprocals of filtrate flow rate and porosity of the thickened slurry. Experiments were carried out to study the effect of stirring speed on flow rate. It was observed that raising the stirring speeds also produced higher flow rates due to both thinner cake and a lower specific filtration resistance. The thin cake obtained is different from cakes formed in conventional filtration. The cake has an irregular surface which is spiral in shape. Moreover, the filtration resistance of the cake decreases with increasing stirring speed. It is believed that the smaller particles are swept out of the cake leading to smaller resistance. In addition, recommendations are included for constructing a new high pressure, thin cake filter for further work.