Plate-type high-shear filter thickener; construction and scale-up

The construction is presented of an original, dynamic, plate-type filter with reciprocating motion scrapers generating shear stresses tangential to the surfaces of the filter screens in the filtered suspension in order to sweep away the retained solids. It is shown that when such filters operate at relatively large filtrate fluxes and the pulp washing occurs in the regime close to that of the perfect mixing, high purity of the pulp is obtainable. Evidence is provided that scale-up of the operation and of the apparatus must involve the same shear rate in the clearances between the filter screens and the scrapers. The filtration kinetics in the apparatus are analyzed and compared with those observed in the Nutsche filter with cake deposition at the same pressure difference. The advantages of the apparatus presented are discussed.