GB1374358A - Method of purifying and fractioning particle suspensions and an apparatus for carrying out the method - Google Patents

Abstract

1374358 Pulp screening machine; centrifugal separators SEE AHLFORS 29 Feb 1972 [1 March 1971] 9375/72 Headings B1D and B2P Wood pulp is screened by passing inwards through an outer, rotating coarsely perforated drum 2 and an inner, finely perforated drum 1 which may rotate (Fig. 1) or be fixed (Fig: 2, not shown), drum 2 having external and possibly internal formations 43 which agitate the pulp to break up fibre agglomerations and clean the drums. In Fig. I pulp enters the machine tangentially at A and is filtered through a very coarse screen 39 (aperture 20-25 mm dia.) before reaching the outer drum 2, whose rotation induces centrifugal separation of heavy particles. Blades 35 rotating with drum 2 constitute a mixer and centrifugal pump to force the pulp inwards through the drums. Fractions rejected by screen 39, drum 2 and drum 1 are respectively discharged through outlets C, G and L, and accepts is discharged at M. Vanes 38, inside rotating drum 1, are fixed to create pulsations in the pulp which clean the drum. In Fig. 2 wherein drum 1 is fixed vanes 38 (not shown) would rotate. At least one of vanes 38 could deliver flushing water to the surface of drum 1. Additional inlets F and H enable diluting water to be delivered to the space outside drum 2 and the space between the drums. The drums are rotated by separate electric motors and in opposite directions in Fig. 1. Surface formations 43 on the drums may be uniformly distributed or arranged in axial or circuferentially spaced zones. Drum 2 may have perforations of 4 to 8 mm. dia. and drum 1 may have perforations of 1 to 2.5 mm. dia. or slots 0.20 to 0.60mm. wide. The illustrated machines have vertical axes but they could be horizontal.