GB1177768A - A Method and Device for Achieving High Purity and Whiteness in Cellulosic Pulp - Google Patents

Abstract

1,177,768. Separating wooden chips. R. ZEMANEK and M. CARSKY. 22 Dec., 1966 [24 Dec., 1965], No. 57399/66. Heading B2H. [Also in Division D2] In a process for the elimination of wooden impurities from cellulosic pulp, wooden chips after their delignification are passed in an aqueous suspension on a set of rotary bodies so as to separate according to their width chips of a required size from chips exceeding that size. After delignification e.g. by boiling with Ca bisulphite or Na bisulphite or sulphate, pulp from a pit or rinsing filter (not shown) is fed to a box 1 from which it overflows on to a first inclined set of rotary rolls 3 revolving in the same direction and at the same angular velocity with a constant gap 4 maintained between adjacent rolls. Relatively pure chips of a required size fall through the gaps 4 on to a stationary screen 6 of a thickening or dewatering device 5 where removal of water takes place by means of rails 7 which are mounted transversely between endless chains 8 and wipe against the upper and lower surfaces of the screen. The coarse impure chips and knots are delivered to a vortex defibrator 9 where, due to the turbulence created by a rotary conical screw 11, the relatively pure surface layer of the chips is peeled off from the dark impure inner layer. The mixture obtained overflows through a pipe 12 on to a second set of rotary rolls 13 having between them gaps 14 of smaller dimension than the gaps 4 of the first set. The relatively pure chips passing through the gaps 14 are passed with the first lot of pure chips into a dewatering apparatus and thence to a defibrator. The mixture of coarse impure chips and knots discharged from the set of rolls 13 may be fed by a screw conveyor to a knot mill. The rolls 3, 13 may have a crosssection in the shape of a circle, a spherical triangle, or a spherical pentagon.