GB1106842A - Manufacture of cellulosic pulp - Google Patents

Abstract

1,106,842. Bleaching pulp; treating cellulosic pulp. ELECTRIC REDUCTION CO. OF CANADA Ltd. 24 Jan., 1966 [25 Jan., 1965], No.3131/65. Headings D1P and D2W. Raw fibrous cellulosic pulp obtained in a chemical pulping process by the chemical digestion of a fibrous cellulosic material is passed to a first bleaching stage in which it is partially bleached with an aqueous solution containing chlorine or chlorine dioxide or both, the aqueous solution containing chlorine or chlorine dioxide or both is removed from the wet mat of partially bleached pulp, the partially bleached pulp is treated with hot alkali in a caustic extraction step, washed and passed to at least one further bleaching stage and a portion of the effluent from the washing of the extracted pulp is recycled to the mat of partially bleached pulp to displace water from the mat. The volume of effluent which is recycled is preferably not greater than the volume of water present in the mat thus displacing an equivalent volume of water from the mat and the partially bleached pulp is preferably washed before the recycled effluent is passed through it. As shown, in Fig. 1 partially bleached pulp is passed from a chlorinator through line 1 to washer 2 where it is taken up as a mat on the wire mesh periphery of rotating drum 3 where it is washed with hot water from a wire 4 and the effluent from the washer is drawn by means of a vacuum pump through line 5 to seal tank 6 to waste, and then passed to repulper 7 where it is mixed with sodium hydroxide solution entering through line 8 and steam entering through line 9 the hot mixture being then passed to caustic extraction tank 10 and washer 13 where it forms a mat on the wire mesh periphery of rotating drum 14 as is washed by means of hot water passing through line 15. The effluent from the washer 13 is drawn through line 16 to seal tank 17 a portion being pumped by pump 23 via lines 18 and 19 to the surface of the washed mat of pulp fibres on the surface of the drum 3 to displace the water from the mat which passes in a line 5 and seal tank 6 to waste, a portion is recycled via line 12 to washer 13 and returned to the seal tank, a portion is pumped by pump 20 via line 21 to extraction tank 10 and a portion is passed out through line 22 for recovery and reuse in the recovery stages for the overall pulping process.