Patent ID: 7182835

Claim:
A method for bleaching chemical pulp comprising dewatering said chemical pulp to a concentration of 25–40%, bleaching said dewatered chemical pulp in a first bleaching stage with chlorine dioxide to produce a partially bleached chemical pulp, bleaching said partially bleached chemical pulp in a second bleaching stage with alkaline bleaching chemicals to produce an alkaline bleached chemical pulp, bleaching said alkaline bleached chemical pulp in a third bleaching stage with chlorine dioxide to produce a bleached chemical pulp, dewatering said bleached chemical pulp to a concentration of from 10–40%, producing a filtrate thereby, and recycling the main portion of said filtrate directly to the pulp before the first chlorine dioxide stage to control said pulp concentration of said dewatered chemical pulp to from 8–15% in said first bleaching stage.