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Abstract

In a method and apparatus for treating pulp, a peroxide treatment of chemical pulp, i.e., both sulphite pulp and kraft pulp, is used to quickly reduce the Kappa number of the pulp. The method involves treating a chemical pulp with at least hydrogen peroxide or its equivalent, the kappa number of which chemical pulp has been brought to a level below 20 by either at least cooking or cooking and delignifying. The pulp is treated in a fast alkaline or neutral peroxide stage (Pk) (e.g. a small reactor having a volume of, or proportional to, less than about 90 cubic meters for 1500 tons per day pulp treatment) to reduce the kappa number by 1-10 units, and preferably by 3-7 kappa units, in which treatment the reaction time is less than 10 minutes, and is preferably less than 5 minutes. The pulp is then transferred substantially without intermediate washing of any type to a bleaching tower, and then bleached further in an acidic bleaching step (e.g. a D or Z step) in the bleaching tower.

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First Claim