Appeal No. 2001-0098 3
Application No. 08/875,424
(d) transferring the pulp from the acid tower to the tower of the second
treatment stage,
(e) in the second treatment stage tower treating the pulp with a complexing
agent at a pH of between 4-9;
(f) washing, pressing, or both washing and pressing the pulp; and
(g) bleaching the pulp with hydrogen peroxide using 5 to 20 kg
peroxide/adt and 0-15 kg oxygen/adt.
36. A method of pre-treating, prior to bleaching with peroxide, cellulose
pulp, to improve bleachability of the pulp, using an acid tower, and a tower in a
second treatment stage, comprising the steps of substantially sequentially:
(a) if necessary, adjusting the pH of the pulp to between 2-6 by adding
aminic acid, sulfuric acid, hydrochloric acid or another acid which does not contain
oxidizing perhydroxyl ions;
(b) feeding the pulp to the acid tower;
(c) treating the pulp in the acid tower at substantially the pH, between 2-6,
to which it has been adjusted in step (a), at a pressure of 0-20 bar, at a
temperature of 75-130oC, and for 20-240 minutes, so that acid treatment
decreases the kappa number by 1-9 units;
(d) transferring the pulp from the acid tower to the tower of the second
treatment stage;
(e) in the second treatment stage tower treating the pulp with chlorine
dioxide and adding chemicals to the pulp to adjust the metal profile of the pulp
prior to, or in combination with, the chlorine dioxide treatment;
(f) washing, pressing, or both washing and pressing the pulp; and
(g) bleaching the pulp using hydrogen peroxide.
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