Process for peroxide bleaching of chemical pulp in a pressurized bleach vessel

摘要

A process for chlorine-free bleaching of chemical pulp in association with the production thereof, where a suspension of the pulp preferably has a concentration exceeding 8% of cellulose-containing fiber material and where the pulp entering into a bleaching line is preferably fed continuously through at least one bleaching vessel in the bleaching line, is treated with at least one acid for adjusting the pH to a value below 7, and with a chelating agent, and is subsequently bleached in at least one stage to a brightness exceeding 75% ISO, preferably exceeding 80%, with hydrogen peroxide or the corresponding quantity of another peroxide, employed in a quantity exceeding 5 kg/BDMT, where the peroxide bleaching takes place at elevated temperature and at a pressure in the bleaching vessel which exceeds 2 bar and where the cross-sectional area of the bleaching vessel exceeds 3 m.sup.2 and the area of the metal surface exposed towards the interior of the bleaching vessel is less than 4 V m. sup.2, where V indicates the volume in m.sup.3.