Patent ID: 6149766
Filing Date: 2000-11-21
Classification: D21C

Abstract:
A process for chlorine-free bleaching of chemical pulp in association with the production thereof, using no chlorine and no chlorine compounds, comprising the steps of:(a) providing a chemical pulp having a pulp suspension with a consistency exceeding 8% of cellulose-containing fiber material;(b) treating the chemical pulp with at least one acid for adjusting the ph of the pulp to a value below 7;(c) treating the pulp with a chelating agent;(d) pumping said pulp into at least one bleaching vessel by means of a medium consistency pump to aid in pressurizing said bleaching vessel; and(e) bleaching the pulp in a bleaching stage to a brightness exceeding 75% ISO during the bleaching stage using hydrogen peroxide employed in a quantity exceeding 5 kg/BDMT or a corresponding quantity of another peroxide;wherein said bleaching stage is effected in a bleaching vessel at a temperature exceeding 90.degree. C. and at a pressure exceeding 2 bar, and an area of metal surface exposed on an interior of the bleaching vessel is less than 4V m.sup.2, where V indicates a volume of the bleaching vessel in m.sup.3.