BLEACHING OF CELLULOSE PULP IN A FIRST CHLORINE DIOXIDE BLEACHING STEP

摘要

The invention concerns a method for bleaching cellulose pulp having an MC consistency in a first step with chlorine dioxide in a bleaching sequence with several bleaching steps. The pulp is bleached in this first chlorine dioxide step in a first phase at a lower temperature of 60 +/- 10 °C during a retention time of from 30 seconds to 30 minutes, after which the pulp is heated by at least 10 °C to a reaction temperature of 90 1/- 10 °C for a second phase, which has a retention time of 60-200 minutes. With this process modification of a first chlorine dioxide step, an efficient destruction of undesired organic acids is obtained, while at the same time improved viscosity/strength of the pulp can be obtained of the finally bleached pulp with a whiteness of approximatels 90 % ISO.