| abstract |
In the chlorine-free bleaching process using ozone, the pulp suspension is fed with vigorous stirring or blending, at a temperature of 15 to 80 ° C, preferably 40 to 70 ° C, and at a pH of 1 to 8, preferably 2 to 3, in contact with the ozone-containing gas. The ozone-containing gas contains 20 to 300 g / m.sup.3.n., Preferably 50 to 150 g / m.sup.3.n., Of ozone. A maximum of 2% by weight is used. preferably 0.05 to 0.5 wt. ozone, based on absolutely dry pulp. In order to be able to use this process for a pulp suspension in the range of medium consistency, i.e. for a pulp suspension with a substance density of 3 to 20% by weight, preferably 5 to 20% by weight, most preferably 7 to 15% by weight, a gas is introduced. containing ozone at a pressure of 1 to 15 bar, preferably 1.1 to 10 bar, into the pulp suspension. The process can also be carried out in multi-stage bleaching one or more times |