Process and apparatus for producing bleached cellulose

A process for producing bleached chemical pulp comprising:

• subjecting a suspension containing lignin and chemical pulp to a first process step for oxygen-assisted bleaching in a first reactor, wherein oxygen required for the first process step is supplied to the first reactor at least partly in the form of oxygen-containing nanobubbles via a first introduction device in a first transport conduit supplying the suspension to the first reactor;
• subjecting the suspension to a second process step for oxygen-assisted bleaching in a second reactor downstream from the first reactor, wherein oxygen required for the second process step is supplied to the second reactor at least partly in the form of oxygen-containing nanobubbles via a second introduction device in a second transport conduit supplying the suspension to the second reactor from the first reactor;
• and
• subjecting the suspension to a third process step for oxygen-assisted bleaching in a third reactor downstream from the second reactor, wherein oxygen required for the third process step is supplied to the third reactor at least partly in the form of oxygen-containing nanobubbles via a third introduction device in a third transport conduit supplying the suspension to the third reactor from the second reactor;
• wherein the second process step is different than the first process step, and wherein the third process step is different than the first process step and the second process step;
• and
• wherein the first process step for oxygen-assisted bleaching is preceded by a wash stage in which wash water is supplied to the suspension, wherein the oxygen-containing nanobubbles are supplied to the first reactor at least partly by a wash introduction device that is located in a feedline supplying the wash water to the wash stage and that generates the oxygen-containing nanobubbles in the wash water for the wash stage.