Abstract

The aim of this study was to compare refiner bleaching with conventional laboratory bleaching by means of hydrogen peroxide and magnesium hydroxide. Refiner bleaching in this study was a part of the ATMP (advanced thermo mechanical pulping) process, in which bleaching chemicals are added to the first stage refiner. Unbleached reference pulp which underwent similar mechanical treatment as refiner bleached pulp was used for laboratory bleaching. Bleaching efficiency was found to be almost equal for pilot scale refiner bleaching and conventional laboratory bleaching. A brightness increase of 10 ISO% was reached with addition of 26 kg t^-1 hydrogen peroxide leading to a final brightness of 66 ISO% using both methods. Slightly more COD (52 kg t^-1 compared with 46 kg t^-1) was generated in refiner bleaching compared with conventional laboratory bleaching to equal brightness with the same chemicals added.