Mo Och Domsjo Aktiebolag

Sten L Haggstrom

Jonas A Lindahl

John R Bergstrom

Ernst B Tiberg

Greta K Fossum

A method is provided for controlling the supply of delignifying and/or bleaching chemicals in the continuous delignification and/or bleaching of lignocellulosic material such as wood and pulp in a through flow delignification and/or bleaching stage which commprises admixing the lignocellulosic material with delignifying and/or bleaching chemicals and flowing the lignocellulosic material under delignifying and/or bleaching conditions through the stage while controlling the addition of the delignifying and/or bleaching chemicals according to the ratio of the quantity of delignifying and/or bleaching chemicals consumed to the quantity of delignifying and/or bleaching chemicals originally charged, referred to hereinafter as relative consumption, the time and the temperature in a manner to maintain substantially constant the relative consumption of delignifying and/or bleaching chemicals at a predetermined time by the lignocellulosic material during flow through the stage.

Process for controlling the supply of delignifying and/or bleaching

A process is provided for the acid bleaching of cellulose pulp with peroxides at a pH within the range from about -0.5 to about 3, followed immediately by aqueous alkaline extraction of the dissolvable lignin without intermediate washing.

Process for the acid bleaching of cellulose pulp with peroxides

A process is provided for the bleaching of cellulose pulp, particularly for the peroxide bleaching of high yield pulp, which comprises forming a suspension of lignocellulosic pulp material; mixing the suspension in a mixing zone with a bleaching agent while adjusting the temperature of the pulp suspension to within the range from about +10.degree. C. to about -10.degree. C. of a temperature within the range from about 40.degree. to about 95.degree. C. at which bleaching is to be carried out; quickly dewatering the pulp suspension to a pulp consistency within the range from about 18 to about 50%, equal to or at most 5% less than the pulp consistency of the pulp suspension charged to the mixing zone; passing the dewatered pulp suspension to the bleaching zone before its temperature can change substantially from the adjusted temperature; carrying out the bleaching with a bleaching agent at the selected bleaching temperature within the range from about 40 to about 95.degree. C.; and recycling the bleaching liquor recovered from the dewatering to the mixing zone while maintaining a temperature in the recycled liquor to bring the pulp suspension to within said range of the bleaching temperature during the mixing with bleaching agent.

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Overhornas, Sweden

Sten L Haggstrom