Process for bleaching a paper pulp with ozone and chlorine...

Details Process for bleaching a paper pulp with ozone and chlorine... Process for bleaching a paper pulp with ozone and chlorine...

D - Textiles, Paper

21

C

D21C 9/14 (2006.01) D21C 9/10 (2006.01) D21C 9/153 (2006.01)

Patent

CA 2247532

Process for bleaching a paper pulp in which the said pulp is subjected successively to the action of ozone and then of chlorine dioxide, or vice versa. The process according to the invention is characterized in that the paper pulp treated is a so-called "low concentration" pulp with a consistency of less than or equal to approximately 5% by weight, the mixing of the ozone with the pulp being carried out in a rotary stirrer in which the pulp is stirred at a low speed while ozone is injected into the pulp, so as to obtain a fluidized pulp, the tangential peripheral speed of the pulp at the walls of the rotary stirrer being less than or equal to approximately 12 m/s but greater than or equal to approximately 2 m/s, the contact time between the ozone and the pulp being between 1 min and 20 min and the amount of ozone injected into the rotary stirrer being between 1 kg and 20 kg of ozone per t of paper pulp on a dry basis, the pulp being maintained in the fluidized state for substantially the entire duration of the reaction with the ozone.

Procédé de blanchiment d'une pâte à papier, dans lequel ladite pâte est soumise successivement à l'action de l'ozone, puis à celle du dioxyde de chlore, ou vice-versa. Selon l'invention, le procédé est caractérisé par le fait que la pâte à papier traitée est une pâte dite « à faible concentration », avec une consistance inférieure ou égale à environ 5 % en poids; le mélange de l'ozone avec la pâte s'effectue dans un agitateur rotatif, où la pâte est agitée à faible vitesse pendant que l'ozone est injecté dans la pâte; on obtient ainsi une pâte fluidisée, la vitesse tangentielle périphérique de la pâte sur les parois de l'agitateur rotatif étant inférieure ou égale à environ 12 m/s, mais supérieure ou égale à environ 2 m/s; le temps de contact entre l'ozone et la pâte se situe entre 1 et 20 min et la quantité d'ozone injectée dans l'agitateur rotatif varie de 1 à 20 kg d'ozone par t de pâte à papier à l'état sec; la pâte est maintenue à l'état fluidisé pendant presque toute la durée de la réaction avec l'ozone.

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