Date of Award

12-1984

Degree Name

Bachelor of Science

Department

Paper Science and Engineering

First Advisor

Dr. Philip Whiting

Abstract

Refiner peroxide bleaching trials were carried out at the Abitibi-Price Research pilot plant using a Sunds-Defibrator CD300 pilot-scale refiner. Results show that, at the pilot scale, blowline addition of bleach liquor gives better brightness gains than addition in the refining zone. Using this technique, brightness gains equivalent to tower bleaching can be obtained when the bleaching parameters are properly controlled. The most important factors were post-refiner retention time and temperature, and the alkali charge in the bleach liquor. These three factors were shown to be highly interdependent. Refining pressure (temperature) was shown to have little effect on brightness gain in this system but did effect both the bleached and unbleached brightness of the TMP. As in tower bleaching, it was found that chelation of metal ions is essential if maximum bleaching efficiency is to be achieved. Refiner blowline bleaching had no effect on pulp strength other than that expected from peroxide bleaching under more standard conditions. A mathematical model of peroxide bleaching was also developed with the intended use of calculating the required bleaching parameters for a mill system.

Other experiments showed that refiner dithionite (hydrosulphite) bleaching holds promise but that the best overall system might be refiner blowline peroxide bleaching followed by dithionite bleaching in a second stage. Computer modelling of this two-stage system and a cost analysis of the results showed that as much as a 30% reduction of chemical cost can be achieved if two-stage bleaching is used instead of peroxide bleaching alone.

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