Recent Control Experiences in Peroxide Bleaching of Mechanical Pulp, 1999 International Mechanical Pulping Conference Proceedings

Tom J.L. Gustavsson, Bertil Olsson & Dr. Gerdt H. Fladda

BTG Pulp & Paper Technology AB

Peroxide is becoming one of the most widely used chemicals for ECF and TCF bleaching of Kraft pulp and also for mechanical and de-inked pulps. Better control of the bleaching processes is therefore desired. For this purpose, the instruments of today for residual peroxide measurement have not been reliable enough.

A new instrument has been tested in different types of bleach plants for different pulp processes. The measurement is done batchwise on filtrate extracted from the process. The measuring method is based on catalytic decomposition of peroxide and the result is measured with a manometric method. The instrument is absolute calibrated and the instrument design and measurement method allow a measuring range for residual hydrogen peroxide up to 5000 ppm. This is very important in mills where they have grade changes with varying residual peroxide levels. Excellent results have been obtained in the field both when it comes to monitoring and controlling processes, where peroxide-containing filtrate is re-circulated.

This paper will give an overview of the measuring method and the design of the instrument. It will also present experiences obtained from two Scandinavian CTMP mills. The applications will be presented with focus on process improvements due to control strategies used. The paper will show that it is possible to save 10% peroxide while stabilizing the process and maintaining quality targets, incorporating control strategies involving accurate residual peroxide measurement.