Chlorine Dioxide Delignification Practices in Canada, 1996 Pulping Conference Proceedings

Doughs C. Pryke

Consultant

Douglas W. Reeve

University of Toronto

The speed of implementation of complete replacement of chlorine dioxide for chlorine in the first stage of chemical pulp bleaching, i.e., chlorine dioxide delignification, has been remarkable. Beginning in 1989, the production of pulp using chlorine dioxide as the only chlorine-containing bleaching agent, often referred to as “Elemental Chlorine Free” (ECF), has grown quickly. Almost ninety percent of bleach plants in Canada will produce ECF in 1996, totaling 8.2 million tonnes of bleached pulp. ECF pulp now accounts for almost seventy percent of Canadian bleached chemical pulp production. Chlorine dioxide delignification is rapidly becoming standard practice in the first stage of bleached chemical pulp bleach plants. Optimum conditions, (based on laboratory bleaching) are well developed for: 1) minimizing cost; 2) maximizing delignification; 3) maximizing pulp quality; and 4) minimizing environmental impact. However, the practical conditions utilized in actual mill scale production of ECF pulps are not well documented. This paper, based on the results of a survey of operating conditions employed by Canadian bleached chemical pulp mills producing ECF grades, describes mill practice for bleaching market pulp to high brightness where...