Softwood Bleaching Practices in Canada: Analysis of the 2003 PAPTAC Bleaching Committee "Best Practices" Survey, 2005 Engineering, Pulping & Environmental Conference

ECF bleaching is now firmly established in Canada. Bleached kraft pulp mills are no longer concerned with the transition to chlorine dioxide-based bleaching, but with optimization of chemical consumption and cost reduction.

Since the last survey in 1999, softwood bleach plants have decreased total chlorine dioxide use by 5%. However, the kappa number of the pulp entering the bleach plant has also decreased: by 8% for oxygen-delignified softwood, and by 7% for “conventional” softwood (i.e. without oxygen delignification). Furthermore, hydrogen peroxide use has increased by 13%. This means that although pulp mills are sending less lignin into the bleach plant, they are actually using 5-6% more oxidizing chemical per unit of lignin, and to reach a lower final brightness than before.

However, more detailed analysis of the data showed that most of these changes are primarily due to mills with “high” relative chemical consumption, especially in the case of the conventionally-delignified softwood bleach plants. When the mills were sorted and grouped by their overall Sequence Kappa Factor (the relative amount of ClO2 and H2O2 used in bleaching), there are clear differences between the “low” and “high” relative chemical consumption mills.