New On-Line Measurement for Pulp Bleaching, 1998 Pulping Conference Proceedings

One problem facing pulp mills is insufficient information for bleach plant control: the Kappa number is not entirely indicative of bleaching chemical requirements, and the brightness and residual measurements do not provide feedback on bleaching effectiveness or pulp bleachability. Such factors as the wood species, pulping conditions, and the use of hemicellulase enzymes change the relationship between Kappa number and bleach requirement. This, in turn, increases variability in the bleach plant operation and results in a higher chemical usage than necessary.

We have developed an instrument that gives a mill feedback on its bleaching chemical requirements and pulp bleachability. The instrument operates on-line by taking a sample of pulp, measuring lignin content, rapidly bleaching the pulp sample with chlorine dioxide, and measuring the resulting bleached brightness. This instrument enables mills to measure the changes in bleaching chemical requirements directly, which provides a means to characterize and improve bleach plant operations. The instrument is able to measure and quantify the effect of enzyme treatment on pulp.