Improving Chlorine Dioxide Bleaching Efficiency by Selecting the Optimal pH Targets, 2005 Engineering, Pulping & Environmental Conference

When operating chlorine dioxide (D) bleaching stages under mill conditions, it is important to establish reasonable operating targets and ranges. The relationship between optimal pH, acceptable range for pH control, chlorine dioxide bleaching efficiency and mill specific parameters such as wood species, pulp quality, and chemical charge were examined. The D stages of 8 separate fiberlines were simulated in the laboratory using mill pulps obtained from the various bleach plants studied. Both hardwood and softwood species were examined. Each simulated D stage is examined over a range of final pH targets and ClO2 charges to determine the relationship of pH to bleaching efficiency. The chemistry of chlorine dioxide and lignin reactions has been well documented and general recommendations on optimal pH published previously. Our work shows that, in practice, the optimal pH for a specific D stage varies with mill specific parameters and we will categorize these practical relationships in order to draw some general conclusions. Mill data were used to validate the relationship.