Effect of Pretreatment with Green Liquor, AQ and Polysulfide on the Performance of an Extended Batch System, 1998 Pulping Conference Proceedings

Extended delignification technology enhances the selectivity in the digester by removal of additional amounts of lignin without decreasing yield. The batch systems utilize displacement concepts for pre-treatment with black liquor before digesting with white liquor. A disadvantage with the extended delignification process is the yield loss that occurs as extended pulping is implemented. This will cause an increase in the load going to the recovery. However, use of yield enhancing additives retains more hemicelluloses and increases the pulp yield at a particular kappa number.

AQ, polysulfide, sodium sulfide and green liquor react with wood components during the pulping process.

These additives may be effective in increasing the delignification rate and also preserving the yield of pulp. The objective of this study is to determine how these additives react when used in a modified batch extended delignification process.

Replacing the 3% white liquor with green liquor decreases delignification but a significant increase in yield is measured. The use of green liquor instead of white liquor will enable us to lower the causticizing requirement at a mill. Use of AQ in a modified batch system results in a small increase in delignification but a higher increase in yield. The best improvement in delignification and yield is with AQ in HBL treatment stage. Using 0.1% AQ pulp yield can be increased by about 2%. An increase in delignification rate was observed with polysulfide pre-treatment in WBL or HBL stages of a RDH cooks. A yield increase of about 1% was measured at kappa numbers above 20.

When AQ and PS are used in combination, there is a higher delignification, but the benefits on yield are minimum. The most optimum way to use polysulfide and AQ is to use polysulfide in the WBL stage and AQ in the HBL stage.