EXTENDING DELIGNIFICATION TH AQ POLYSULFIDE

The kappa number of fibers entering the bleach plant must be lowered t o meet the requirements of the Environmental Protection Agency's Clust er Rule. The options proposed ofr decreasing the kappa number include using oxygen delignification and/or extended digested delignification. Extended digested delignification can be implemented by modifying the cooking process (EMCC, RDH SuperBatch, or EnerBatch) or by using chem ical additive [anthroquinone (AQ) or polysulfide (PS)]. Even though ox ygen bleaching and modified cooking are proved technologies that can d ecrease the kappa number to the bleach plant, these two options requir e large capital investments, and the load to the recovery boiler is in creased. The use of chemical additives AQ and PS is a low-capital-inve stment option for decreasing the kappa number and minimizing the impac t on the recovery boiler. Additionally, a higher bleached pulp yield i s possible.