Extended Kraft Delignification

Modified cooking involves concentration profiling such that  

Digesters are getting larger, in part to accommodate longer, lower temperature cooks and so improve pulp quality. 

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In kraft pulping it is possible to delignify to a lower kappa number without undue carbohydrate loss by a process known as extended delignification. This involves adding alkali in two or more stages so as to maintain a fairly constant alkali concentration during the cook. The process is important as it reduces the extent of bleaching required subsequently and reduces the environmental impact of the bleach plant. 

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