Digester additives are used to improve the cooking process of chemical pulping. Anthraquinone (AQ) is used to improve yield, improve pulp quality or debottlenecking, whereas dispersing agents or wetting agents may be used as replacement for tall oil or to improve homogeneity and improve pulp quality.
Anthraquinone (AQ) is delivered as a 50 % waterborne dispersion, containing small amounts of emulsifier and stabiliser that give easier handling properties. It can be used in alkaline or neutral cooking processes like kraft, soda and NSSC. The AQ goes through a redox cycle that gives a catalytic effect, reducing peeling and increasing the delignification speed. This can be used to lower the Kappa, lower the H-factor, lower chemical demand and also to increase yield.
Digester aids are surface active chemicals that improve penetration of the cooking liquors and drive air out of the wood chips. They can also disperse and stabilise neutral extractives in wood. Digester aids can be used in all chemical and semi-chemical pulping processes and as replacement for tall oil. The effect is a more homogenous cook and the level of extractives in the pulp out of the digester is reduced. Synergy effects with Anthraquinone are often seen.