Potential contribution of anion exclusion to hydroxide penetration in green liquor-modified kraft pulping

Abstract

Abstract Partial substitution of green liquor for white liquor in kraft pulping reduces calcining energy and reportedly enhances product properties. However, a full-scale trial showed that pulper rejects increased when green liquor substitution levels approached 10%. Imaging experiments and laboratory pulping runs demonstrate that the slower diffusion of hydroxide in the presence of green liquor carbonate is likely responsible for the elevated rejects. Green liquor substitution becomes increasingly more viable with decreasing chip thickness. Hence, such an approach should be especially suited to sawdust pulping where diffusion is not rate determining.