Black liquor impregnation of Scots pine sawdust and chip screenings

Fine wood particles (sawdust and chip screenings) and wood chips made of Scots pine were impregnated with kraft pulping liquor and the results were compared. The effect of removing the smallest fractions from the fine wood particles was also studied. The fine wood particles differed significantly from the chips. Some differences were observed even between sawdust and chip screenings but the removal of the smallest fractions had only minor effects on the impregnation. Pine chip screenings generated residual liquors with lower EA than sawdust in the beginning of the impregnation but with higher EA sorption and consumption. In addition, pine chip screenings produced lower impregnation yields than sawdust, indicated by lower residual liquor dry solids and TOC contents. Pine chips again generated residual liquors with higher EA than fine wood particles and the EA sorption and consumption were substantially lower.