Green Liquor Impregnation in Kraft Pulping - Effect of Different Inorganic Components, 2000 Pulping / Process & Product Quality Conference Proceedings

T. Hultholm, B. Lonnberg--Green liquor impregnation prior to kraft cooking has from time to time been suggested as a method to improve the quality of the pulp produced. The objective of this work was to study the effect in an impregnation stage of the main components of green liquor, i.e. HS - , OH - and CO3 2- , each and in various combinations before kraft cooking of spruce wood. A "pure" HS - - solution was prepared by dissolving Na2S in water and neutralising the OH - ions with acid until no effective alkali could be demonstrated by titration. NaOH and/or Na2CO3 was then added to this solution. HS - -free liquors were prepared by dissolving of NaOH and/or Na2CO3 directly in water.

The results indicate that if no effective alkali (OH - ) was present in the initial impregnation stage, both HS - and CO3 2-could react with wood in a way that reduced the EA consumption later in the process in comparison with cases where effective alkali was present in the first stage. The fastest cook (lowest H-factor demand) was achieved with all three components present in the impregnation stage. Removal of CO3 2- increased the H-factor demand at kappa numbers above 30. Impregnation with a liquor containing only HS - resulted in the best pulp viscosity.