Cooking of cellulose pulp in a cooking liquor containing preevaporated black liquor

摘要

The method is for cooking of cellulose pulp in which the raw material, preferably in the form of chips, undergoes a successive elevation of temperature towards the cooking temperature while the chips are first impregnated with an impregnation liquor followed by cooking in a cooking liquor that is preferably alkali. Through the addition of pre-evaporated black liquor, either as early as the impregnation stage or during the subsequent cooking stage, an improved delignification process is achieved in which the pulp obtains improved properties, primarily with respect to strength/viscosity for a given degree of delignification, and also with respect to yield. The method can be used both for continuous cooking and for batch cooking of cellulose pulp.