Patent ID: 7351306

Claim:
A method for the production of cellulose pulp, comprising: adding an impregnation liquor to an impregnation stage; treating wood chips in the impregnation stage with the impregnation liquor at an impregnation temperature; cooking the wood chips in a cooking stage by using a cooking liquor having a cooking temperature of 150±20° C., the cooking temperature being higher than the impregnation temperature; withdrawing black liquor from the impregnation stage, the withdrawn black liquor being at the impregnation temperature and having a first concentration of dry matter (TS); subjecting the withdrawn black liquor to a pressure reduction in a pressure-reduction vessel to form a pressure-reduced black liquor having a second concentration of dry matter (TS), the second concentration being higher than the first concentration; conveying the pressure-reduced black liquor to an evaporation stage; in the evaporation stage, forming a partially evaporated black liquor, the partially evaporated black liquor having a third concentration of dry matter (TS), the third concentration having a dry matter (TS) concentration that is at least 10% higher than a dry matter (TS) concentration of the second concentration of the pressure-reduced black liquor; adding the partially evaporated black liquor to the cooking liquor at a start of or during a delignification stage; and cooking the wood chips in the cooking stage to produce cellulose pulp.