COOKING PROCESS OF LIGNOCELLULOSE MATERIAL

摘要

A method for digesting a lignocellulosic material is provided with which the yield of pulp at the same Kappa number is improved and the proportion of effective alkalis to be added at the same Kappa number is reduced. The method is a continuous digestion method using a digester equipped inside with a top zone, an upper digestion zone, a lower digestion zone, and a digestion/cleaning zone which have been arranged in this order from the top toward the bottom, each zone having a strainer disposed at the bottom, and a black liquor extracted through at least one of the strainers being discharged from the digestion system. In the method, a first digesting liquor comprising an alkaline digesting liquor having a specific composition is fed to the top of the digester or to a portion precedent thereto, a second digesting liquor comprising an alkaline digesting liquor containing sodium hydroxide as a major component is fed to the upper digestion zone, and a third digesting liquor comprising an alkaline digesting liquor similar to the second digesting liquor is fed to the digestion/cleaning zone.