COOKING OF LIGNOCELLOSIC MATERIAL

摘要

PROBLEM TO BE SOLVED: To reduce the Kappa number at the same effective alkali addition ratio and improve the pulp yield at the same Kappa number in a method for cooking a lignocellulosic material. SOLUTION: This method comprises using hardwood or coniferous chips, adding an alkaline cooking liquor containing a polysulfide sulfur at 3-20 g/L concentration expressed in terms of sulfur content and further the sulfur content in an amount of 45-100 wt.% and an effective alkali in an amount of 45-79 wt.% based on the respective total amounts contained in the alkaline cooking liquor introduced into the cooking system to the top of a permeating vessel and further feeding an alkaline cooking liquor containing a quinone compound in a specific amount based on the bone-dry chips to the permeating vessel or the bottom of an upper cooking zone in the continuous cooking method using two vessel digesting devices comprising the permeating vessel installed in front of a digester and a column top zone, the upper cooking zone and a lower cooking zone installed from the top to the bottom in the interior of the digester, a strainer arranged in each zone bottom and capable of discharging a cooking black liquor extracted from at least the one strainer of the respective strainers to the outside of the cooking system.