Recycle cooking wood chips with the residue liquid removed out of lignin by calcification for increasing pulp yield and reducing waste water discharge

Abstract

A large amount of low-concentration wastewater is produced during the production of chemical mechanical pulp. Due to low concentration, a large amount of energy is consumed by evaporation to prepare its concentrated liquor for combustion; resulting high cost in treating the waste liquor by the evaporation-combustion method. In order to solve this problem, a new method to treat chemical mechanical pulping waste liquor by directly calcification reaction is developed to remove out of lignin and generate sodium hydroxide in the treated residue liquid for recycle cooking wood chips; and thereby to improve the pulp yield and reduce waste water discharge. The pulp yields by recycle cooking are in the range of 86.7%–90.59%, being 9.6%–13.3% higher than that of the initiate cooking without the treated residue liquid. By the method, it reduces 90.6% of the cooking and milling waste liquor in the modeling pulp mill applying the recycle cooking wood chips technology.