Principles of Kraft Cooking and Computer Simulation of Continuous Digester

Abstract

The computer model was developed to simulate two-vessel Kamyr continuous digester. The model was a static model that simulated steady state processes for process optimization and retrofit feasibility studies. A new equation that described cellulose degradation by dissolved lignin was incorporated in our model, which made it possible to evaluate the effects of multiple points of black liquor extraction. One of the kraft digesters of Nippon Paper Industries was designed by MCC^TM（Modified Chemical Cooking）．Prior to the startup, simulation was performed to predict pulp yield and strength properties of hardwood pulp. Simulation shows that higher pulp viscosity and yield were obtained at a given kappa number by several modified cooking methods. The dissolution of the hemicelluloses was best understood by separately considering the two major types：glucomannan and xylan. The content of xylan in MCC cooked pulp was higher than that of the conventional pulp because xylan remained relatively stable to alkali. As hardwood chips contain more xylan than softwood chips, it was predicted that the pulp yield increase in MCC^TM and EMCC^TM（Extended Modified Chemical Cooking）would be more pronounced in hardwood kraft pulp than in softwood kraft pulp.