Improvement of Hardwood Pulp Yield in Continuous Kraft Cooking and Estimation of Pulp Yields (Part II)-A Mill Trial at a Continuous Digester-

Abstract

The optimal conditions of isothermal cooking (ITC) for the improvement of pulp yields were applied to a mill trial using mixed hardwoods, polysulfide (PS) , anthraquinone (AQ) and a continuous digester. PS cooking liquor containing 70% of total alkali and AQ (0.02%on wood) were charged into a chip-feeding circulation line, and then kraft cooking liquor containing 30% of total alkali was introduced into three circulation lines, i.e., top-cooking, bottom-cooking, and washing, where temperature reached about 130-145°C. Results from laboratory cooks of the mixed hardwoods showed that a linear correlation existed between pulp yields and ratios of xylose to glucose (X⁄G ratios) , liberated from the pulps by an acid hydrolysis. Pulp yields at a mill trial could be estimated by knowing X⁄G ratios of the mill pulps. It was indicated that the PS-AQ ITC under the optimal conditions gave pulps with 0.235X⁄G ratios at kappa number 18-19. It means that PS-AQ ITC shows about 7% higher pulp yields than laboratory kraft cooking and at least about 1.4% yield increases compared with the kraft ITC.