Pitch reduction in a kraft aspen integrated mill pulping fresh chips

摘要

A kraft mill running aspen as its furnish uses approximately 20 metric tons/day of talc.The mill wanted to replace talc in its process because the handling and preparation took 6 work hours per day.The mill had tried various dispersants,but none performed to its expectations.The mill wanted to prevent the brown stock screens from plugging and either maintain or reduce the final pulp dirt counts,without affecting pulp quality.The mill decided to try a proprietary pitch dissolver/dispersant other than nonyl/alkyl phenol ethoxylates or ethoxylated alcohols.(The latter two pitch dispersants are considered to be carcinogenic.) The following results were obtained:Brown screens did not plug during the pitch dissolver/dispersant application period.Colloidal pitch decreased by 68% in the final bleached pulp filtrate.3.3% more dichforomethane (DCM) extractives were removed from the bleached pulp during the trialphase (from 76.8% reduction on chip to dry bleached pulp to 80.1% reduction).The overall bleached pulp dirt count did not change.The average count remained at 3.4 ppm.The pulp ash content decreased from 1.44% to 0.71% as the talc was shut off,a reduction of about 51%.The bleached pulp strength factor was unaffected.The paper machine efficiency improved by 30 h/month and the wire life increased by 15%.Precipitated calcium carbonate (PCC) consumption increased by 0.5%.