Influence of Sulfite Pulp Fines Separation on Oxygen Delignification and Peroxide Bleaching

The fact that primary fines show significantly higher lignin and extractives content does suggest a certain potential for cost reduction in bleaching, when primary fines are separated beforehand. These potential savings result on the one hand from a lower use of chemicals for pulp bleaching and, on the other hand, from the use of separated fines as an additive in other processes and products.

The objective of this master's thesis was to quantify the potential savings corresponding to a certain degree of sulfite pulp fines separation based on bleaching trials. For these investigations, a stirred bleaching reactor was purchased and put into operation. With this bleaching reactor it is possible to reproduce (in terms of temperature, pressure, duration etc.) industrial oxygen delignification and peroxide bleaching steps. Fines were separated beforehand using a lab-scale pressure screen. The samples were analyzed before and after a given bleaching step and the impact of separation on the final product properties was evaluated in the lab.

The results of these laboratory analyses show that the expected effect of fines on bleaching could be demonstrated. After the performed lab scale bleaching experiments, not only a lower kappa number could be achieved by fines separation, but also a higher brightness. Even though some unexpected effects occurred by just separating fines from pulp, an overall positive effect could be shown.