Chip Thickness vs. Kraft Pulping Performance, Part 3. Effect of New Optimized Chip Quality on Continuous Cooking, Oxygen Delignification and Bleaching of..., 1994 Pulping Conference Proceedings

Panu Tikka, Hannu Tähkänen

The present paper describes a study where a fiber line starting with continuous two vessel vapor/liquid Kamyr cooking was fed with conventional chips and improved chips from a separate woodyard using GS-chipping and complete thickness screening. The wood supply was the same in both cases, 100 % Finnish pine pulp wood. In the study, two days of improved sample chips were run in between two days of reference with conventional chips at 1150 – 1250 ADt/d production rate. Synchronized chip and pulp samples were taken and analyzed in laboratory. The results were more dramatic than in our earlier work with different kraft batch systems. The kappa number decreased rapidly by three units after switching to improved chips. Rejects were reduced by 85 %. Pulp strength improved by about one tear index unit at tensile index 70 throughout the fiber line in spite of extended delignification. Laboratory bleaching results indicated easier oxygen delignification in terms of lower alkali consumption. Final bleachability was about the same in both bases. The physical and chemical performance of the cooking system improved in terms of pulp strength delivery: Brown stock pulp strength compared to that of the laboratory counterpart from the same chips was 89 % for pulp from improved chips and 83 % for pulp from conventional chips.