Effect of Recirculation on pulp Properties in Refining of Bleached Hardwood and Softwood Pulps with a Conical Refiner, 1999 Papermakers Conference Proceedings

Petteri Soini, Markku Partanen

The effect of recirculation on pulp properties has recently been discussed in some technical papers. Laboratory studies with a disk refiner have indicated that flow recirculation may improve strength properties especially in bleached hardwood pulp refining. The results of trials with bleached softwood pulp were also positive, but to a minor degree.

A series of pilot-scale refining trials were conducted to evaluate the effect of recirculation on pulp properties when the fibers are refined with a modern conical refiner. The effect of recirculation was studied with Scandinavian long-fiber kraft pulp and with South American short-fiber kraft pulp. Both recirculation rate and production rate were altered.

Results of these trials were opposite of the findings of the disc-refiner trials. The recirculation with the modern conical refiner had a slightly negative effect on fiber and sheet properties of the pulps studied. Only the tear strength of hardwood kraft pulp was slightly higher when recirculation was applied.

The only advantage of recirculation with a modern conical refiner seems to be when starting up a refiner to prevent unrefined pulp from entering the paper machine and during short operational shutdowns of the paper machine.