HIGH-YIELD PULPING - A COMPARISON OF LABORATORY AND PILOT-SCALE SECONDARY REFINERS

E. regnans cold soda and radiata pine thermomechanical (TM) and chemithermomechanical (CTM) pulps were prepared in a Sunds Defibrator CD300 pressurized pilot plant refiner. The pulps were secondary refined with different disc refiners, including the CD300, a Sunds Defibrator open discharge ROP-20 and a laboratory open discharge Bauer, as well as a bar refiner, the PFI mill. The handsheet strength properties were compared; it was found that the PFI mill developed significantly higher strengths than the disc refiners for the cold soda pulps. The Bauer appeared to produce more fines compared with the CD300 and the ROP-20. For the TM and CTM pulps, the PFI produced poor handsheet strength properties due to fibre damage; it was concluded that this equipment should not be used for secondary refining of these long fibre pulps. Of the disc refiners the preferred choice for secondary refining was the ROP-20. Different primary pulps were produced with the CD300, and it was found that reproducibility as a primary refiner was excellent. There was some scatter of results when it was used as a secondary refiner. To study the effect of storage of washed and unwashed eucalypt cold soda and pine TM pulps, both primary and secondary samples were stored at 4-degrees-C for different time periods and evaluated. It was concluded that chemimechanical pulps, particularly those treated under alkaline conditions, should not be stored in the unwashed condition for more than 1 to 2 weeks prior to secondary refining.