Refining Mechanisms and Development at TMP Properties in a Low Consistency Refiner, 2007 International Mechanical Pulping Conference

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First stage high-consistency (HC) mechanical pulps of Norway spruce (Picea abies) were processed in a low-consistency (LC) refiner in order to reduce the total energy consumption without sacrificing pulp quality properties. The present study has shown that the main difference between the low- and high-consistency pulps was that the low-consistency pulps contained a smaller fraction of long fibres compared to the high-consistency pulps. It was possible to increase the tensile index with 10 units in only one pass LC refining in such a way that the tensile index reached a level which was comparable with TMP from a secondary mill refiner.

The two-stage HC-LC layout for treatment of coarse mechanical pulp is mainly a concept in research due to lack of control mechanisms of low-consistency refiners. The operation of the LC refiners is demanding due to a narrow operating window, with a plate gap down to a few fibre widths. The plate clearance in a high-consistency refiner is several times larger. The need to control the process operation is essential in order to create a pulp of desired quality. Thus, it is necessary to collect more information from the process. The topical information of interest is associated to the gap clearance and the flow phenomena as well as the fibre coverage of the bars and the stresses applied to the fibres. The present investigation has combined the objective of lower energy consumption at maintained pulp quality with an objective to increase the fundamental comprehension of what is happening in the refining zone. The latter is sought by experimental research associated to gap, vibration and pressure measurements. Only through basic understanding of the real mechanisms it is possible to design and control the fibre treatment process.