Development of fiber properties in full scale HC and LC refining

The aim  of this work was to evaluate in more detail how fibers are developed during high consistency (HC) and low consistency (LC) refining. Three TMP mainline processes in mill operations were investigated for two configurations, one with only HC refining and the other with HC refining followed by LC refining. LC refining gave a similar increase in tensile index with increasing specific energy for the three lines, despite differences in the fiber property profiles of the feed pulps. At a given tensile index, LC refined pulps had a lower light scattering coefficient compared with only HC refining in the respective TMP line, but similar fiber length, strain at break, tear index and freeness. For two of the three lines, tensile index increased more with specific energy in LC than in HC refining. Whether installation of LC refining in a TMP line improves energy efficiency or not, depends on which pulp property(ies) the efficiency is related to, and also on the possibilities to optimize efficiency in the HC stages. Fiber curl decreased significantly for all LC refiners and remained unchanged or increased with higher energy in HC refining, although samples were tested after hot disintegration. Thus, the decrease of fiber curl contributed to the increase in tensile index in LC refining. When assessing the performance of LC refiners, fiber curl needs to be considered. Other fiber properties developed in different ways in HC and LC refining, resulting in different fiber property profiles for the two configurations.