Interstage fractionation and low consistency refining for TMP. Part 1: Energy consumption and pulp properties

摘要

The impact of an interstage fractionation followed by a low consistency refining (LCR) stage prior to a high consistency refining (HCR) was studied. We present the resulting energy consumption and pulp property changes when different energy input ratios (energy at LCR/energy at HCR) are applied to the long fibre fraction obtained at the interstage screening. Three basic processes were studied: (1) a high consistency (HC) refining, (2) a low consistency (LC) refining, and (3) fractionation followed by an LCR stage and an HCR stage in series applied to the long fibre fraction, and recombination. We applied different energy levels to the long fibre fraction, from 100% of the secondary stage refining energy at LC and 0% at HC to 0% applied at LC and 100% at HC, as well as three intermediate ratios of the energy applied at LC. Properties were altered when excessive energy was transferred to the LCR. Adjustment of the LCR/HCR ratio prevented large losses in terms of tensile and tear strength. For 17 to 29% energy savings (to reach 100 CSF), the loss in tensile increased from 6 to 9%, whereas the tear changed insignificantly. Fractionation is significant in altering the energy-pulp property relationship, except in the case of tensile strength. Overall these results demonstrate that there is a considerable range of options for reducing the energy input while maintaining the quality of the final pulp through the use of fractionation and a combination of low and high consistency processes.