Low consistency (4 %) refining is also a common unit operation when processing recycled
pulps. It is always used when pulps are produced for packaging grades and is becoming more
common also for improved grades of deinked pulps intended for use in magazines (SC and
LWC) and improved news. The goal is as mentioned in other chapters to improve strength properties,
or optimise the fibre length distribution both for the recycled chemical and mechanical
pulp fibres. If the objective is to improve strength the refining is optimised to fibrillate fibres
without cutting while if the goal is to optimise the fibre length for some specific product generally
that fibre cutting is allowed. In the case of deinked pulps low consistency refining can also
be used as an extra disperser after or instead of the more expensive high consistency disperger
to disperse print ink and other contaminants that can be flotated in the post-flotation.
an upstream MC-bleach tower (stand pipe) where a reductive bleaching agent, normally sodium
dithionite is used.