The repulping, refining and hot dispersing processes are considered in this first part “Pulp Treatment Processes” of the review paper about “Stock Preparation”, which focuses on the process engineering aspects of the unit operations used in the production of virgin and recycled pulps. Chemical and physical-chemical aspects are beyond the scope of this paper, as are pulp dilution, transport and storage.
The pulp treatment processes refer to the unit operations aim- ing at altering and/or upgrading the fibrous raw material and associated solid materials and contraries (inks and various contaminants). They include re-pulping or disintegration, refining or beating, hot dispersing and mixing. Pulp disintegration has curiously never been of great interest to the paper science community, and hence remains an area of investigation where quite substantial benefits could be gained through reductions in energy consumption. Some new approaches will be presented that get round the difficult concept of pulp apparent viscosity, which is really an aspect of rheology. One of the main operations in stock preparation is obviously pulp. While the effects of refining on fibres have been extensively studied in the past, its engineering parameters have not. For example, we do not yet know how to extrapolate refining results from the pilot to the industrial scale. It is even difficult to compare the effects of conical and disc refiners on the same pulp. It seems that only an integrated approach can improve our understanding of this process; one such will be proposed, building on fundamental engineering principles.
Then, the paper goes on to consider hot dispersion, an important process step in the field of paper recycling and deinking, to complete the effects of pulping and/or refining in terms of ink detachment, alteration of contaminants and fibre conformability. Hot dispersion is generally combined with bleaching because of the high temperature, consistency and mixing effect.