The effect of fibre flocculation on fluidized bed expansion behaviour

To meet tighter environmental regulations, further efforts by paper mills will be required to reduce fresh water consumption and rejects loads by moving towards closed-cycle papermaking. However, an excessive build-up of dissolved and colloidal substances in process waters will occur with major impacts on paper machine runnability and paper quality. Adsorption of specific contaminants on modified solid sorbents in a fluidized bed reactor prior to recycling is proposed. Previous results with simulated and paper machine whitewaters showed that the bed expansion follows Richardson and Zaki predictions but corrections are required to take into account the pulp suspension properties. This study shows that fibre flocculation contributes significantly to the lifting effect of beads. However, bead's properties also interfere with the flocculation process. Both phenomena are dependent on pulp fibre length, fibre coarseness, and flow rate but also on bead density and size.