Assessment of pulp machine white water quality at market kraft pulp mills

The bleaching of pulp is a significant cost, yet the brightness achieved in the bleaching plant can be diminished in the pulp machine because of white water (WW) quality. Monitoring WW quality can control these losses. A method was developed to assess WW quality that allows differentiation between the effect of fibers, fines, and dissolved solids (DS) in the WW. It was found that the quality of the WW varied greatly from mill to mill. The brightness loss was mainly affected by the presence of fines, through a combination of their concentration and color. The DS were significantly less detrimental to the optical properties of the final furnish. None of the constituents present in the pulp machine WW caused significant brightness reversion (except the hardwood fine fractions). It is therefore recommended that a monitoring procedure for WW quality at the mill site be used to diagnose and prevent the occurrence of brightness problems. Such monitoring offers a way to reduce bleaching costs.