Centrifugal Separation
A continuous purification process that uses centrifugal force to separate dense and heavy contaminants from lighter cellulose fibres in a pulp slurry prevents downstream equipment damage. High-velocity rotation within a conical chamber generates hydrocyclone rejection when heavier particles move toward the outer wall and exit through the bottom tip of the unit. The clean stock, being lighter, concentrates in the centre and rises through the overflow outlet.
Yield Penalty
Discarded material from the underflow nozzle contains not only unwanted sand, glass, metal and plastic debris but also a portion of usable wood pulp. Minimising this loss of good fibre is essential for maintaining the overall efficiency of the mill. Operators use multiple stages of cleaners where the rejected stream from the primary unit is fed into secondary and tertiary cleaners to recover as much fibre as possible.
When the system is unbalanced, too much usable fibre is lost, increasing the production cost of the finished paper.
Reject Rate
The ratio of rejected material to the total incoming feed determines the configuration of the separation system. This rate must be monitored continuously to ensure that the cleaning cells are not blocked by dense grit. High rejection rates protect the paper machine from abrasive wear but can lead to excessive waste and effluent treatment challenges if not carefully controlled.
