The goal of knot separation is to remove uncooked wood particles and other heavy debris from the pulp stream. Knot separation typically follows cooking and precedes brownstock washing; however, modern continuous digester fiberlines may introduce knotting after washing or even after oxygen delignification.
Andritz uses a closed knot separation system that comprises a pressurized screen (primary knotter) and a vertical atmospheric knot reject washer (secondary knotter). This system effectively separates the knot debris from the pulp, recovers good fiber for reuse, prevents the accumulation of impurities in the pulp, and reduces fiber loss and effluent load.
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