4. Purification

The aim of this purification phase is to remove all residual impurities from the pulp to be sent to the machine: logs, incuits, pellets, plastics, inks, sands, etc.

Two types of scrubber are used: vortex scrubbers (hydrocyclones or "cleaners") and pressure classifiers ("screens").

At the head of the machine, several types of purifier are installed in series:

• first, a first group of vortex scrubbers, for coarse cleaning of heavy particles;

• and then, just before the head box, a second group of pressurized binders, for finer purification.

For some types, notably those with 100% recycled fiber, the head-end purification process only includes pressurized binders, as the recycled fiber preparation itself has already removed the...