White water

In papermaking, the white water is the flow of water that occurs during mechanical dewatering in the wire section of the paper machine. Most of it is used again in the process. A small part is - if no closed water cycle is implemented - after separation of solids to process wastewater.

On Fourdrinier paper machines, a distinction is made between white water 1 (from the direct run-up and register section), white water 2 (from the suction group) and white water 3 (from the suction chest roll or Gautsch).

The white water 1 contains only small amounts of fiber and primarily fine fillers. The waste takes place through hydromechanical drainage in the area of the register rollers or foils, i.e. in the first and second third of the screen. It represents the largest relative amount of white water and is returned directly to the head mixer as dilution water.
The white water 2 is created by vacuum suction in the suction group, i.e. in the last third of the screen. It already contains large amounts of loosened fibers and is mixed back into the feed in the mixer preliminary stage.
The white water 3 contains almost only fillers and dyes, since it is removed from the already finished fleece. White water 3 is usually returned to a material collection stage or sorting of coarse material and only then used for the return mixture.

In single-sieve cylinder mold paper machines, there is only direct white water, which, due to the type of drainage, is not as heavily polluted as the white water of the Fourdrinier machine. The white water 3 of the Fourdrinier machine arises as press water outside the wire section. The same applies to handcrafting.

By setting the retention , the solids content in the white water should be kept low in order to limit the cleaning effort on the pulp catcher unit, the reaction time of the headbox control, the pumping effort, the risk of deposits and possibly wear.