Editing Kraft process (section)

===Washing===
The brownstock from the blowing goes to the washing stages where the used cooking liquors are separated from the cellulose fibers. Normally a pulp mill has 3-5 washing stages in series. Washing stages are also placed after oxygen delignification and between the bleaching stages as well. Pulp washers use [[countercurrent flow]] between the stages such that the pulp moves in the opposite direction to the flow of washing waters. Several processes are involved: [[thickening]] / [[Concentration|dilution]], [[displacement (fluid)|displacement]] and [[diffusion]]. The '''dilution factor''' is the measure of the amount of water used in washing compared with the theoretical amount required to displace the liquor from the thickened pulp. Lower dilution factor reduces energy consumption, while higher dilution factor normally gives cleaner pulp. Thorough washing of the pulp reduces the chemical oxygen demand ([[chemical oxygen demand|COD]]).

Several types of washing equipment are in use:
* Pressure diffusers
* Atmospheric diffusers
* Vacuum drum washers
* Drum displacers
* Wash presses