The purpose of installing the Brown Stock Washing System is to wash the pulp after the cooking process to recover chemicals and other organic compounds. This system operates on a counter-current washing principle, where hot water is used in the final washer, and black liquor is sent to the recovery section from the first washer. The washers are designed to operate using a barometric leg vacuum system.

The inlet consistency of the washer is generally between 1.5% and 2.5%, and the discharge consistency is around 10%. A shredder repulper is installed at the inlet of the next washer to create a homogeneous mixture with a consistency of 1.5-2% by using the filtrate from the previous washer.

The filtrate from each washer is collected into a filtrate tank and used in the previous washer for dilution purposes. Due to the dilute nature of the liquor, foam generation can occur, which is controlled by installing a foam breaker in a foam tank.