Wash water treatment – saving water and energy
The ANDRITZ wash water treatment process is designed to keep the wash water loop closed.
The wash water cleaning system keeps operating costs to a minimum and allows highest wash water cleaning efficiency. The wash water tanks provide efficient cleaning and storing of the re-used water.
The wash water treatment process
During the raw material washing process, sand and wood particles are separated, but remain in the wash water. The treatment system extracts the particles and cleans the water so that it can be re-used in the system.
The ANDRITZ cyclone tank is the first step in this cleaning process. The used wash water is fed tangentially into the cyclone tank and starts to rotate. Due to the centrifugal forces in the cyclone, all heavy impurities move down to the bottom of the tank, where they are extracted. The pre-cleaned wash water overflows into the wash water collecting tank. This collecting tank has two chambers.
The first chamber is used for settling and extracting of fines. The clean water overflows into the second chamber, which is used at the same time as storage for the wash water before it is re-used in the chip washing process. Impurities collected at the bottom of the wash water collecting tank are also removed.
The filtrate from the ANDRITZ plug screw feeder is used to heat the wash water in the collecting tank. It is pre-cleaned in the ANDRITZ Hydrasieve inclined screen. The impurities separated are collected and dewatered in a screw press to minimize fiber losses.