Cleaning of raw material by chip washing
ANDRITZ chip cleaning consists of three stages – the chip washer itself, the chip pump, and the dewatering screw.
The function of the ANDRITZ chip washer is to clean the raw material – the wooden chips – by separating them from foreign materials such as stones, metal, and sand. This system is of utmost importance to ensure high performance of the refining system while minimizing wear on the refiner itself.
Chips are supplied in a continuous flow from the silo and enter the chip washer via a special inlet chute. As they fall into the wash water, they are agitated by a paddle wheel over a weir to the outlet. In this way, heavy contaminants are separated from the chips and eliminated through a sluice arrangement at the bottom of the washer. The floodgate empties into the ANDRITZ trash collecting screw which transports the trash material into a container for removal.
The chips are then transported to the ANDRITZ pump sump by the flow of water. This pump sump creates the best suction effect for the ANDRITZ chip pump. Additionally, the sump enables the collection of wash water and chips whenever it is necessary to drain the pipe between the chip pump and the ANDRITZ dewatering screw; for example when the chip washing system is shut down.
The chip pump transports the chip/water mixture to the dewatering screw. The pump is an open-impeller centrifugal design. The very strong turbulence of the water in the pump cleans sand, earth, small stones, and so on, off the chips.
The dewatering screw is designed for the following main activities
- Dewatering the material (free water and water on the surface)
- Cleaning off sand, dirt, and small stones
- Continuous material handling into the mixing screw or to the pre-steaming bin
After this, the screw conveys the chips to the pre-steaming bin.