Refining - Process Info
Refining - Introduction and background
Wood chips are transported from a chip washing system through a screw system, to the buffer bin. The buffer bin feeds a plug screw, which feeds the chips to the pressurized system prior to the primary stage refiner. In the buffer bin chips are preheated with steam.
Into the refiner wood chips are fed between two circular discs.
The chips are defibrated between the patterned discs and blown together with generated steam to a pressure cyclone prior to the second stage refiner. In the pressure cyclone the steam is separated.
The pulp is fed between the discs in the second stage refiner to be further grounded.
From the second stage refiner the pulp is blown to another pressure cyclone where generated steam is separated.
The steam separated in the pressure cyclones is led to the heat recovery.
Pulp from the second stage refiner falls down on a transporting screw where it is diluted to 4 – 5 % consistency with white water (cloudy filtrate). The diluted pulp falls into a latency chest.
During refining the fibres are ”stressed”, i.e. the fibres are bent and creased. In the latency chest the fibres can ”stress off”, i.e. straighten, during stirring.
After the pulper the pulp consistency is regulated and pumped to a screening system.
For a more efficient steam separation and less fiber following the steam a new device the mechanical steam separator has been developed. This device will replace the pressure cyclone and the feed screw into the refiner.
The mechanical steam separator has a high speed rotor (1500/1800 rpm).