Wood Logs Processing

Wood logs with diameters ranging from 50 to 250 mm and lengths of 6 meters are received at the factory. Debarking of these logs is performed either at the source or in the factory, as the bark is a non-fibrous material and is not useful for the pulping process. Debarked logs are fed into chippers to be cut into chips approximately 25 mm x 25 mm x 3 mm thick. This size facilitates the impregnation of cooking liquor into the chips during the cooking process. The chips from the chipper are then fed to screens where accepted chips are separated from oversized materials and dust. The accepted chips are stored in a silo before being fed to the digester. Oversized material is sent to a rechipper, and the resulting chips are screened again.

Chipper: The chipper consists of a fabricated drum equipped with four chipping knives and one dead knife. Two feed rolls are provided in front of the chipper to pull the logs. The chipper is typically equipped with a startup motor with a variable frequency drive (VFD) to avoid jerk loads during startup.

A hydraulic system is generally provided for the hood and dead knife changing. Limit switches and rotation sensors are included to prevent accidents.

Chip Screen: The chip screen is a triple-deck system that separates accepted chips, oversized chips, and dust. It is rope-hung with an oscillation arrangement. The mesh size for accepted chips is 40 x 40 mm, while the dust screen has a diameter of 6 mm perforations. The screen has a movable eccentric assembly with bearing housing and base frame. One side is coupled with a vat and the other with a counterweight for balancing.

Rechipper: The rechipper is similar to the main chipper but has a lower capacity to process the oversized material from the chip screen. It has three fly knives on the drum and one dead knife.