Vertical digester system for panelboard fibers

ANDRITZ produces digester systems for the treatment of raw materials prior to the pressurized refining system for the production of MDF fiber.

To produce high quality fiber, it is essential to treat the raw material with respect to its unique properties. The internal bond strength of the material must be reduced before the material is processed in the refiner. This is a fundamental rule to ensure uniform fiber quality.

ANDRITZ vertical digester

In order to soften the raw material and weaken the internal bonds, the material is heated to a weakening point. ANDRITZ offers digester systems to heat and prepare the raw material. This process is called cooking, steaming, or digesting.

ANDRITZ offers different cooking, steaming, or digesting systems with respect to the transport behavior of the raw material. Basically, there are two designs in use: vertical and horizontal. Both systems are heated with pressurized steam and operate under steam pressures of 6-10 bar(g). In both systems, the feedstock is fed in continuously from a plug screw feeder.

The vertical digester system

The vertical digester system is preferable for raw materials with good transportation behavior, such as wood chips. The chips are fed into the system. Based on the retention time required to treat the feedstock, the system can be operated with different heights of chip pile in the digester.

After digesting, the raw material is transported from the vessel with a discharger system which meters the feedstock according to the throughput capacity to the pressurized refiner.

The refiner itself is fed by a ribbon feeder screw. The ribbon feeder moves the feedstock continuously to the refiner while allowing the heat in the refiner-produced steam to flow against the feeding direction of the material back to the digester system.