Chip treatment

The chip pretreatment stage is a key process in all mechanical pulping processes and serves to create the best pre-conditions for uniform and desired fiber separation in the subsequent refining stage.

The preferred chip pretreatment solution depends on the type and quality of the incoming raw material as well as the target characteristics of the final end product. For chemi-mechanical pulps, uniform and efficient chemical impregnation is the most important pre-condition in order to achieve high-quality pulp at low operating costs.

Valmet´s PREX-impregnation system is today the most renowned and appreciated system on the market, offering the best solution in terms of pulp quality, flexibility, availability and cost per ton.

Presteaming bin

Presteaming softens the raw material before the screw feeder and makes it easier to compress, thus improving the dewatering capability and decreasing the wear of the screw feeder.

Plug screw feeder

Valmet Plug Screw Feeder feeds chips continuously into a pressurized or liquid-filled vessel. The plug screw feeder compresses the chips to remove pitch, water and remaining air, without shortening the fiber length.

Impregnator

The sudden expansion of the chips in the impregnator enables the chips to instantly soak up the impregnation chemicals provided to the impregnator.

Retention bin

The function of the retention bin is to provide sufficient reaction time for the impregnated chips. Steam is added to obtain optimum reaction temperature.