Description of product system

Description of product system

Paper production, a brief description of the process

Fig. 1a Outline of paper production process
Fig. 1a Outline of paper production process

Raw materials processing

Wood

The process for the production of Kraftliner and Semichemical Fluting starts with wood coming from the forest to the mill. Most of the wood is delivered to the mill in the form of pulpwood logs but also a substantial part is brought as wood chips from saw mills nearby. The pulpwood logs have to be debarked and chipped before further processing. Therefore the logs have to pass through a barking drum and a chipper.

The chips produced are screened to take away wood dust as well as oversized chips and knots. The oversized chips are reprocessed to get proper chip dimensions and brought back to the chip flow. The chips are stored in a chip pile before processing in the pulp department.

Recovered paper

The raw material for Testliner (including White Top Testliner) and Wellenstoff recovered paper is delivered as bales, and kept on stock by grade.

With a pre-selection method, it is possible to determine the suitability of a certain recovered paper mix for the stock preparation and paper process. The stock preparation is done in accordance with a recipe for each paper grade and grammage. The grades of recovered paper are put on the conveyor to the pulper in the ratio mentioned in the recipe.

 

Pulping and stock preparation

Pulping and stock preparation of primary fibres

The wood chips are normally cooked to pulp for Kraftliner production by the kraft cooking process. It is a highly alkaline cooking process with caustic soda and sodium sulphide as active cooking chemicals. The cooking takes place in a digester at high pressure and a temperature of 150 -170 oC. The pulp yield is normally around 55% i.e. 1000 kg of dry wood gives 550 kg of pulp.

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Paper production

The stock passes through one or two headboxes onto the paper machine. The paper web is formed from the head box onto the wire and dewatered through the wire primarily by the action of gravity and suction/vacuum. Further dewatering by mechanical means takes place in the press section where water is taken out of the sheet by pressing between felts. The final drying takes place in the drying section of the paper machine where the sheet runs against steam heated cylinders to get its final dryness of 91-93%. The collected water is reused for diluting the thick stock coming from the stock preparation.

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