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Fiber variability of European spruce and wood assortments for improved TMP production - Applications at Stora Enso Corbehem

Stora Enso is a paper company with production units in many European countries and worldwide. The Stora Enso Corbehem Mill in France is part of the Publication Paper division. The main quality demands of the products are high levels of brightness, surface properties, printability and good strength properties for high runnability in papermaking and printing. The wood raw material used is a mixture of sawmill chips and pulpwood and also of spruce and poplar. Raw materials are supplied from a northern supply area (Northern France, Belgium and Germany) and a southern area (Central and Southern France). Prior to the EuroFiber project, new process equipment had been installed. The goal of the sub-project at Corbehem was to improve the LWC paper quality and runnability through a more favourable wood utilization.

Today the wood from the different regions is handled separated at the wood yard and mixed into the mill in defined proportions. The availability and prices are better for sawmill chips. It would thus be beneficial if more sawmill chips could be introduced. Questions to be answered were: Is it important to separate the raw materials from the two regions? Could a more favourable wood mixture be used with respect to availability, costs and quality, considering also the changed situation due to new process equipment? Very clear results are normally needed to convince about changes.

The combined results from the characterization of wood and fiber properties in various wood raw material alternatives and the refining trials performed on such different materials in laboratory and pilot scales were interpreted from the Corbehem perspective. Commercial-scale mill trials were designed in order to answer the questions above. In the trials, different types of materials from the two regions and proportions of sawmill chips were compared. During the trials, comprehensive measurements were performed on wood raw materials and pulps. Also the quality of the paper was carefully followed; the trials were performed under full-scale production of sellable paper.

Samples were taken from all tested raw materials and the samples were analysed for wood density and fiber length. The data showed that there were no systematic differences in wood density and fibre length between the two regions. There was, however, one big difference compared to normal and daily supply: during the trials, the wood from the south was transported by truck instead of by train transport. Therefore, the delivery time was shorter than under normal operation and more similar to the one for wood from the north.

The process conditions in pulp production were exactly the same during the trials as at normal operation. The stability in and control of operation was as usual and the specific energy used was also the same.

The pulp analyses showed that there were differences in fiber length after the first refining, which were related to the percentage of sawmill chips. The difference could, however, be handled by the process. After the complete process, there were no differences in the main pulp properties between the pulps from different wood sorts. With the process equipment installed in the Corbehem mill, the process has the strongest impact on the final fiber quality. And with similar pulp properties, no significant differences in the paper properties were observed when the different wood sorts were run during the trials. More studies are needed for further optimisation.

The results were so convincing that an action plansoon was implemented:
- The wood from the different regions will not be handled separately, which will simplify and decrease the cost of wood handling.

- The content of sawmill will be controlled and be increased. Larger raw material volumes will then be availability and at a lower cost.

- With these measures, the Corbehem mill will be able to decrease the cost of the pulp, increase its certified wood content, while producing the same paper quality.

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Reported by

Stora Enso Corbehem
Rue de Brebieres BP 2
62112 Corbehem
France
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