Studies of Wood and Wood Handling

To achieve the optimal balance between economy and quality, debarking studies represent a crucial tool, leveraging proximity to the factory and expert knowledge.

Significant savings can be realized by identifying the most effective method for debarking wood. For instance, if a facility with a wood cost of one billion kronor can reduce wood losses by just one percent, this translates to savings of ten million kronor. Regularly handling wood from various sources or sizes not only saves money but also ensures a more consistent pulp quality through a more uniform blending of wood in the debarking drum.

A debarking study is an extensive process, beginning with the systematic selection of approximately 200 logs from different batches at the wood yard. A section of wood is cut from each log to ensure that damage from harvesting or transportation does not affect the analysis. For each sample, bark or sapwood is removed with a knife to measure bark content, dry matter content, density, and diameter.

The selected batches are then processed through the debarking drum, and samples are taken to determine the amount of wood in the bark fraction, as well as wood chip samples that pass through the chip screen to measure bark content. These tests allow for the calculation of bark content, debarking efficiency, and wood loss for each batch, guiding discussions on optimizing the drum operation or the mixture of different wood types.

The residence time in the drum is measured by color-marking approximately 100 logs and timing from input until the logs exit the drum. Since heavy and long logs tend to move more quickly and have a shorter residence time than other logs, it's crucial that the selection of color-marked logs represents the wood used in a representative manner.

Understanding how different wood species interact with existing processes and how their chemical composition affects the final product is crucial for making informed decisions about the use of new raw materials.

Another question under investigation is how much of a specific wood species can be blended into the pulp without compromising the quality of the resulting mass. This entails determining optimal blending ratios to achieve desired properties of the pulp while efficiently utilizing available resources and minimizing waste.

Furthermore, it is also of interest to examine the effects of changes in chip size on the chip mixture. By modifying chip size, one can influence the distribution of different fractions within the chips, which in turn can have implications for the structure, strength, and other important properties of the pulp. Therefore, it is necessary to evaluate how different chip sizes affect process efficiency and the quality of the final pulp to optimize the production process and ensure consistent product quality.

In RISE's pilot cooking facility, we have the ability to use up to six input baskets to keep different wood species or chip fractions separated throughout the cooking process. This means that we can conduct cooking of up to six different raw materials or chip fractions in the same cooking step and under the same conditions, providing unique flexibility and opportunities for detailed experiments.

After defibration, we can analyze yield, kappa number, viscosity, rejects, chemical composition, and physical properties separately for each pulp or for different blends, entirely according to the customer's specific needs and requirements. One of the most important properties to study is the physical dimensions of the chips, especially in kraft cooking where chip thickness is crucial to achieve optimal impregnation.

After cooking, the different pulps undergo a bleaching process to evaluate bleachability and the properties of the resulting pulps, such as strength and optical properties. With RISE's custom refiner and experimental paper machine, we can then take the investigation one step further and evaluate the paper's properties, providing a comprehensive analysis of the material's performance.

Interest in wood investigations is high for several reasons. During periods of rising wood prices, it may be of interest to explore the effects of different blends, such as including eucalyptus in birch pulp. In other cases, the focus may be on blending effects of aspen. Since both aspen and eucalyptus are easy to cook compared to birch, they absorb cooking chemicals from the birch, requiring careful control of the blending level to avoid variations in quality.

For customers in Europe, it may also be interesting to evaluate wood species such as poplar, oak, and beech, whose cookability differs from that of birch. Sometimes the process does not start with chips; we may receive the wood raw material in the form of logs that we process ourselves by debarking and chipping before cooking. This is particularly common when the customer wants to test a wood species that is not normally used and where chips cannot be taken from the existing chip yard.