Community Research and Development Information Service - CORDIS

Refiner process optimisation for better product quality and reduced energy consumption at different wood raw material properties

The objective of Andritz was to obtain a better understanding of the relationships between wood properties, process design, and operation and product properties, to be able to offer better process solutions. The following results related to this objective were obtained from the measurements on wood and the trials performed in a laboratory refiner, in pilot scale and in commercial scale in mills:

A. Large differences exist in wood and fibre properties, both between and within trees. Some major findings are:

- Correlations and trends prove that wood density and virgin fibre length are two major parameters useful for the practical selection of wood for spruce in Europe. These parameters reflect the influence of geography, latitude, altitude, age of trees, etc. on pulp properties such as light scattering coefficient, tear strength and surface smoothness. Equal density and fibre length in a tree grown in Norway, Sweden or France bring similar paper properties. These parameters can probably be used in a similar way within other regions, too, for certain species.

- Juvenile wood fibres have thinner fibre walls and tend to be shorter than mature fibres.

- Slabwood, especially from final cuttings, represent 100% mature wood, while top logs and logs from first thinning mostly consist of juvenile fibres.

- Slabwood gives significantly better strength properties than pulpwood.

- Pulpwood chips with low density give pulps with better optical properties.

- The wood type has greater influence on pulp properties than the refining method used to produce TMP.

- The low-density wood consumed more energy than the high-density wood from each of the three countries.

- The wood with short fibers requires more energy than the wood with long fibers. Based on these results, the papermakers will in the future have new possibilities to select the wood, which they are using in their mills according to the needs of the end product (paper & board). The selection can be based not only on wood species but also on other parameters like basic wood density and virgin fibre length, which can give more information about the suitability of the wood. The results also have influence on the design of processes and equipment in the future, which is important for both equipment suppliers and process engineers who plan new plants.

B. Process Applications:

- Sorting of Wood: In order to make full use in pulp production of the fundamental knowledge we have on the differences on wood qualities, we have to develop techniques and skills for planting, growing, harvesting, sorting and separate storage of wood with different properties in the forests, sawmills and in a paper mill.

- Refining: The pilot plant trials which were carried out in Springfield (OH, USA) demonstrated that refining of mature long fibres, which mainly come from slabwood (sawmill chips), need 10V 15% less SEC. Thus, mills can expand their productions by using such wood and still use the existing refiners and refiner motors. Freeness of the TMP can be decreased by mainly using sawmill chips. The equipment can remain the same. With high-intensity refining (RTS), similar pulp strength can be achieved at lower specific energy consumption on the same wood species and quality. Typical energy savings are in the range of 300V 400kWh/t. Even higher energy savings could be achieved, if both advantages were superimposed. In that case the savings could be in the range of 500V 700kWh/t. This still has to be proven. High-intensity refining is also known to give better surface properties compared to conventional TMP. Thus, by combining the effects of the wood species and process options, new possibilities appear. Energy consumption has a direct impact on the emission of greenhouse gases and thus these findings and new process designs may help to achieve the goals of the Kyoto Protocol in the future.

- Dewatering and Bleaching: It is well known today that there exist big differences in the bleaching response of different wood species, e. g. softwoods (spruce, pine, fir) and hardwoods (aspen, poplar, birch). Certain differences in the drainage capacity of roundwood and sawmill chips have also been experienced in various TMP installations, but no clear dependencies are known today. However, little is known about the effects of basic density and virgin fibre length on the bleaching response or dewatering behaviour of such fibres. Thus, no predictions can be made on future process design without doing further research work.

- Process Control: New developments in process control try to make use of model predictive control systems to optimise the pulp quality and production quantity while minimising operating costs. Correlations and trends based on wood density and fiber length, which were developed in the EuroFiber project, can be used in such advanced process control packages to achieve the goals.

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