M&T Compression Refining
Compression Refinig - Refining technology for higher end-product quality and higher process efficiency
Introduction
For the production of paper and board a lot of energy is needed. To realize significant savings in the specific energy consumption, breakthroughs in technologies are needed. For the development of new breakthrough technologies in paper production, Holland depends on foreign leading companies, specialized in paper production machinery. Nevertheless the Dutch paper industry made a big step in breakthrough technology with the development of the Compression refiner, a complete new technology. The compression refiner realizes a 40% lower energy consumption, 30% lower steam consumption and an increased lifetime of a recycled fiber compared to traditional refiner technology.
Refining
In Holland the fiber raw material for the production of paper and board is 75% recycled fiber and 25% imported virgin fiber. Virgin fiber raw material has to be mechanically treated to be used for paper production. This so-called refining-step makes the fibers more flexible to improve inter-fibre bonding in the paper sheet.
The traditional refining technology squeezes the fibers between to indented metal plates. Hereby the fibers loose rigidity and the fiber surface is roughened. In this form the fibers have a higher fiber-fiber bonding and create better paper properties. The refining process consumes a lot of energy. Furthermore the damaging of the fiber reduces the recyclability of the fibers. Also the formation of fine materials during refining (“fines”) decreases the dewatering and increases the steam consumption during the drying process.
The idea
In 2000 the paper producers in the project started investigating the essential functions and mechanism of refining in order to develop a technology for a new fiber treatment without the drawbacks of traditional refining. This investigation was performed in the EET funded project “Fibre Raw Material Technology” (Vezelgrondstoftechnologie). The results of this research showed that the main fiber property for developing the paper properties is the fiber flexibility. A roughened surface will only significantly increase the energy consumption for dewatering and drying, while the positive effect of fiber surface roughness on the paper properties is low.
Fibre surface damage is caused by the shear forces introduced in conventional refining technique. The cooperation in this project resulted in the development of a Compression refiner. The Compression refiner technology refines the fibers with only compression forces. This leads to a much higher efficiency and less fiber damaging, and therefore improves the sustainability and recyclability of fibres.
The Compression refiner
The Compression refiner develops the fiber properties for paper making with compression forces instead of shear forces. The fundamental technique for Compression refining is the development of a rotating drum in which the fiber slurry (pulp) is treated with rotating indented rollers on the drum surface. The pressure of the rollers on the drum surface controls the refining energy. Applying a speed difference between the rollers and the drum might create a controllable shear force on the fibers.
The Compression refiner treats the fiber in such a way the fibers will transform from a tube form to a collapsed tube form. This increases the fiber flexibility and therefore the fiber-fiber bonding and thus the paper properties. The treated fiber has less fiber surface damaging resulting in lower dewatering- and drying energy consumption during processing . Furthermore this less damaging technique preserves the fiber in a way that a fiber can perform more recycle cycles and thus eventually more fibers will be available for recycling.
The main challenge at the end of the EET project was the transformation of a batch process to a scalable continuous concept of compression refining. The big challenge in the design is the prevention of shear forces during high pulp loads.
In this follow up EET project the paper producing partners together with the Wageningen University (Wageningen UR) and Bouma Technical services developed a continuous operating machine based on the compression refining principle. With this equipment an insight in the most important factors dominating the compression refining effect could be achieved for scaling up. Based on this knowledge a small scale industrial demonstration Compression refiner is developed.
Result
This new development resulted in a reduction of the energy consumption for fiber treatment. Due to a reduction of fibre surface damage a reduction in the dewatering and drying energy could also be achieved. Furthermore due to a less destructive processing of the fibers the fibre cycle is extended and more fiber material will available for recycling. This means that besides the lower energy consumption this technique will lead to a lower impact of paper production to the environment due to a higher recyclability and therefore a lower consumption of virgin fibers.
The Compression refiner will reduce the energy consumption for refining with 40%. Due to a better dewatering performance the amount of process chemicals for dewatering control can be reduced with approximately 5%. The highest impact of compression refining is the reduction of the steam consumption during drying. A reduction of 30% of drying energy is calculated. Because more than half of the total energy consumption of the paper industry is drying energy, at least 15% reduction of the total energy consumption for papermaking can be achieved with the introduction of Compression refining.
The Dutch paper- and board industry is ready for the Compression refiner. Also from foreign countries there is a lot of interest in this new technology. When this new technology replaces the traditional refining techniques, significant savings for the industry will be achieved.
Project Partners
Bouma Technical Services, Wageningen UR Papier en Karton, Smurfit Kappa Roermond Papier, Sappi R&D.
Contact
Arie Hooimeijer a.hooimeijer@kcpk.nl
