TheWall: High-efficiency fiber treatment for consistently high product quality
Interview with Hartmut Langner, Paper and Board Mill Varel.
2017-03-30 - With TheWall, Voith has developed a disperser filling that makes it possible to treat fibers more efficiently. The Varel paper and board plant has been using the filling since May 2016. Hartmut Langner, paper production foreman at Varel, explains why the company was looking for an alternative to the previously used disperser filling and why the decision was made to go with TheWall from the Voith product portfolio.
Hartmut Langner: The production capacity of the de-inking line 4.3 is 420 metric tons of furnish per day. White, printed recovered paper is prepared here for white papers with a grammage ranging from 120 to 200 g/m². We are now successfully using Voith’s new TheWall disperser filling in this line.
What were your main reasons for looking for alternative providers of disperser fillings for line 4.3?
Langner: We had been noticing for some time that there was potential for improvement in the previously used filling. What is especially important to us is product reliability and consistent product quality. We always need to ensure that our end product satisfies the high quality demands of our customers. This took considerable time and effort with the previously used disperser filling and involved a lot of uncertainty. We were also dissatisfied with the service life of the industry-standard disperser fillings that we had been using.
Why did you decide to go with TheWall, which is a relatively new concept?
Langner: I think the overall package is coherent. One key point was the long service life. Until now, we've sometimes had to replace the equipment after relatively short runtimes. With TheWall, we have a service life that is five times as long. The material that Voith uses for this shows almost no signs of wear. In addition, the continuous structure of TheWall lowers the risk of material fractures, making it possible for us to reduce unplanned downtimes and save on costs.
Besides the long service life, what do you see as being the main advantage of TheWall?
Langner: All in all, the design of TheWall guarantees good stock guidance and highly efficient stock treatment. Practically all of the energy is used for dispersing the pulp, thereby producing results that are clearly better than products we used previously. Quality fluctuations in the raw material can be more readily compensated for with TheWall, meaning that the product quality is kept at a consistently high level. Even when there are considerable fluctuations in the raw material – a common enough occurrence for us with the recovered paper we use – the disperser now operates with uniform effectiveness. The consistent stock treatment intensity ensures that the subsequent flotation separates off contaminants as required. This uniformly high pulp quality is essential for us when it comes to ensuring a high level of process reliability for the production of paper. Moreover, the design makes a wide range of applications possible, speeding up our production considerably. With the fillings we previously used, we only had the option of setting the gap at a range of 0.1 to 0.6 millimeters. With TheWall, we have had very good experience working with gap widths of up to three millimeters.
One way that we improve the stock flow right from the start of the raw material feeding process is by using optimized rotor vanes at the inside edge. Another way is by situating the so-called breaker bars even before the actual dispersion zone to provide uniform distribution of the stock. Voith has developed a new concept for the dispersing process that is fundamentally different from all familiar high and low-teeth concepts. Voith has narrowed the gaps between the individual teeth here to a defined height. The resulting wall diverts the fibers at each of the rows of teeth, thereby dispersing stickies and dirt specks better. The end result is exceptionally good stock treatment, which is the basis for high-quality paper production. Many applications are already proving that the dispersion quality remains consistent throughout the entire service life.