Screening and fractionation traditional technology now with new perspectives

Screening is one of the most important process stages in waste paper preparation for obtaining optimum finished stock quality. Modem screen basket technologies help to open up the way for new, highly efficient preparation concepts, both for graphic and for packaging grades. In mechanical pulp production as well as in approach flow systems, screens also play an important role in determining the quality of the finished product. Fractionating is a special screening application following different objectives. Whereas smooth perforated baskets have been used so far for the classical fractionation in waste paper preparation, profiled slotted baskets are now being increasingly used. The demands on fractionation systems have also changed. Today, for instance, the traditional fibre displacement into short fibre and long fibre fractions is no longer exclusively in the foreground in waste paper preparation, increasingly important is the production of a short fibre fraction with minimum disturbing components. The challenge for papermakers is the integration of fractionation systems in preparation concepts with maximum efficiency in removal of the disturbing components. The long fibre fraction, where the disturbing components are now concentrated, requires particularly intensive further processing. The paper describes how the new Voith Sulzer modular designed MultiSorter with proven C-bar screen basket technology can optimize the fractionation process. Based on extensive comparative measurement work in mill and pilot plant operation, machine and operation parameters such as rotor and basket design, stock consistency, reject rate and specific throughput are discussed. Finally, three system concepts show how fractionating and screening can be intelligently combined.