Stock preparation, i.e LC (low consistency)-refining and fractionation, is one of the major tools for the papermaker to control paper properties. The design and the running of a stock preparation plant is however much based on practical experience and a deeper understanding of the underlying processes for fibre treatment and fibre separation is to a large extent lacking. Both energy consumption along the whole papermaking process chain and the product properties are affected by the stock preparation. Three areas are focussed in the present research.

The goal of the cluster is to produce stocks that allow a reduction in the grammage of paper and paperboard by 10%, through a more efficient use of available resources (energy and fibres); in addition, to reduce energy consumption by an additional 10% in stock preparation.

At Innventia refining is studied in a more multifaceted manner than the one commonly used. Instead of compare refining conditions at the same refining intensity the present work put the focus on the hydrodynamic condition in the refiner and its effect on fibre properties. Industrial scale refiners are used for the research in Innventia pilot plant. The work is both of a fundamental character but also of direct practical use in designing and running refiner systems in mills. A gap clearance sensor is a valuable tool to follow the power - gap clearance response of the refiner when changing conditions or change the properties of the pulp. High speed imaging is used to get new insights into the refining process. 

 

Fractionation

To use the variability of the fibres in the tree to enhance paper properties by applying pulp fractionation and selectively use the different fibre types is an attractive idea. The largest potential is to fractionate according to wall thickness. This is possible to achieve by the use of hydrocyclones which, however, has many drawbacks when integrated in the stock prep plant. The purpose of the fractionation project is to optimize the design of a new hydrocyclone design that fractionate without the enrichment of fines in the finer fraction.
Stock preparation strategies
The design and the operation of the stock preparation have an impact on how efficiently available resources, fibre and energy, are managed. The refining does not only consume energy for the refining process. It also have a profound effect on the overall energy consumption to produce the paper as it affects the energy consumption in dewatering especially to dry the paper. Any reduction in grammage due to a more targeted property profile of the paper is also directly reducing the energy consumption to reach a certain functionality. The project will evaluate different stock preparation strategies and there effect on fibre and energy consumption at process conditions similar to industrial papermaking (lab scale and pilot scale trials).