Concert of Apparent Viscosity of Pulp for Beating Analysis and the Development of the Paper Properties, 1996 Papermakers Conference Proceedings

A hydrodynamic model of refining process was developed based on the equations of motion. The model assumes that the pulp suspension behaves as an equivalent fluid with a given apparent viscosity. The studv of the rheological behaviour of the pulp carried out in a beater, yields an important result: it is a shear-thinning fluid Moreover, the apparent viscosity of pulp depends on the consistency, on the fibre dispersion, on the fibre aspect ratio and on the shear rate applied The model contributed to a better understanding of the refining process both for a fundamental explanation of the behaviour of pulp suspensions in the beaters and for the establishment of the running conditions in the beating processes. According to EFPG analyse, it was shown that the energy transfer depends on the rotation speed selected and the resulting apparent pulp viscosity. To select the best refining conditions for a given refiner, an optimisation method must be used Several factors must be taken into account - the pulp consistency, the pulp composition, the tangential speed the beating mode, the set point of the control variable. Furthermore the determination of the optimal beating conditions depends on the desired paper properties. The hydrodynamic model was used to interpret the refining results obtained in a Hollander beater for four different beating modes: constant gap clearance, constant loading force, constant total power and constant net power. For each trial, the physical properties of the paper were measured and the energy efficiency coefficients (EEC) were calculated. Significant energy savings (30% with respect to the total specific energy consumption) can be achieved in beating by selecting the best refining conditions according to the model.