Effect of Operating Parameters and Rotor Body Shape on Flow Conditions and the Performance of a Pressure Screen, 1996 Pulping Conference Proceedings

J. Niinimtäki

O. Dahl

T. Tirri

H. Kuopanportti

University of Oulu

J. Hautala

Valmet Oy, Stockprep.

Pressure screens are widely used to fractionate or remove stock impurities in the pulp and paper industry. These are simple devices, but their performance is greatly affected by flow conditions in the screen basket. The purpose of this work was to determine the effect of operating parameters and rotor body shape on flow conditions and thereby on the performance of a pressure screen. The pilot screening system at the University of Oulu was equipped with a pressure measurement and sampling facilities in order to obtain pulp samples from three axial positions in the screen basket and the accept chamber. The screening experiments were performed using a slotted screen basket and hydrofoil-type rotors with cylindrical and conical rotor bodies, and the differences were evaluated. The effects of operating parameters such as reject rate, feed consistency, rotor frequency and hydraulic capacity on the performance of the screen were tested with the cylindrical rotor body. The results indicated, that the behaviour of the pressure screen is mainly explained by changes in the flow conditions in the screen basket. Thus an understanding of the flow conditions in the pressure screen basket is beneficial, especially for optimization of the screening process. The results also suggested that a conical rotor body reduces axial mixing and thereby improves the screening performance.