Fundamentals of Screening: Effect of Screen Plate Design, 2000 Pulping / Process & Product Quality Conference Proceedings

F. Julien Saint Amand, B. Perrin--Various screen plates were tested with a chemical pulp (bleached softwood) and a mechanical pulp (SGW) under different operating conditions with an experimental pressure screen, which was had been designed to simulate various screening and fractionation conditions at the industrial scale.

The screen plate design parameters investigated were slot width, slot design and profile height for the slotted screen plates, and hole diameter for the drilled screen plates (smooth surface). The comparative trials were performed with two types of rotors (foil and blade rotor) under various "screening" conditions with fine slots(0.10 to 0.15 mm). The "fractionation" conditions were investigated with the foil rotor only, with larger slots (0.15 to 0.25 mm) and with holes (1 and 1.4 mm).

Compared to the machined screen plate design, the wedge wire screen plate design increased significantly the passage of the fibres through the slots and reduced the cleanliness efficiency, but did not improve the selectivity of the removal of shives as well as flat shaped contaminants. The reduction of the height of the screen plate profiles reduced the passage of the fibres through the slots. The selectivity of the separation between fibres and shives was slightly improved. The conventional fractionation conditions with holes were less effective.

The proposed analysis of the screening process, in terms of particle capture probabilities and slot passing probabilities with respect to the micro-flow conditions at the surface of the screen plate, highlights the experimental results and allows conclusions to be drawn regarding the removal of other contaminants.