Fibre length fractionation caused by pulp screening. Smooth-hole screen plates

Improved fibre fractionation, and selective processing of the resulting pul p fractions is a way to produce higher quality, more uniform pulp A pilot-p lant screening study determined the conditions of optimal fractionation, an d verified screening performance equations, It showed that fibre length fra ctionation and pulp consistency changes during screening are both related t o volumetric reject ratio, R-v, by a fibre passage ratio, P(I). This ratio quantifies the dependence of the ability of the fibre to go through a singl e aperture in the screen an the fibre length. The effects of aperture size, fluid velocity through the aperture, and R-v on P(1) were determined. A new definition of fibre length fractionation efficiency was proposed, similar to long fibre removal efficiency, brit which penalizes short fibre removal and is therefore more indicative of the fibre length separation. For a larg e aperture screen plate, the maximum fractionation took place at relatively large R-v. For smaller diameter apertures, the best fractionation occurred at a significantly lower R-v,. The maximum fibre fractionation occured for an intermediate hole size of 1.0 mm.