Fibre length fractionation caused by pulp screening

Fibre passage through small screen apertures is strongly dependent on fibre length, l. This results in significant changes in the fibre length distribution and pulp consistency during pressure screening. Performance equations have been derived to describe the changes in fibre concentration and length distribution caused by the screen. These changes are described in terms of a fibre reject thickening function, t(l), and a fibre removal efficiency function, e(l) Both functions are theoretically related to the volumetric reject ratio of the screen, R-v, by a fibre Passage ratio function, P(l), which characterizes the length dependence on fibre passage through a single screen aperture. Experimental trials on a small industrial pressure screen demonstrated that t(l) and e(l) were well predicted by P(I) over a large range of R-v and l In addition, the pulp reject thickening factor and the average fractionation efficiency were theoretically related to P(I), and shown to compare well with experimentally determined values.