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 distrib ution and pulp consistency during pressure screening. Performance equations have been derived to describe the changes in fibre concentration and lengt h distribution caused by the screen. These changes are described in terms o f a fibre reject thickening function, t(l), and a fibre removal efficiency function, e(l) Both functions are theoretically related to the volumetric r eject ratio of the screen, R-v, by a fibre Passage ratio function, P(l), wh ich characterizes the length dependence on fibre passage through a single s creen aperture. Experimental trials on a small industrial pressure screen d emonstrated that t(l) and e(l) were well predicted by P(I) over a large ran ge of R-v and l In addition, the pulp reject thickening factor and the aver age fractionation efficiency were theoretically related to P(I), and shown to compare well with experimentally determined values.