Effect of Fibre Properties on Flocculation and Fractionation of Cellulosic Fibres in Dry State

This paper investigates a fractionation method ofcellulosic fibres in dry state. Although processing ofcellulosic fibres in airstream has been utilised fordecades in airlaid processes, no attempts tofractionate fibres in dry state have been reported. Ourmain goal is to determine how fibre properties andfibre consistency affect fibre flocculation and thus thebehaviour of fibres in fractionation. Also evaluationsof quality and capacity of fractionation operation aremade. Pulp flocculation behaviour is measured withdigital imaging and image recognition techniquebefore and after the fractionation device. A doubleview,orthogonal imaging approach is appliedobtaining statistics of three-dimensional shape,dimensions and coordinates of detected fibre flocs.Fraction and fibre properties are determined withMetso Fractionator and Metso Fiberlab. Results showthat fibre behaviour in a given system stronglydepends on the pulp properties. Flocculation wasfound to be strongly dependent on fibre consistency.Evaluation of fractionation operation was done withhelp of calculations of mass-reject rates andseparation efficiencies. Calculations showed thathighest separation efficiencies can be achieved withsystem when mass-reject rate is between 0.30 and0.40.