Abstract
This paper investigates a fractionation method of cellulosic fibres in dry state. Although processing of cellulosic fibres in airstream has been utilised for decades in airlaid processes, no attempts to fractionate fibres in dry state have been reported. Our main goal is to determine how fibre properties and fibre consistency affect fibre flocculation and thus the behaviour of fibres in fractionation. Also evaluations of quality and capacity of fractionation operation are made. Pulp flocculation behaviour is measured with digital imaging and image recognition technique before and after the fractionation device. A doubleview, orthogonal imaging approach is applied obtaining statistics of three-dimensional shape, dimensions and coordinates of detected fibre flocs. Fraction and fibre properties are determined with Metso Fractionator and Metso Fiberlab. Results show that fibre behaviour in a given system strongly depends on the pulp properties. Flocculation was found to be strongly dependent on fibre consistency. Evaluation of fractionation operation was done with help of calculations of mass-reject rates and separation efficiencies. Calculations showed that highest separation efficiencies can be achieved with system when mass-reject rate is between 0.30 and 0.40.