Low consistency refining of mechanical pulp : process conditions and energy efficiency
The thesis is focussed on low consistency (LC) refining of mechanical pulp. Theresearch included evaluations of energy efficiency, development of pulpproperties, the influence of fibre concentratio ...
Adjusting refining intensity by changing refiner plate design and rotational speed : Effects on structural fibre properties
La modification des proprietes des fibres a l'aide de divers types de plaques a l'etape primaire du raffinage a ete etudiee. Des procedes de raffinage ayant une vitesse de rotation, une temperature et un pretraitement variable ont ete soumis a l'essai dans deux combinaisons. Une vitesse de raffinage plus elevee et/ou une plaque plus vigoureuse entraine un accroissement du nombre de fibres fractionnees dans le sens de la longueur de la paroi de la fibre. Les resultats indiquent aussi qu'en accroissant le ramollissement par la chaleur, il est possible de preserver la longueur de la fibre et en meme temps d'obtenir un degre eleve de fractionnement de la paroi des fibres. La combinaison de la vitesse de rotation, de la temperature et du type de plaque rend possible la modelisation de la structure de la fibre.
Effects of pulp furnish and refiner speed on residence time in a high-consistency refiner
Pulp residence time in the refining zone of a high-consistency laboratory refiner was measured at different rotational speeds for chemithermomechanical pulp (CTMP) at 20% consistency using a technique developed by Ouellet et al. [J. Pulp Paper Sci. 22(8): J301 (1996) ]. The results were compared with (a) previous results obtained with kraft pulp and (b) predictions from the mathematical model developed by Miles and May [J. Pulp Paper Sci. 16(2): J63(1990]. Lower rotational speeds produced longer residence times, as expected from the theory. However, the residence time of CTMP was found to be much lower than of kraft pulp under similar operating conditions. The CTMP results also were in better agreement with the theory. The discrepancy between kraft and CTMP was explained through high-speed video observations of pulp flow in the refiner, which showed two distinct flow regimes. The radial location where transition from one regime to the other takes place was found to depend on furnish properties and rotational speed, and theoretical considerations allowed us to use this information to estimate the ratio of friction coefficients in Miles and May's theory. Application : the ability to predict residence time in refiners accurately is a key to better control and understanding of the refining process. This paper demonstrates the validity of an existing theory for the flow of pulp in refiners.