Towards a Better Understanding of Pulp Suspension Flows, 2006 Papermaker’s Conference
In the papermaking process, the pulp flow is subjected to a series of accelerations, aiming at deflocculating the suspension, followed by decelerations. This results in energy consumption. However, the literature does not clearly account for the fraction of energy that is used for deflocculation. Pulsed Ultrasound Doppler Velocimetry and High Speed Video were applied in order to get a better understanding of flow in pipes, using an experimental loop. The results were compared to Computational Fluid Dynamics simulations. The same techniques were then utilized with a headbox pilot.
In all the cases, it was found that, even at high shear rates, energy consumption contributes to get a better fluidized pulp without breaking all fiber flocs. Indeed, though a reduction of the size of the flocs was obtained when the flow velocity was increased, many flocs were still present in the near the wall region, showing that the fibres were not as well dispersed as could be expected from the velocity profiles and pressure loss measurements.