Characterizing rheological behavior and fluidization of highly refined furnishes for process optimization

In this work, highly refined SWBKP (softwood bleached kraft pulp) furnishes, referred to here as XFC, were studied from the perspective of fiber suspension handling in processing. The rheology of the furnishes was studied with a rotational rheometer using a non-standard flow geometry to understand the viscosity development at different consistencies and the impact of temperature. The rheological data was used to evaluate the mixing conditions in tanks as well as fluidization conditions in process pipes. For fluidization analysis during pipe flow, two optical methods were implemented, namely Optical Coherence Tomography (OCT) and High-Speed Video (HSV) imaging. OCT was used to determine the small-scale floc structures near the pipe wall where the shear stress is highest and HSV was applied for observing flow instabilities and XFC suspension uniformity at the pipe scale. All these issues can be significant to decide what is the minimum flow rate required for a process pipe to get sufficient fluidization of XFC suspensions.