Improving Green Liquor Clarifier Performance with a Packed Bed of Dendrite Fibers, 2003 Fall Technical Conference

As mills add incremental capacity and move toward closed-cycle operation, the amount of liquor fed to the green liquor clarifier may increase beyond its design optimum. The resulting reduction in solids removal leads to contamination of the lime system and increased dead load in the liquor cycle. This is in part due to circuitous flow patterns inside the clarifier which carry more solids with them as they increase in magnitude. This paper shows that the addition of a packed bed of dendrite fibers can interfere with such patterns, causing the green liquor clarifier to act more like a plug-flow vessel, a system which is ideal for sedimentation because there is no axial mixing. This change is shown by the increase in the parameter α in the Weibull distribution model, where a high α value signifies approaching plug flow. Increasing the thickness of the bed further increases α. The random orientation of fibers in the bed acts as a resistance to nonaxial flow components, reducing the angular and radial components of velocity, that characterize mixing in the clarifier. The best results were obtained when the bed was placed such that all of the entering fluid had to pass through the bed in order to leave through the overflow port. It was also discovered that for green liquor systems, the contribution of filtration to the solids removal efficiency was around 5% and decreased with time, suggesting packed fiber addition to be a promising low-cost and low-maintenance means to increase the capacity of existing clarifiers.