Modeling of solid‐bowl batch centrifugation of flocculated suspensions

Abstract

Solid‐bowl batch centrifuges are used to thicken particulate and flocculated suspensions in many varied applications. The volume fraction dependent material parameters of compressive yield stress and hindered settling function are used to describe the solid‐liquid separation of a two‐phase system caused by centrifugal acceleration. The solution of the transient conservation of momentum and mass equations in radial coordinates gives the volume fraction distribution as a function of time for the two cases of the initial suspension networked or un‐networked. Analytical solutions are given for the equilibrium distribution and the small‐scale time dependence. The governing equations for the transient behaviors are solved using a 4th‐5th order Runge‐Kutta adaptive step‐size numerical method. The results show three zones of behavior: a consolidating bed, a sedimentation zone, and a clear‐liquor zone. The volume fraction within the sedimentation zone is constant for the initially networked case, and constant with radius but diminishing with time for the initially un‐networked case. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Models of rotary vacuum drum and disc filters for flocculated suspensions

“…The network yields if p y (/) is exceeded and the rate at which fluid exudes is determined by the solid-liquid drag or hindered settling function, R(/). This description has been used to model saturated dewatering processes such as dead-end pressure filtration, 7 batch thickening 8 and batch centrifugation, 9 for example. During dewatering by air displacement or vacuum pressure, particulate networks also exhibit a capillary pressure, p cap , at the air-liquid interface due to surface tension and the curvature of the particles.…”

Pseudo two‐dimensional modeling of sediment build‐up in centrifuges: A compartment approach using compressional rheology

“…20 and 21 from the bowl wall, w(0, T) 5 0, to the top of the sediment, /(Z sed , T) 5 / g . See Stickland et al, 9 for full details of the numerical scheme.…”

“…The consolidation of the accumulated solids is calculated in each compartment at each timestep using the approach of Stickland et al 9 This is performed in parallel with the particle trajectory calculations described earlier. The initially unconsolidated height of solids in the sediment of each compartment is given by the particle trajectory calculations and is assumed to be at the gel point, thus / 0 5 / g .…”

One‐dimensional model of vacuum filtration of compressible flocculated suspensions

“…As a first step, this theoretical work presents a one-dimensional mathematical model for vacuum and centrifugation [6][7][8] for flocculated slurries. In particular, the filtration model of Landman and White 9 is used here to describe the saturated processes of cake formation and cake consolidation.…”