Modeling of Solid-Bowl Batch Centrifugation of Flocculated Suspensions Anthony D. Stickland Particulate Fluids Processing Special Research Centre, Dept. of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria, Australia, 3010 Lee R. White Centre for Complex Fluid Engineering, Dept. of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 Peter J. Scales Particulate Fluids Processing Special Research Centre, Dept. of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria, Australia, 3010 DOI 10.1002/aic.10746 Published online December 12, 2005 in Wiley InterScience (www.interscience.wiley.com). Solid-bowl batch centrifuges are used to thicken particulate and flocculated suspen- sions 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 4 th -5 th 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, 52: 1351–1362, 2006 Keywords: solid-liquid separation, solid-bowl batch centrifugation, consolidation, sedi- mentation, thickening, flocculated suspensions, Runge-Kutta numerical method Introduction Centrifuges are used extensively by many industries to per- form solid-liquid separation, from dewatering biosludges in wastewater treatment to performing delicate protein separation. In two-phase systems, the centrifugal buoyancy due to the phase density difference causes the solids to thicken against the bowl of the centrifuge. There are two basic types: thickening and filtering centrifuges (the centrifugal analogies for gravity thickening and gravity filtration, respectively), which can be operated in batch, semi-continuous, or continuous modes. In thickening centrifuges, the bowl wall is solid: the particles settle against the wall of the centrifuge and form a cake, and the liquor is withdrawn from above the cake. Disc, decanter, and tubular centrifuges are examples of thickening centrifuges. Disc centrifuges have internal conical discs to aid sedimenta- Correspondence concerning this article should be addressed to P. J. Scales at peterjs@unimelb.edu.au. © 2005 American Institute of Chemical Engineers AIChE Journal 1351 April 2006 Vol. 52, No. 4