CFD modeling of the creaming zone of batch gravity separation with coalescence

Abstract

Gravity separation of liquid-liquid dispersions is present in many industrial applications, and it involves the complex governing mechanisms of creaming and coalescence in concentrated mixtures. The aim of this work is to model the laminar creaming zone of batch gravitational separation with coalescence using CFD tools. The numerical results were compared to the experimental decay curves of bottle tests. The initial DSD representation by the population balance model was obtained with the Gauss-Legendre Quadrature. The number of velocity groups and the application range of the drag modifier showed to be a function of the initial DSD profile and polydispersity, respectively. The coalescence models evaluated were the constant coalescence efficiency, the critical approach velocity and the film drainage for a deformable partially mobile interface. The coalescence models parameters were calibrated for a determined initial condition (phases volume fraction and droplet size distribution (DSD)) and then applied for different initial conditions. All models were able to model the separation of all initial conditions with the same calibrated parameters, although the drainage model did not need to be calibrated. This suggests that when employed in the modeling of a continuous separator, these can be calibrated by the decay curves of bottle tests.

Graphical Abstract

Keywords:

• Coalescence
• gravitational separation
• CFD
• creaming
• liquid-liquid dispersions