Two-phase CFD modelling of gas dispersion in the fluidization bed of a reflux flotation cell

Abstract

This study presents one of the first 3D transient, two-phase CFD investigations of the novel Reflux Flotation Cell (RFC), resolving its internal hydrodynamics and coupled gas–liquid flow behaviour. The multiphase flow was modelled using a Eulerian-Eulerian framework with drag closure to evaluate the effects of superficial gas velocity (j G ), feed flux (F), wash water flux (W), and underflow flux (U) on gas holdup (α G ), turbulence, and interface dynamics. Simulations successfully captured the transient α G evolution dictated by j G and U and the model predicted increased turbulence intensity in the sparger region relative to the downcomer. Vortical structures characterized the fluidization bed section due to counter-current interactions of bubble plume and wash water stream with turbulent kinetic energy showing a coupled dependence on j G and W up to a critical threshold. Three distinct gas–liquid interface regimes were identified: above-channel, stabilised interface, and flooding-with transitions primarily governed by U. The interface-stabilised regime’s reflux mechanism enhanced phase segregation and system throughput. Under these conditions, the inclined channel geometry induced significant turbulence decay, transitioning the flow toward a quasi-laminar state. Predictions indicated that an intermediate W of 0.63 cm/s yields favourable hydrodynamic conditions consistent with optimal separation performance. At high U, simulations suggest limiting j G to ∼1.0 cm/s to prevent flooding. Overall, this study establishes CFD as a predictive framework for resolving RFC hydrodynamics, forming a foundation for future process optimisation, design refinement, and scale-up.