Effect of Turbulence on the Separation of Liquid−Liquid Dispersions in Batch Settlers of Different Geometries

Abstract

The separation of batch dispersions is affected by the initial turbulence present in the settler which reduces the initial sedimentation rate and the onset of interfacial coalescence. As the turbulence decays, these rates gradually increase, giving rise to sigmoidal sedimentation and coalescence profiles. A model is presented which describes the separation of a dispersion of height H0 and holdup ε0 with an initial drop diameter φ0, and interfacial coalescence time τd allowing for the turbulence decay time td and coalescence incubation time t0. For a given holdup ε0, the drop diameter φ0 and initial turbulence are themselves functions of the mixing conditions. The model is used to describe experimental data for both water-in-oil and oil-in-water dispersions for different liquid−liquid systems ranging from a heavy crude to a water-like model oil. The effect of physical properties, holdup, initial turbulence, and settler geometry is investigated.