ARTICLE:

• Separation of Liquid-Liquid Dispersions  download article

S. Hartland
Department of Chemical Engineering and Industrial Chemistry, Swiss Federal Institute of Technology, Universitatsstrasse 6, 8092 Zurich, Switzerland

ABSTRACT

A model is presented which predicts the variation in the heights of the sedimenting and coalescing interfaces with time using two parameters namely the initial drop diameter ф₀ and coalescence time τ₀ of a single drop at an interface for a given dispersion of known height H₀, dispersed phase hold-up ε₀ and physical properties. The model predicts the separation time t_f in terms of the initial sedimentation velocity v₀ and maximum coalescence rate ψ_i.
If the variation in t_f with ε₀ is known, it is possible to generate families of sedimentation and coalescence profiles corresponding to different initial hold-ups and heights. The coalescence profiles give the height of coalesced water as a function of time at different hold-ups. This variation may be replotted in terms of the variation in separated water with hold-up at different times. Such water cut curves are often determined in the crude oil industry since crude oil is opaque so the sedimentation cannot be observed and only the separated water is visible. However, the model equations for the sedimentation and coalescence profiles may be so expressed to predict the water cut curves and the associated position of the sedimenting interface. The water cut curves and the families of the sedimentation and coalescence profiles are thus interchangeable.
This is verified using experimental data for both crude oil and model oil systems. The variation in hold-up within the batch dispersion with time and position is measured using an array of γ-rays to follow the sedimentation of drops in the opaque crude oil. The sedimentation profile is obtained from these results with the help of the Kynch theory.

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