A study of phase separation of secondary dispersions

Abstract

The literature pertaining to the formation and techniques of separation of secondary liquid-liquid dispersions has been critically reviewed. The different methods for determination of drop size distribution were also reviewed. The coalescence of a secondary dispersion of toluene in water has been investigated using beds of fibrous material made of glass wool. The variables studied were superficial velocity, bed height, dispersed phase ratio and fibre diameter. The inlet drop size,< 50 um, was measured by a Coulter Counter TAII, while the exit coalesced drops, >10-3m, were measured by photography. Effluent dispersed phase concentration was also analysed by Horiba Oil Analyzer. Confirmation of a critical velocity of 1.5 x 10-2 m/s and a critical bed height of 6 x 10-2 m was obtained. At these conditions the separation efficiency was found to be 80%. The experimental single phase pressure drop data were found to be best presented by the Carman-Kozeny equation. The two phase pressure drop was correlated by a modified form of the Blake-Kozeny equation. A theoretical comparison of drop capture mechanisms revealed that interception and sedimentation were predominant. An equation describing the drop capture rate was formulated. A combination of drop release mechanisms, i.e. drip point, ballooning and jetting was observed and the exit drop size was found to increase with increase of fibre size. The saturation profiles were predicted, using the relative permeability correlations, and compared to those predicted from the pressure drop expression. Experimental filter coefficients were compared with available models, and found to vary over a magnitude of 800 for the same operating conditions.