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Fine drops pose a separation problem in batch gas-agitated liquid—liquid systems, such as pyrometallurgical and liquid—liquid extraction processes because a small amount of the more dense liquid phase remains dispersed in the less dense liquid phase in the form of fine drops long after agitation has ceased and the bulk liquid phases have separated. In this work the origin of drops with diameters between 10 μm and 100 μm was investigated. Three sources were identified: the disintegration of liquid columns entrained by gas bubbles as they cross the liquid—liquid interface, drop erosion resulting from collisions with large gas bubbles, multiphase drop rupture at the upper liquid—gas interface. Liquid entrainment was found to be the principal source of fine drops for systems with low liquid—liquid viscosity ratios, whereas drop erosion inside the upper liquid phase and to a lesser extent multiphase drop rupture were found to be the principal sources of fine drops at high liquid—liquid viscosity ratios. Criteria for minimizing fine drop formation in these systems are proposed.

The synthesis of a good flowsheet for a multicomponent separation problem constitutes a formidable task even for a small scale problem. The number of alternate, feasible separator sequences increases rapidly as the number of components in the mixture and the number of allowed separation methods increase. Some methods to select a sequence are almost purely heuristic to permit rapid screening among the alternatives without a guarantee of optimality. Another is based on dynamic programming and for special problems can in principle locate the best sequence, but it is notably time consuming. This paper uses primal and dual bounds in a branch and bound strategy to develop a procedure for locating a small number of nearly optimal separation sequences; furthermore, the optimal sequence must be among those found. Restrictions necessary for the dynamic programming approach can be relaxed (serial structure, high product purity), and in principle the method should generally be significantly faster. Two examples illustrate the approach.

In this paper the synthesis problem of distillation-based separation sequences that separate a number of multicomponent feed streams into a number of multicomponent products is addressed. A synthesis strategy is proposed that consists of: (a) the development of a distillation-based superstructure that has embedded many separation configurations as well as options for splitting, mixing and by-passing; (b) simulation runs performed for each of the distinct distillation columns involved in the superstructure; and (c) the mathematical formulation of the distillation-based superstructure as a mixed-integer linear programming problem which has as unknowns the stream interconnections. The solution of this mathematical formulation results in the optimal configuration of distillation columns that can perform the desired separation task, as well as in the optimal allocation of by-passes. The synthesis strategy is illustrated with the first two example problems while the third example demonstrates the use of the proposed approach as an initialization procedure for the general separation problem.

This is the fourth part of a series of papers on hydrocyclones. In Part I general considerations were presented, in Part II a pressure drop correlation was given, while in Part III a cyclone separation number was derived whose value was determined experimentally. An optimal cyclone shape was indicated. In this paper rules are given that enable hydrocyclones to be designed for any separation problem in which the size of the particles to be separated is known. Constructional details and items to be observed in designing a cyclone or cyclone battery are discussed. Finally the design method is illustrated by an example.