Liquid-liquid extraction - Selecting, calculating and designing equipment

The two previous articles ( and ) were devoted to equipment description and modeling. The present fascicule, which is inseparable from the two previous ones, deals with issues relating to equipment selection, sizing and industrial implementation.

In addition to its efficiency in material transfer, the economic interest of an industrial device will be proportional to its specific flow rate (volume treated per unit area of the extractor's cross-sectional area). However, although it seems logical to maximize the three parameters that influence it (transfer coefficient, interfacial area and transfer potential), there is no device that can modify any of these parameters separately.

To meet these objectives, a wide variety of equipment has been developed. It is estimated that there are at least twenty different types of equipment in industrial use. This diversity leads the engineer, when designing a solvent extraction plant, to decisions that can be delicate and at best subjective in the absence of pilot-scale experimentation on the system under consideration.

The fundamental problem of how to calculate liquid-liquid extractors economically and optimally on the basis of purely theoretical data has still not been solved to our complete satisfaction. With the exception of a few cases where empirical correlations are available, the use of prototype tests is essential in almost all cases, and the most recent advances have essentially led to the definition of more reliable rules for extrapolating these tests to the dimensioning of industrial equipment.