Non-Agitated Gravity Flow Extractors

Spray Column. The simplest differential extractor is the spray column (Fig. 18a.), which depends upon the initial dispersion of the dispersed phase to create favorably sized droplets. There is no means provided to redisperse this phase if any coalescence occurs. Although the equipment is simple and inexpensive, it is difificultto obtain more than one stage extraction. The passage of the dispersed phase ind uces considerable backmixing of the continuous phase, particularly in larger diameter columns. 

Flow by Drop Size control by Stagewise Continuous Differential 

Gravity alone Gravity alone Perforated Place Column Spray Column Packed Column 

Centrifugal Force Flow through baffles Westfalia Extractor Robatel Extractor Podbielniak Extractor Alfa Laval Extractor 

In contrast with vapor-liquid columns, tray efficiencies are very low (5 to 30%) in liquid-liquid systems. The trays do limit continuous phase backmixing as well as provide drop redispersion, but at the expense of reduced capacity. 

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Figure 18. Non-agitated gravity flow extractors, (a) Spray, (bj packed, and (c) perforated plate.

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