Scaleup Oldershaw columns

Scaleup from Oldershaw column. One laboratory-scale device that found wide application in supplying efficiency data is the Oldershaw column (Fig. 8.13 Ref. 207). This column is available from a number of laboratory supply houses and can be constructed from glass for atmospheric operation or from metal for superatmospheric separations. Small hole diameters and small tray spacings are used. Typical column diameters are 1 to 3 in. 

Fair et al. (203) investigated scaleup of Oldershaw column data to commercial columns. Over the region of practical interest (50 to 35 percent of flood), the commercial point efficiency was either equal to or slightly higher than the Oldershaw column efficiency. Fair et al. concluded that the Oldershaw column efficiency la essentially a point efficiency measurement, and recommend this point efficiency for the design of commercial columns. A mixing model can be used to convert the point efficiency to overall column efficiency. This will enhance the commercial column efficiency. In a later paper (145), Chan and Fair include an additional correction for weir height this correction will also enhance the commercial column efficiency. A conservative approach proposed by Fair et al. is to apply the Oldershaw cal urn n effi-... 

Previous work with Oldershaw columns (209-211), however, spells a note of caution to Fair et al. s conclusion. For a fixed system, higher Oldershaw column efficiencies were measured under cellular foam conditions than under froth conditions. For this reason, Gerster (212) warned that when cellular foam can form, scaleup from an Oldershaw column may be dangerous. The conclusions presented by Fair et al. (208) do not extend to Oldershaw columns operating in the Cellular foam regime. Other considerations for scaleup from pilot columns (above) may also be important. The scaleup procedure recommended by Fair et al. (208) is... 

The Oldershaw mating provides values of the point efficiency. It is still necessary to correct this efficiency to the Mutphree and overall effidencfea, and approaches for this will be given later. For the moment It is important to consider the potential importance of die Oldershaw scaleup method a specific definition of the system may not be necessary the matter of vapor-liquid equilibria can be bypassed (in effect, the Oldershaw column serves as a multiple-stage equilibrium still) and efficiency modeling can be minimized or even eliminated. 

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