Stripping Exhausting Column

The feed F splits the column into two sections. The accepted conventions dictate that we refer to the light species and, therefore, that the upper section be called the enriching section and the lower section be called the stripping (exhausting) section. 

The exhaustive U, Pu extraction step is best achieved in pulsed columns rather than in mixer settlers in order to keep the contact time lower at the very high radiation level. This operation is expected to produce as its main product a HAW raffinate that is virtually free of Pu (and Np, U) a scrub appears therefore superfluous and would dilute only the HAW. In order to attain still a good extraction efficiency within a few stages, A/O phase ratios < 3 should be avoided. This ratio corresponds to a TBP saturation by heavy metals of about 18%. Considerable amounts of Zr are therefore co-extracted, being however present essentially as inactive isotope. Either a complexing or a reductive stripping is advisable in order to keep the aqueous flow small and the acidity sufficiently high to avoid hydrolysis of Zr. 

The experimental techniques used were modifications of those previously described, Styrene (Monsanto Co.), divinylbenzene and trimethylol propane triacrylate (Polysciences Inc.) were freed from inhibitor and residual trace polymer by column chromatography on aluminium oxide. Monomers were used immediately after purification. For the actual grafting runs, low density polyethylene films (thickness, 0.12 mm. Union Carbide) were placed as strips (4 x 2 5 cm) in lightly stoppered pyrex tubes (15 x 2.5 cm) containing styrene/solvent solutions (20 ml) at 20 1°C For irradiation, the tubes were held on a circular rack surrounding a 1200 Ci cobalt-60 source The tubes were positioned such that the surfaces of the film were perpendicular, or near perpendicular, to the plane of the radiation At the completion of the irradiation, the grafted polymer films were removed from the monomer solution and exhaustively extracted in... 

Although not used in this book, other texts refer to the section of the column above the feed tray as the rectifying or the enriching section. In this section the vapour flow is greater than the liquid flow. The lower section is referred to as the stripping or exhausting section. Here the vapour flow is smaller than the liquid flow. 

The feed to be fractionated, which can be a liquid, a vapor, or even a combination of both, enters the column at some central location rather tiian at one of the ends of the cascade as had previously been the case. This results in a division of the column into two parts, the rectification or enriching section above the feed tray, and the stripping or exhausting section below it. The upper section serves to enrich the vapor in the more volatile components, a portion of which is ultimately withdrawn as liquid "overhead product" or "distillate." In the lower section, residual volatile components are progressively stripped off the liquid and conveyed upward as vapor, while the downward flow of liquid becomes enriched in fhe heavier or less-volatile components. 

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