This is the second part of a two-part paper dealing with the fluid mechanics and mass transfer in structured packings for distillation column service. The first part elucidated pressure drop, flooding, and liquid holdup. The second part covers the generation of effective interfacial area and provides a general correlation for predicting the mass-transfer efficiency as a function of surface type, packing geometry, phase flow conditions, and fluid properties. The mass-transfer model has been tested against a variety of commercial structured packings, for distillation pressures ranging from 0.33 to 20.4 bar. In all cases the fit of the data is excellent, with the possible exception of the highest pressures, where additional factors of axial mixing appear to have an effect.

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A high-gravity vapor−liquid contactor (“Higee”) was studied under distillation conditions using a semiworks scale system. The cyclohexane/n-heptane test mixture was used at operating pressures of 166 and 414 kPa and under total reflux conditions. Rotational speeds ranged from 400 to 1200 rpm. Data were collected on mass transfer efficiency, pressure drop, and hydraulic capacity. As many as six transfer units were achieved in a bed depth of 21 cm, with efficiency being directly proportional to speed of rotation. Models were developed for mass transfer and pressure drop, and the earlier packed bed flooding model of Sherwood, which includes a gravity term, was found to represent the vapor capacity of the contactor. Sufficient information is given to enable the preliminary design of a system containing a high-gravity vapor−liquid contactor. Because the test mixture has been widely used for conventional contactor studies, means for comparing high-gravity contacting with other methods are now available.

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