Rectification transfer units

For absorption the same plate designs as for rectification are used. However, the efficiency of a practical stage is lower in absorption than in rectification. Therefore, besides the conventional columns, equipment with highly intensive contact of the phases, like in a jet washer or spray tower, is used. Hence, in contrast to rectification, the mass-transfer concept (Figure 2.3.3-4), in which gas and liquid transfer units... 

The advantage of rectification in a thin-layer evaporator in the pressure range of 1 -25 mbar is the small operating volume of the rectificator and the distillation unit. From this, a lower mixture residence time, a small specific pressure drop of a transfer unit, high vapor load and a low sensitivity to fouling mixture components results. 

Table 6.2 Number of Theoretical Stages and Gas Mass Transfer Units for Rectification (Absorption) of 1,000 ppm Heavy Impurity down to 1 ppm...

The distillation tower is the most important equipment used in rectification units. The different types of rectification towers and schemes have been described already in the preceding sections. In addition to towers, there are also other major items of equipment used in the rectification unit. These are essentially units used for heat transfer. Heat exchangers play a very important role not only in rectification units, but also in petroleum processing as a whole. All the heat exchangers used in the petroleum industry can be classified as follows ... 

In the conceptual design stage of a rectification unit, the initial objective is to determine the reflux number and the quantity of theoretical stages required to achieve the desired fractionation split at minimum costs. As a result of this procedure, the heat and mass balances of the column including the internal liquid and vapour flows get known, which are essential for the column design as well as for the selection of the type of internal mass transfer equipment best suited for the specific separation task. 

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