Other Column Arrangements

In the attempt to improve the flexibility of batch distillation operation as a whole, a closer look at alternative column configurations has been undertaken in the last few years. These different kinds of columns have been known since the 1950s, but a thorough understanding of their dynamic behaviour and features has only recently been achieved.

In the batch stripper represented in Figure 4A, the feed is charged to the reflux drum, while multiple cuts are withdrawn from the bottom of the column sequentially. In the middle-vessel batch column (Figure 4B), the feed is charged to an intermediate vessel, and the product/impurity removal is accomplished simultaneously from both the top and the bottom ends. The reboilers of both columns may be considerably smaller than the reboiler of a batch rectifier.

Potential improvements in column productivity, with respect to conventional batch rectifiers, may be very large when using these alternative configurations. However, to date it is not possible to provide general guidelines for determining a priori the best column configuration for a certain separation.

Figure 4 Sketch of (A) a batch stripper and (B) a middle-vessel batch column.

A preliminary simulation with a simplified model (or even with a short-cut one) should be used to assess the most profitable configuration for separating a given feed (amount and composition), subject to the given purity constraints.

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