Batch Distillation

With process plants becoming increasingly larger, there has been a tendency for the chemical and petroleum industries to focus attention on the use of continuous distillation because this approach becomes progressively more economical as the scale of operation grows. As a result, batch distillation has become a somewhat neglected unit operation. There are, however, many areas where batch distillation can be used more economically than continuous. Batch sizes are available from about 300 to more than 5000 gal. A 300 gal unit is shown in Figure 9.

Advantages

The main advantage of batch distillation is its flexibility. A single unit can, by changing reflux ratios and boil-up rates, be used for many different systems. It also is possible to separate more than two components in the same column, whereas with continuous distillation, at least

Figure 9. Batch distillation/solvent recovery silhoutte mask.

N — 1 separate columns are required to separate N components.

A batch distillation process is very simple to control, and there is no need to balance the feed and draw-off, as is the case with the continuous distillation approach.

Batch distillation is particularly useful when applied to feeds containing residues that have a tendency to foul surfaces as these residues remain in the still and cannot contaminate the rectification column internals. For aqueous systems-handling materials that leave very heavy fouling, it is possible to heat with direct steam injection into the still and thus alleviate problems of buildup on the heat transfer surfaces.

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