Fig. 6. The tree structure and flowsheet of ternary separation; (a) tree structure; (b) one flowsheet in which the lightest component A is obtained in the first column; (b) another flowsheet in which the heaviest component C is obtained in the first column.

In general, for convenience, it is better to substitute tree structure for flowsheet in the synthesis of separation sequence.

Note that the following assumptions are implied in this text if without particular specification:

(1) Each column section has enough theoretical stages to implement a sharp separation.

(2) The feeding mixture belongs to the categories: ideal mixture, nearly ideal mixture and nonideal mixture but without azeotropes formed.

(3) The relative volatilities between the feeding mixture are higher than the general limitation in which special distillation processes have to be used, i.e. a > 1.2.

(4) Components are ranked according to their volatilities. For example, for the mixture A, B and C, A is the most volatile, while C is the least volatile in the decreasing order.

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