Choice of Sequence for Simple Nonintegrated Distillation Columns

3 CHOICE OF SEQUENCE FOR SIMPLE NONINTEGRATED DISTILLATION COLUMNS 

In addition to being restricted to simple columns, the observations are based on no heat integration (i.e. all reboilers and condensers are serviced by utilities). Difficulties can arise when the heuristics are in conflict with each other, as the following example illustrates. 

Example 11.1 Each component for the mixture of alkanes in Table 11.2 is to be separated into relatively pure products. Table 11.2 shows normal boiling points and relative volatilities to indicate the order of volatility and the relative difficulty of the separations. The relative volatilities have been calculated on the basis of the feed composition to the sequence, assuming a pressure of 6 barg using the Peng-Robinson Equation of State with interaction parameters set to zero (see Chapter 4). Different pressures can, in practice, be used for different columns in the sequence and if a single set of relative volatilities is to be used, the pressure at which the relative volatilities are calculated needs, as much as possible, to be chosen to represent the overall system. 

Use the heuristics to identify potentially good sequences that are candidates for further evaluation. 

Heuristics have been proposed for the selection of the Heuristic 1. Do D/E split last since this separation has the sequence for simple nonintegrated distillation columns1. smallest relative volatility. 

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