On the basis of the cost data, F = 7.72 and hence from equation 11.67:

Values of R are now selected and substituted in this equation with the corresponding values of n and —dn/dR taken from the previous table until a balance is attained. This occurs when R = 1.25

or approximately 150 per cent of the minimum reflux condition.

11.7.8. Multiple Column Systems

In considering multicomponent systems, a feed of say A, B and C has been fed to a single column and the top product, mainly pure A, is obtained with bottoms of mainly B and C. If each component is required pure, then a two-column system is required in which the bottom stream is fed to the second column to separate B and C. With more components in the feed, more columns will be required and their arrangement becomes more complex. This is a typical problem in the petrochemical industry and a paper by Eliceche and Sargent(42) offers particularly helpful advice.

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