Study Questions for
“Separation Process Principles” by
J. D. Seader and Ernest J. Henley
Chapter 9
1. Rigorous computer-based methods for multicomponent distillation are readily available. Why then is the FUG approximate method still useful and widely applied?
Section 9.1:
2. What does the acronym FUG stand for?
3. When calculating multicomponent distillation, why is it best to list the components in order of decreasing volatility? In such a list, do the two key components have to be adjacent?
4. When making a preliminary estimate of the distribution of feed components between distillate and bottoms, when is it reasonable to assume perfect splits for nonkey
components?
5. How are feed conditions established at the feed location of a distillation column?
6. What does the Fenske equation compute? Be precise! Is it a theoretical or empirical equation? Is it an exact equation? If not, what assumptions are made in its derivation?
7. Does the Fenske equation assume constant molar overflow as in the McCabe-Thiele method?
8. For what conditions should the Fenske equation be used with caution?
9. Is use of the Fenske equation restricted to the two key components? If not, what else can the Fenske equation be used for besides the estimation of the minimum number of equilibrium stages, corresponding to total reflux?
10. Can a distillation column be operated at total reflux?
11. Can a distillation column be operated under conditions of minimum reflux? If not, why not?
13. What is the difference between a Class 1 and a Class 2 separation?
14. Which Underwood equation is used to compute the minimum reflux of a Class 1 separation?
15. Why is the Class 1 Underwood equation useful even if the separation is Class 2?
16. What is internal reflux? How does it differ from external reflux? Does the
Underwood equation compute internal or external reflux? How can one be determined from the other?
17. What makes the derivation of Underwood's minimum reflux equation for Class 2 separations difficult?
18. What two assumptions are necessary to derive Underwood's equation for a Class 2 separation?
19. What Underwood equations must be solved for a Class 2 separation? Does the method of solution depend on whether a nonkey component distributes or not?
20. For a Class 2 separation, under what condition might the Underwood method give an unreliable estimate of minimum reflux?
21. What is the optimal range of values for R/min R?
22. Is the Gilliland correlation for actual stages and reflux theoretical or empirical? If the latter, how was the correlation developed?
23. What key parameter is missing in the Gilliland correlation?
24. What optimal ratio of N/min N does the Gilliland correlation predict?
25. When can a serious problem arise with the Gilliland correlation?
26. How can the Fenske equation be used to determine the optimal ratio of rectifying to stripping stages? Is it accurate? If not, what alternative equation is preferred? Is the alternative equation always reliable?
27. What is the best method for estimating the distribution of nonkey components at the actual (operating) reflux?
Section 9.2:
28. Is the Kremser method a group method? What is meant by a group method?
29. What is the Edmister method for estimating the effective stripping factor?
