Page 285 - Distillation theory

P1: JPJ/FFX P2: JMT/FFX QC: FCH/FFX T1: FCH
0521820928c07 CB644-Petlyuk-v1 June 11, 2004 20:18

7.9 Exercises with Software 259

of pinch method with optimization by distribution of trays among sections, by
distribution of heat loads among pumparounds, and with the choice of the way of
stripping in each side stripping.
Optimal cross-sections of joining of previous and posterior two-section columns
at calculation by method “tray by tray” of “Petlyuk columns” and of columns with
side strippings are cross-sections of previous columns closest by composition to
1
points S .
Calculation of necessary tray numbers at heteroazeotropic and heteroextrac-
tive distillation can be carried out by method “tray by tray” upward with optimiza-
tion by number of sections, by number of phases from the decantor for refluxing,
and by distribution of trays among the sections.

7.8. Questions

1. In which direction should one calculate the bottom section for split 1,2 : 2,3 ... n
using the method “tray by tray”? What about the top section?
2. Which components are product ones in the top product for split 1,2,3 : 3,4,5?
Which are impurity ones? Which are key ones?
3. What makes impossible the calculation of a two-section column by method “tray
by tray” for intermediate split in the direction upward or downward?
4. Where should the composition point x f −1 at the first tray above the feed cross-
section at quasisharp intermediate separation be located for the necessary tray
numbers in this section to be minimum? Infinite?
1
5. How can one find the coordinates of point S at a set composition x D and set
r
r
parameter (L/V) for split 1,2 : 3,4,5 ?
6. Where in the concentration simplex is the composition point in that cross-section
of the top section where concentration of light key component at the intermediate
split is maximum located?
7. What is the pseudoproduct of the second section above the feed cross-section of
the main column with side strippings if its products in the direction downward are
D, S 1 , S 2 , S 3 , B?
8. Why can one calculate the column of heteroextractive distillation by method “tray
by tray” in the upward direction?

7.9. Exercises with Software

1. Determine the necessary tray numbers and liquid and vapor flow rates in the top
and bottom sections of the column at optimal location of the feed tray for sepa-
ration of mixture of pentane(1)-hexane(2)-heptane(3)-octane(4) of composition
0.2, 0.3, 0.15, 0.35 at split 1: 2,3,4, reflux excess coefficients 1.2 and 1.5, product
purities (top and bottom): a) 0.99, 0.98; b) 0.95, 0.99; c) 0.98, 0.98.
2. Same for split 1,2,3:4.
3. Same for split 1,2:3,4.