Page 222 - Distillation theory

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196 Distillation Trajectories in Infinite Complex Columns and Complexes

a) 1 2 b) 1 c) 1
1,2
1,2
1,2,3
2,3 1,2,3 2
1,2,3

2,3
3
3 2
3
1
1
1 1
d) 1,2 e) f) g)
1,2
3
1,2,3
1,2,3 2 2 1,2 2
2 1,2,3
2,3
2,3 23
,
3
3 3
Figure 6.12. Some complex columns for ternary mixtures: (a) with side rectifying; (b) with side
stripping; (c) Petlyuk column; (d) with prefractionator; (e) more operable Petlyuk column; (f)
with divided wall; and (g) with divided wall for extractive distillation.

sequence: (1) of direct split (1 : 2,3); (2) of indirect split (1,2 : 3); and (3) of pre-
ferable split (1,2 : 2,3).
To transform each separation sequence into distillation complex, it is sufficient
to exclude one reboiler, one condenser, or both and to replace them by liquid
or vapor flows from the other column (Fig. 6.12). This figure for the sequence
with preferable separation of flows in the first column shows some additional
modifications (Fig. 6.12e,f).
Columns with side stripping (Fig. 6.12b) are used at refinery beginning with the
first decades of the twentieth century (see Watkins, 1979).
Columns with side rectifiers (Fig. 6.12a) are used at air separation with obtain-
ing of oxygen, nitrogen, and argon. The extractive column with side rectifier in one
body (Fig. 6.12g) was offered recently (Emmrich, Gehrke, & Ranke, 2001). Such
column takes the place of extractive distillation column and of entrainer regen-
eration column. It was shown that the application of such a column for recovery
of benzene from the mixture with nonaromatic hydrocarbons compared with two
columns effects energy saving of 15% ÷ 20% and capital costs saving of approxi-
mately 20%. The fraction of hydrocarbons C 6 with high content of benzene (from
catalytic reformate or from hydrogenated product of benzine pyrolisis) is the feed
of the extractive column and N-formylmorpholine is the entrainer.