Page 294 - Distillation theory

P1: JPJ/FFX P2: FCH/FFX QC: FCH/FFX T1: FCH
0521820928c08 CB644-Petlyuk-v1 June 11, 2004 20:20

268 Synthesis of Separation Flowsheets

1,2
a) 1 2 b) 1

1,2,3 1,2,3

2,3
3 3 2

1

1,2
c)

2
1,2,3 2

2,3

3
Figure 8.1. Sequences of simple columns for ternary mixtures: (a) the
direct sequence, (b) the indirect sequence, and (c) the prefractionator
sequence.
prefractionator and complex column were examined. It was shown that for this
mixture if the flowsheet with prefractionator and complex column is excluded, in
concentration triangle there are three large, approximately equal by area, regions
of preferability adjacent to vertexes. At large content of component A, direct split
(A: B,C) is preferable in the first column; at large content of component C, indi-
rect split is preferable in the first column (A,B : C); at large content of component
B, three-column sequence is preferable (A,B : B,C) → (A : B),(B : C). As far as
the flowsheet with prefractionator and complex column is concerned, its region of
preferability will occupy the bigger part of the area of the concentration triangle.
It was shown in other works (Agrawal & Fidkowski, 1998) that, while estimating
the expenditures by summary vapor flow V, the region of preferability of Petlyuk
columns occupies the whole area of the concentration triangle.
However, while estimating expenditures by thermodynamic efficiency η
(Agrawal & Fidkowski, 1999), as has to be expected, the region of preferabil-
ity of Petlyuk columns occupies only a small part of the area of the concentration
triangle, compared with sequences of simple columns and other distillation com-
plexes.