Page 72 - Distillation theory

P1: JPJ/FFX P2: FCH/FFX QC: VINOD/IYP T1: FCH
0521820928c03 CB644-Petlyuk-v1 June 11, 2004 20:12

46 Trajectories of Distillation in Infinite Columns Under Infinite Reflux

2 2
a) b)

2
4
1 3 x B
x B 8
x D
x F x F
7
1 1 4 1 4
5
x D
6
3 3

2 2
c) d)

x D

x D
x B
x F x F
1 4 1 4

x B

3 3
Figure 3.4. (a) Product region under infinite reflux for given x F and different
number of trays and D/F. Ideal four-component mixture (K 1 > K 2 > K 3 > K 4 ),
line1−x D atN=∞andx F1 <D/F<(x F1 +x F2 ),line2−x D atN=∞and(x F1 +
x F2 ) < D/F < (x F1 + x F2 + x F3 ), line 3 − x D at N =∞ and (x F1 + x F2 + x F3 ) <
D/F < 1, line 4 − x B at N =∞ and 0 < D/F < x F1 , line 5 − x B at N =∞ and x F1 <
D/F < (x F1 + x F2 ), line 6 − x B at N =∞ and (x F1 + x F2 ) < D/F < (x F1 + x F2 +
x F3 ), line 7− x D at D/F = 0, line 8− x B at D/F = 1; (b) distillation trajectory for
split 1 : 2,3,4; (c) distillation trajectory for split 1,2 : 3,4; (d) distillation trajectory
for split 1,2 : 2,3,4. Product regions are shaded, bottom region is darker shaded.
Short segments with arrows, conjugated tie-lines liquid–vapor.

belonging to the possible top product region at set feed composition (light shaded
region to the left of point F), if these points lie at the same c-line and material
balance line. Feasible points of distillate at R =∞ and N =∞ lie on lines 1, 2,
and 3; feasible points of the bottom product lie on lines 4, 5, and 6.
As can be seen in Figs. 3.3 and 3.4, at R =∞, N =∞, and with the increase of
the parameter D/F, the top product point shifts from the unstable node (vertex
1) to the feed point and the bottom product point shifts from the feed point
to the stable node (to vertex 3 in Fig. 3.3 or vertex 4 in Fig. 3.4). For this, the
number of distillate components increases and the number of the bottom product
components decreases.