Page 209 - Distillation theory

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0521820928c06 CB644-Petlyuk-v1 June 11, 2004 20:17

6.4 Trajectories of Intermediate Sections of Extractive Distillation Columns 183

D

2
F 1
F 2 a)

B

S
m
+
N
m
x '
D
3
1
−
N
m
2

b)

S m

N + m

' x
D
1 3

−
N
m
2
R
Figure 6.7. A region (bundle) of intermediate section Reg w,int (shaded) of ideal
1,3
ternary mixtures (K 1 > K 2 > K 3 ) for two-feed column: (a) quasisharp split
(x D,2 > 0); (b) sharp split (x D,2 = 0).
Figure 6.7 shows for comparison the trajectories of quasisharp (a) and sharp
(b) reversible distillation in the intermediate section for ideal mixture (K 1 > K 2 >
K 3 ). This figure shows that, at movement of pseudoproduct point from the vicinity
of continuation of side 1-3 to this continuation itself, there is transformation of
reversible distillation trajectory: it disintegrates into two parts – into one that lies
inside the triangle and into the part that lies at side 1-3. We note that similar
transformation also takes place at passage from quasisharp distillation to sharp
one for the top and bottom sections. The stationary point S m at this transformation
+
stays at the internal part of reversible distillation trajectory. Point N passes to
m
−
side 1-3. Point N passes from vertex 3 to its vicinity at side 1-3.
m