Page 261 - Distillation theory

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

7.3 Design Calculation of Two-Section Columns 235

Table 7.1. Product concentration of non-key impurity
components

η D = η B , x D4 , x B1 ,
mol. fraction mol. fraction mol. fraction
0.999 6·10 –10 3·10 –6
0.990 5·10 –7 2·10 –4
0.950 1·10 –4 4.4·10 –3
0.900 1.2·10 –3 1.71·10 –2

shows the little concentrations of non-key impurity components in the products
x D,4 and x B,1 found for this example.
Figure 7.6 shows section trajectories for different points (x f −1 ) sh at segment
lin
[x f −1 ] sh for this example at purities η D = η B = 0.99. Figure 7.7a shows how the
lin
tray number in the sections and in the whole column depends on these points.
Similar dependences are shown at Fig. 7.7b for purity η D = η B = 0.9. A decrease
of purity of products, as it was written above, leads to an expansion of segments
[x f−1 ] and [x f ]. Therefore, the last points in Fig. 7.7 exceed the limits of segments
sh
[x f −1 ] sh and [x f ] .
lin lin
Figure 7.8a shows the calculation trajectory of the sections at η D = η B = 0.99
sh
sh
and [(x f −1 ) sh − (x ∞ ) ]/[(x min sh − (x ∞ ) ] = 0.3 for two values (L/V) r , one
)
lin f −1 lin f −1 lin f −1 lin
of which is close to minimum. One can make out from this figure that at a mode
x D
2
x
F
x B

1 4

3
Figure 7.6. Section trajectories at quasisharp inter-
mediate split for the equimolar pentane(1)-hexane(2)-
heptane(3)-octane(4) mixture for L/V = 1.3(L/
V) sh , (L/V) sh = 0.614,η D = η B = 0.99 at different
min
min
sh
points (x f −1 ) sh at segment [x f −1 ] . Separatrix sharp
lin lin
3,4 1,2
R
split section regions Reg sep,r and Reg R are shaded.
sep,s
1,2 3,4