Page 262 - Distillation theory

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

236 Trajectories of the Finite Columns and Their Design Calculation

N
a) 30

tot
20
str
10 rec
∞
x − x
−1
0 f min f − ,1 ∞ sh
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 x f − ,1 sh − x f − ,1 sh
N
b) 10
tot
8
6
str
4
rec
2
∞
x − x
−1
0 f min f − ,1 sh
∞
−0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 x f − ,1 sh − x f − ,1 sh
Figure 7.7. Number of trays in each column section at quasisharp intermediate
split for the equimolar pentane(1)-hexane(2)-heptane(3)-octane(4) mixture for L/V =
sh sh
1.3(L/V) min , (L/V) min = 0.614,η D = η B = 0.99 (a), and η D = η B = 0.90 (b) at different
sh
points (x f −1 ) sh at segment [x f −1 ] . tot, total, rec, rectifying, str, stripping.
lin lin
close to the mode of minimum reflux the trajectories of sections come close to
2
2
points S and S , in the vicinity of which they sharply change their direction. In
r s
the points of turn of trajectories compositions at neighboring trays show but little
difference, which leads to the big number of trays in sections and in the whole
column.
Figure 7.8b shows the dependence of tray number on the value of (L/V) r for
this example. It is typical that an increase in the excess reflux factor leads to a sharp
growth in the little concentration of non-key impurity components in the products:
−7
x D,4 = 1.0 · 10 −12 , x B,1 = 1.4 · 10 −6 at (L/V) r = 0.455, x D,4 = 7.3 · 10 , x B,1 = 3.1 ·
10 −4 at (L/V) r = 0.713.
Figure 7.9a shows calculation trajectories of sections for equimolar azeo-
tropic mixture acetone(1)- benzene(2)-chloroform(3)-toluene(4) at η D = η B =
sh
)
0.99; (L/V) r = 0,778 and (x f −1 ) sh = (x ∞ ) sh + 0.5[(x min sh − (x ∞ ) ]. The sep-
lin f −1 lin f −1 lin f −1 lin
1,3
aratrix trajectory bundle of the stripping section Reg R for this example has a
sep,s
2,4
number of characteristic peculiarities that are rendered the clearest by a projection
perpendicular to edge 2-4 (Fig. 7.9b) to which the points of the bottom product
belong.
The main peculiarity consists of the fact that at the value of parameter (L/
V) r = 0,778 the structural conditions of trajectory tear-off are broken in a