Environmental Engineering Reference
In-Depth Information
FEED LINE
2
1
1
3
0.9
4
0.8
5
0.7
y
=
x
line
0.6
0.5
0.4
Equilibrium line
0.3
0.2
0.1
0
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
Liquid mole fraction (H
2
O)
x
B
x
F
x
D
Figure 4.23
LANL, Example 4.6: HNO
3
and H
2
O.
A reboiler and partial condenser are each an equilibrium stage.
In general, if no azeotropes or side streams are involved, you can separate
n
products
with
n
1 columns.
It is necessary that vapor and liquid compositions are different at the equilibrium con-
ditions that one plans to use (i.e., no azeotrope), otherwise no separation will occur
beyond the azeotropic condition.
Distillation is different from evaporation because both components in distillation are
appreciably volatile. In evaporation, usually only one component is vaporized.
The products need to be thermally stable over the temperature range of operation.
No components which react exothermally (i.e., generate heat) should be present. These
reactions can “run away” and form explosive conditions.
The McCabe-Thiele graphical method uses three important types of line: the operating
lines, an equilibrium line and a
q
-line (feed line).
−
4.6
Questions
4.1 Show that higher relative volatilites correspond to a greater distance between the
vapor-liquid equilibrium line and the
y
x
line.
4.2 Show that the result of Question 4.1 corresponds to easier separation by distillation.
=
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