Environmental Engineering Reference
In-Depth Information
Calculate:
L
,
D
, and the composition of
A
in the
L
stream coming off the reboiler. Use
a McCabe-Thiele diagram. Be sure to label the equilibrium curve and the operating
line.
Solution
(see Figures 4.13 and 4.14):
Definition of a partial condenser:
y
D
and
x
1
are in equilibrium:
The material balances give a slightly different answer than that obtained from the
McCabe-Thiele analysis shown in Figure 4.15. The McCabe-Thiele analysis is only
an approximate solution, and it may be that the discrepancy comes from the need for
more equilibrium data points to obtain a more accurate equilibrium curve.
Schematic:
Equilibrium data:
D
y
A
x
A
Partial condenser
0
0
0.35
0.10
0.70
0.30
Plate
0.90
0.50
0.95
0.70
Reboiler
1.0
1.0
feed (
V
)
L
Figure 4.12
Schematic and equilibrium data for partial condenser, Example 4.4.
D
,
y
D
= 0.8
L D
=
2
LD
=
2
1
V
=100mol hr
Overall material balance:
VLD DD D
2 3
∴
D=
33.3 mol hr and
L=
66.7
mol
=+ =
+ =
2
/
hr
LV
=2 3
⇒
slope of top operating line
3
L
V
,
y
= 0.3
Figure 4.13
Equilibrium stages and passing streams, Example 4.4.
Material balance on
A
:
xL
+
08
.
D
=
03
.
V
3
1
Vapor
x
3
=0.05
(See Figure 4.13)
Liquid
Figure 4.14
Partial condenser on Stage 1, Example 4.4.
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