Environmental Engineering Reference
In-Depth Information
∆
B
Pure Solvent (
B
)
1. 0
∆
D
V
N
−1
0. 8
V
N
0. 6
x
B
or
y
B
0. 4
0. 2
Pure Solute (
A
)
Pure Diluent (
D
)
0
0 .2
0. 4
0 .6
0. 8
1 .0
O
N
−1
F
x
A
or
y
A
O
N
+1
and
D
O
N
Figure 5.22
Phase diagram for Example 5.4.
5.9
Minimum and total reflux
Minimum reflux corresponds to the overlap of an operating line and a tie-line (infinite
stages at a pinch point). This concept is similar to minimum solvent flowrate for an
extraction process without reflux. Total reflux corresponds to the minimum number of
stages. Remember that total reflux means that no streams are going into or out of the
column, so that
F
,
B
, and
D
are zero, and
=
.
Example 5.4: countercurrent separation with reflux
Problem:
Refer to Figures 5.21 and 5.22. Given:
V
0
/
F
=
0
.
4;
O
N
+
1
/
D
=
3
.
On the phase diagram (Figure 5.22):
x
AF
=
0
.
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