Environmental Engineering Reference
In-Depth Information
x
A
1
=
.
0
06
y
0
=
.
0
0
v
D
=
is pure solvent;
Y
AD
=
0
.
0
82, same concentration as the
V
1
stream (solvent-free basis) since
V
D
is
pure solvent.
Determine (a) the number of equilibrium stages; and (b) location of the feed stage.
Solution
:
Mass balance on reflux distillation column:
x
AD
=
0
.
V
N
=
V
D
+
O
N
+
1
+
D
.
Since
V
D
is pure
B
and
O
N
+
1
and
D
have no solvent present, the line connecting pure
B
and
O
N
+
1
and
D
must contain
V
N
, which must also be on the solubility envelope
since it is an outlet equilibrium stream. Therefore,
V
N
corresponds to
y
AN
=
0.33 from
Figure 5.22.
O
N
1
+
D
BV
N
BO
N
+
1
=
0
.
33
=
82
=
0
.
4
(measuring horizontal distances)
V
N
0
.
1
+
(
D
/
O
N
+
1
)
=
0
.
4
.
(
V
N
/
O
N
+
1
)
Rearranging:
O
N
+
1
V
N
0
.
4
=
3
=
0
.
3
.
1
1
+
Mass balance on upper section
:
D
=
V
N
−
O
N
+
1
.
Therefore,
D
is on line through
V
N
and
O
N
+
1
.
D
V
N
D
O
N
+
1
=
O
N
+
1
V
N
=
0
.
3
x
=
33)
,
again measuring horizontal distances
,
x
+
(0
.
82
−
0
.
so
x
=
0
.
21
=
horizontal distance to left of
V
N
for point
D
.
Mass balance on total column:
F
+
B
=
D
B
=
V
0
−
O
1
∴
B
is on line through
F
and
D
and also on line through
V
0
and
O
1
.
Hence, (a) two equilibrium stages are necessary for separation.
(b) Feed plate is second plate since we do not switch to
B
.
No rectifying section needed.
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