Environmental Engineering Reference
In-Depth Information
methods such as flash distillation, reverse osmosis, ultrafiltration, or another extraction
column.
In Figure 5.19,
O
N
+
1
is the reflux stream
and
O
N
+
1
D
=
reflux ratio
.
The analysis on the upper and lower sections is not dependent on the method used to
recover the solvent phase.
Mass balance on upper (enriching) section:
[Remember: the enriching section corresponds to increasing concentrations of solute.]
=
V
N
−
O
N
+
1
=
V
N
−
1
−
O
N
O
n
=
.
V
n
−
1
−
(5.14)
is on the line
O
N
+
1
V
N
.Ifthe composition of
O
N
+
1
(which has the same
composition as the extract product) and
V
N
are known as well as the total flowrates, one
can locate
So the point
, which is then used to step off stages for the enriching section.
Mass balance on lower (stripping) section:
V
f
−
1
−
O
f
=
(5.15)
V
1
−
O
2
=
V
0
−
O
1
=
.
So the point
is on the line
V
0
O
1
.Ifthe compositions and total flowrates of
V
0
and
O
1
are known,
can be located.
Overall mass balance on the column:
F
+
V
0
−
O
1
=
V
N
−
O
N
+
1
where
F
is the feed
+
=
.
F
(5.16)
Therefore,
F
are on the same line
.
Procedure for solving extraction with reflux problems
1 Plot equilibrium data.
2 Plot the concentrations of the known variables:
V
0
,
F
,
D
(same as
O
N
+
1
),
O
1
(
O
1
is on
the phase envelope).
3 Find
V
N
from mass balances around solvent separator (it is a saturated stream).
4 Find
using mass balances and the internal reflux ratio.
5 Locate feed position.
The optimum feed location is where you switch from using one
point to another (i.e.,
point
F
), see Figure 5.20.
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