Environmental Engineering Reference
In-Depth Information
O
N
+1
V
N
M
O
1
V
0
Figure 5.13
To plot the delta
point: 1 L
ocate the points corresponding to the
compositions of
V
0
(solvent),
O
N
+
1
MV
0
(feed), and
O
1
(exit raffin
ate). 2 Find
point
M
fro
m a co
mponent balance or the lever-arm rule. 3 Make line
O
N
+
1
MV
0
.
Exte
nd lin
e
O
1
M
to the saturation curve (this is point
V
N
). 4 Extend
O
N
+
1
V
N
and
O
1
V
0
; the intersection is at
.
Example 5.2: countercurrent extraction
Problem:
A 1000 kg/hr stream of a solution containing 30 wt% acetic acid and 70 wt% water is
to be fed to a countercurrent extraction process. The solvent is 99% isopropyl ether
and 1% acetic acid, and has an inlet flowrate of 2500 kg/hr. The exiting raffinate
stream should contain 10 wt% acetic acid. The equilibrium data are the same as given
in Table 5.1 for the cross-flow Example 5.1. Find the number of equilibrium-limited
stages required.
Solution:
Known:
O
N
+
1
=
1000
,
y
AN
+
1
=
0
.
70
,
y
BN
+
1
=
0
.
30
V
0
=
2500
,
x
A
0
=
0
,
x
B
0
=
0
O
1
=
?
,
y
B
1
=
0
.
10 (and it's on the saturation curve)
.
Method (see Figure 5.14):
1 Plot equilibrium data from previous example (plotting the conjugate line will be
really helpfu
l for dra
wing tie-lines in this case).
2 Plot the line
V
0
O
N
+
1
and the point
O
1
.
3 Find the mixing point:
2500(0
.
01)
+
1000(0
.
30)
z
BM
=
=
0
.
14 (and it's on the line
V
0
O
N
+
1
)
.
2500
+
1000
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