Environmental Engineering Reference
In-Depth Information
Solution:
(a) Mass balance (basis
F
=
100 mol
/
hr) on entire column:
+
S
F
=
V
D
+
B
(overall)
( since
S
F
=
B
=
V
D
)
y
S
S
x
F
F
+
=
y
D
V
D
+
x
B
B
y
D
V
D
=
0
.
95
x
F
F
0
.
05
x
F
F
B
0
.
05
x
F
F
F
10
−
3
x
B
=
=
=
0
.
05
x
F
=
1
.
5
×
.
Mass balance around control volume:
(0)
S
y
n
S
+
x
n
−
1
B
=
x
B
B
+
B
S
x
n
−
1
−
B
S
x
B
.
y
n
=
Minimum S corresponds to the maximum slope of the operating line.
To determine the maximum value of
B
∴
/
S
, substitute values for y
n
and x
n
−
1
which
correspond to intersection of operating and equilibrium line. Rearranging the mass
balance equation:
B
S
(0
B
S
(1
10
−
3
)
8
.
3 (0
.
03)
=
.
03)
−
.
5
×
S
B
=
S
F
=
10
−
3
0
.
03
−
1
.
5
×
=
0
.
11 moles steam
min
/
moles feed
.
0
.
27
(b) Actual steam rate
=
2.5 times the minimum.
11)
100
feed
mol
hr
mol
hr
∴
S
=
2
.
5(0
.
=
27
.
5
B
S
100 mol/hr
27.5 mol/hr
=
∴
actual
=
3
.
6
.
Actual operating line is:
10
−
3
)
10
−
3
.
The line can be graphed by plotting two points. We already know one set of points:
(0, 1.5
y
=
3
.
6
x
−
3
.
6(1
.
5
×
=
3
.
6
x
−
5
.
5
×
10
−
3
). The other will be at
x
×
=
0.03:
10
−
3
y
=
3
.
6(0
.
03)
−
5
.
5
×
=
0
.
10
.
From Figure 4.18, three theoretical stages are required.
Side streams
(see Figure 4.19)
1 The operating line for the top and bottom sections are still drawn as before.
2 The
q
-line for the feed is still drawn as before.
3Tolocate the middle operating line
x
S
must be known. The middle operating line begins
at the top operating line at the point
x
x
S
and ends at the point where the
q
-line for
the feed intersects the bottom operating line.
=
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