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141
CHAPTER 14 SOLUTIONS
14.1
Effect of absorbent rate and number of stages on absorption
(a)
Double
L
to 474 kmol/hr.
Then, the absorption factor for nbutane is doubled to 2.70.
The number of stages remains at 4.
From the Kremser equation, Eq. (14.5),
41
2.70 1
0.01193
2.70
1
1
1 0.01193
0.9881
K
K
A
A
+
−
φ=
=
−
−φ
= −
=
Or, 98.81% absorption of nbutane
(b)
Double number of stages to 8.
The absorbent rate remains at 237 kmol/hr
Then the absorption factor for nbutane remains at 1.35.
From the Kremser equation, Eq. (14.5),
81
1.35 1
0.02519
1.35
1
1
1 0.02519
0.9748
K
K
A
A
+
−
=
−
=
Or, 97.48% absorption of nbutane
Doubling the absorbent rate is more effective than doubling the number of stages.
This effect is confirmed by the Kremser plot.
The result is more dramatic
at larger number of stages.
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14.2
Determining a feasible operating pressure for distillation
Follow the procedure of Figure 7.9.
First find a suitable pressure at the top.
Using a simulation program with the UNIFAC equation for estimating
K
values
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 Spring '08
 Debelak

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