Page 269 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

270 Chapter 10 Absorption and stripping

Raschig rings (1 size) available in the plant stores may be used for random packing. The equilibrium
00
o
data (mole fraction) for ammoniaeairewater system at 30 C is given (below) in Table P10.1a.
Table P10.1a Equilibrium data (mole fraction) for ammoniaeairewater system at 30 C.

x 0 0.0126 0.0167 0.0208 0.0258 0.0309 0.0409 0.0503 0.0739
y 0 0.0151 0.0201 0.0254 0.0321 0.0390 0.0527 0.0671 0.1050

Basis: 1 hr.
It is assumed that if any water vaporizes into the gas stream, the quantity is small, and hence, the
same is neglected. NH 3 removed exits along with the liquid exit stream. The gas flow and mole
fractions are derived from the inflow data considering 90% removal of NH 3 from inlet gas.
For (L/G) min condition.
Exiting liquid stream composition x 1 is in equilibrium with y 1 (¼ 0.1).
Hence based on equilibrium data in Table P10.1a.
x 1 ¼ 0.0708 and L min ¼ (6.7 e 0.67) / (0.0708 e 0) ¼ 79.14 kmol.
Fig. P10.1A shows the component flow rates and stream compositions for operation at (L/G) min .

kmol mf kg
NH 3 0.67 0.011(y 2 ) 11.39
Air 60.26 0.989 1747.54
60.93 1.0 1548.93
kmol mf kg
(2) – 0(x ) 0
NH 3 2
H O 79.14 1 1424.52
2
30°C
∼1atm 79.14 1.0 1424.52
L
G
min kmol mf kg
6.03 0.0708 102.51
NH 3
H O 79.14 0.9292 1424.52
(1) 2
85.17 1.0 1527.03
Nm 3 kmol mf kg
≈ 1000 kg/m 3
NH 3 150 6.7 0.1(y ) 113.9 ρ L
1
Air 1350 60.26 0.9 1747.54
1500 66.96 1.0 1861.44
ρ 30° = 1861.44
1500 × (303/273)
= 1.118 kg/m 3
FIGURE P10.1A
Material balance for operation with (L/G) min .