ChE 150B
Problem Set 10
Due November 4, 2009
Problem 1. It is desired to reduce the ammonia content of 0.05 m
3
/s of an ammoniaair
mixture (300 K and 1 atm) from 5.0 to 0.04 mol% by water scrubbing.
There is available
a 0.3mdiameter tower packed with 25mm ceramic Raschig rings to a depth of 3.5 m. Is
the tower satisfactory, and if so, what water rate should be used? At 300 K, ammonia
water solutions follow Henry’s law up to 5 mol%, with m = 1.414.
Liquid:
Density = 998 kg/m
3
Viscosity = 0.8 cp
Diffusivity = 1.64 x10
5
cm
2
/s
Gas:
Viscosity = 1.84x10
5
Pas
Diffusivity = 0.28 cm
2
/s
Mass transfer is controlled in the liquid phase such that K
y
= k
L
c
L
/m, where K
y
is the overall gas
phase mass transfer coefficient, k
L
is the liquidphase mass transfer coefficient, and c
L
is an
empirical constant related to packing type. The value of k
L
can be calculated from the following
expression:
5
.
0
757
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 Winter '08
 Pines
 Distillation, reflux, reflux ratio, mass fraction toluene, mm Raschig rings

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