Page 174 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

148 5 Principles for Gas Separation

with 200 kg of activated carbon. The expected breakthrough efficiency is 90 %.
Estimate its breakthrough time. Assume K x ¼ 20 s 1 and packing density of
3
400 kg/m .
3
6. An activated carbon column is used to remove tribromomethane (2.89 g/cm )
from the air at standard condition. The mass flow rate of air is 2.5 kg/s and the
3
concentration of the pollutant in the inlet air stream is 0.0025 kg/m . The bulk
3
density of the activated carbon is 500 kg/m , and the mass transfer coefficient of
2
1
the adsorbent K x ¼ 25 s . The adsorption bed is 2 m deep and 1.5 m in
cross-sectional area. The designed adsorption efficiency is g ¼ 0:95. That is,
x
the breakthrough point of the bed is considered to be when the outlet concen-
tration reaches 5 % of the inlet concentration. Estimate the life time of this
column.
7. A packed bed is designed to remove SO 2 by pure water absorption from a
sulfuric acid plant. The incoming SO 2 concentration is 10 %. The water flow
rate is 1.5 times the minimum water flow rate and the inert gas flow rate

G = 500 kg/hr. The tower operates at an average temperature of 30 °C and
1 atm. The equilibrium data for SO 2 in air and water at this temperature.

(g SO 2 /100 g
Partial pressure p SO 2 Solubility c SO 2
(mmHg) water)
0.6 0.02
1.7 0.05
4.7 0.10
8.1 0.15
11.8 0.20
19.7 0.30
36.0 0.50
52.0 0.70
79.0 1.00

If the corresponding mass transfer coefficients are

k y a ¼ 0:6634L 0:82

k x a ¼ 0:09944L 0:25 G 0:70

2
where L and G are the liquid and gas flow rates in kg/(m h)
(a) determine minimum water flow rate,
(b) the equilibrium line,
(c) the operating line is the same figure,
(d) the gas phase mass transfer coefficient at the gas inlet,
(e) the gas phase mass transfer coefficient at the gas outlet,
(f) the liquid phase mass transfer coefficient at the liquid inlet,
(g) the liquid phase mass transfer coefficient at the liquid outlet.