Page 173 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

5.2 Absorption 147

y y 1 x x 1 L
¼ ð1 þ eÞ ð5:59Þ

1 y 1 y 1 1 x 1 x 1 G
This equation also indicates that the amount of liquid to gas ratio is reduced by
enhanced chemical absorption.

5.3 Practice Problems

1. The concentration of acetone (C 3 H 6 O) in a machine shop is 3 ppmv. The density
3
of acetone vapor is 2.01 kg/m under standard conditions. A carbon filter bed is
3
used for air cleaning. The airflow rate through the filter is 0.05 m /s. Determine
a. The adsorption capacity of the activated carbon filter using Yaws data
(1995).
b. The total amount of carbon needed for the bed, assuming the working
adsorption capacity is 75 % of the saturated adsorption and the bed service
life is 1 year.

2. In a machine shop, the concentration of acetone (C 3 H 6 O) in the room air is
3
0.00001 kg/m . An activated carbon filter is used in an air recirculation system
to remove the acetone. The bulk density of the activated carbon is 400 kg/m 3.
The airflow rate of the recirculation system is 20 l/s. The cross-sectional area of
2
the bed is 1.5 m . Determine
a. The speed of the adsorption wave
b. The length of the bed if the bed is to be replaced every 30 days.

3. A carbon adsorption unit is designed to control the emission from an air stream
3
having 250 ppmv of toluene flowing through the bed at a rate of 1,500 m /min.
The process works 24 h/day at 27 °C temperature and 1 atm pressure. Assume
the working capacity of the carbon is 0.15 kg toluene/kg of carbon. Determine
the amount of carbon needed in all beds of a 4-bed adsorber if two beds are
online for 4 h and then regenerated while the other two working.
4. A carbon adsorption unit is designed to control the emission from an air stream
3
having 250 ppmv of toluene is flowing through the bed at a rate of 1,500 m /min.
Calculate the cross sectional area of a bed if maximum allowable superficial
velocity through the bed is 20 m/min.
5. A carbon adsorption unit is designed to control the emission from an air stream
having 2,500 ppmv of ethylene glycol vapor is flowing through the bed at a rate
3
of 1,500 m /min at a temperature of 27 °C and pressure of 1 atm. Calculate the
working adsorption capacity of the carbon. Assume that the working adsorption
capacity of the bed is 50 % of the adsorption capacity, and that the bed is filled