Encyclopedia of Environmental Science and Engineering, Volume I and II

VAPOR AND GASEOUS POLLUTANT FUNDAMENTALS 1219

For adsorption the particles are usually dumped into a

column as a packed bed (Figure 6). In commercial adsorp-

tion columns, equilibrium concentrations are not attained

uniformly, but for convenience the rate of adsorption is

assumed to be proportional to C. See below under Reaction.

The time t 3 in which breakthrough (Cig at the exit equals

the permissible set amount) occurs may be established by

analyzing the differential component mass balance assuming

that the transport of material again is governed by diffusion

through a film

N k C Ci g ig( ig)

*

(12)

in which Cig* is the gas phase concentration in equilibrium

with the absorbed concentration Cis at the same elevation.

GAS STREAM OUT

GAS STREAM IN

FILM

SOLIDPHASEGASPHASE

z 0 dz

L

z inlet

c)

a) b)

vz

vz

Co

C=C(t,z=z 0 )

t 4 >t 3 >t 2 >t 1

t 3 t 4

t 2

t 1

Cio

z 0

FIGURE 6 (a) Pictorial representation. (b) Schematic model showing a differential

element over which a mass balance is made. (c) Pollutant concentration as a function

of time at various heights.

1 2 3 4 5 6 7 8 9 10

1.0

c

c 0

SIMPLE LANGMUIR

DISSOCIATIVE

LANGMUIR

COMPETITIVE

LANGMUIR

K 1 C 1

FIGURE 5

C022_001_r03.indd 1219 11/18/2005 2:32:44 PM