Geoscience Reference
In-Depth Information
Solubility Data for SO
2
c
= (g of SO
2
)/(100 g H
2
O)
p
(kPa)
y
=
p
/101.3
x
= (
c
/64)/(
c
/64 + 5.55)
0.5
6
0.06
0.0014
1.0
11.6
0.115
0.0028
1.5
18.3
0.18
0.0042
2.0
24.3
0.239
0.0056
2.5
30
0.298
0.007
3.0
36.4
0.359
0.0084
16.3.3 m
aterial
(m
ass
) b
alanCe
The simplest way to express the fundamental engineering concept/principle of material or mass bal-
ance is to say, “Everything has to go somewhere.” More precisely, the law of conservation of mass
says that when chemical reactions take place, matter is neither created nor destroyed. What this
important concept allows us to do is track materials, that is, pollutants, microorganisms, chemicals,
and other materials from one place to another. The concept of material balance plays an important
role in environmental treatment technologies where we assume a balance exists between the mate-
rial entering and leaving the treatment process: “What comes in must equal what goes out.” The
concept is very helpful in evaluating process operations. In air pollution control of gas emissions
using a typical countercurrent flow absorber, the solute (contaminant compound) is the material
balance. Figure 16.5 illustrates a typical countercurrent flow absorber in which a material balance
is drawn. The following equation can be derived for material balance:
Y
1
-
Y
2
= (
L
m
/
G
m
)(
X
1
-
X
2
)
(16.2)
where
Y
1
= Inlet source concentration.
Y
2
= Outlet solute concentration.
L
m
= Liquid flow rate (g-mol/hr).
G
m
= Gas flow rate (g-mol/hr).
X
1
= Outlet composition of scrubbing liquid.
X
2
= Inlet composition of scrubbing liquid.
Equation 16.2 is the equation of a straight line. When this line is plotted on an equilibrium dia-
gram, it is referred to as an
operating line
(see Figure 16.5). This line defines operating conditions
within the absorber; that is, what is going in and what is coming out. The slope of the operating line
is the liquid mass flow rate divided by the gas mass flow rate, which is the liquid-to-gas ratio or (
L
m
/
G
m
). When describing or comparing absorption systems, the liquid-to-gas ratio is used extensively.
The following example (using Henry's law) illustrates how to compute the minimum liquid rate
required to achieve desired removal efficiency.
■
EXAMPLE 16.2
Problem:
Using the data and results from Example 16.1, compute the minimum liquid rate of pure
water required to remove 90% of the SO
2
from a gas stream of 84.9 m
3
/min (3000 acfm) containing
3% SO
2
by volume. The temperature is 293 K and the pressure is 101.3 kPa (USEPA, 1981, p. 4-20).
Given:
Inlet gas solute concentration (
Y
1
) = 0.03
Minimum acceptable standards (outlet solute concentration) (
Y
2
) = 0.003
Search WWH ::
Custom Search