Page 231 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

7.5 Formation of CO and CO 2 207

The rates of formation of O, OH, and H are usually assumed to be at equilibrium
and they can be estimated from the following reactions
1
O 2 $ O
2 ð7:29Þ
1

K P;O ¼ 3;030 exp 30;790=Tð Þ atm 2
1 1
H 2 O $ O 2 þ H
2 4 ð7:30Þ
K P;H ¼ 44;100 exp 42;500=Tð Þ atm 3=4

1 1
H 2 O þ O 2 $ OH
2 4 ð7:31Þ
K P;OH ¼ 166 exp 19;680=Tð Þ atm 1=4 :

The overall reaction for the oxidation of CO is

1
CO þ O 2 $ CO 2 ð7:32Þ
2
It is very sensitive to temperature. The chemical equilibrium constants at dif-
ferent temperatures can be found in Table 3.2 above.
Dryer [10] gave an empirical equations for the consumption rate of CO and the
rate of formation of CO 2 as follows

dCOŠ 14:6 0:25 40;000 1250 1 1 3
½
2
½
¼ 10 exp ½ COŠ H 2 O½ Š O 2 Š 4 mol cm s
dt RT
ð7:33Þ

dCO 2 Š 14:75 0:4 43;000 2;200 1 1 3
½
2
¼ 10 exp ½ COŠ H 2 O½ Š O 2 Š 4 mol cm s
½
dt RT
ð7:34Þ
7.6 Formation of SO 2 and SO 3

Nearly all fossil fuels contain sulfur atoms. Some of the sulfur in fuels is eventually
oxidized to SO 2 and SO 3 . Typical values for the sulphur content of various fuels are
given in Table 7.4 [51]. Sulphur in coal is present in both organic and inorganic
forms, the latter being pyretic sulphur (FeS 2 ) and sulphates (Na 2 SO 4 , CaSO 4 ,
FeSO 4 ). Organic sulphur is present in the form of sulphides, mercaptanes, bisulp-
hides, thiophenes, thiopyrones, etc. These organic compounds are also found in
crude oils and gases.