Power Plant Engineering

Fig. 13.2

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POLLUTION AND ITS CONTROL
419
13.9 FOSSIL FUEL POLLUTION
The exhaust gases and particulate matter emitted from combustion systems affect the environ-
ment in several ways. The major classifications are:
13.9.1 URBAN AIR POLLUTION
It including:
1. Photochemical smog
The reactants are nitric oxide (NO), unburned hydrocarbons (UHCs), and sunlight (i.e., pho-
tons). The products (after a few hours of time) are oxidants such as ozone (O
3
) and peroxyacetyl nitrate
(PAN = CH
3
CO
3
NO
2
),
6
5
° C
4
3
2
1
0
1900
1950
2000
2050
Inc
rea
s
e 
in Gl
ob
al
T
emp
.
Year
Obseved
in Past
Present
Expected
Solar
Heat
in
Reflection
Blocked
CO &
Particulates
Global Warming
2
Earth
Fig. 13.3 Increasing global temperature due to green house effect.
aldehydes (RCHO, where R = a hydrocarbon radical, e.g., the methyl radical, CH
3
), and aerosol haze.
An intermediate product is nitrogen dioxide (NO
2
), which gives a brownish color to the atmosphere and
reaches a peak concentration about half way through the reaction process, at the time at which the
original NO is significantly converted to NO
2
. The smog products are eye irritants and they diminish
lung capability. The different hydrocarbon gases have significantly different smog forming potential.
Methane, for example, is very unreactive, whereas ethylene (C
2
H
4
) and propylene (C
3
H
6
) are quite
reactive. Thus, the smog impact of the hydrocarbon emitted is determined not only by its concentration,
but also by its photochemical reactivity.