Power Plant Engineering

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

Increase in Global Temp.

Ye a r

Obseved

in Past

Present

Expected

SolarHeat

Reflectionin

Blocked

CO &

Global WarmingParticulates^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.

2. Carbon monoxide (CO)


3. Sulfur dioxide (SO 2 )


4. Nitrogen dioxide (NO 2 )


5. Toxic gases, vapors, and heavy metals


6. Particulate matter