Power Plant Engineering

Carbon Monoxide (CO): It is a colourless, highly noxious gas which forms where the combus-
tion of fuels containing carbon proceeds under(possibly local) air starvation. In modern DG sets,
optimisation of air/fuel mixture formation and use of constant pressure type turbo charging, successfully
reduces the CO content of exhaust gases even with the poorest qualities of fuel grades. This type of
engine design meets even the stringent standards set by such environmental agencies like TA-Luft of
Germany.
Non combusted Hydro carbons(HC): Hydro carbons contained in the exhaust gas consists
of a multitude of various organic compounds. However, the HC contents of exhaust gases for modern
4-stroke diesel engines burning heavy fuel are very low and are not a matter of environmental debate.
Soot, Dust: Solids contain in exhaust gases of diesel engines burning heavy fuel not only consist
of soot (carbon) resulting due to incomplete combustion of the fuel but also due to dust and ash particles
from the fuel and the lube oil, the quality of the combustion air and from the abrasion products. Even
though, these constitutes the major source of visible dark coloration, of exhaust gases, soot particles
only account for a relatively low percentage of total dust concentration. Based on the ash content of the
fuel and the lube, the soot quantity also varies as shown in the table below.
Fuel
Gas Oil
Heavy Fuel Oil
Ash content — Fuel%
0.01
0.10
Ash content — Lube%
1.50
4.00
Soot (Carbon) mg/m
3
15.00
15.00
Fuel ash mg/m
3
4.00
40.00
Lube oil ash mg/m
3
3.00
8.00
Overall analysis of environmental laws will take us into two pronged environmental considera-
tions.
I. Long term consideration on implementation of actual system emission limits. This should take
into account existing technology, cost competitiveness, consideration to burn only low grade, tertiary
fuels, demand technology life-cycle, nature of project and plant gestation and country objectives.
II. Short term aspects mainly centred on maintaining desired ambient air qualities. This will
bring us to the debate emission levels. The ground level dispersion of emission components are easily
met far below existing standards by the modern 4-stroke diesel engines while burning heavy fuel.
In view of the above, adequate chimney/stack heights for guiding the exhaust gases away from
the ground level can easily ensure low dispersions at ground level after emission at relevant designed
chimney heights based on sulphur contents in the fuel.