Power Plant Engineering

13.16 ENVIRONMENT CONCERNS AND DIESEL POWER PLANTS
With the emergence of liquid fuel based power stations in India, the question of environment
pollution has become a matter of raging debate. The coal based thermal power stations, in its earlier
stages of inception, were far more polluting? It was because of the combination of sulphur-based pollut-
ants, nitrogen based gaseous matter and also particulate matter with very high ash content being released
in the atmosphere.
Globally, environmental regulatory authorities are increasingly concerned with NO
x
and SO
x
emissions and are liable to consider introducing stringent regulatory standards in the future. While the
levels of SO
x
emissions is the function of sulphur content inhered in the fuel being used for combustion?
NO
x
is created by the chemical activity between atmospheric oxygen and nitrogen during combustion.
The level of NO
x
depends on the combustion conditions.
Optimal combustion in a diesel engine depends upon the achievement of the right balance of
equation between compression/combustion pressure, compression ratio, air-to-fuel ratio and mean ef-
fective pressure. The toughest of the emission standards currently being considered by various national
and international agencies, calls for limitation of NO
x
emissions to 600 ppm(15% O
2
) for generator sets
operating on ocean bound vessels. The shore-based power stations shall demand for further lower limits
due to proximity to the human inhabitation.
Burning heavy fuel in diesel engine is convenient mainly due to economics of residual fuel
combustion for power generation. Diesel engine designers’ world over will increasingly come under
pressure to introduce superior combustion features for producing lower levels of SO
x
and NO
x
.
The exhaust gas composition of emissions or pollutants given above is for using furnace oil of
different grades and varying sulphur contents. The exhaust gas of medium speed engines comprises of
a host of constituents. In the case of combusting heavy fuel like furnace oil, these emanate either from
combustion air and fuel used, or they are reaction products, which get formed during the combustion
process. Only some of these are considered to be pollutants for the atmosphere:

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POWER PLANT ENGINEERING