Environmental Engineering Reference
In-Depth Information
By far, the greatest environmental and health impact is due to fossil fuel combustion in fur-
naces, stoves, kilns, boilers, gas turbines, and the internal combustion engine, which powers our
automobiles, trucks, tractors, locomotives, ships, and other mobile and stationary machinery. The
combustion process emits pollutants through smoke stacks, chimneys, vents, and exhaust pipes,
such as particulate matter, oxides of sulfur and nitrogen, carbon monoxide, products of incomplete
combustion, and volatile toxic metals. Some of these pollutants are toxic to humans, animals, and
vegetation per se, whereas others transform in the atmosphere to toxic pollutants, such as ozone,
organic nitrates, and acids. The pollutants are advected by winds and dispersed by atmospheric
turbulence over hundreds to thousands of kilometers, affecting sensitive population and biota far
removed from the emission sources. Particles, besides containing toxic and potentially carcino-
genic agents, often envelope whole subcontinental areas in a haze that reduces visibility and the
enjoyment of the landscape and a starry sky.
Great strides have been taken, especially in the more affluent countries, for limiting the emis-
sions of air pollutants from the combustion sources. For example, most particles can be filtered
out of the flue gas by electrostatic precipitators or fabric filters. Sulfur oxide emissions can be
reduced by wet or dry limestone scrubbers. Nitric oxide emissions can be reduced by catalytic
and noncatalytic injections of chemicals into the flue gas. The catalytic converter, which is now
applied to gasoline fueled automobiles in many countries, reduced the emissions of automobiles
significantly compared to the uncontrolled predecessors. Diesel engines, with proper tuning, are
also emitting less pollutants, although a magic box like the catalytic converter has yet to be found
for diesel engines. Alas, little or no emission control devices are applied to the myriad of dispersed
sources, such as residential furnaces, stoves and fireplaces, and smaller industrial facilities.
The less affluent countries, because of more pressing economic needs, do not yet avail them-
selves of emission control devices. Consequently, air quality in those countries is much worse than
in the more affluent ones. Because air pollutants do not stop at national boundaries, surrounding
countries may feel the effect of emissions from neighboring states. It is incumbent on the more
affluent societies to help the poorer ones in controlling air pollutant emissions, because the health
of the whole human population and ecology of the planet is at stake.
Finally, this chapter has not addressed the great looming risk of global warming due to an-
thropogenic greenhouse gas emissions from fossil fuel usage. This will be the subject of the next
Problem 9.1
Calculate the emission rate of SO 2 (lb/s) from a large coal-fired power plant that uses 2 million
short tons (1 short ton
2000 lb) per year having a coal sulfur content of 2% by weight.
Problem 9.2
Calculate the emission rate of SO 2 per fuel heat input (g/GJ) of a large coal-fired power plant that
uses coal having a heating value of 30 MJ/kg and a sulfur content of 2% by weight.
Search WWH ::

Custom Search