Ask A Scientist Chemistry Archive

     
name         Susana I.
status       educator
age          30s

Question -   Could you please explain what are the main differences
between SO2 and NOx? That is, what  their sources are, how they can be
controlled and whether one is easier to reduce/control than the other?
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This topic is way too large to even begin to answer satisfactorily in a
forum like NEWTON BBS. SO2 is one of the oxides of sulfur (SO3) is the
other. NOx (where x stands for various amounts of oxygen because nitrogen
has several oxides). The best that I can do is give you some websites where
you can extract the particular information you require. I got these by doing
a Google Search on: "SO2 NOx sources control"
  http://www.evomarkets.com/assets/presentations/pres_2-997960244.pdf
http://www.nrdc.org/air/pollution/benchmarking/default.asp
The web site below is one of the home pages of the Department of Energy. On
that web page is a "search" option. Click on that and then enter in the
inquiry box the terms  "SO2 NOx sources control". That too is a Google
search, but is restricted to DOE documents. There you will find a "ton" of
info.
http://www.netl.doe.gov/
Sorry I could not be more specific but your inquiry has so many facets it
would require pages to even begin to address.

Vince Calder
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Susana,

Your question requires a lengthy explanation but I hope I can keep it
brief.

SOx and NOx are typically byproducts of combustion of fossil fuels.  SOx
or SO2 is generated when fuels are burned that contain high sulfur
content. As combustion is an oxidation process, carbon is converted to
CO2 and sulfur to SO2.  Controlling the emission will typically require
some type of scrubber.  It can be a dry scrubber where the off-gas is
mixed in a fluidized bed of lime creating gypsum CaSO4, or a wet
scrubber where the off-gas is contacted with an alkaline water solution
creating Na2SO4.  In either case, the waste products must be dealt with.
Many power plants have moved to a low sulfur coal to avoid the
environmental problems.

NOx on the other hand can not be controlled through fuel.  Nitrogen is
in the atmosphere and if temperatures in the combustion zone get high,
N2 is converted to NO2.  This has be dealt with by burner manufacturers
incorporating advanced technology into burners which reduces NOx
significantly.  Please search the internet for "low NOx burners".

Bob Hartwell
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