NO formation tendency characterization for biomass fuels

A4 Conference proceedings


Internal Authors/Editors


Publication Details

List of Authors: Konttinen J, Hupa M, Kallio S, Winter F, Samuelsson J
Editors: Jia L
Place: New York
Publication year: 2005
Publisher: American Society of Mechanical Engineers, ASME
Book title: Proceedings of the 18th International Conference on Fluidized Bed Combustion
Start page: 225
End page: 235
ISBN: 0-7918-4698-9


Abstract

When a solid fuel, such as coal, biomass or a mixt. of these fuels, enters a hot fluidized bed, the volatile carbon and nitrogen compds. are released, while some nitrogen and carbon remains in the solid char. Volatile nitrogen can form reactive species such as NH3, HCN and tar-​nitrogen. These can react in the presence of oxygen to NO (and some N2O)​. Some part of volatile nitrogen is always reduced to N2. During combustion of the char residue, some part of the char-​nitrogen forms NO (or N2O) and the rest is converted to N2.

Usually the std. fuel anal. is not enough to allow for accurate NO emission predictions in large scale fluidized bed combustion. This paper presents NO formation tendency characterization results from novel lab. measurements in a small-​scale fluidized bed combustor. The lab. results of this paper give a good insight into the distribution of fuel nitrogen between reactive and non-​reactive (N2) volatile components and char-​nitrogen. A NO formation tendency database is formed based on the results, including data on biomass-​, waste-​, peat- and coal-​type fuels. The combustion test results show that the cumulative conversion of fuel nitrogen to NO under lean, non-​staged fluidized bed combustion is 20 - 50 % (850°C with O2 in excess)​. For biomass and peat, nearly all reactive nitrogen (forming NO) is released from the fuel during pyrolysis. NO formation during char combustion is significant with coal.

With the help of the database, a reasonable est. of the max. non-​staged NO emission in fluidized bed combustion can be obtained. Normally, air staging is utilized to reduce NO emissions. Effects of air-​staging can be studied by means of modeling. In case of a BFBC boiler, the data can be used as input in the design or modeling of air staging for freeboard. For CFBC, the data can be used as input in the NO prediction where the once formed NO is further reduced by char carbon.

Last updated on 2019-20-10 at 03:10