5.4. Conclusions
Due to the high contents of volatile matter of agricultural
residues and the need to maintain the temperatures in the
combustion furnace below the melting point of the ash, high
concentrations of the unburnt pollutants may be expected in
the flue gas. However, it is possible to limit the emission of
these pollutants by adopting a suitable furnace design. The
content of N is relatively low for agricultural residues so that
low emissions of NOx and N2O may be expected. However,
for NOx and N2O emissions, other parameters, apart from the
fuel nitrogen contents, are important. For example, due to
the low contents of fixed carbon in agricultural residues as
well as the insignificant content of CaO in some residues,
the catalysing effects of char and CaO on the reduction of
NOx will be negligible. Consequently, agricultural residues
may emit higher concentrations of NOx than coals of
comparable nitrogen contents. Where the emissions of
these pollutants are too high, NOx emission reduction techniques
(e.g. staged combustion, SNCR) which have been