4. Due to the high contents of volatile matter and the low
particle densities of the agricultural residues as well as
the need to operate at temperatures below the melting
points of the ash, high concentrations of the unburnt
pollutants as well as ash may be expected in the flue
gas. However, it is possible to control these pollutants
by adopting a suitable furnace design and by application
of staged combustion. The contents of N and S are relatively
low for agricultural residues so that low emissions
of SO2, NOx and N2O may be expected. However, the
combustion of some residues may lead to higher
emissions of NOx. In such cases NOx emission reduction
techniques (e.g. staged combustion, SNCR) which have
been found useful during the combustion of wood or
related biomass, may be applied to the combustion of
agricultural residues.
5. Where coal power plants exist within the residue production
regions, an economical way of tapping the
energy from the residue would be co-firing. The combustion
and emission characteristics are not negatively
affected during co-combustion. However, further developments
and research is still needed with respect to
burner design, fuel processing and the problems of fouling,
slagging and corrosion.