4.5. Handling of agricultural residues with low ash melting
point
Furnace–boiler systems for combustion of agricultural
residues are often designed to keep the temperature in the
combustor below about 9008C to reduce slagging and
formation of molten agglomerates e.g. by using watercooled
walls and/or flue gas re-circulation [51]. Further, a
careful design of the internals is necessary to avoid contact
of the hot gases that may contain low-fusion point particulates
with high-temperature surfaces [22].
Apart from furnace design considerations some of the
suggested or applied solutions for the problems resulting
from the low melting points of the ash from agricultural
residues are:
² use of additives;
² use of alternative bed materials in the case of fluidized
bed combustion; and
² blending of biomass with other fuels e.g. coals, lignite.
Combustion additives have been used before in boilers to
enhance combustion efficiencies, to reduce emissions of
CO, hydrocarbons, particulates, NOx and SO2, as well as
to control agglomeration, fouling, slagging and corrosion
[42]. Combustion additives are solid, liquid or gaseous
substances, which can change the physical and/or chemical
characteristics of a fuel in order to achieve some of the
above-mentioned results.