3. A major difficulty as concerns the firing of some agricultural
residues is the lowmelting point characteristics of the
ash. This property of the residues poses serious design and
operation problems. These include agglomeration, fouling,
slagging and corrosion. It is therefore important that the
analysis of the ash characteristics should be the first step in
choosing the combustion system and combustion conditions
of a given agricultural residue. Here again, twostage
combustion may provide a solution in the design of
the combustion system. In the first stage, the process of
gasification may be carried out at low temperature and a
significant quantity of the ash may be removed below the
grate. The configuration of the furnace should be such as to
promote the removal of the ash from the flue gas. Through
application of secondary air in the second combustion
stage, the complete combustion of the escaping combustibles
can then take place in an atmosphere with less
ash. Coupled to such design considerations, the use of
additives should be considered.