disappeared indicating further combustion of char in the
bed. In the case of the corn cobs, the flame in the freeboard
appeared for a longer period. When the flame died down, the
temperature fell rapidly. This indicated that the wood chips
were more evenly distributed in the bed than the corn cobs.
During combustion of rice husks Preto et al. [34] observed a
considerable degree of freeboard burning of volatiles, particularly
during over-bed feeding. A similar phenomenon
was also observed by the current authors during the combustion
of coffee husks in a 150 mm diameter FBC. There was
increased freeboard combustion during over-bed feeding
which led to an increase in freeboard temperature within
the region near the feed point in the splash zone whereas
the bed temperature fell (Fig. 5). Whereas for wood chips,
the temperature in the combustor remained more or less the
same in all positions, irrespective of the feeding method. It
is important to mention that the examples given above,
although more interesting as far as understanding the
mechanisms of the combustion of agricultural residues,
may not be valid for large-scale plants, where the mixing
is generally better. Recently, in-bed feeding is being practised
in the new wood combustion plant at Altenburg in
Bavaria, Germany [81].