J. Sterneus et al., Measurements of fluid dynamics and reaction conditions in the bottom zone of large-scale CFB combustors, J I ENERG, 73(497), 2000, pp. 184-190
Despite the rapid technical development of circulating fluidised bed (CFB)
combustion, knowledge of the detailed combustion chamber processes is insuf
ficient as most attention has been given to the overall performance of the
boilers. However, knowledge of the detailed processes is necessary for furt
her improvement of the technique. The present work focuses on the combustio
n chamber processes and, in particular, on the bottom part. The question to
be addressed concerns the properties of the bottom zone and the existence
of a dense bottom bed. In the cases studied, the 600 MWth CFB boiler in Gar
danne, France, and the 12 MWth CFB boiler at Chalmers University, dense bot
tom beds were found with bed material moving predominantly upwards in the c
entre and downwards at the walls. The behaviour of the bottom beds in the t
wo boilers was similar in most respects, but the measurements in the larger
boiler revealed, in contrast to the fluctuation between oxidation and redu
ction in the 12 MW boiler, constantly oxidising conditions at the measureme
nt position, which are most likely related to insufficient dispersion of be
d material across the 35 m(2) cross-section.