The Dynamics of Large Particles in a Four-Compartment
Interconnected Fluidized Bed.
F.F. Snieders, A.C. Hoffmann, Dept. of Chemical Engineering, University
of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
and
D. Cheesman and J.G. Yates, Dept. of Chemical and Biochemical
Engineering, University College London, Torrington Place, London
WC1E 7JE, UK.
M. Stein and J.P.K. Seville Dept. of Chemical Engineering, University
of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Keywords: Interconnected fluidized bed; large particles;
circulation; distribution; positron emission particle tracking.
Summary
In order to investigate the potential of a four-compartment interconnected
fluidized bed for the combustion of biomass, the behaviour of
cylindrical pellets in a bed material of glass ballotini was characterized
as a function of the operational parameters. This involved
The circulation rate of the bed material itself was also measured
to relate it to that of the pellets. The results show that control
of the material circulation rate can be achieved either by varying
the excess gas velocity in the two vigorously fluidized ('fast')
compartments or the aeration rate in the two slow ones, the latter
option being the better. The fast compartments were found to act
as ideal mixers, while little mixing took place in the slow ones
at the aeration rates used. Segregation of pellets relative to
the bed material was observed, mainly in the slow compartments,
in some cases leading to pellets getting stuck low in the slow
beds. It was found that the best option for avoiding problems
with segregation and controlling the circulation rate of both
pellets and bed material was to aerate the slow beds at superficial
velocities under the minimum fluidization velocity. The draw-back
in doing so is that dead-spaces will develop in these beds.