Particle mass flux in the freeboard of a fluidized bed boiler
Journal article, 1989
The flux of descending particles has been
measured in the freeboard of a fluidized bed
boiler. The lateral and vertical distributions
of the flux were studied and the influence of
the superficial gas velocity and the static bed
height analyzed. A tube bundle located in the
bed surface region made it possible to investigate
the effects of tubes on the entrainment
of particles from the surface of the bed.
The particle flux was relatively constant
across the freeboard except near the wall,
where it was about twice as large as the average.
In the vertical direction, the flux decreased
exponentially with height except
close to the bed, where the rate of decay was
less than at higher elevations. The tube bundle
was found to inhibit the splashing of bed
particles when the bed is below the tubes.
A model is used for the estimation of the
vertical particle flux and concentration
profiles in the freeboard. It is based on separate
treatment of small and coarse particles
and calculation of trajectories of ejected bed
particles. The calculated freeboard values
describe the experimental data satisfactorily
except close to the bed, where a considerable
discrepancy is observed.