BULK-DENSITY DISTRIBUTIONS OF SOLIDS IN THE FREEBOARD OF A GAS-SOLID FLUIDIZED-BED

The freeboard region above the bubbling zone of a gas-solid fluidized bed provides the space not only for the disengagement of particles but also for additional contact and reaction between the particles and ga s. The flow pattern and behavior of particles as well as their bulk-de nsity distribution in the freeboard have a significant impact on the e fficiency of fluidization. The results of numerous previous experiment al studies indicate that the bulk density of solids essentially decrea ses exponentially as a function of the height of the freeboard. In the present work, this distribution has been obtained by first deriving t he Fokker-Planck equation from the linearized equation of motion of a single particle and then transforming this Fokker-Planck equation into that for the bulk-density distribution of solids. Its simplification to the one-dimensional case readily gives rise to an exponential distr ibution and agrees well with the available experimental data.