(521c) Studying the Effects of Fluidized Bed Scale On the Solid Dynamics Using Sophisticated Optical Probe

Faraj Zaid, and Muthanna H. Al Dahhan, Department of Chemical and Biological Engineering, Missouri University of Science and Technology, Rolla, MO

Gas-solids fluidized-bed reactors have the found widespread applications in industry due to a number of advantages. The radial and axial profiles of solids holdup and particle velocities in these reactors are important fluid dynamic parameter. In this work, sophisticated optical probes that can measure simultaneously both solids concentration and velocity and their time series fluctuation have been used. The effects of the bed size of these parameters have been investigated using two different fluidized beds (0.14 m and 0.44 m in ID). The radial and axial solids holdup and particle velocity profiles have been studied at the same three dimensionless axial and radial positions in both units. Air was used as the fluidizing gas and different particle sizes glass beads (ρ_s=2500 kg/m³, d_p=210 and 70 μm) and copper (ρ_s=5300 kg/m³, d_p=200 μm), as were used as solids material. The bed aspect ratio before fluidization was set at two. Both fluidized beds were equipped with a porous-plate (pore size: 40 μm) distributor. The effect of the bed scale on solids dynamics has been studied at a range of different superficial gas velocities U.

Using simple and reliable calibration method, the measured solids concentrations by the probe can convert to solids holdup. In both fluidized beds the solids holdups increased towards the wall. Same trends were reported by Mabrouk et al. (2005). Additionally, it was found that the radial particle velocity profile was nearly parabolic in both fluidized beds. The dimensionless group proposal by Glicksman (1988) and Glicksman, et al (1993) for hydrodynamics similarity have been also examined in this work using local measurements. The detailed result and analysis will be discusses and presented in this talk.

References

[1] Mabrouk et al., “Scale effects on fluidized bed hydrodynamics” Inter. J. of Chemical Reactor Eng 3, Article A18; 2005.

[2] Glicksman (1988), “Scaling relationships for fluidized beds” Chem. Eng. Sci. 43

[3] Glicksman et al (1993) Simplified scaling relationships for fluidized beds. Powder Technol. 1993; 77:177-199.

Keywords: Fluidized beds, optical probe, solids holdup, spatial distribution, particle velocity