FLUID DYNAMIC SIMILARITY OF CIRCULATING FLUIDIZED-BEDS

The effects of scale-up on the fluid dynamics of circulating fluidized beds (CFB) are investigated using a single cold laboratory facility with the ability to recycle fluidization gas mixtures of adjustable density and viscosity. By matching five dimensionless parameters, experiments employing plastic, glass and steel powders achieve fluid dynamic similarity with high-temperature CFB risers of 0.32, 0.46 and 1 m diameter. Comparisons of results obtained with the plastic and glass powders indicate that static pressure and its fluctuations scale with the riser and particle diameters, respectively. Experiments with the steel powder exhibit incipient choking behavior consistent with the greater analogous bed size that they simulate. The onset of choking with plastic and steel powders is well predicted by the correlation of Yang [Powder Technol., 35 (1983) 143]. Experiments with coated glass beads suggest that the magnitude of the particle Coulomb friction coefficient affects the fluid dynamics of the CFB in the limit where this coefficient is small.