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Hydrodynamic and scale-up studies of spouted beds

University of British Columbia

The scaling relationships proposed by Glicksman (1984) for fluidized bed scale-up have been modified to provide a full set of scaling parameters for spouted bed scale-up. A force balance for particles in the annulus region leads to addition of two non-dimensional parameters, the internal friction angle (φ) and the loose packed voidage (ε₀) to the original Glicksman scaling relationships. Experimental verification of the full set of modified scaling parameters was conducted, first in a series of small spouted beds, then in larger columns up to 0.914 m in diameter, and finally in a pair of high temperature (500 °C) beds. Both viscous and inertial forces were important for the conditions investigated so that no simplifications could be made to the full set of scaling parameters. It is demonstrated that the full set of modified scaling parameters is valid for spouted beds when all dimensionless parameters are matched between the prototype and model beds. A fibre optic probe was used to measure voidage profiles in spouted beds of diameter 0.152 m. The voidage in most of the annulus was found to be somewhat higher than the loose-packed voidage and increased with increasing spouting gas flow rate, contrary to usual assumptions. The voidage decreased with height in the core of the fountain for low spouting gas flow rates, but first increased with height and then decreased towards the top of the fountain at higher gas flow rates. Radial profiles of local voidage were roughly parabolic in the lower portion of the spout and blunt in the upper portion. The same fiber optic probe was also used to measure spout diameters based on significantly higher counts of output electric pulses in the spout region than in the annulus. The flat wall of semi-cylindrical spouted bed columns was found to cause considerable distortion of spout shapes which became approximately semi-elliptical. The often-used McNab (1972) equation was found to underestimate the spout diameters in a full-column, with an average deviation of 35.5%. A second fibre optic probe system was used to measure profiles of vertical particle velocities in the spout and fountain regions. In addition, a fibre optic image probe was employed to measure particle velocity profiles in the annulus. In the spout, radial profiles of vertical particle velocities were near Gaussian in shape. Particle velocities along the spout axis in a half-column were 70% lower than in a full-column of the same diameter as the half-column under identical operating conditions. In the half column, particle velocities adjacent to the front plate were approximately 24% lower than a few millimeters away for the conditions studied. In the annulus region, there was a 28% difference between particle velocities adjacent to the column wall and those only 2 mm away. Measurements of pressure profiles and gas flow distributions in the annulus were carried out, while the influence of elevated pressures on bed hydrodynamics was also examined.

Thesis/Dissertation

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2009-06-04

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http://hdl.handle.net/2429/8724

Chemical and Biological Engineering

University of British Columbia

UBCV

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