Spout Geometry of Fine Particle Conical Spouted Beds Equipped with Fountain Confiner

The spouted bed regime is an alternative gas-solid contact method to fixed and fluidized beds for the treatment of coarse particles (d_p >1 mm). Despite its benefits, the main limitation of this technology lies in its scaling up. Accordingly, the ratio of the gas inlet diameter to particle diameter, D₀/d_p, cannot be higher than 20-30. The use of internal devices, such as draft tubes and fountain confiner, have allowed to increase the D₀/d_p ratio to 1000, and ensure stable operation even with ultrafine particles (d_p<0.1 mm).

With the aim of designing spouted beds for industrial applications, heat and mass transfer rates must be optimized. These two parameters are significantly conditioned by the cross-flow of solid particles from the annulus into the spout, which depends on the spout geometry. Accordingly, runs have been carried out in a fountain confined conical spouted bed to assess the spout-annulus interface along the bed, which is the information required to determine the average spout diameter. With this aim, an optical system fitted with a borescope has been used to track particles in the bed. These runs have been carried out in a wide range of contactor angles, air inlet diameters and draft tubes differing in the aperture ratio. The effect of the air inlet velocity on the spout diameter has also been ascertained.

The results show that the spout expansion increases when the air velocity is increased. However, the effect of the contactor angle, the draft tube aperture ratio and the air inlet diameter is not straightforward, as their individual effect depends on the other geometric factors. Regarding the spout geometry, the maximum expansion is observed close to the bed surface. The results obtained allow a better understanding of fine particle spouting hydrodynamics in conical beds, which is essential information for their scaling up.