Minimum Spouting Velocity for Fountain Confined Conical Spouted Beds of Fine Particles

Mikel Tellabide*, Idoia Estiati, Aitor Pablos, Haritz Altzibar, Roberto Aguado and Martin Olazar
University of the Basque Country; Dept. Chemical Engineering
PO Box 644, 48080 Bilbao, Spain
*T: +34-94-601-5994; F: 94-601-3500; E:mikel.tellabide@ehu.es

Nowadays, fluidized beds are commonly used in industrial operations when fixed are not suitable. Nevertheless, these contact methods perform poorly when particle size exceeds 1 mm. Mathur and Gishler (1) developed the spouted bed regime and the main difference with the fluidized bed lies in the cyclic movement of the particles. This regime has been successfully applied in operations with coarse particles, those of irregular texture, wide size distribution and sticky ones.

Despite the great versatility of this contact method, it has severe problems when scaling up, specifically those involving a key parameter, as is the ratio between the inlet diameter and particle diameter (2). In fact, the inlet diameter should be no more than 20-30 times larger than the average particle diameter in order to achieve stable spouting. Thus, values of this ratio greater than 30 lead to unstable regime due mainly to slugging formation. Therefore, a draft tube must be used to avoid this problem, and therefore attain stable operation. Nevertheless, operation with fine particles in a draft tube spouted bed leads to severe entrainment, which is a serious problem in most physical and chemical processes conducted in spouted beds.

A novel internal device called fountain confiner has been designed to allow operation with fine particles. In fact, this device avoids even the need for a draft tube and improves greatly solid circulation and gas-solid contact (3). This device confines the fountain, stabilizes the system and changes the trajectory of the gas leading to an additional contact between the gas and the solid in the fountain.

The main aim of this work is to study the hydrodynamics of the fountain confined spouted bed and propose a correlation for predicting the minimum spouting velocity in a wide range of operating conditions and particle properties. Runs have been carried out following an experimental design in order to allow a reliable data analysis. Once the factors of greater influence have been identified, correlations have been developed for the calculation of the minimum spouting velocity for fountain confined conical spouted beds with and without different types of draft tubes and particles of different size and density.

The results show that the most significant factors are static bed height, gas inlet diameter and particle properties. Minimum spouting velocity increases as the height of the static bed and particle size and density are increased and gas inlet diameter is decreased.

REFERENCES

1. B. Mathur, P.E. Gishler, A technique for contacting gases with coarse solid particles, AICHE J. 1 (1955) 157–164.
2. Olazar, M.J. San Jose, A.T. Aguayo, J.M. Arandes, J. Bilbao, Stable operation conditions for gas-solid contact regimes in conical spouted beds, Ind. Eng. Chem. Res. 31, (1992) 1784–1792.
3. Pablos, R. Aguado, M. Tellabide, H. Altzibar, F.B. Freire, J. Bilbao, M. Olazar, A new fountain confinement device for fluidizing fine and ultrafine sands in a conical spouted beds, Powder Technol. 328, (2018) 38-46.