Influence of Geometric Factors of Confined Conical Spouted Beds on Fine Particle Entrainment

Idoia Estiati, Mikel Tellabide*, 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

The spouted bed is a fluid-particle contact technique that has been successfully applied to systems where fluidization has yielded unsatisfactory results. Conical spouted beds are highly versatile in the gas flow rate, allowing operating with particles of irregular texture, fine particles and those with a wide size distribution and sticky solids, whose treatment is difficult using other gas-solid contact regimes. These features of the conical spouted beds make them attractive for different applications.

The ratio between the inlet diameter and particle diameter limits the scaling up of spouted beds (the inlet diameter should be smaller than 20-30 times the particle diameter). The insertion of a draft tube is the way to overcome this limitation.

Many applications of conical spouted beds require the use of inert materials and/or catalysts. Therefore, they involve operations using mixtures made up of coarse (waste) and fine (inert and/or catalyst) particles, which require rather high gas velocities due to the presence of coarse particles, thereby leading to fine particle entrainment. As a result, this loss of material (catalyst) involves high cost, damage to the environment and a poor gas-solid contact. In order to avoid these problems, a modification of the conventional spouted bed regime has been proposed by our research group (1). This modification consists in a new internal device called fountain confiner, which stabilises the operation 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 study is to assess the potential of the fountain confiner for avoiding fine particle entrainment in conical spouted beds. Accordingly, runs have been carried out using different contactors, fountain confiners and types of draft tubes. The performance of the different alternatives has been compared in order to ascertain the optimum configuration for reducing fine particle entrainment. The materials used for operation are glass beads of 4 mm diameter and bread crumbs of 0.41 mm diameter.

The results show that the fountain confiner reduces fine particle entrainment and ensures a better contact between the gas and the solid. Furthermore, particle entrainment is minimized using the longest confiner and a nonporous draft tube provided with the lowest height of the entrainment zone.

REFERENCES

1. Altzibar, I. Estiati, G. Lopez, J.F. Saldarriaga, R. Aguado, J. Bilbao, M. Olazar, Fountain confined conical spouted beds, Powder Technol. 312, (2017) 334–346.