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A novel borescopic technique together with the monitoring of pressure fluctuation signals (power spectral distribution, PSD) has been used to track fine particles and characterize solid flow dynamics in fountain confined conical spouted beds. Radial and axial particle velocity profiles have been obtained for different configurations, and spout-annulus and fountain core-periphery interfaces have been delineated. The downward particle velocities in the annulus peak at intermediate positions in this zone, whereas the upward velocities in the dilute zones (spout and fountain core) peak at the axis or close to this position. Among the different configurations analysed in this work, the system without draft tube shows the greatest vertical particle velocities in almost all the different radial and axial positions. The evolution of the spout size along the bed depends on the configuration used, but all of them differ from those commonly reported in the literature. Thus, the spout expands from the bed bottom to the surface, without any neck at an intermediate bed level. Furthermore, the cross-sectional spout shape has been delineated in the systems with open-sided draft tube, and significant spout expansion is observed due to air percolation from the spout into the annulus through the opened faces. Finally, the average spout diameters of the systems without draft tube and with open-sided draft tubes have been compared with those predicted by literature correlations. Those proposed by San Jose et al. and Volpicelli et al. provide the best fit for the configurations without draft tube and with open-sided draft tube, with their relative errors being 9.83% and 8.88%, respectively.

Bed symmetry has been analysed in fountain confined conical spouted beds operating with fine particles. Thus, vertical particle velocities and the spout shape have been determined in a wide range of spouting air velocities and bed configurations. Bed symmetry is widely accepted in the spouted beds without draft tubes or with nonporous ones, but this is not the case when open-sided draft tubes are used. Thus, radial particle velocity profiles differ depending on the cross-sectional angular plane considered in the open-sided draft tubes. The spout expands preferentially along the tube opened surface, and is wider as spouting air velocity and aperture ratio are increased. The literature correlations proposed for the average spout diameter have been analysed and no one is valid for estimating this parameter in the whole range of spouting air velocities and configurations analysed in these systems operating with fine particles. This work has received funding from Spain's Ministry of Science and Innovation (PID2019-107357RB-I00 (AEI/FEDER, UE)), the Basque Gov- ernment (IT1218–19 and KK-2020/00107) and the European Commis- sion (HORIZON H2020-MSCA RISE-2018. Contract No.: 823745). M. Tellabide thanks Spain's Ministry of Education, Culture and Sport for his Ph.D. grant (FPU14/05814). I. Estiati thanks the University of the Basque Country for her postgraduate grant (ESPDOC18/14).

A methodology based on the borescopic technique has been developed and validated for tracking solid movement within a conical spouted bed. The procedure developed and fine-tuned allows monitoring the descending and ascending optical flow of both spherical and irregular particles in the annulus (dense zone) and spout (dilute zone) in the bed. A high speed camera (up to 16,000 fps) fitted with a fiber optic continuous light source was used for recording, and an image treatment algorithm modified and adapted to account for differences in particle shape and bed density (dilute or dense) was applied to the registered data. The procedure allows gathering information on the velocity of particles in a wide range of sizes, from a few millimeters ( d p ¯ = 7 mm) to micrometers ( d p ¯ = 93 μm).

The design factors of fountain confined conical spouted beds have been assessed in order to determine their best combination for scaling up and enhancing fine particle retention. The results evidence that the length of the confiner and the height of the draft tube entrainment zone are the key design factors, causing the highest entrainment reduction. Thus, the optimum confiner length is within the range of 2-3 times the bed surface diameter and the desirable height of the entrainment zone is approximately 1-2 times the tube diameter. This study also concludes that the best system for attaining high stability with minimum elutriation is the one equipped with an open-sided draft tube with an aperture ratio of around 20%.

The spouted bed regime is an alternative to fixed and fluidized beds due to the excellent gas-solid contact and the high reduction in operating pressure drop. Nevertheless, the most important limitation of this technology lies in its scaling up, since the inlet diameter/particle diameter ratio must be below 20–30 to avoid bed instability. In order to overcome this limitation, a new internal device called fountain confiner has been developed, which stabilises the system and allows operating with fine particles even without any type of draft tube. Runs have been carried out using the fountain confiner in order to analyse the stability of beds composed of very fine particles and the characteristic hydrodynamic curves (pressure drop vs. air velocity) have been obtained. The use of this new device allows attaining highly stable operation regimes, widening the operational range to 4 times that of plain spouted beds, and increasing the inlet diameter/particle diameter ratio from 20–30 to 1000. Moreover, the optimum distance between the bed surface and the lower end of the confiner has been delimited for the range of operating conditions studied, 0.06 - 0.08 m (between 1 / 2 and 1 / 3 the confiner diameter), since it is a key parameter for system stability. Finally, the effect of several geometric factors and the scaling up of this technology has been analysed for fine particles of different size and density.

[EN] A rigorous model based on hydrodynamic considerations and mass and energy balances has been proposed for batch drying of fine sand in a fountain confined conical spouted bed. The results show that the proposed model predicts acceptably the evolution with time of moisture content in the solid and the final moisture content for the different operating conditions, with the mass transfer coefficient being the only adjustable parameter., This work has been carried out with the financial support from the Ministry of Economy and Competitiveness of the Spanish Government (CTQ2016-75535-R (AEI/FEDER, UE)), the University of the Basque Country UPV/EHU (US14/37) and the collaboration of Novattia Desarrollos Ltd. Aitor Pablos and M. Tellabide thank The University of the Basque Country (UPV/EHU) and the Ministry of Education, Culture and Sport (FPU14/05814), respectively, for their Ph.D. grants