• Energy Research

[ES] Se ha desarrollado y validado una metodología basada en la técnica boroscópica para seguir el movimiento del sólido dentro de un reactor spouted bed cónico. El procedimiento desarrollado y perfeccionado permite monitorizar el flujo óptico descendente y ascendente de partículas tanto esféricas como irregulares en la zona anular (zona densa) y en el spout (zona diluida). Para la grabación se utilizó una cámara de alta velocidad (de hasta 16.000 fps) equipada con una fuente de luz continua de fibra óptica, y se aplicó a la imagen un algoritmo de tratamiento de imágenes modificado y adaptado para tener en cuenta las diferencias en la forma de las partículas y la densidad del lecho (diluido o denso). El procedimiento permite recopilar información sobre la velocidad de partículas en un amplio rango de tamaños, desde unos pocos milímetros (dp=7 mm) hasta micrómetros (dp=93 μm). [EN] A methodology based on the borescopic technique has been developed and validated for tracking solid move- ment 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 ( dp=7mm) to mi- crometers (dp=93μm) Este trabajo se ha realizado con el apoyo financiero de Ministerio de Economía y Competitividad de España (Proyectos CTQ2016-75535-R y RTI2018-098283-J-I00), los Fondos Europeos de Desarrollo Regional (FEDER) y la Universidad del País Vasco UPV/EHU (US16/21). Aitor Atxutegi agradece su beca de doctorado de la Universidad del País Vasco UPV/EHU (PFI15-2017). Mikel Tellabide agradece al Ministerio de Educación, Cultura y Deporte de España su beca de doctorado (FPU14/05814). This work has been carried out with the financial support from Spain’s Ministry of Economy and Competitiveness (Projects CTQ2016-75535-R and RTI2018-098283-J-I00), the European Regional Development Funds (ERDF) and the University of the Basque Country UPV/EHU (US16/21). Aitor Atxutegi is grateful for his Ph.D. grant from the University of the Basque Country UPV/EHU (PFI15-2017). Mikel Tellabide thanks Spain's Ministry of Education, Culture and Sport for his Ph.D. grant (FPU14/05814)

Abstract Many applications of the conical spouted beds involve operations using coarse and fine particle mixtures, which require high gas velocities due to the coarse particles, thereby leading to fine particle entrainment. In order to avoid entrainment, a new device has been proposed to confine the fountain. Thus, a study has been conducted on the influence the geometry and configuration of both confiner and draft tube have on particle entrainment, operating pressure drop, operating air flow rate and maximum cycle time. The results show that the fountain confiner greatly stabilises the operation and significantly reduces (above 50%) particle entrainment, but its influence on the other parameters is of rather low significance. Furthermore, the distance between the lower end of the device and the bed surface has a great impact on the performance of the spouted bed regime. Entrainment monitoring throughout time showed that its rate depends on the configuration, but remains constant with time.

[ES] Se ha desarrollado un novedoso dispositivo interno denominado confinador de la fuente, que estabiliza el sistema y permite operar con partículas finas, incluso sin ningún tipo de tubo central. Dada la estabilidad que este dispositivo confiere al sistema, se requieren velocidades mínimas de spouting menores que en los sistemas convencionales, por lo que las correlaciones de la literatura sobreestiman este parámetro hidrodinámico. Por ello, se han realizado ensayos con este novedoso dispositivo para estudiar la hidrodinámica y la influencia que tienen los factores geométricos y operativos sobre la velocidad mínima de spouting en spouted bed cónicos de fuente confinada, con y sin tubos centrales. Los lechos están formados por arena fina y partículas de aserrín. A partir de un diseño experimental se pudo comprobar que, aunque ciertos factores influyen en determinadas configuraciones, los de mayor influencia en todas las configuraciones son las propiedades del sólido, la altura del lecho estático y el diámetro de entrada del gas. Por lo tanto, se han propuesto nuevas correlaciones para predecir la velocidad mínima de spouting en cada configuración. [EN] A novel internal device called fountain confiner has been developed, which stabilizes the system and allows operating with fine particles, even without any type of draft tube. Given the stability this device confers upon the system, lower minimum spouting velocities than in conventional systems are required, and therefore the correlations in the literature overestimate this hydrodynamic parameter. Accordingly, runs have been carried out using this novel device in order to study the hydrodynamics and the influence geometric and operating factors have on the minimum spouting velocity in fountain confined conical spouted beds, with and without draft tubes. The beds are made up of fine sand and sawdust particles. Based on an experimental design, it was ascertained that, although certain factors are influential in given configurations, those of greater influence in all the configurations are the solid properties, static bed height and gas inlet diameter. Therefore, new correla- tions have been proposed for predicting the minimum spouting velocity in each configuration. Este trabajo ha recibido financiación del Ministerio de Economía y Competitividad de España (CTQ2016-75535-R y PID2019-107357RB-I00 (AEI/FEDER, UE)) y de la Comisión Europea (HORIZON H2020- MSCA RISE-2018. Contrato nº: 823745 ). M. Tellabide agradece al Ministerio de Educación, Cultura y Deporte de España su beca de doctorado (FPU14/ 05814). I. Estiati agradece a la Universidad del País Vasco su beca de posgrado (ESPDOC18/14).

Abstract This study examined elutriation, attrition, and segregation in a conical spouted bed with a fountain confiner and incorporating an open sided draft tube. Fine silica sand with a wide particle size distribution was employed as a model material, operating in both the batch and continuous modes. The use of a fountain confiner is crucial when operating with fine particles, because otherwise the bed rapidly exhibits significant entrainment. The extent of attrition was quantified using a tracing technique based on differently-coloured sand fractions as well as monitoring size distributions by sieving. Particle breakage was found to be the primary attrition mechanism, and the fountain confiner was determined to limit the elutriation of fine particles resulting from breakage. Consequently, only a small fraction of the finest particles were entrained from the bed. The incorporation of a confiner increased operational stability while reducing segregation, especially in the upper half of the bed where the majority of segregation typically occurs. Thus, the bed was perfectly mixed apart from very minimal segregation close to the wall and at the bottom of the contactor. These results provide a basis for the design and operation of larger scale equipment for the continuous drying of materials.

Abstract 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%.

Abstract 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.

Abstract Conventional spouted beds have been extensively used in many real-life applications but are not suited for all types of materials, especially fine particles, which require internal devices to improve their motion in the spouted bed. However, unlike conventional spouted beds, there are almost no mechanistic or empirical models available for the design of spouted beds with internals. Given the availability of an extensive but not experimentally designed database, the main purpose of this study is to present an analysis of neural networks and empirical models in terms of their suitability to fit and predict average cycle times in conical spouted beds with and without draft tubes. The parameters investigated are particle size, density, contactor angle, gas inlet diameter, static bed height, and draft tube features. Although the amount of information is always a key factor when fitting models, the size of the database used in this study strongly affects the fitting performance of empirical models, whereas artificial neural networks are more influenced by how the data are scaled. Results of model verification show that both techniques are suitable for predicting average cycle times for data outside the range covered by the database.

Abstract Pressure fluctuation analysis has been used to identify different flow regimes in spouted beds. Although this is a promising cost-effective tool for process control and design purposes, it has hardly been used in spouted beds operating with fine and irregular particles. Therefore, the aim of this paper is to apply pressure fluctuation analysis to spouted beds operating with fine and irregular particles, either without tube or equipped with draft tube. The minimum spouting velocities estimated by the spectral analysis in systems without tubes differ from those obtained based on the characteristic curves in the range from 10.60% (sand) to 3.50% (glass beads). Thus, the main novelty of this study lies in the application of pressure fluctuation and spectral analyses in spouted beds operating with fine and irregular particles by considering the influence of the internal devices. Therefore, the methodology proposed based on both hydrodynamic and spectral analyses is a feasible and promising alternative for delimiting the minimum spouting velocity and stable operating conditions in industrial processes, especially when the aim is process control and scaling up.

Abstract A study has been carried out on the hydrodynamic performance of a fountain confinement device used in conical spouted beds for the treatment of Geldart A and B type particles. Stability and particle elutriation have been analysed for beds provided only with this device and those provided with this device and two types of draft tubes, namely, open sided draft tube and nonporous draft tube. Stability is greatly improved when only the fountain confiner is used, but the draft tubes are required for significantly avoiding bed elutriation in spouted beds. The modified conical spouted bed has been located in a map of operating conditions together with the remaining gas-solid contact regimes. The fountain confiner provides a dramatic increase in the applicability range of spouted beds. Thus, unlike the traditional use of spouted beds for Geldart D type particles, this device allows operation with Geldart A, B and D particles, with a small fraction of C particles.