An evaluation of the solid hold‐up distribution in a fluidized bed of nanoparticles using radioactive densitometry and fibre optics

Abstract

An experimental study was conducted to assess the solid hold-up distribution in a fluidized bed of zirconia and aluminum nanoparticles. For this purpose, two different techniques, radioactive densitometry and fibre optic measurement, were used. The results showed that while the fluidization of these nanoparticles occurs in the agglomeration state, it performs homogeneously in terms of phase concentration. This matter is important especially when a polymerization reaction should take place uniformly on the surface of nanoparticles, where the monomer is the fluidizing gas. Both techniques presented uniform solid hold-up distribution over the cross-section, although the fibre optic method overestimated the overall solid concentration, which was obtained based on bed expansion results. The radioactive densitometry was, however, capable of properly predicting the phase concentration within the bed according to the bed expansion observation. Finally, the effect of bulk density on the fluidization of nanoparticles was discussed by comparing the fluidization of different types of particulate materials.On a mené uneétude expérimentale pourévaluer la distribution de rétention de solide dans un lit fluidisé de nano particules de zircon et d'aluminium.À cette fin, deux techniques différentes, la densimétrie radioactive et la mesure par fibres optiques, ontété utilisées. Les résultats montrent qu'alors que la fluidisation de ces nano particules survientà l'état d'agglomération, elle est relativement performante en termes de concentration de phase. Cet aspect est important, car une réaction de polymérisation devrait se produire uniformémentà la surface des nano particules, le monomèreétant le gaz fluidifiant. Les deux techniques ont mis enévidence une distribution de rétention de solide uniforme dans la section transversale, bien que la méthode par fibres optiques ait surestimé la concentration de solide globale, obtenueà partir des résultats d'expansion du lit. Cependant, la densimétrie radioactive est capable de prédire de manière correcte la concentration de phase dans le lit d'après l'observation de l'expansion de lit. Enfin, l'effet de la masse volumique apparente sur la fluidisation des nano particules est examiné en comparant la fluidisation de différents types de matériaux particulaires.

Encapsulation of nanoparticles by polymerization compounding in a gas/solid fluidized bed reactor

“…These results are consistent with the results obtained in our previous work 17. It was mentioned that the fluidization of zirconia and aluminum occurs in agglomerate state as shown in Figure 9.…”

“…According to the experiments,17 it was understood that by increasing the gas velocity, large agglomerates are broken to smaller ones due to higher drag force in higher gas velocities. Therefore, in the range of gas velocity where we did the fluidization experiments, the agglomerate size are smaller for higher gas velocity for a given particle type.…”

“…After the desired reaction time, ethylene flow was stopped and the system was flushed with nitrogen. The gas velocity in the reactor for aluminum and zirconia was 5 and 10 cm/s, respectively, which are much higher than minimum fluidization velocity of these powders 17. The temperature and the pressure in the reactor were kept constant for a given reaction, and varied within range of 65–75°C and 140–280 kPa, respectively, during the series of runs in this study.…”

“…The approach investigated consisted of evaporating the Ziegler–Natta catalyst before it entered the fluidized bed reactor, and then condensing the resulting vapor on the particle surface in the reactor. As there is no thermal gradient in the reactor, all particles having the same temperature due to the mixing action of the fluidization process,17 the catalyst vapors uniformly deposit on the particle surface. Therefore, it would be anticipated that the polymerization reaction is uniformly applied on the particles.…”

Hydrodynamics of a gas–solid fluidized bed with thermally induced interparticle forces

“…Therefore, the marginal values of the Hausner ratio established by Gledart for the naturally cohesive powder cannot be essentially valid for all kinds of cohesive particulate beds. Similarly, Esmaeili et al [57] found that the Hausner ratio criterion introduced by Geldart cannot satisfactorily predict the Agglomerate Particulate Fluidization (APF) and Agglomerate Bubbling Fluidization (ABF) [2] behaviors of nano size cohesive particles.…”