Improvement of the Fluidizability of Cohesive Powders through Mixing with Small Proportions of Group A Particles

• Published in: Canadian journal of chemical engineering 2005-12, Vol.83 (6), p.930-943
• Main Authors: Ajbar, A., Alhumazi, K., Asif, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; cohesive powder; Exact sciences and technology; Fluidization; gas fluidization; group A; group C; Hydrodynamics of contact apparatus; time series
• ISSN: 0008-4034; 1939-019X
• DOI: 10.1002/cjce.5450830602

The gas fluidization behaviour of fine cohesive powders, classified as Geldart group C, is known to be characterized by cracks and channels leading to severe non‐homogeneities in the bed. Geldart group A particles, on the other hand, are known to show more homogeneous and regular fluidization behaviour. This paper studies the effects of the addition of small proportions of group A on the fluidization behaviour of a group C powder. Differential pressure fluctuations data at a sampling frequency of 200 Hz were recorded for two cases. In the first case, the bed contained only group C powder while in the second case small amounts of group A particles were added to the existing group C powder. Visual/image observations coupled with time series analysis showed that the addition of small proportions of group A particles substantially improved the fluidization behaviour of the bed even at low superficial gas velocities, leading to a more uniform fluidization. Evaluation of mean and standard deviations has shown the advantage of mixing the two powders as it allowed larger pressure fluctuations and smaller standard deviations. Power spectra, on the other hand, showed that unlike group C, for which fluctuations were small in magnitude and broadband in structure, the mixture showed stronger periodic behaviour as result of the attenuation of the small and rapid fluctuations caused by the flow of gas in the cracks and channels. Advanced methods such as the principal component analysis of the embedded trajectories allowed a quantitative comparison between the fluidization behaviour of the two systems. Il est connu que le comportement de fluidisation par un gaz de poudres cohésives fines, formant le groupe C de Geldart, se caractérise par des fissures et des canaux menant à de sévères non‐homogénéités dans le lit. Par ailleurs, les particules du groupe A de Geldart sont connues pour montrer un comportement de fluidisation plus homogène et plus régulier. On étudie dans cet article les effets de l'ajout de petites proportions de particules du groupe A sur le comportement de fluidisation d'une poudre du groupe C. Des données de fluctuations de pression différentielles à une fréquence d'échantillonnage de 200 Hz ont été recueillies pour deux cas. Dans le premier cas, le lit contenait uniquement la poudre du groupe C, tandis que dans le second cas, de petites quantités de particules du groupe A ont été ajoutées à la poudre du groupe C existante. Les observations visuelles coup