Particle clusters in and above fluidized beds

Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

“…The particle clusters may not be forming in the freeboard to any significant degree, but in the fluidized bed itself. This was confirmed in Cocco et al (2010) with high-speed video measurements in the fluidized bed. As shown in Fig.…”

“…5. Direct evidence of particle clusters was observed and reported by Cocco et al (2010). Using a modified borescope connected to a high-speed Phantom V7.2 camera, Cocco et al were able to resolve particle clusters well above the bed in the freeboard.…”

“…It is unknown whether the clusters exist in the denser emulsion phase and get ejected into the less dense bubble phase, or if the clusters are solely a product of the bubble phase in the fluidized bed (Cocco et al, 2010). In the first case, clustering is prolific and bed hydrodynamics may be strongly coupled to the level of particle clustering.…”

“…Fortes et al (1987) observed similar-sized clusters which were stable up to a Reynolds number of 1800. Cocco et al (2010) used a high-speed camera connected to a customized boroscope to reveal these particle clusters in the freeboard region of a fluidized bed containing fluidized catalytic cracking (FCC) equilibrium catalyst with a median particle size of 72 microns and 12 % fines (defined as particle with a size smaller than 44 microns). In fact, 30 % of the particle behavior in the freeboard was found to resemble particle cluster formation with an average particle cluster size of 11 particles.…”

“…The same study by Cocco et al (2010) used the highspeed camera with a boroscope to reveal that particle clusters existed in the fluidized bed as well as above the fluidized bed. The region surrounding a passing bubble showed that most of the particles were behaving as weakly-bound clusters.…”