Flow characterization in high-velocity fluidized beds using pressure fluctuations

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Abstract

Fast fluidization flow characteristics were studied using instantaneous pressure signals in a fast fluidization unit with 0.152 m i.d. and 8.4 m height using a Zeolite FCC catalyst. The data confirmed that a fast fluidized bed can usually be divided into two main regions, a dense region at the bottom and a dilute region at the top. Within both regions the mean void fractions are essentially constant along the height. The void fraction in the dense region appears to be independent of the solid circulation rate and varies only slightly with the superficial gas velocity. Upward moving instabilities were detected within the dense region of the bed with a fairly constant wave speed over a wide range of flow parameters. These have similarity to phenomena in slugging fluidized beds. The results suggest that the solids in the dense region of a high-velocity fluidized bed are present in three different forms—relatively stagnant in a dense annulus region, very dilute in a core region, and in the form of waves rolling upward between the core and dense annulus.

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