Flow structure and thickness of annular downflow layer in a circulating fluidized bed riser

Date

2004-04-08

Author

Kim, SW
Külah, Görkem
Bi, HT
Lim, CJ
Grace, JR

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Flow structures were determined in a circulating fluidized bed (CFB) riser (0.203 m i.d. x 5.9 m high) of FCC particles (d(p)=70 mum, rho(s)= 1700 kg/m(3)). A momentum probe was used to measure radial momentum flux profiles at several levels and to distinguish between upward and downward flow regions. Time-mean dynamic pressure (DeltaP(m)) decreases towards the wall in the range U-g=5-8 m/s, G(s)=10-340 kg/m(2) s. The thickness of the annular downflow layer based on DeltaP(m)=0 reaches a maximum with increasing height. The annular downflow layer disappears locally with increasing solids mass flux (G(s)) at a constant gas velocity, with achievement of the dense suspension upflow (DSU) regime. A new correlation is developed to predict the time-mean thickness of solids down-flowing layer based on solids mass flux and momentum flux. It successfully accounts for the variation of the annular layer thickness with height and Gs, and covers a wide Gs range right up to near the onset of the DSU regime.

Subject Keywords

Momentum probe, Annular downflow layer thickness, Core-annulus structure, Hydrodynamics, Fast fluidization, Circulating fluidized bed

URI

https://hdl.handle.net/11511/42833

Journal

POWDER TECHNOLOGY

DOI

https://doi.org/10.1016/j.powtec.2004.03.011

Collections

Department of Chemical Engineering, Article

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Citation Formats

S. Kim, G. Külah, H. Bi, C. Lim, and J. Grace, “Flow structure and thickness of annular downflow layer in a circulating fluidized bed riser,” POWDER TECHNOLOGY, pp. 48–58, 2004, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/42833.