Circulating fluidized beds solids flow structure

In circulating fluidized beds two main attrition sources, namely the riser and the return leg, may be distinguished. Although a lot of information is available about solids flow patterns and flow structures inside the circulating fluidized bed risers, no systematic investigations have been found in the open literature on the influence of riser geometry and flow conditions inside the riser on attrition. With respect to attrition occurring in the return leg, the work of Zenz and Kelleher (1980) on attrition due to free fall may be mentioned (cf. Sec. 4.3). 

The flow structure within circulating fluidized beds is very complex and exhibits axial as well as horizontal non uniformities as it is shown in Fig 9 Unless the solids holdup is very low and the gas velocity very high... 

Horio, M., and Takei, Y. Macroscopic structure of recirculating flow of gas and solid in circulating fluidized beds, in Preprints for 3rd Int. Conf. on CFB, Nagoya, Japan (Oct. 15-18, 1990). 

Pugsley, T. S., Berruti, F., Godfroy, L., Chaouki, J., and Patience, G. S. A Predictive Model for The Gas-Solid Flow Structure in Circulating Fluidized Bed Risers, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 41-48. Somerset, Pennsylvania (1993). 

The hydrodynamic model development for a circulating fluidized bed follows the same approach as bubbling and turbulent beds. In the macroscale, the gas-solid flow is characterized by a coexistence of a bottom dense region and an upper dilute region. The flow in the radial direction can be described by a core-annular structure with a dense particle region close to... 

Wei F, Jin Y, Yu ZQ. Macro visualization of gas solids flow structure in high density circulating fluidized beds. In Avidan AA, ed. Circulating Fluidized Bed Technology IV. New York AIChE, 1994b, pp 588-596. 

Horio et al. (1989) experimentally verified their proposed circulating fluidized bed scaling laws. The solid-to-gas density ratio was not varied in the tests thus they effectively verified the simplified set of scaling laws. Two cold scaled CFBs, fluidized using ambient air, were used in the verification. Good agreement in the axial solid fraction profiles was obtained for most of the conditions tested. An optical probe was used to verify similarity in the annular flow structures and the cluster velocities. 

Arena U, Cammarota A, Marzocchella A, Massimilla L. Solids flow structures in a two-dimensional riser of a circulating fluidized bed. J Chem Eng Japan 22 236-241, 1989. 

Koenigsdorff R, Werther J. Gas-solids mixing and flow structure modeling of the upper dilute zone of a circulating fluidized bed. Powder Technol 82 317-329, 1995. 

Liang W-G, Zhu J-X. A core-annulus model for the radial flow structure in a liquid-solid circulating fluidized bed (LSCFB). Chem Eng J 68 51-62, 1997. 

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