Circulating fluidized beds solids mixing

Rhodes et al. (1991) conducted RTD measurements to study longitudinal solids mixing in a circulating fluidized-bed riser by pulse-injection of a sodium chloride tracer. 

For the case of horizontal gas mixing, Werther and co-workers [70, 71] have shown that, for the bed solids they used (quartz sand, dp = 0.13 mm, Geldart group B), horizontal gas mixing in the top part of the circulating fluidized bed in the core zone can be described by the model for gas dispersion in turbulent singlephase flow [72]. The Peclet number... 

Arena, U., Marcozhella, A., Bruzzi, V., and Massimilla, L. Mixing Between A Gas-Solids Suspension Flowing in a Riser and a Lateral Gas Stream, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 660-664. Somerset, Pennsylvania (1993). 

Wei, F., Chen, W., Jin, Y., and Yu, Z. Axial solids mixing in cocurrent downflow circulating fluidized bed, in Proceeding of 5th National Meeting on Chemical Reaction Engineering (in Chinese), Tianjing (1993). 

Milne, B. J., and Berruti, F. Modelling the mixing of solids in circulating fluidized beds, in Circulating Fluidized Bed Technology III (P. Basu, M. Horio and M. Hasatani, eds.), pp. 575-580. Pergamon Press, 1991. 

Intelligent design of circulating fluidized bed boilers depends on sufficient understanding of the physico-chemical hydrodynamics occurring in the combustors, such as chemical kinetics of coal combustion and pollutant formation, hydrodynamics of gas-solid two phase flow, mixing of gas and solids, distribution of heat released, and heat transfer between immersed... 

The thorough mixing of the solid leads to effective gas-solid heat exchange with an excellent heat-transfer characteristic and hence a uniform temperature distribution in the reaction space. Heat-transfer coefficients are typically 100-400 kJm h K and for small particles can be as high as 800 kJm h K. For fine particles and at high reaction rates, circulating fluidized-bed reactors with separation and recycling of the soUd are particularly suitable. 

Hirschberg B. Solids mixing and segregation in a circulating fluidized bed. PhD dissertation. Technical University Hamburg-Harburg, 1997. 

Chesonis DC, Klinzing GE, Shah TT, Dassori CG. Hydrodynamics and mixing of solids in a circulating fluidized bed. Ind Eng Chem Res 29 1785 1792, 1990. 

Du B, Wei F, Wang F. Effect of particle size on solids mixing in a FCC riser. In Werther J, ed. Circulating Fluidized Bed Technology VI. Frankfurt DECHEMA, 1999, pp 405 10. 

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. 

Werther J, Hirschberg B. Solids motion and mixing. In Grace JR, Avidan AA, Knowlton TM, eds. Circulating Fluidized Beds. London Chapman and Hall, 1997, pp 119-148. 

Westphalen D, Glicksman L. Lateral solids mixing measurements in circulating fluidized beds. Powder Technol 82 153-168, 1995. 

In circulating fluidized bed combustors, the volatile release and combustion are important with regard to pollutants emissions, heat release patterns and the subsequent reactivity of the char particles. For coals with high volatiles content, the release of volatiles is important in the selection of the feed point location, since the time constant for volatiles release and combustion is much shorter than the char burnout time. In addition, solid mixing and rate of devolatilization determine the region of volatile release. 

Milne B.J. and F. Berruti, "Modelling the Mixing of Solids in Circulating Fluidized Beds", CFB III Edited by P. Basu, M. Horio and M. Hastani 575-580 (1990). 

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