High-velocity fluidization

Circulating fluidized beds (CFBs) are high velocity fluidized beds operating well above the terminal velocity of all the particles or clusters of particles. A very large cyclone and seal leg return system are needed to recycle sohds in order to maintain a bed inventory. There is a gradual transition from turbulent fluidization to a truly circulating, or fast-fluidized bed, as the gas velocity is increased (Fig. 6), and the exact transition point is rather arbitrary. The sohds are returned to the bed through a conduit called a standpipe. The return of the sohds can be controUed by either a mechanical or a nonmechanical valve. 

Yerushalmi, Y., and Avidan, A., High Velocity Fluidization, in Fluidization, (J. F. Davidson, R. Clift, and D. Harrison, eds ), 2nd edition, Academic Press, New York (1985)... 

Squires, A. M., Gasification of Coal in High-Velocity Fluidized Beds, loc. cit. (1975b)... 

Squires, A. M., The City College Clean Fuels Institute Programs for (i) Gasification of Coal in High-Velocity Fluidized Beds (ii) Hot Gas Cleaning, Symp. Clean Fuels from Coal, I.G.T., Chicago (1975c)... 

Avidan, A. A. and Yerushalmi, J. (1982). Bed Expansion in High Velocity Fluidization. Powder Tech., 32, 223. 

Schnitzlein, M.G. and Weinstein, H. (1988). Flow Characterization in High-Velocity Fluidized Beds Using Pressure Fluctuations. Chem. Eng. Sci., 43,2605. 

Burovoi, I. A., Dracheva, T. V, and Ibraev, A. Kh., Semi-Industrial Testing of the Fluidized-Bed Acid Leaching of Zinc Calcine, Tsvet, Metal. 44(10), 16(1971) Chem. Abs. 76,36,301 (1972). Cankurt, N. T., and Yerushalmi, J., Gas Backmixing in High Velocity Fluidized Beds, Second Intern. Conf. Fluidization. Cambridge, pp. 387-393 (1978). 

During a visit to the Institute of Chemical Metallurgy in June 1979,1 was astonished by the range, sophistication, and aptness of high-velocity fluidization research in progress there, only five years after the Institute had been reinstated with Kwauk as its director. Already, the work had cast... 

Avidan, A. A. Bed expansion and solid mixing in high-velocity fluidized beds, Ph.D. dissertation, The City University of New York (1980). 

Squires, A. M. "Gasification of Coal in High-Velocity Fluidized Beds, in Feature Energy Prod. Syet., Lect. Pap. Int. Semin., Meeting Data 1975, Volume 2,509" (Denton, J. C., and Afgan, N. H eds.). Academic New York. (1986). 

Arena, U., Cammarota, A., and Pistane, L. High velocity fluidization behavior of solids in a laboratory scale circulating fluidized bed, in Circulating Fluidized Bed Technology (P. Basu, ed.), pp. 119-128. Pergamon Press, 1986. 

Cankurt, N. T and Yerushalmi, J. Gas mixing in high velocity fluidized beds, in Fluidization (J. Davidson and D. Kearins, eds.), pp. 387-392. Cambridge University Press, 1978. 

Attrition index (AI, wt%). A fresh catalyst sample is subjected to high-velocity fluidization for a long time. In this process, wear on the particles occurs as they are... 

Grace JR (1990) High-Velocity Fluidized Bed Reactors. Chem Eng Sci... 

Weinstein H, Shao M, Schnitzlein M (1986) Radial variation in solid density in high velocity fluidization. In CFB Technology, Pergamon press, pp 201-206... 

Figure 1 Typical fluidized bed reactors, (a) Low-velocity fluidized bed, and (b) high-velocity fluidized bed. 

In the high-velocity fluidized bed, the bed ean be operated in turbulent, fast fluidization, dilute transport, and downer flow regimes. In the turbulent regime, the bubble/void phase gradually becomes indistinguishable from the emulsion phase, and the particle entrainment rate increases significantly with increasing gas velocity. Upon further increase in gas velocity, the bubble/void phase eventually disappears and the gas evolves into a continuous phase in the fast... 

Yerushalmi Y, Avidan A. High velocity fluidization. In Davidson JF, Clift R, Harrison D, eds. Fluidization. 2d ed. New York Academic Press, 1985. 

Bi HT, Grace JR. Flow patterns in high-velocity fluidized beds and pneumatic conveying. Can J Chem Eng... 

Brereton CMH. Fluid mechanics of high velocity fluidized beds. PhD diss.. University of British Columbia, Vancouver, 1987. 

Dry RJ, Christensen IN, White CC. Gas-solids contact efficiency in a high-velocity fluidized bed. Powder Technol 52 243-250, 1987. 

Grace JR. Heat transfer in high velocity fluidized beds. In Hetsroni G, ed. Proc 9th International Heat Transfer Conference, Jerusalem, 1990, pp 329-339. 

Grace JR, Lim KS. Reactor modelling for high-velocity fluidized beds. In Grace JR, Avidan AA, Knowlton TM, eds. Circulating Fluidized Beds. London Chapman and Hall, 1997, pp 504-524. 

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