Regimes of fluidization

The spouting regime of fluidization is used for the fluid-solid noncatalytic reactions, especially drying and combustion. 

As fluidized beds are scaled up from bench scale to commercial plant size the hydrodynamic behavior of the bed changes, resulting, in many cases, in a loss of performance. Although there have been some studies of the influence of bed diameter on overall performance as well as detailed behavior such as solids mixing and bubble characteristics, generalized rules to guide scale-up are not available. The influence of bed diameter on performance will differ for different flow regimes of fluidization. 

FIG. 17-6 Solids concentration versus height above distributor for regimes of fluidization. 

Zenz, F.A., Regimes of fluidized behaviour, in Davidson, J.F. and Harrison, D., (eds.). Fluidization, Academic Press, London, 1971. 

Six different regimes of fluidization are identified in Figure 6.11 and its legend. Particulate fluidization, class (b) of the figure, is desirable for most processing since it affords intimate contacting of phases. Fluidization depends primarily on the sizes and densities of the particles, but also on their roughness and the temperature, pressure, and humidity of the gas. Especially small particles are subject to electrostatic and interparticle forces. 

Figure 6.11. Six regimes of fluidization identified with increasing gas superficial velocity (Grace, 1982).

Yerushalmi J, Cankurt NT. 1990. Further studies on the regimes of fluidization. Powder Technol. 24 187-201. 

Because Lanneau had worked in steel equipment, it remained for Kehoe and Davidson (1971) to describe the transition from bubbling to what they dubbed the turbulent regime of fluidization. 

Yerushalmi, J., and Cankurt, N. T. Further studies of regimes of fluidization, Powder Technology 24, 187-205 (1979). 

In the last several decades, many gasification processes have been developed using all three regimes of fluidization bubbling fluidized bed, circulating fluidized bed, and transport reactor. Each gasification process exploits the particular characteristics of a fluidization regime. 

Most fluidized bed partial oxidation processes are operated in the turbulent flow regime of fluidization. However, DuPont operated a circulating fluidized bed catalytic reactor process for maleic anhydride production in Spain, featuring regeneration of the catalyst (by oxidation) on the downcomer side of the circulating system. 

Principal Features of Different Types (Regimes) of Fluidized-Bed Reactors... 

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