Internal circulating bubbling fluidized

These parts are used in fluidized beds for various purposes. For example, gas distributors and various types of baffles are installed to decrease the size of the bubbles. Moreover, draft tubes are used to enhance gas or solid circulation. Other devices such as horizontal baffles limit circulation and backmixing of solids and gas. Horizontal or vertical tubes are used for heat management. Devices used to control or improve fluidization behavior, to improve fluidization of cohesive particles or to achieve solids recovery are within the various internals met in fluidized bed reactors (Kelkar and Ng, 2002). Immersed tubes in small diameter beds may lead to slugging. Furthermore, attrition of particle breakage may change the size distribution and possibly change the fluidization behavior. 

Gaglia BN, Hall A. Comparison of bubbling and circulating fluidized bed industrial steam generation. Proceedings of the 1987 International Conference on Fluidized Bed Combustion, ASME, 1987, pp 18-25. 

In fluidization, a suspension of fine solid particles behaves like a liquid during the upflow of a supportive gas or liquid phase. Thus the bed of fluidized solid itself may be analyzed similarly to liquid systems. The gas-lift effect produces internal recirculation, by providing a descending flow of high particle concentration and an ascending flow of low particle concentration. This effect resembles the circulation in bubble columns. Whereas bubble columns contain dispersed gas and a continuous liquid phase, the fluidized bed comprises the bubble phase and the emulsion phase in which particles have gained fluid-like properties by the interstitial gas flow. 

All the models proposed for fluidized bed membrane reactors have the same limitations. These models are phenomenological models that make use of closure equations originally derived for fluidized bed without internals. Although it is known that the presence of internals (membranes and permeation of gas through them) may vary the behavior of bubbles, mass transfer and solid circulation inside the bed, reliable closure equations for membrane assisted fluidized bed are not yet available. A way to solve this problem is to use a so-called multi-scale modeling of dense gas-solid systems, where low level... 

---