Various Types of Fluidized Beds

Numerous types of fluidized bed reactor designs exist within each of the two categories mentioned in the previous subsection, some of them are illustrated in Fig 10.7. The key issues leading to re-design of the primary bubbling bed are also indicated. 

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Kono, H., Attrition Rates of Relatively Coarse Solid Particles in Various Types of Fluidized Beds , AIChE Symp. Ser., 205(77) 96 (1981)... 

In this context Contractor et al. (1989) eonclude that the relative attrition rate depends on the attrition test method used. Knight and Bridgwater (1985) subjected spray-dried powders to a compression test, a shear test, and a test in a spiral classifier. They found that each test gave a different ranking of the materials. Werther and Reppenhagen (1999a) observed this phenomenon as they subjected various types of fluidized bed catalysts to both a cyclone attrition and a jet attrition test, each simulating one of the three major attrition sources in fluidized bed systems (cf. Sec. 5). 

Kono H. Attrition rates of relatively coarse solid particles in various types of fluidized beds. AIChE Symp Ser 77 96-106, 1981. 

Various types of fluidized bed dryers have been studied, developed, and operated in many industrial processes according to the respective process, product, operational safety, and environmental requirements. It is important to become familiar with the specific characteristics of different fluidized bed types in order to make a logical and cost-effective selection. It should be noted that in many instances several different types may provide similar performanee at the same cost. 

In an Oak Ridge study [61] various types of fluidized-bed reactors were compared. Systems investigated were (a) a sodium-cooled fast reactor, (b) a gas-cooled system, (c) an organic-moderated reactor, (d) a heavy-water-moderated reactor, and (e) a light-water system. A detailed study of this latter system was carried out to compare its characteristics and performance with solid-fuel heterogeneous pressurized-water reactors. The results indicated that both the light-water-moderated and organicmoderated fluidized reactors showed promise, while the gas-cooled, the D20-cooled, and the fast (unmoderated) reactors were found to be less satisfactory for application of the fluidized-bed technique. 

Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 11-24. After an introduction (Chapter 11) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21-24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions. 

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. 

The range of fluid rates for various types of conical fluidized bed operation can therefore be summarized as follows ... 

Fig. 6 Various types of animal cell bioreactors (A) roller bottle (B) rotating disk (C) stirred tank with a marine impeller (D) tank with a pulsating agitator (E) stirred tank with a spin filter (F) airlift (G) fluidized bed and (H) hollow fiber. (View this art in color at WWW. dekker. com.)...

Equipment for heterogeneous reactions is particularly flexible, since each phase can be processed more or less independently. In the fluidized-bed reactor (Fig. 1-4) the reactants flow continuously through and out of the reactor, but the solid-catalyst phase is withdrawn, regenerated, and returned. In the lime kiln (an example of a gas-solid noncatalytic reactor) the two phases pass continuously and countercurrently through the reactor. In heterogeneous liquid-solid polymerization systems the slurry of catalyst and reaction mixture flow together through the reactors. Walas, Brotz, and particularly van Krevelen have summarized the various types of... 

Various types of modified FBDs have been developed and applied in many industrial processes. Modified FBDs are applied to overcome some of the problems and disadvantages encountered in conventional fluidized beds. 

Internal baffles can be inserted into a fluidized bed to divide the bed into several compartments. Various types of baffles can be used, for example, wire mesh, perforated plate, turn plate, louver plate, and ring [92]. In addition, the internals can be placed horizontally or vertically (Figure 8.22). Horizontal baffles are frequently used. The objective of inserting baffles (horizontal and vertical) is to limit bubble growth and coalescence [93,94]. Hence, the baffled fluidized bed is useful to process group B and D particles because large bubbles are formed with such particles. The effect of baffles on the gas and... 

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