Fluidized beds, multistage

In fluidized-bed adsorbers, the combination of high gas rate and small adsorbent particle size results in suspension of the adsorbent, giving it many of the characteristics of a fluid. Fluidized bed adsorbers, therefore, lend themselves to truly continuous, countercurrent, multistage operation. Adsorbent inventory is minimized. 

TABLE 9.14. Performance Data of Fluidized Bed Dryers Batch and Multistage Equipment (a) Batch Dryers... 

Fluidized bed units such as the multistage unit of Figure 15.20 suffer from some loss of efficiency because the intense mixing eliminates axial concentration gradients. They do have the merit, however, of not being bothered by the presence of foreign solid particles. 

Fig. 13. Multistage spout-fluid-bed reactor. 1, spouted bed 2, perforated plate 3, spray nozzle 4, air header 5, fluidized bed.

Li, X. G., Liu, D. L. and Kwauk, M. (1982). Pneumatically Controlled Multistage Fluidized Beds. II. Proceedings of Joint Meeting of Chemical Engineers, S1ESC and AlChE. Beijing Chemical Industry Press. 

The cyclone separates solid particles from the outlet gas. Several cyclones may be combined to form a multistage cyclone system. More than one multistage cyclone system can be placed inside or outside the bed. Other types of gas-solid separators (e.g., filters) are also used for gas-solid separation although the cyclone is most widely adopted in fluidized beds. The dipleg/standpipe returns the particles separated by the cyclone into the dense bed. The outlet of a dipleg may be located in the freeboard or immersed in the dense bed. 

Various configurations have been developed for muitistaging of fluidized beds using the pneumatically controlled downcomer, as shown in Fig. 38. Figure 38A shows the fundamental concept of multistaging of fluidized beds, with a downcomer between two adjacent beds, each downcomer being supplied with a separate stream of control gas. Consequently, there are as many control gas streams as there are stages. 

Fig. 38. Configurations for multistage fluidized beds using the pneumatically controlled downcomer. [After Kwauk, 1974 Liu and Kwauk, 1980 Liu et al., 1981.]...

Kubota and Sekizawa69 measured the solids concentration distribution in a multistage three-phase fluidized bed under a wide range of system conditions. The system conditions analyzed by them are summarized in Table 9-f. 

Because of the general formulation of the proposed model it is believed to be applicable in the design of both single and multistage fluidized bed filters. 

For highly reactive systems in which the majority of particulate collection in the emulsion phase occurs in a relatively short distance from the distributor plate, multistage fluidized beds have been employed (, j4). Because of the general formulation of the present model, it may be employed for determining multistage fluidized bed filtration efficiencies. This includes a variation in the characteristics of each stage such as bed depth and collector size. 

In Fig. 6 the present model predictions of the multistage efficiencies calculated from Eqn. (41) are shown to compare closely to the experimental data of Patterson and Jackson ( ). Because of the importance of electrical effects noted for this system, (12) the Coulombic force term in Eqn. (32) was included. Values of Qp and Qac were arbitrarily set as shown in Figure 5. It should be noted that along with pressure drop information the present model may be used for optimizing the depths of each stage in a multistage fluidized bed filter. 

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