Multistage fluid bed

For slow reactions, the shallow fluid beds have been organized into a cocurrent multistage fluid bed (MSFB) reactor as shown in Fig. 33 (Yan, Yao, Wang, Liu and Kwauk, 1983). In this reactor, solids are carried up by the flowing gas stream, and once they reach the top, they are collected through a funnel and recirculated to the bottom by means of a pneumatically controlled downcomer. 

Chemical activity Apparent contact time 3 < T < 30 sec Stability of operation Homogeneous temperature in bed LJDt = 1-2 High activity excess reaction in dilute phase Low activity decrease of reaction yield Dilution with inert particles Multistage fluid bed... 

Particle size distribution Weight mean diameter 50 < dp < 70 jum + 80 jum, 5-20 wt. % -40 /tm, 10-30 wt.% Improved fluidity Good fluidization Decreased catalyst loss and attrition Se vere erosion if particles are coarse Difficulty in recovering particles <10 /am Installation of internals Multistage fluid bed with horizontal baffles... 

Several investigations have been made on the flow characteristics in multistaged fluid beds. Nishinaka et al. (N6, N8, N9) have measured the average bubble holdup, the lateral distribution of bubble holdup, and the longitudinal dispersion of solid particles in four- and eight-stage fluid beds installed with various horizontal baffles. As shown in Fig. 25 the average bubble holdup (except for beds baffled with tube plates) is correlated by the equation of Nishinaka et al., (N8) ... 

B. Finish dryer multistage fluid bed with dehumidified air... 

Single-stage/multistage fluid beds Simultaneous fluidization of entire bed... 

Figure 15.10 A multistage fluid bed dryer. (From Alves-Filho et al., 1998.)...

Multistage fluid bed Batch dryers Batch dryers Suspended state dryers not recommended... 

Column dryer with internal tube Multistage fluid bed... 

Fig. 13. Multistage spout-fluid-bed reactor. 1, spouted bed 2, perforated plate 3, spray no22le 4, air header 5, fluidi2ed bed.

Figure 33. The cocurrent multistage (co-MSFB) fluid-bed reactor. (Yon, Yao, Wang, Liu, and Kwauk, 1983.)...

This is a reversible, exothermic reaction carried out adiabatically in a multistage, fixed-bed reactor with axial flow of fluid and interstage heat transfer for temperature adjustment see Figure 1.4. The catalyst is promoted V205. 

Spray and fluid bed drying technologies can be combined into one multistage process to accomplish the tasks discussed above. Figure 355 shows as an example the two-stage arrangement of a spray dryer and a vibrating fluid bed. Further... 

In polymer industries, wherever spray dryers are used they are primarily used as predryers of a multistage system. Final drying is normally done in a fluid bed, which is... 

An agitated multistage steam dryer with concurrent flow of steam and the product has been developed successfully in Japan to dry 15 tons per day of dewatered sludge. Steam at 360°C at flow rates up to 3600 kg/h enters the dryer and exits at 150°C, giving a volumetric heat transfer coefficient of up to about 100 W/(m K). Unlike a fluid bed, the low-steam velocities cause little entrainment in the exhaust stream, which is cleaned in a cyclone. To... 

Continuous adsorption mainly takes place in single or multistage fluidized beds (Figs. 4-4 and 4-20b). Small mesh sieves are used with an adsorbent downcomer or large mesh sieves with the adsorbent raining through the holes (for more information on fluid dynamics see [4.41, 4.42], on residence time [4.43], and on pressure drop, flow through particles, particle concentration... 

In polymer industries, wherever spray dryers are used they are primarily used as predryers of a multistage system. Final drying is normally done in a fluid bed, which is either stationary or vibrated type. Stationary fluid beds are used when spray-dried powder leaving the drying chamber is directly fluidizable. The vibrated type of fluid bed is used for products that, on leaving the spray dryer, are not readily in a fluidizable state owing to their particle form, size distribution, or wetness. 

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. 

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