Fluidized and Spouted Beds

A wide range of operating conditions is used commercially. Performance data are in Table 12.19. Gas velocities cover a rai e of 3-20 times the minimum fluidizing velocity or 0.1-2.5 m/sec. Bed expansion ratios are up to 3 or so. As in fluidized bed drying, bed deptte are low, usually between 12 and 24 in. Evaporation rates are in the range 0.005-1.0 kg/(secKm.  

TABLE 12.15. Alphabetical List of Some of the Materials that Have Been Successfully Compacted by Roll Presses 

Acrylic resins, activated carbon, adipic acid, alfalfa, alga powder, alumina, aluminium, ammonium chloride, animal feed, anthracite, asbestos 

Barium chloride, barium sulfate, battery masses, bauxite, bentonite, bitumen, bone meal, borax, brass turnings 

Cadmium oxide, calcined dolomite, calcium chloride, calcium oxide, carbomethylcellulose (CMC), carbonates, catalysts, cellulose acetate, ceramics, charcoal, clay, coal, cocoa powder, coffee powder, coke, copper, corn starch 

Initial particle size distribution often is in the range of 50-250 pm. The product of Table 12.19(a) is 0.7-2.4 mm dia. 

---

Employing wood chips, Cowan s drying studies indicated that the volumetric heat-transfer coefficient obtainable in a spouted bed is at least twice that in a direct-heat rotaiy diyer. By using 20- to 30-mesh Ottawa sand, fluidized and spouted beds were compared. The volumetric coefficients in the fluid bed were 4 times those obtained in a spouted bed. Mathur dried wheat continuously in a 12-in-diameter spouted bed, followed by a 9-in-diameter spouted-bed cooler. A diy-ing rate of roughly 100 Ib/h of water was obtained by using 450 K inlet air. Six hundred pounds per hour of wheat was reduced from 16 to 26 percent to 4 percent moisture. Evaporation occurred also in the cooler by using sensible heat present in the wheat. The maximum diy-ing-bed temperature was 118°F, and the overall thermal efficiency of the system was roughly 65 percent. Some aspec ts of the spouted-bed technique are covered by patent (U.S. Patent 2,786,280). 

Like enzymes, whole cells are sometime immobilized by attachment to a surface or by entrapment within a carrier material. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for transformation of substrate. A great variety of reactor types have been proposed including packed beds, fluidized and spouted beds, and air-lift reactors. A semicommercial process for beer used an air-lift reactor to achieve reaction times of 1 day compared with 5-7 days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavour profile that was attributed to mass transfer limitations. 

Because of the unavoidable tendency of granular solids to become triboelectrically charged when handled, it is no surprise that electrostatic phenomena are often quite pronounced in fluidized and spouted beds. The vigorous motion of fluidized particles—with constant particle-particle and particle-wall contacts—guarantees that electrical charging will take place. Electrostatic adhesion and cohesion, observed and recorded in the very earliest experimental investigations of fluidization, were immediately identified as experimental nuisances to be overcome. Somewhat later, the hazardous nature of electrostatics came to be appreciated. 

After a review of the customary calculation methods [97] for both essential classes of dryers (convective and contact dryers), the dimensioning methods for spray dryers [98, 99], fluidized and spouted bed dryers [100, 101, 102], cascading rotary dryers [103], pneumatic conveying dryers [104], conductive-heating agitated dryers [105] and layer dryers [106] were presented. They all confirmed the initially made conclusion that the scaling up of dryers is still made today without dimensional analysis and the model theory based thereupon. 

Spray onto dispersed powder (cf. powder clustering, agitation methods above) Atomized liquid feed is sprayed into circulating dispersion of already-dried particles. Hot gases maintain dispersion. Spray granulation, spouted and fluidized bed granulation Fluidized and spouted beds, Wurster apparatus... 

Fluidized and Spouted Beds 362 Sintering and Crushing 363 References 370... 

At the same time, the more traditional tabletting techniques in the pharmaceutical industry were improved and modernized which led to higher production capacities, better tablet qualities, as well as more variability in product shape and composition. Other agglomeration methods were also introduced such as fluidized and spouted beds, mixers of various kinds, etc. 

Inspite of the obvious, good conditions for agglomeration, a high probability of coalescence between particles, it took several decades and the beginning of interdisciplinary evaluation of processes before, by design, fluidized and spouted beds were utilized for agglomeration [B.42, B.57]. 

Because of the high gas velocities, solids loading ratios, and momentum loss in the collision zone, the pressure loss in ISDs is much greater than in pneumatic dryers, but it is comparable with that of fluidized and spouted bed dryers [44,45], The impinging stream configurations can, however, compete in various aspects with the classical systems for drying of particulates and pastes (Table 21.11). 

Kutsakova VE, Romankov PG, Rashkovskaya NB. Some kinetic relationships of the drying process in fluidized and spouted beds. Zhurnal Piikladnoi Khimii. 37(10) ... 

Binder granulation can be achieved in different types of mixers ranging from rotating drums and pans to high shear mixers and fluidized and spouted beds. During the present analysis, the accent is put on fluid... 

Simons SJR, Seville JPK, Clift R, Gilboy WB, Hosseini-Ashrafi ME. Application of gamma-ray tomography to gas fluidized and spouted beds. In Beck MS, Campogrande E, Morris M, Williams M, Waterfall RC, eds. Tomographic Techniques for Process Design and Operation. Southampton Computational Mechanics Publications, 1993, pp. 227-238. 

---