Spouted beds, continuous drying

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). 

Drying of Shelled Corn in a Continuous Operation in a Laboratory-Scale Spouted Bed... 

Madhiyanon, T. Soponronnarit, S. Tia, W. Industrial-scale prototype of continuous spouted bed paddy dryer. Drying Technology 2001, 19(1), 207-216. 

A number of factors influence the selection of a dryer from the many different types available. These factors are dominated by the nature of the feed, whether it be granular solids, a paste, a slab, a film, a slurry, or a liquid. Other factors include the need for agitation, the type of heat source (convection, radiation, conduction, or microwave heating), and the degree to which the material must be dried. The most commonly employed continuous dryers include tunnel, belt, band, turbo-tray, rotary, steam-tube rotary, screw-conveyor, fluidized-bed, spouted-bed, pneumatic-conveyor, spray, and drum dryers. 

Fluidized bed dryers have replaced some of the conventional dryers, e.g., rotary or conveyor dryers in many instances. Among some of the recent developments in fluidized bed drying is the idea of applying microwave energy field continuously or intermittently in a fluidized or spouted bed. Use of superheated steam will probably become more popular in some applications in the future. 

The wheat drying studies were carried out in a spouted bed predryer of rectangular cross section equipped with a draft tube, and also in a cylindrical afterdryer (Table 14.1 and Table 14.2). The experimental conditions and the data of the batch- and continuous-drying experiments are presented in Table 14.7 through Table 14.10. 

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