Spouted beds continuous operation

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

J. Bilbao, M. Olazar, A. Romero, J.M. Arandes, Design and operation of a jet spouted bed reactor with continuous catalyst feed in the benzil alcohol polymerization, Ind. Eng. Chem. Res. 26 (1987) 1297-1304. 

The three-phase continuous countercurrent fluidized-bed reactor and the spouted-bed reactor have been used on the laboratory scale. Pruden and Weber88 have shown that the countercurrent mode of operation for hydrogenation of a-methyl styrene performs better than the cocurrent fixed-bed operation under similar reaction conditions. 

Inspite of the last statement, continuous operation of spouted beds normally does require the separation of product from over- and undersized agglomerates both off-scale material streams, the oversized after crushing to below maximum product size, are recirculated (Fig. 7.89b). 

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

The presence of the draft tube in the reactor allows to achieve other desirable features. In conventional spouted beds, the spout (jet) is in continuous contact with the annular solids over the entire height of the bed and, to achieve a stable operation, it must be able to support the surrounding annular bed. To provide this support, the spout must be at a greater pressure than the annulus. Because of this pressure difference, there is continuous percolation of gas into the annular region and, if the bed is too deep, the spout can easily collapse. The bed height at which this transition occurs is termed the maximum spoutable height (Mathur and Gishler, 1955). The presence of the draft tube removes this limitation. 

Suspended Particle Techniques. In these methods of size enlargement, granular soHds are produced direcdy from a Hquid or semiliquid phase by dispersion in a gas to allow solidification through heat and/or mass transfer. The feed Hquid, which may be a solution, gel, paste, emulsion, slurry, or melt, must be pumpable and dispersible. Equipment used includes spray dryers, prilling towers, spouted and fluidized beds, and pneumatic conveying dryers, all of which are amenable to continuous, automated, large-scale operation. Because attrition and fines carryover are common problems with this technique, provision must be made for recovery and recycling. 

Porous or particulate fixed bed electrodes have been recognized as the more efficient three-dimensional cathodes used for metal electrodeposition from dilute solutions, mainly due to their uniform effective conductivity of the solid phase. However, electrode clogging due to metal electrodeposition restricts their use as only for very dilute solutimis in which the long operational time would justUy their use [11, 12]. In order to overcome this Umitatimi and make the electrochemical process continuous, mobile electrodes, such as fluidized, spouted, and inclined bed electrodes, were proposed [13-16]. In these electrodes, the conductivity of the... 

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