Spouted beds spout shape

The fact that in a steadily spouting bed the spout assumes a stable shape implies the existence of a state of dynamic equilibrium among the various forces acting on the spout-annulus interface. Since these forces arise from the movement of both solids and gas, the shape of the spout provides a valuable clue to an understanding of the entire dynamics of spouted beds. The spout shape has, therefore, received considerable attention. 

Equation (9) is a dimensional equation where SI imits should be used. Equation (9) is good to 5.6% at room temperature. He et al. (1998a) employed a fiber-optic probe to measure the spout diameter in a semicylindrical and a full cylindrical spouted bed and found that the presence of the flat front plate in the semicylindrical bed considerably distorted the spout shape. They found that the McNab equation underestimated the spout diameter in a full cylindrical bed by an average of 35.5%. Under pressure, the McNab equation can also introduce error up to 65.5% at a pressure of 343 kPa (He et al., 1998b). Spout diameter tends to increase with increasing pressure. 

The spouting vessel is conunonly either cylindrical or conical in shape (Fig. 2). With the former it is preferable to have a short conical base tapering down to the inlet orifice, so that the solids in the annulus can easily slide into the gas jet region without forming any dead zone at the base. Most of the work outside the Soviet Union has been carried out in this type of vessel, while spouting in conical vessels has received particular attention in the Soviet Union, and has been extensively discussed in a book by Romankov and Rashkovskaya (R4). The general discussion of spouted bed behavior in this review is in the context of a cylindrical column. 

The solids movement in a spouted bed is initiated by the interaction between the particles and the high-velocity gas jet, so that particle flow in the spout region shapes the entire solids-flow pattern. While a mutual dependence between the solids flow in the spout and in the annulus is inherent to a spouted bed, it is nevertheless convenient to discuss the flow in the spout and in the annulus separately. 

Typical fluid bed processors are illustrated in Fig. 1. Fig. lA is a simple fluid bed, usually with a conical shape at the bottom of the chamber, leading to inducing spouted particle flow more or less depending on the angle of the conical chamber. The spray is supplied from the top toward the fluidized bed in agglomeration and into the bed in a tangential direction in coating. Elutriated particles from the fluid bed are... 

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. 

In the French Oil Machinery Co. stationary basket extractor (Fig. 10.3-5), extract percolates through beds of solids contained in a circular array of sector-shaped compartments with perforated bottoms and drains into sumps positioned below the beds. Unlike crossflow extractors, the solids do not move." Instead, the solid feed spout and solids discharge zone rotate about the circle and the extract feed and discharge connections are switched periodically. These extractors are like automated diffusion batteries in which downflow is used but, because extract backmixes in each sump, the extract concentration leaving a stage is somewhat different from that entering the next stage. 

The shape and dimensions of the active carbon particles change as a result of their processing in the spouted bed, as shown schematically for a particle with layers removed to different degrees in Figure 2. 

However, in various coating and granulation experiments a change in the shape of the distribution is observed, for example a dispersion of the distribution. In Fig. 7.45 the results of five different coating experiments are shown, which were conducted in Wurster equipment, a conventional fluidized bed apparatus (FB) in top and bottom spray configuration, and a spouted bed apparatus (SB) in top and bottom spray configuration. Although identical initial conditions were used and the process conditions are comparable (see Tab. 7.6), different final distributions are achieved. This effect cannot be explained by the common model of Eq. 7.34, but it underlines the influence that different types of equipment with different flow patterns may have on the process result. 

A spouted bed is essentially a conically shaped chamber with a cylindrical section on top supplied with air... 

A nonuniform pillow-shaped expansion with open structure, such as potato cubes produced by microwave-enhanced spouted bed drying, restructured blue honeysuckle snacks containing starch produced by MWVD, and microwave-expanded imitation cheese (Arimi et al, 2008 Yan, 2011 Liu et al, 2009). 

Coarse solids too large for ready fluidization can be handled in a spouted bed [33]. Here the fluid is introduced into the cone-shaped bottom of the container for the solids instead of uniformly over the cross section. It flows upward through the center of the bed in a column, causing a fountainlike spout of solids at the top. The solids circulate downward around the fluid column. Such a bed has found particular use in drying wheat, peas, flax, and the like (43]. 

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