Underflow plenum

The fourth type of inlet we wish to describe is that of swirl vanes. As shown in Fig. 1.3.8 d, a swirl-vane assembly allows the gas to enter the cyclone parallel to the axis of the cyclone The swirl-vane assembly is positioned between the vortex finder (or, in case of a straight-through device, see below, a central solid body) and the outer (body) wall of the cyclone. This type of inlet is often inserted in cylindrical-bodied cyclones rather than in cylinder-on-cone or conical-bodied geometries. When it is, we refer to the separator as a swirl tube. Swirl tubes are often of small size (by commercial standards) and are most commonly arranged in a parallel array on a common tube-sheet within a pressure-retaining vessel. They are normally fed from, and discharge into, common, but separate overflow and underflow plenums. 

Fig. 11.5.1. An electrical analog of a parallel arrangement of two cyclones sharing common overflow and underflow plenums...

The fluidization chamber may be open (as in Fig. 7.38), or it can follow the segmentation of the plenum by means of partitions (weirs). Solids transportation from one segment to the next takes place as overflow or underflow. In the case of underflow, openings that cover all the width of the equipment or just a part of it can be used. Smaller underflow openings (so-called rat holes ) can be placed to the right... 

Fig. 12,1.10. A commercial installation consisting of a parallel arrangement of two cyclones sharing a common underflow hopper and overflow plenum (or header ). Note blower in bottom left-hand side of image pulls gas through the cyclones. Also note the specially designed erosion-resistant elbow just ahead of the cyclones. Courtesy Fisher-Klosterman Inc.

One commercially available system comprising a parallel arrangement of cyclones, called swirl tubes , is the multicyclone unit illustrated in Fig. 16.2.2. The solids-bearing feed stream enters the separator vessel via a centrally located pipe at the top of the vessel. The feed exits this inlet pipe near its bottom end from where it flows radially outwards - between two tube sheets - and into the feed chamber or plenum. The solids-bearing gas then enters the individual swirl tubes wherein it is split into a solids-laden underflow stream and a clean-gas overflow stream. 

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See also in sourсe #XX -- [ , , ]

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