Multiplicity of Steady Standpipe Flows

For a standpipe system, different flow patterns of steady-state flows may exist, depending upon the ranges of operational parameters of the system. This phenomenon is commonly known as the steady-state multiplicity. We introduce the general concepts of the steady-state multiplicity based on the standpipe system in 8.3.3, in which the solids in the feed hopper are kept in a steady moving bed motion. 

For a system with a fixed y, the steady-state multiplicity may be revealed by the curve of superficial velocity of solids Up versus Ap, as illustrated in Fig. 8.17, where a hysteresis loop is formed between two branch (upper and lower) curves [Chen et al., 1984], The upper branch corresponds to Regimes 2, 3, or 4, whereas the lower one corresponds to Regime 1. At Ap less than (Ap)i, the system is operated on the upper branch of the curves, while it is operated on the lower branch of the curves at Ap larger than (Ap)2- Between these two 

In standpipe systems, aeration from the side is often implemented to provide a lubricating effect for the solids flow. Aeration is also used in process applications to provide a stripping gas to remove undesirable gas entrained by the solid particles in the standpipe flow. With side aeration, the multiplicity of flows in the standpipe becomes much more complicated. The flow patterns of solids and gas depend not only on Ap and y but also on the aeration locations and aeration rates. For a single aeration point, the possible number of flow regimes increases to 12 [Mountziaris and Jackson, 1991]. 

---

Figure 8.17. Schematic illustration of multiplicity of steady standpipe flows (after Chen et al., 1984).

---