Fluidization slugging

DiFelice, R., Rapagna, S., and Foscolo, P. U., Dynamic Similarity Rules Validity Check for Bubbling and Slugging Fluidized Beds, Powder Technol., 71 281 (1992a)... 

Fluidized Bed Tests. These tests have direct relevance to all applications where particles are subjected to conditions of fluidization. Some authors believe that these tests can also to some extent simulate the stress of pneumatic transport. Coppingeretal. (1992) found at least a good correlation with the attrition resistance in dense-phase pneumatic conveying when they tested various powders in a slugging fluidized bed. 

Baeyens, J. and Geldart, D., An investigation into slugging fluidized beds, Chem. Eng. Set., 29 (1974) 255-265. 

Another type of fluidization is the slugging fluidization. It represents the case where the bubbles form slugs of gas, usually when the size of the bubbles is about one-third the diameter of the bed. In general, slugging is undesirable because it is accompanied by high pressure, which may cause dangerous vibrations to the reactor. 

A regime map of Fo versus the solid volume fraction, ap, for various gas-solid flows was presented by Hunt (1989), as shown in Fig. 4.3. Hunt (1989) suggested that except when Fo > 1 and ap > 0.1, use of the pseudocontinuum model is inappropriate. Thus, from Fig. 4.3, it can be seen that the pseudocontinuum model is applicable to packed beds, incipient fluidized beds, and granular flows, whereas it is not applicable to pneumatic transport flows, dilute suspensions, bubbling beds, and slugging fluidized beds [Glicksman and Decker, 1982 Hunt, 1989]. 

Figure 11.9 Fluidization regimes in batch fluidized bed at low multiples of minimum fluidization velocity (a) packed bed (b) incipient fluidization (c) bubbling fluidization (d) slugging fluidization (c) pneumatic transport.

Figure ] 3.3-3 Pressure drop diagram for fluctuating and slugging fluidized beds, from Kunii and Levenspiel [3]). 

Figure 4.6 Schematic of two-phase model representation of bubbling or slugging fluidized-bed reactor.

Hovmand S. Davidson JF. Chemical conversion in a slugging fluidized bed. Transactions. Institution of Chemical Engineers 1968 46 190-203. 

Kehoe PWK, Davidson JF. The fluctuation of surface height in freely slugging fluidized beds. AIChE Symp Ser 69(128) 41-48, 1973a. 

Andersson S, Johnsson F, Leckner B. Fluidization regimes in non-slugging fluidized beds. Proceedings of the 10th International Conference on Fluidized Bed Combustion. San Francisco, 1989, pp 239-247. 

Di Felice et al. (1992a) investigated the validity of the full set of scaling laws for bubbling and slugging fluidized beds. They used an experimental facility that permitted the pressurization of different diameter test sections to match the scaling parameters. Minimum fluidization measurements, video measurements of bed expansion, and pressure fluctuation data were used to compare the similarity of five different bed eonfigurations. Three of the beds were scaled properly. 

Farrell (1996) experimentally evaluated the importance of the solid-to-gas density ratio (Ps/pf) for scaling the hydrodynamics of bubbling and slugging fluidized beds. Two bed materials, polyethylene plastic (pg = 918kg/m ) and a dolomite/limestone sorbent mixture (ps = 2670 kg/m ), were used to create a mismatch in the density ratio. The size of the particles was chosen so that the remaining simplified scaling parameters were matched. The internal angle of friction was similar between the two materials. 

DiFelice R, Rapagna S, Foscolo PU. Dynamic similarity rules validity check for bubbling and slugging fluidized beds. Powder Technol 71 281, 1992a. 

Figure 35 Pressure fluctuation signal from a slugging fluidized bed and their cross-correlation function. (Roy et al., 1990.) At = 0.12 X 0.12m = 1.6 m silica sand bed, dp = 240(a) Original signal from pressure probes (upper row 1.5 m...

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