Slugging bed

Figure 35. Pressure drop flow diagram for slugging bed.

Equation 8 has not been rigorously tested on freely bubbling beds because of the difficulty of making precise independent measurements of Dg or Ug under such conditions. It has been verified for slugging beds, however, as is shown in Figure 3. In the case of slugging, the surface level of the bed oscillates considerably, and in this case, the maximum bed height is used for H in Equation 8. 

The internal friction angle is also important for slugging beds (Zenz and Othmer, 1960). DiFelice et al. (1992 a, b) did not report their values it could be that the disagreement they found in their slugging bed tests was due to mismatches of the internal friction angle. 

Broadhurst, T. W., and Becker, H. A., Measurement and Spectral Analysis of Pressure Fluctuations in Slugging Beds, Fluidization Technology, Hemisphere Publishing Corporation, New York, 1 63 (1976)... 

Kokkoris et al. (1991, 1995) suggested another method to impair catalyst attrition. In a small scale slugging bed they reduced the attrition rate of zeolites by addition of only very small quantities of various fine solid lubricants. In the case of graphite the reduction was up to 30%. The fines were assumed to reduce attrition by forming a protective coating that... 

Kokkoris, A., and Turton, R., A Phenomenological Model Predicting the Attrition and the Reduction of Attrition due to the Addition of Solid Lubricants in Slugging Beds, Powder Tech., 84 39 (1995)... 

In tall, narrow beds the gas voids may coalesce producing a slugging bed. This condition is generally undesirable owing to its unsteady nature and the difficulty of scale-up. 

Applying the simple two-phase theory to the slugging bed, the average slug velocity in continuous slugging flows can be expressed by [Ormiston et al 1965]... 

The maximum height of expansion of the slugging bed, Hmm, can also be obtained by... 

Figure 45 illustrates the plot of (f/c f mf)/cb versus (C/g Umi) according to Eq. (5-8) for fluidized beds. In the figure, Eq. (5-4) is also shown for slugging beds. The mean gas holdup for the FCC-catalyst bed is taken from Fig. 36. The plot for the FCC bed shows clearly that the bed is fluidized smoothly, without slugging. The plot also shows data for a bed of fluidized glass beads of mean diameter of 287 m. (Data are taken from W13 cf. Fig. 14). The bed behavior is seen to approach that of the slugging bed as(f/c f/mf) increases beyond 20cm/sec. Also, the averagers is approximately 0.8 for Uq < 20 cm/sec, showing the possibility of bulk recirculation of the emulsion.

---