Fluidized beds expansion

Findings with PDU. Work with the PDU largely paralleled the bench-scale reactor tests there was one important addition—extensive three-phase fluidization studies. As was mentioned, the PDU is equipped with a traversing gamma-ray density detector that is capable of measuring bed density to within dbO.Ol specific gravity units. Thus, we could measure and correlate fluidized bed expansion as a function of liquid and gas velocities and physical properties, and could also determine the... 

Materials Minimum Fluidization Velocity and Fluidized Bed Expansion Ratio. AIChE Symp. Ser., 74(176), 176. 

Jiang, P. Lin, T.J. Fan, L.-S. High temperature and high pressure three-phase fluidization—bed expansion phenomena. Powder Tech. 1997, 90, 103. 

The most fundamental and also practical tasks in fluidization are to describe the transition from a fixed bed to a fluidized bed, and to predict the fluidized bed expansion as a function of the flow rate and of the rheological behaviour of the fluid. For the fluidization with Newtonian liquids, the bed expansion is usually well described by the Richardson and... 

Equation (78) gives an accurate prediction of fluidized bed expansion characteristics for the laminar regime and applies equally well to fixed and suspended particle systems. 

Equation (84) provides accurate quantitative predictions of particulate fluidized bed expansion characteristics in both laminar and turbulent flow regimes. For the intermediate flow regime, only a qualitative trend was observed. Equation (84) is slightly different in dependence of voidage from the drag coefficient suggested by Wen and Yu (1966) as shown here ... 

Babu SP, Shah B, Talwalkar A. Fluidization correlations for coal gasification materials— minimum fluidization velocity and fluidized bed expansion ratio. AIChE Symp Ser 74(176) 176-186, 1978. 

A second route to Umf is by putting U = Ums or Re = Re f) and e = Emf in one of the many fluidized bed expansion equations relating e to C7 (or Re) that have been proposed in the literature, a subject discussed below. This could provide a reasonable second estimate of 7mf but, because the expansion equations are usually correlations based on the whole range of e from Emf to Ec or even to unity, they are likely to be less accurate at the E f extremity than an equation such as Eq. (17) which is tailored to this extremity. 

Fouda AE, Capes CE. Hydrodynamic particle volume and fluidized bed expansion. Can J Chem Eng 55 386-391, 1977. 

Vb = Lb(1 — e), enables e to be calculated from Lb from the initial values of these variables in the packed bed. Before applying the AP relations (derived in the previous chapter) to the analysis of fluidized bed expansion, a brief account of the salient experimental findings will be given. 

For group B and D particles, nearly all the excess gas velocity (U — U,nj) flows as bubbles tnrough the bed. The flow of bubbles controls particle mixing, attrition, and elutriation. Therefore, ehitriation and attrition rates are proportional to excess gas velocity. Readers should refer to Sec. 17 for important information and correlations on Gel-dart s powder classification, minimum fluidization velocity, bubble growth and bed expansion, and elutriation. 

GLS Fluidized with a Stable Level of Catalyst Only the fluid mixture leaves the vessel. Gas and liquid enter at the bottom. Liquid is continuous, gas is dispersed. Particles are larger than in bubble columns, 0.2 to 1.0 mm (0.008 to 0.04 in). Bed expansion is small. Bed temperatures are uniform within 2°C (3.6°F) in medium-size beds, and neat transfer to embedded surfaces is excellent. Catalyst may be bled off and replenished continuously, or reactivated continuously. Figure 23-40 shows such a unit. 

Measurement of the expansion of a gas-liquid fluidized bed provides a measure of the holdup of solids or of the corresponding combined holdup of gas and liquid. From such measurements, the holdup of liquid may be calculated if the gas holdup has been determined independently. 

Rough correlations have been made of minimum fluidization velocity, minimum bubbling velocity, bed expansion, bed level fluctuation, and disengaging height. Experts recommend, however, that any real design be based on pilot plant work. 

Figure 7. Bed expansion as a function of bed diameter at a fluidization velocity of 0.20 m/sec. (From DeGroot, 1967.)...

Tsutsumi, A., Nakmoto, S., Mineo,T., and Yoshida, K., A Novel Fluidized-Bed Coating of Fine Particles by Rapid Expansion of Supercritical Fluid Solutions, Proc. 1st Int. Particle Technol. Forum, pp. 452-455, Denver, CO (1994)... 

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