Fluidization smooth

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.

Equation 6-108 is also a good approximation for a fluidized bed reactor up to the minimum fluidizing condition. However, beyond this range, fluid dynamic factors are more complex than for the packed bed reactor. Among the parameters that influence the AP in a fluidized bed reactor are the different types of two-phase flow, smooth fluidization, slugging or channeling, the particle size distribution, and the... 

Properties of particles that are conducive to smooth fluidization Include rounded or smooth shape, enough toughness to resist attrition, sizes In the range 50-500 im dia, a spectrum of sizes with ratio of largest to smallest In the range of 10-25. 

Minimum bubbling velocity timb is defined as the gas velocity at which bubbles first appear in aggregative fluidization. For coarse uniformly-sized particles, for example those in Geldart group B, it is usually the case that M i, = u /- However, very fine non-uniformly sized particles such as those in group A exhibit smooth bed expansion and no bubbling until a gas velocity considerably in excess of the minimum... 

Particulate fluidization, where the fluidizing medium is usually a liquid, is characterised by a smooth expansion of fhe bed. Liquid-solid fluidized beds are used in continuous crystallisers, as bioreactors in which immobilised enzyme beads are fluidized by the reactant solution and in physical operations such as the washing and preparation of vegetables. The empirical Richardson-Zaki equation (Richardson... 

The use of internals can improve the smoothness of fluidization, when this is desirable. The use of vertical cylindrical tubes immersed in the bed is a representative example. These tubes are sufficiently long to extend from the distributor to the top of the bed. For this type of beds and for perforated plate distributors, the following corr elation can be used for the estimation of fluidized-bed porosity in gas-solid fluidization (Hilal, 2000) ... 

Among the properties of particles most conducive to smooth fluidization are the following ... 

Some smoothed data of expansion ratio appear in Figure 6.10(c) as a function of particle size and ratio of flow rates at minimum bubbling and fluidization. The rather arbitrarily drawn dashed line appears to be a conservative estimate for particles in the range of 100 pm. 

Properties of particles that are conducive to smooth fluidization include rounded or smooth shape, enough toughness to resist... 

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