Fluidized catalyst beds emulsion viscosity

In the preceding section, the flow properties of fluidized catalyst beds have been clarified mainly on the basis of experimental observations. In the case of FCC catalyst, the apparent viscosity of the emulsion is usually very small, and the emulsion shows good fluidity. Catalyst particles once charged into a fluidized bed reactor are usually in service for several months. Hence it is justifiable to prepare the particles very carefully, so that the fluidized bed shows the best fluidization possible. This kind of careful preparation is usually impractical in the case of single-pass particles such as coal, mineral ores, or grain. 

It is interesting to see how far modern technology for fluidized catalyst beds has served to achieve good fluidization. Our criterion of good fluidization is a gas-fluidized bed of a low viscosity liquid (such as water), where the low-viscosity liquid would set the lower limit to the fluidity of the emulsion. Such a gas-fluidized liquid bed is the well-known bubble column, which has been studied extensively. Our objective is to understand the behavior in the recirculation flow regime, since the superficial gas velocity of practical interest is usually more than 30 cm/sec for fluidized catalyst beds and for these conditions intense recirculation of the emulsion has been observed (note Fig. 2 and Section II,D,3). 

In summary, the calculations show convincingly that modern fluidized-catalyst-bed technology has attained an emulsion fluidity nearly equivalent to that of low-viscosity liquids. With such fluidity, data obtained for a bubble column shed light on the performance of a fluidized catalyst bed, and vice versa. 

When the velocity profile of the emulsion phase is similar to that of the liquid phase in a bubble column, Eq. (4-11) will apply to the fluidized catalyst bed. This similarity seems to be well justified as mentioned in Sections III,A,4-5, although there is no direct calculation of the turbulent kinematic viscosity from the measurement of velocity profile in the fluidized catalyst bed. 

The correlation shown in Figs. 32 and 33 as curve A-A is the turbulent kinematic viscosity of the emulsion phase of fluidized cracking catalyst beds estimated by an indirect method explained in Section IV,C in relation to axial dispersion of the emulsion. The correlation is given in cm-sec units by... 

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