Fluidization by Particle Size Adjustment

It was mentioned earlier in the chapter that catalyst powders with carefully specified particle size distribution have been prepared to ensure good fluidization characteristics. It is well known that even addition of fine particles to a powder of coarser particles tends to improve its fluidization characteristics. Experiments were thus conducted on binary particle mixtures, each consisting of a fairly close particle size distribution (Yang, Z., 1982). 

Synergism caused by the addition of Group C particles was found from both SEM microscopy and video macroscopy (Xia and Kwauk, 1985) to be associated with adhesion of these line particles on the coarse particle. Nevertheless, more appropriate analytical, or even theoretical, ground needs to be found to account for the initial rise and later fall in the value of the dimensionless time 0 as the mass fraction of fines increases from zero to unity. 

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Previous studies of our work group demonstrated that isomaltose exhibits a distinct higher affinity towards certain dealuminated p-zeolites as opposed to other carbohydrates like fructose or glucose [94, 109]. Sucrose is not adsorbed at all. As a consequence, a process could be developed which directly removes the isomaltose from the reaction solution by adsorption onto zeolite. For this purpose a fluidized bed reactor has been utilized with a special focus on the separation of the two solid phases (Fig. 14). The biocatalyst containing entrapped dextransucrase is produced by the jet-cutter method [110] the alginate beads have a mean particle size of 0.5 mm. To accomplish an adequate high density of biocatalyst, silica flour (30% w/v) is included. The particle diameter of the second solid phase (zeolite) is adjusted to 10 pm. As a consequence, zeolite is loaded with isomaltose inside the reactor and can then freely exit the reactor together with the product solution, whereas the biocatalyst is retained inside the fluidized bed reactor [92, 94],... 

Originally, the gas distributors in fluidized beds were made of perforated steel plates (see Fig. 7.70, top). The size of the holes, in most cases the diameter of circular bores, the percent open area, defined by the sum of all hole areas, sometimes the distribution pattern of the holes in the plate, and the gas pressure in the plenum below the distribution plate, which, together with the other dimensions, defined the gas flow rate, were major design parameters. To obtain a good, stable fluidized bed, the gas velocity has to be uniform across the entire area of the bed and must be adjusted such that, as a result, the solid particles are in a suspended state. 

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