Agglomeration dense phase

The contact in the dilute phase and the transition zone is different from that in the dense phase. The former is related to mass transfer between the gas phase and an agglomerate of solid particles, whereas the latter is mainly related to mass transfer between bubbles and emulsion including a certain amount of directly contacting catalyst. Upcm consideration of hindered settling of the swarm of particles (S16, Z7), we also find contact efficiency to be a function of the population density of particles. Normalizing by the Ig of the main dense phase, eg.de, e/ e.de is chosen as a variable... 

A size distribution of particles is always desired rather than a single size in a fluidized bed. The two-phase theory of fluidized-bed operation is suspect when a bed contains appreciable lines, and models based on uniform particles should be used with caution. The dense phase in such cases should really be regarded as consisting of two phases emulsion and clusters of lines (d < 40 pm). Indeed, the results of Yadav et al. (1994) on commercial propylene ammoxidation catalyst clearly show that the lines agglomerate. A critical level of lines (30%) was found in terms of bed expansion, aeratability, and cluster size at which fluid-bed behavior is optimum. They proposed a model that takes the two dense phase components (emulsion and cluster) into account. Adding lines widens the limits of operable gas velocities and minimizes the segregation of particles. 

I. Dense Phase Tumble/Growth Agglomeration apparatus producing movement of a densely dispersed mass of particulate solids. 

This equation defines the Stokes diameter Xstokes on the basis of the density contrast Ap = ps - pm between solid and fluid phase. It should not be confused with the density contrast Ap between the porous particle phase (with Pp.etr) and the fluid. Such a definition might be meaningful for dense agglomerates with defined porosity, which can be measured by nitrogen adsorption (Staiger et al. 2002), or may be deduced from the powder bulk density (Barthel et al. 1998) or from sediment properties (Katzel 2007, pp. 183-187). However, it should be avoided for fractal aggregates, where the concept of uniform porosity fails for several reasons (no defined surface, size-dependent and locally varying porosity). 

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