Agglomerate formation

In the suspension methods, agglomerate formation occurs by hardening of feed droplets into soHd particles, by layering of soHds deposited from the feed onto existing nuclei, and by adhesion of small particles into aggregates as binding soHds from the dispersed feed are deposited. The product size achievable in these methods is usually limited to ca 5 mm and is often much smaller (see Drying). 

Sometimes particles are encouraged to agglomerate to yield granules, for example, for pharmaceutical applications which may require the addition of liquids or other binders. In the ceramics, paint, plastics and rubber industries, however, reducing or eliminating agglomerate formation is of overriding importance. 

In addition, because of the chemical interaction between transition metal ions and the support established during anchoring, it is possible to prevent migration, sintering and agglomerate formation during subsequent thermal treatments, in contrast with species deposited by mere impregnation which are mainly physically adsorbed. 

Fig. 3 Granule growth mechanisms (A) agglomerate formation by nucleation of particles (B) agglomerate growth by coalescence (C) layering of a binder-coated granule and (D) layering of a partially filled binder droplet. (From Ref John Wiley and Sons, Inc.)...

During the tests, fuel and bed material samples were collected. These samples were mainly investigated with SEM-EDS, Bulk elemental analyses were also carried out. The unproblematic behaviour of the bed material was confirmed and no agglomerate formation was observed except in the close proximity of occasional quartz centres that were unintentionally present in bed. It was observed that the majority of the bed particles were coated with several thin superimposed layers. The composition of each layer was different. The outermost coating layer contains a significant amount of magnesium. It may be this outermost layer that hinders the agglomeration of the particles in this new bed. 

It is expected that these reactions, which occur between adsorbed PVAm sequences near the silica particle surface, transform the flexible polyelectrolyte layer into a more rigid one (Fig. 6). Agglomerate formation occurring between the PVFA-co-PVAm chains should be avoided. 

The spray flux captures the impact of equipment operating variables on nucleation, and as such is very useful for scale-up if nucleation rates and nuclei sizes are to be maintained constant. The overall impact of dimensionless spray flux on nucleation and agglomerate formation is illustrated in Fig. 21-106, with agglomerates increasing with increased spray flux as clearly governed by Eq. (21-106) for the case of rapid drop penetration. 

FIG. 21-106 Agglomerate formation vs. spray flux. Lactose powder with water and HPLC solutions. [Ajier Hop-good (loc. cit.).]... 

The liquid spray rate to a spouted bed may be limited by agglomerate formation in the spray zone causing spout collapse [Liu and Litster, Powder Tech., 74, 259 (1993)]. The maximum liquid spray rate increases with increasing gas velocity, increasing bed temperature, and decreasing binder viscosity (see Fig. 21-171). The maximum... 

Figure 18.9 shows the effect of filler particle size on extruder throughput for PP filled with talc. Several reasons account for reduction in throughput as the particle size decreases. Increasing the surface area of filler makes mixing more difficult because of agglomerate formation. Smaller particle sized talc has lower bulk density which decreases the conveying efficiency of screw. The relatively large amount of air supplied with the particles decreases the conveying efficiency and increases the time required to extract air. The amount of talc added affects the ratio of throughput, Q, to the screw speed. Ns (Figure 18.10). As the concentration...

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