Particle flocculators

In a gas stream cariying dust or fume, some degree of particle flocculation will exist, so that both discrete particles and clusters of adhering particles will be present. The discrete particles composing the clusters may be only loosely attached to each other, as by van der Waals forces [Lapple, Chem. Eng., 75(11), 149 (1968)]. Flocculation tends to increase with increases in particle concentration and may strongly influence collector performance. 

Latex particles may flocculate when injected in a reservoir with high formation temperatures. When the particles flocculate, shrink, and harden, they form a more effective blocking agent than the dispersed, expanded, and softer particles [1654]. 

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

For both kinds of polymer-grafted particles, flocculation was induced either by changing the temperature or by adding a nonsolvent for the stabilising polymer. In this way critical flocculation temperature (c.f.T) and critical flocculation vol. fractions of non-solvent (c.f.v.) values were obtained, in general as a function of . 

Table I lists some characteristic wave lengths from the work of Gregory (9). The calculations of f shown in Figure 2 are taken from the work of Clayfield and Lumb.(lO) By using these calculations one can determine the attractive energy per pair of particles at various separation distances, and determine for any particular value gf Aj2i> Xj, and radius (a) the critical value of H that makes U j 21= kT, where k is the Boltzmann constant and kT is the average vibrational energy of a pair of particles flocculated at separation distance H. If Uj2l is greater than -kT the particles will nearly always bounce apart on collision, but if it is less than -kT the particles tend to flocculate.

In the earlier literature on steric stabilization there was a tendency to ignore the importance of anchoring sites for steric stabilizers. Without strong anchors the adsorbed molecules are easily swept aside in collisions, as has been so well illustrated with polystyrene adsorbed onto carbon blacks in hydrocarbon solutions in these systems particles flocculate in every collision.(11)... 

Polymer Adsorption and Particle Flocculation in Turbulent Flow... 

In summary, polymeric flocculants generally increase peri-kinetic flocculation rates compared with perikinetic coagulation rates. This is not necessarily true for orthokinetic flocculation, and experimental results in the literature are seemingly in conflict. Collision rate theory predicts that the polymer adsorption step may become rate limiting in orthokinetic flocculation. The present study was designed to elucidate the relationship between polymer adsorption rates and particle flocculation rates under orthokinetic conditions. 

The behaviour of suspensions of fine particles is very considerably influenced by whether the particles flocculate. The overall effect of flocculation is to create large conglomerations of elementary particles with occluded liquid. The floes, which easily become distorted, are effectively enlarged particles of a density intermediate between that of the constituent particles and the liquid. 

Soluble polymers are widely used to control the state of dispersion of fine-particle suspensions. Depending on the polymer, and how it is applied, they can serve to enhance stability (dispersants) or to promote aggregation of the particles (flocculants). The topics covered in this chapter are intended as an overview of the use of polymers for stability control in mineral-particle suspensions with particular emphasis on flocculation processes. A brief discussion of stabilisation by polymers is included for completeness. 

Dickinson, E., Eriksson, L. (1991). Particle flocculation by adsorbing polymers. Advances... 

From a manufacturing perspective, the excipients used may be very difficult to handle or process. This may lead to any number of problems during compounding, such as foaming, sedimentation, phase separation, particle flocculation, or formation of bubbles. To determine the cause of these problems, careful consideration and planning must be exercised in engineering a plant to ensure reproducible batches that can be efficiently compounded and filled. It is therefore essential that the behavior of each excipient in the formulation be well understood. 

Petzold G, Schwarz S, Lunkwitz K (2003) Higher efficiency in particle flocculation by using combinations of oppositely charged polyelectrolytes. Chemical Engineering and Technology 26 48... 

Slow mix zone this is the zone where particle flocculate and settle,... 

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