Coalescent binders

Modeling and Simulation subsection.) It is necessary to determine both the mechanism and kernels which describe growth. For fine powders within the noninertial regime of growth, all collisions result in successful coalescence provided binder is present. Coalescence occurs via a random, size-independent kernel which is only a func tion of liquid loading, or... 

Both these limits restric t the maximum rate of liqiiid feed or binder addition for given inlet gas velocity and temperature. The liquid feed rate may be fui ther restricted to avoid excess coalescence or quenching. 

It is instructive to simplify the above picture somewhat and consider the coalescence or sticking of two particles schematically shown in Fig. 13. One can assume that due to shear forces in the mixer, a fluidized bed in the present case, the two particles posses a relative velocity U0 which ensures collision at some point on their trajectory and possible sticking under appropriate conditions. It is essential that some binder be present at the point of contact, as depicted in the figure. From this simplified picture, allmechanisms... 

Figure 13. Coalescence of two binder-covered particles (granules).

Conditions of Coalescence. The outcome of the collision of two binder-covered particles is determined by the ratio of the initial kinetic energy of the system and the energy dissipated in the liquid bridge and in the particles. This can be expressed analytically by the definition of a so called Stokes number, St... 

In a real process, both binder surface tension as well as viscosity will act to dissipate energy and ensure sticking and coalescence, but no simple analytical solution exists for this case. It was also demonstrated by Ennis (Ennis et al., 1991) that conditions based on viscous dissipation are more restrictive then those based on capillary forces and hence the discussion of granulation regimes is limited, in this paper, to the former. 

Acrylic emulsions tend to flow nicely leveling out rather than giving a three-dimensional effect sometimes offered in various oils. In the absence of a pigment, acrylic emulsions give a milky white appearance. As the water evaporates, the binder particles coalesce forming a tight film. When dried, the film is clear and becomes water insoluble. 

The collision of the broken wet segments during spheronization can result in two effects deformation and coalescence. The migration of moisture or soluble binders from the core to the surface of the pellets improves surface... 

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