In spray drying there are two ways of agglomeration: the spontaneous and
the forced, both in a primary and secondary form. (Fig. 86)
During the
spray drying process the aim is to produce particles with a big surface/mass
ratio, i.e. small particles. The reconstitution in water of a powder consisting
of small particles is however difficult and requires intensive mixing in order
to disperse the powder, before it is totally dissolved. Bigger particles
exhibit a better dispersion, but the solubility is negatively affected during
the drying operation, as discussed on page 123 forward.
By
agglomeration both a good dispersion and a complete solution are obtained.
Type definition examples
- Spontaneous primary Random, unprovoked collision of primary spray particles
All atomization devices
- Forced primary Intended collision between primary spray particles from
different atomization devices Collision of sprays from different nozzles
- Spontaneous secondary Random, unprovoked collision of primary spray
particles and fines Multi-Stage or Integrated Filter Dryers
- Forced secondary Intended collision between primary spray particles and
fines returned to the atomization zone Normal type when Fines Return is applied
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