Particle Agglomeration: Why It is Required and How It is Done

Posted by Enurga on June 14th, 2019

Spray drying is a widely used technique for producing a variety of industrial grade powders. The main objective of such manufacturers is to ensure that the obtained particles possess good mechanical stability to avoid breakage during transit, has the right density for packaging and dosage purposes and can rehydrate easily for final consumption. To ensure all these things, spray pattern techniques are used that can reveal important information related to nozzle’s core angle, presence of streaks and voids, local surface area of drops per unit volume, asymmetry ratio and patternator number.

Sometimes, particles produced by simple spray drying technique have smaller diameter than even 50μm. Such smaller size can further lead to problems like poor flowability and slow reconstitution or lump formation during the process of rehydration. Therefore, to get rid of these problems, the agglomeration step is carried out in order to increase the particle size and modify its structure so that the final quality of the powder can be improved.

In industry, the process of powder agglomeration can be carried out by either retaining fine particles through integrated filter bags inside the dryer or recirculating them which have already been separated from the exhaust air.

These fine particles can be separated from the exhaust air stream with the aid of cyclones or bag filters. They can be added either back into the fluid beds of drying chamber (inside or outside) or blown back to the main drying chamber or to the generated droplets close to the atomizer or combination of all these possibilities.

The growth and structure of agglomerates obtained through the process of agglomeration depend on a variety of factors such as collision probability, force and direction/geometry of the impact and surface properties of colliding particles.

However, the big challenge with existing spray drying systems is to control the location of fine particle insertion so that agglomeration degree can be adjusted to the desired extent in any specific condition and for every considered making process.

Process of Particle Agglomeration

This process requires collision of two or more particles that is followed by adhesion. In order to create stable bridges between particles, at least one of the collision partners must have an adhesive surface at the moment of impact.

A particle stickiness can be directly associated with drying kinetics. Usually, a particle is known to be sticky or say adhesive when its surface reaches the viscosity value of 106 to 108 Pa∙s and the material whose viscosity lies in this range is known to be in rubbery state.

So, optimization of agglomeration during spray drying and right spray pattern testing techniques are necessary for the production of better quality powders in terms of mechanical stability and rehydration behavior.