urban agglomeration

In agglomeration by growth, larger particle aggregates form as fine particles repeatedly attach themselves to agglomeration nuclei or already grown grains. To achieve this, the particles move within drums, discs, fluidised beds or mixers and repeatedly collide with one another. If they stick together upon impact, the agglomerate grows. The driving mechanisms are liquid bridges, solid bridges, adhesive forces and mechanical interlocking. A simple, model-based description of particle size growth uses a growth rate dr/dt, for example:

dr/dt = k · β · n

• r is the agglomerate radius
• It's time
• k is a system-specific constant
• β is the probability of adhesion per collision
• n is the collision rate.

The higher the probability of adhesion and the collision rate, the faster the agglomerate grows. Such equations are idealised models, but they help us to understand the influence of process parameters such as rotational speed, liquid addition or filling level on particle growth.

An important application of agglomeration is granulation (pelletising), in which specific granules are produced as the final product.