Drying and Dewatering: reducing cost, improving quality

Reducing energy use and material loss by controlling agglomeration spray drying


A large fraction of powdered formulations in food industry is produced by spray drying. The major reason to use spray drying is usually the potential to achieve good powder properties. However, the lack of control of agglomeration negatively impacts operation efficiency of spray dryers and leads to significant material losses during large scale production. The new StAgglop project aims to develop scaling-relations to manage sticky behavior and agglomeration in spray drying.

Balancing energy consumption and powder quality

Spray drying can achieve good powder properties while balancing energy consumption and powder properties. While other technologies can achieve superior powder properties – such as freeze drying -the energy consumption is often much higher. While looking to produce powders at lower energy consumption – such as roller drying – this is linked to poorer powder properties for many product groups such as dairy and dairy-related products.

Agglomeration and powder properties

Agglomeration in spray dryers has major influence on powder properties. It occurs when a partially dried droplet collides with another partially dried droplet or with a fully dried agglomerated particle. There is a complex relationship between drying of droplets and agglomeration dynamics. The period, which starts with generation and exposure of a droplet to high inlet air temperature and ends with collision with another partially dried droplet or fully dried agglomerated particle, is crucial for properly managing the agglomeration process.

In industrial practice, agglomeration is optimized by adapting the position or angle of often high-pressure nozzles, air flow pattern and presence of fines return to obtain agglomerated powder of desired quality. This approach is trial-and-error based and needs to be continuously repeated for different spray drying systems and products.

Environmental benefit

Lack of control of agglomeration negatively impacts operation efficiency of spray dryers and leads to significant material losses (in the form of off-spec product) during large scale production. It is estimated that, for the Netherlands, annually 0.9-1.5 PJ energy or 200-300 kton CO2 equivalent emission may be reduced by improving agglomeration control in spray dryers. Moreover, improved agglomeration control will contribute to reduction of fine dust emission from dryers, for which increasingly strict regulations are reinforced by the government.

Pilot-scale spray dryers

This project therefore aims at developing scaling-relations to steer sticky behavior and agglomeration in spray drying. This is developed by firstly, studying drying kinetics, evolution of sticky surface properties and binary particle collisions at the single droplet scale. And secondly, by investigating sticky zones and agglomeration behavior in well-defined spray drying systems to move away from current empirical approaches.

Translation of critical parameters obtained in single droplet drying studies will lead to recommendations for process conditions in spray drying, such as nozzle positions and angles, airflow and temperature.