Spray Drying

What atomization principles are there?

The atomization principle in spray drying describes the process in which liquids are broken down into fine droplets in order to increase the surface area. This enables more efficient heat and mass transfer between the liquid and the hot drying gas. The droplets are formed by special devices called atomizers, which are considered the “heart” of the spray drying process.
There are different types of atomizers used in spray drying and they each work according to different principles.
There are basically nozzle atomizers and rotary atomizers. Nozzle atomizers are usually two-substance nozzles and more rarely pressure nozzles. In rotary atomizers, the liquid is fed into rotating internals where it is broken up into droplets by discs or rotors. Each type has its own advantages and disadvantages, depending on the type of liquid and the requirements of the end product.

What are primary particles?

Primary particles in spray drying are the smallest units of solid substance contained in the liquid suspension. During the spray drying process, these particles are exposed by the evaporation of the liquid carrier and form the basis for the structure of the end product. They can either be present individually or combine to form larger agglomerates, depending on the physical and chemical properties of the suspension and the process conditions.
The smallest newly formed particles in spray drying are often referred to as primary particles, i.e. a droplet becomes a primary particle (if droplet decomposition is neglected). These particles can then agglomerate with others in the spray dryer itself or be specifically recirculated into the injection zone in order to agglomerate there.

What is fine particle recirculation?

Fine particle recirculation is a process in spray drying that aims to improve the efficiency and quality of the end product.Fine particles that are produced during the drying process and would normally be removed from the dryer with the exhaust air flow are fed back into the drying process. This is usually done by special cyclones or filters that separate the fine particles and feed them back into the main dryer stream.

The benefits of this process include:

• Improved particle size: recirculation allows the fine particles to agglomerate with larger droplets or particles, resulting in a more uniform particle size.
• Increased product yield: Less material is lost as the fine particles are reused.
• Optimized product quality: Recirculation can help to improve the flow properties, density and other physical properties of the powder.

This process is often used in the food, pharmaceutical and chemical industries to produce high-quality powder products.