Spray drying is a delicate and demanding process that involves both quality and quantity. Often, people think that quantity and quality are mutually exclusive, but in the world of spray drying, it is crucial to ensure accurate delivery of large quantities of particles. This is because spray drying involves converting a liquid into a powder with a specific particle size and moisture content, a process in which both quality and quantity are key factors in determining the value of the final product.
In the spray drying process, the preparation and concentration of raw materials is the first step. This involves properly concentrating the feed solution to ensure that it can be pumped smoothly into the spray chamber. Sometimes, in order to change the physical properties of the raw solution, it is also necessary to heat treat it.
Atomization is the core part of spray drying, which creates conditions for the rapid and efficient evaporation of water by breaking down the fluid or slurry into fine particles. This process can be achieved by rotating atomization or pressure nozzles, and depending on the process requirements, the spray dryer can be configured with a single or multi-nozzle system.
The way hot air acts as a medium in contact with the droplets is critical to the quality and texture of the dried product. In the room, hot air is introduced from the inlet through a specific flow mode (i.e. an air distributor) and is well mixed with the droplets. This type of contact determines the particle size, quality, and texture of the final product.
The drying process of droplets is divided into two stages: constant speed drying and slow speed drying. In the constant-speed drying stage, the droplets contain enough water inside to evaporate at a constant rate continuously. However, as the moisture gradually decreases, the evaporation process gradually becomes more difficult, and the drying rate slows down, entering the deceleration drying stage. This stage is characterized by an increase in evaporation resistance and a decrease in drying speed.
After the droplets are completely dry, the solid particles need to be separated from the hot air. For this purpose, the spray dryer is equipped with various separation equipment, such as cyclone separators, wet scrubbers, bag filters, and electrostatic separators, among others. These devices ensure that the dry product is completely ** and at the same time ensure that the exhaust air is free of any harmful particulate matter, allowing the air to be safely discharged into the environment.
Considering the complexity of spray drying and its direct impact on the quality of the final product, the design and installation of a spray dryer requires a lot of experience and expertise.