Spray drying is a process used for the production of dry powder from a liquid or slurry which is rapidly dried by using hot gas. It is a commonly used method for drying various thermally-sensitive materials, such as foods and pharmaceuticals. The basic reason behind using this method for drying some industrial products such as catalysts is the consistent particle size distribution. In this process, the air is the heated drying medium. However, if the liquid is a flammable solvent like ethanol or the product is oxygen-sensitive, nitrogen is used as the heated drying medium.
How does the spray drying work?
In this method, the liquid feed that needs to be dried is atomized into very small droplets within a hot drying gas. The use of hot drying gas in the process leads to flash drying of the droplets into solid particles. Then, particles are separated from the drying gas with the help of a cyclone or a filter bag. This separation process provides you with the final spray-dried product. The feed can be a suspension, a solution, or an emulsion, and the final product can be classified as granules, powder, or agglomerates respectively.
Spray drying technique is widely used because, in a single continuous step, it converts the liquid feedstock into a powder with well-defined properties, such as level of moisture, the residual solvent in the powder, particle size, and powder density.
Is Spray Drying Safe?
As stated above, spray drying is used where a mixture of compounds is prepared into its liquid or slurry form which is finally converted into its powder form by using hot gas. As per the food safety aspect, this is the best preservation method. The resulting spray-dried powders possess an excellent agglomeration or reconstitution property, which means that they can be easily dissolved in the solvent for consumption purposes. The safety of a product’s quality and nutritive values remains intact.
One of the best examples of preservation using spray drying is milk. It is highly prone to quick spoilage if it is not stored in ambient conditions. Thus, to extend the shelf-life of milk, the spray drying method is used on a huge scale nowadays.
How is spray drying different from freeze drying? Which is a safer drying method?
Freeze drying is used for a wide range of pharmaceutical formulations when stability in the liquid state is not adequate, storage requirements are too strict, or a solid form of the product is needed. Though it is an established drying process for a long time for a varying range of materials that differ in sensitivity levels, alternative methods such as spray drying are being preferred due to the costs and volumes attached with freeze drying technique.
Spray drying is a relatively new process in the industry; however, it provides a higher capability to work with higher throughput (more continuous than batch) than freeze drying. While spray drying is a faster and less expensive technique, the main drawback associated with spray drying is the higher processing temperature or shear force it needs – the very thing that many customers want to avoid in stringently controlled pharma/bio-tech industries.
Nonetheless, spray drying is a popular method especially in the food industry for spray drying a variety of products, such as egg products, fruit juices, beverages, starch and derivatives, tea and coffee, flavors and color, plant extracts, and more.
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