Spray drying converts atomized droplets of product into a dry powder. Spray drying is a cost-effective, continuous drying method that produces repeatable results. Due to low residence time, spray drying is suitable for heat-sensitive products. In addition, spray drying is also capable of producing homogenous solids from multi-component solutions.
The operation of the spray dryer is relatively simple. A slurry is atomized into the drying chamber in the form of droplets. When these droplets contact the warm gases, they dry to a powder.
The hot gases, generated by either steam coils or a combustion furnace, enter the cylindrical drying chamber at various points, depending on the type of dryer. In the parallel-flow configuration, the air enters through the top; in the mixed-flow configuration, the air enters tangentially; and in the reverse-flow configuration, the air enters though the bottom.
Proper selection of the feed atomizer is critical and is based on experience but governed by the characteristics of the material to be dried. The three type of atomizers are:
Any product which is removed from the chamber by the spent drying gases is separated from them by means of a cyclone or a fabric filter dust collector. The exhaust gases can be further cleaned by a wet scrubber if required. A spray dryer can also be operated in a closed loop using an inert gas, such as nitrogen, as the drying medium.
Swenson spray dryers can be configured for parallel, reverse, or mixed-flow operation.