Working Process and Application of Spraying Drying

The drying technologies are very diverse and besides economical considerations, the choice of drying method for a specific process depends on e.g. the feed type and the desired properties of the end product.

To obtain a cost-effective drying process which gives a product of constant high quality it is critical to have detailed insight into the different elements of the drying technology chosen. Spray drying is one of the technologies where process understanding has moved significantly forward in recent years.

The pulp and paper industry is heavily involved in developing new products from biomass and cellulosic material. In this context there is a constant search for appropriate production methods. One unit operation that comes into play is drying. The drying step in processing biomass and cellulosic material serves several purposes such as reducing transport and storage costs and extending shelf life.

In spray drying the liquid feed is atomized to droplets and contacted with a hot gas which causes the solvent of the droplets to evaporate, leaving dried particles. The particles are subsequently separated from the drying gas in a cyclone or a bag filter. Spray drying is the most widely used industrial process for particle formation and drying. It is extremely well suited to the continuous production of dry solids as either powder, granulates or agglomerates from liquid feeds. Feeds include solutions, emulsions and pumpable suspensions.

Spray drying is a versatile process and therefore it provides good control over the final powder properties such as flowability, particle size, redissolution rate, bulk density and mechanical strength. For example different atomization methods may be chosen to obtain a specific particle size or atomize high viscosity feeds. The most commonly used atomization methods are rotary (wheel) atomizers, pressure and two-fluid nozzles. Also, spray dryers are often equipped with one or more fluid beds for further drying, agglomeration, and dust removal and/or cooling. Fote Machinery produces spray dryers in many types to facilitate drying of many different products. The dryer shown is able to separate the drying into different stages making the drying operation more efficient and at the same time more gentle.