Spray Dryers based on the Single Pass principle employ inert gas as the drying medium without recirculating of the spent drying gas.
This principle is usually applied in two different scenarios:
- In sterile conditions, when spent gas composition and product contact are incompatible
- In R&D dryers used on a very infrequent basis for either solvent based products or potent compounds.
Single pass dryers require less capital investment than closed cycle dryers, but are more costly to operate. Single Pass dryers are almost exclusively available only in single stage models, i.e. for production of fine particles. Typical flow diagram and photos are shown below.