Efficient recovery of active pharmaceutical ingredients (APIs), chemical substances or food powders after drying applications such as spray and fluid bed drying is frequently a problem. The same problem occurs in many milling and micronization applications.
The preferred way to recover these sensitive products is with cyclone collectors due to their direct powder capture. Unlike bag filters or wet scrubbers, cyclones minimize filter or product contamination and product cross contamination and can easily handle a wide range of operating temperature, pressure and moisture conditions.
Spray Drying | General Arrangement
Usual spray drying arrangements (single point, two point and closed cycle) include a high efficiency cyclone and a bag filter.
The cyclone serves the purpose of separating and collecting the dried powder originated in the spray-drying chamber. For some chemical powders, the fraction of product escaping to the bag filter is not considered as first grade product, and thus seen as losses. The main reasons for this are contamination with filter fibers, product cross contamination and risk of heat degradation.
For fine powders with a median diameter in volume (MVD) of less than 5 µm, losses due to low cyclone efficiency can rise to more than 25 %.