To recover these sensible products, cyclone collectors are frequently irreplaceable equipments for allowing a direct powder capture and avoiding product holdup of filters. Cyclones also avoid contamination of filter bags, product cross contamination and product degradation with temperature.
However, product losses due to cyclones’ low efficiency represents a high cost as a consequence of the value of particles.
Where applicable, cyclones have to be complemented with expensive 'food grade' bag filters to increase yield or to avoid emissions to the atmosphere. These filters are usually associated with difficult cleaning and downtime.
Client's needs include a cyclone system which dramatically increases powder yield and is efficient enough to comply with regulatory PM limits, thus avoiding the use of a bag filter.
Typical Spray Drying Arrangement
Usual Spray Drying arrangement (single point, two point and closed cycle) includes 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. In the vast majority of the cases, 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 %.
In fluidized bed arrangements, cyclones are used to recover the fine fraction of the dried powders, collecting or returning it to the bed. This fraction frequently has a very small particle size distribution which results in low yields in the cyclone. Improving the efficiency is crucial both to recover first grade product and to reduce filter bag cleaning and frequent change of bags. Client needs include a cyclone system efficient enough in order to replace the bag filter and complying with regulatory emission limits.