Desiccant Dehumidifiers in Pharmaceuticals
Most substances used in drugs today are hygroscopic and any
absorption of moisture during the manufacturing process will affect the
final weight, quality and durability.
When hygroscopic ingredients are weighed and mixed, it is important
that the products' weight is not influenced by absorption of moisture from
the surrounding air.
In powder form, moisture will affect the flow, caking, compaction and
strength properties of the manufactured solid form.
Yeast, moulds and bacteria require a certain amount of moisture to
support growth. Controlling relative humidity is probably one of the most
important factors in maintaining a sterile environment.
A cool dry environment generally enables faster production, a better
quality product and a longer shelf life. The majority of tableting processes
require humidity control between 20 and 35%RH at 21 to 24°C.
In most pharmaceutical systems, the greatest
moisture load is from the fresh air component
which is typically between 5 and 20% of the total
supply air volume.
Depending on moisture gains across the room, it may only be necessary to “deep dry”
the fresh air component using a pre-cooling coil (> 10°Cdp) and a desiccant
dehumidifier (< 10°Cdp).
Dehumidifier capacity is controlled by an RH sensor installed in the return air duct.
This simple design is often adequate to maintain the required RH in the room.
Air conditioning systems with a low fresh air volume and rooms with excessive
moisture gains from high infiltration rates (negative room pressures), frequent door
usage, product load, etc, will normally require all the fresh air and a proportion of the
return air to be dried.