FBD or fluid bed dryer is used in the pharmaceutical industry for drying wet granules.FBD works on the principle of fluidisation, where the product to be dried is suspended in the drying chamber. Sometimes it is observed that the fluidization of the product is not as per the standard requirements, due to which drying is prolonged or delayed.
The following are the main factors which may affect the fluidization of the product in the drying chamber of the fluid bed dryer.
- Air Velocity
- Filter Choking
- Mesh Choking
- Product Load
- Product Behaviour
- Blockage of the exhaust duct
- Electrostatic charge
- Air Leakage
- Blower Issues
Air Velocity
If the velocity of the inlet air is less, then the wet mass in the product trolley will not be lifted.
To overcome this issue, increase the air flow volume to produce the required product lift.
Filter Choking
Proper fluidization of the product is not achieved if the SS candle filters or the finger bag cloth filters are choked. If these filters are choked, then the lift will not be produced due to the blockage of the escape route of the air.
Use a blowback or filter shaking mechanism to ensure that filters remain clear during the process of drying.
Wash or replace the filter in case of severe choking. If the exhaust filters of the outlet air duct are choked, then the required fluidization will also not be achieved, as the required pressure is not generated.
Define a proper frequency to clean and replace the exhaust filters.
Mesh Choking
The mesh attached at the bottom of the product trolley in FBD has a great impact on fluidisation. The bottom mesh is the direct medium through which inlet air is passed for fluidization. If this mesh is choked or blocked, then the velocity of air will be reduced.
For proper fluidization ensure cleaning and timely replacement of this mesh.
Product Load
The product load in the product trolley of fluid bed dryers plays an important role for fluidization. If
the product is overloaded in the product trolley, then the incoming air will find it difficult to lift the product in the drying chamber, so always load an optimum quantity of the product in the drying chamber.
Product Behaviour
Fluidization of the wet mass in the drying chamber is greatly affected by the behaviour of the product under drying.
If the product to be dried is over-wet it will adhere to the bottom and sides of the bowl, resulting in poor fluidization.
If a product with low melting point is dried at higher temperatures, it will still to the mesh and side walls, resulting in poor fluidization.
Use the pre-heating technique before transferring the product to FBD.
Blockage of the exhaust duct
Fluidisation is also affected by the blocked or clogged return duct, so ensure cleaning of the return duct of FBD at defined intervals.
Electrostatic Charge
Electrostatic charge in fluid bed dryers results in the sticking of fine powder particles on the filters & walls of the fluid bed and affects the fluidization. Ensure proper earthing of the FBD to prevent the establishment of a charge.
Air Leakage
Air Leakage from ducts and gaskets or from any portion of the FBD body results in a pressure drop & has a direct impact on fluidization. Define a frequency for inspection of these parts.
Blower Issues
If the RPMs of the blower motor are lower, it will result in poor fluidization. Blower inspection is required at regular intervals to check its bearings, sound & vibrations.
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