Principle and Working of Fluidized Bed Dryer (FBD)

Fluidized bed dryer (FBD) is well known and widely used equipment in granulation area of pharmaceutical manufacturing. It is used in the granulation process for drying the material to get desired moisture content in the tablet formulation granules required for perfect compression of tablets.

The Principle of Fluidized Bed Dryer:

If air is allowed to flow through a bed of solid powdered material in the upward direction with the velocity greater than the settling rate of the particles, the solid particles will be blown up and become suspended in the air stream.

At this stage, this solid bed looks like the boiling liquid, therefore this stage is called as fluidized. Use of hot air to fluidizing the bed will increase the drying rate of the material.

FBD contains a stainless steel chamber having a removable perforated bottom known as the bowl. Material to be dry is placed in this bowl. Air is introduced from the bottom of the bowl and heated at required temperature by the heaters.

This air is filtered through the filter and then passes through the bed of the material. This airflow is generated by the fans fitted at the top of the equipment. The flow rate and the operating temperature are adjusted by the control panel.

As the flow of air increases, the bed known as FBD bag expands and particles of powder start a turbulent motion. Due to the regular contact with air, the material gets dry. The air leaving the FBD passes through the filter to collect the fine particles of the material.

Fluidized bed dryer has a high drying rate and the material is dried in a very short time. Material remains free-flowing and uniform. FBD bags are finger-like in structure to increase the surface area of the drying bed that helps to increase the drying rate and decrease the drying time during the fluidized bed drying process.
Related: Challenge Test of Solid Flow Monitor in Fluid Bed Dryer

Sometimes particles may develop an electrostatic charge. Burning of the material in the fluid bed dryer equipment is experienced in many cases in different pharmaceutical companies. Outlet filter blockage is a common problem of the fluidized bed dryer equipment. It can cause increasing the pressure in the vessel that can cause an accident during operation. Therefore, handling of the equipment should be done carefully.