Critical Process Parameters Of FBD

FBD or Fluid Bed Dryer Is a type of batch drying equipment used in pharmaceutical industries.

What Is Critical Process Parameters

Critical Process Parameters also known as CPPs are the parameters that should be critically monitored during a specific process. These are critical because they have a direct impact on the process or the product. Parameters of a Fluid Bed Dryer which are critical should be monitored carefully during the drying process to ensure uniform drying.  

Critical Process Parameters Of FBD

Following are the Critical Process Parameters Of Fluidized bed dryers used in pharma,

  • Inlet-Air Temperature
  • Out-Air Temperature
  • Product Temperature
  • Fan Motor Speed
  • Loss On Drying (LOD)

1. Inlet-Air Temperature

Inlet air temperature is the temperature of the air coming from the outside after processing & comes in direct contact with the product.

This inlet air is directly involved in the drying process so temperature monitoring of this incoming air is very important.

A sensor is installed in the inlet air duct which gives the values of the incoming air temperature. This temperature value is displayed on the HMI of the fluid bed dryer.


The products which are granulated by using water as a solvent require high temperatures for drying like 70°C to 

80 °C.

When we give input temperature feed on the HMI of FBD, the heating coil of the FBD heats the air at the input feed temperature & the values are displayed on HMI for visual observation.

The temperature of inlet air should be monitored during the drying operation and the following factors may affect the inlet air temperature.

  • Drop-In Steam Pressure
  • Steam Leakage
  • Electrical Problem in the Case Of Electric Heaters
  • Inlet Temperature Sensor Problem
  • Choking/Blocking of Filters

If any unusual changes are observed in inlet air temperature resolve it immediately otherwise the drying process will not be completed as mentioned in BMR.

2. Outlet-Air Temperature

Outlet air temperature is measured by the sensor installed in the return duct of FBD & is displayed on the HMI of FBD.

The outlet air temperature is always less than the inlet air temperature due to heat exchange.

The Outlet air temperature monitoring provides an estimation about the dryer performance.

Standard values can be taken for each product during validation batches.

3. Product Temperature

The product temperature is the temperature of a product that is dried in the product trolley of the FBD.

This temperature is also displayed on the HMI & is measured by the Product Temperature sensor Probe.

The product trolley or detachable bowl of the fluid bed dryer has an insertion port for the product temperature sensor.

When the material is placed inside the trolley & is locked below the drying chamber, we insert the temperature sensor probe in the port of the product trolley & it gives its temperature value on HMI.


Observation of product temperature for each product during the drying process gives us an estimation regarding the completion of the drying process. The product temperature for each product can be defined during the validation batches.


Suppose we have a product in FBD trolley manufactured by wet granulation method using water as a solvent. The inlet air temperature is 80°C and when drying is completed its product temperature is 50 °C.

Validation is performed for three batches of a product to take values of product temperature, then for upcoming batches if we keep all other parameters same,we can understand from the value of product temperature that our product is about to dry near 50 °C.

Always use a calibrated probe for the temperature monitoring.

4. Fan Motor Speed

Fan motor speed or blower motor speed in the Fluid bed dryer is the speed of the blower at which it pulls 

 air through the product.

In simple words, air pressure or airspeed/velocity is controlled by the speed of the fan.

On slowing the motor speed, there will be reduction in the air pressure or lifting power of the air.

The fan speed is visible on the HMI & it should be critically observed.

The dense products are difficult to lift or fluidize with low blower motor speed so if fluidization is not proper we can increase the speed of a motor fan.

High blower speed produces more fine powder so validate the fan motor speed for each product to get uniform drying.

5. Loss On Drying (LOD)

Loss on drying or LOD is one of the most critical process parameters for FBD during the drying process.

The endpoint of the drying process is always determined by the value of LOD.

We validate the value of loss on drying for each product. Usually, 1 to 3% LOD is required for most of the production but it may vary depending on the nature of the product.

Withdraw sample from the given point of the trolley & check its LOD after defined time intervals.

When the required value of LOD is achieved as mentioned by BMR, we stop our drying process.


If we validate our Critical process parameters we can get an idea of when to take a sample for LOD or at which product temperature our LOD value will be according to the BMR .


Critical process parameters should always be defined for each product using specific equipment.

All these process parameters should be monitored critically from the start of the operation till the completion.

 Any change of these parameters from the standard values should be fixed to avoid any negative effect on the product.

Also Read

  1. Working of fluid bed dryer.
  2. Size Of FBD Sieve
  3. Application of tray dryers in pharmaceuticals.
  4. Quality Assurance Interview Questions
  5. Wet granulation & Dry  Granulation in pharmaceutical industries.
  6. Advancements Granulation Techniques.
  7. End point determination or wet granulation.