Why Finger Shape Cloth Filter Is Used In FBD

Fluid bed dryers are used in pharmaceutical industries for drying of wet granules.If you are not aware of basic structure and functioning of FBD then must read the following article because in this article we will not go into details of FBD construction or its working.

Congratulations & Working Of FBD.

After reading the above article you are now familiar that a cloth filter bag or SS filters are used in FBD.

FBD Finger Bag

The purpose of these filters is to allow the escape of air without product loss.

Why Finger Shape

Did you ever think that why only finger shape or pocket type cloth filters are used in fluid bed dryer?

Why we don’t use straight or curved Shape cloth filter in FBD?


Finger shape cloth filters are also known as candle filters of fluid bed dryer.


Following are the main reasons due to which we don’t use straight or curved shape filters & only we use finger shape cloth filters.

Surface Area

We are familiar that drying chamber of FBD has a specified height & if we use straight or curved shape cloth filters in FBD the drying area will be reduced.

Due to reduced drying area the fluidisation height will be reduced & drying time will be increased.

Due to finger or pocket type construction, the surface area inside drying chamber is increased & due to increased surface area the granules can achieve maximum height during fluidisation & drying time is reduced.

Air Pressure

We know that for strong fluidisation in drying chamber of fluid bed dryer we use high air pressure for lifting of wet mass  which is placed in the product trolley of FBD.

If a straight of curved filter is installed in the drying chamber of fluid bed dryer it will be under the influence of higher air pressure & there will be more chances of rupturing of this type of cloth filter due to higher air pressure.

When finger shape cloth filter or pocket type cloth filter is used in FBD the air escape from various pockets & there are less chances of rupturing of fluid bed dryer cloth filter due to distribution of air pressure into various pockets.


We always use finger shape cloth filters or pocket type cloth filters in fluid bed dryer to increase the surface area for drying due to which drying time is reduced.The other reasons to use this type of filters is to distribute air pressure into various pockets & it help to prevent rupturing of fluid bed dryer filter due to higher fluidisation.

Also Read

  1. Critical Process Parameters Of FBD
  2. Size Of FBD Sieve
  3. Kevlar Rope For FBD
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