1. What is Fluid Bed Dryer (FBD) :

Fluid bed dryer which is used in pharmaceutical industries to dry the wet mass of granules or to remove the moisture content from the wet granules without changing their physical attributes during the process of wet granulation.

FBD is used in different industries like Pharmaceutical, Chemical, Food Processing, Fertilizer and dairy industry.

2. What Are The Types Of Fluid Bed Dryers (FBD) :

There are two types of FBD

• Vertical FBD
• Horizontal FBD

Vertical FBD are most commonly used fluid bed dryers in pharma industries.

3. What Is The Principle Of FBD :

The FBD or fluid bed dryer works on the principle of fluidization where air carrying capacity for granules is greater than the settling velocity of granules.

4.    What is Fluidization Principle :

In fluidization process, hot air is introduced at high pressure through a perforated bed of moist solid particulate. The wet solids are lifted from the bottom and suspended in a stream of air (fluidized state). As the hot air passes between the particles it takes the excess moisture from the particles thus drying the particles.

about:blank Heat transfer is accomplished by direct contact between the wet solid and hot gases.

5. What Are The Components Of A Fluid Bed Dryer :

Following are the main components of fluid bed dryer,

Air Processing Unit

Inlet Air Duct

Outlet Air Duct

Air Gate

Plenum

Drying Chamber

Product Trolley

FBD Filter

Fan Motor (Exhaust System)

Product charging system

Product discharging system

HMI & Control Panel 

6.    Steps of Fluidization :

Step 1: Fluidized bed dryer Loading :

Loading of materials involves adding a fresh batch of wet granules into the product chamber through negative pressure feeding, materials can be sucked from the high shear  mixer chamber through a feeding tube.

Step 2: Air inlet (intake) :

Switching the blower unit on is done from the control panel. Once the blower is operational, the air is drawn continuously from the Air Handling unit and into the tower through the lower plenum.

Step 3: Fluidization :

Inlet air is blown up through the static power bed as the velocity of the air increases so does the space between powder particles until the particles become suspended in a bed the fluidization process is through to occur in five stages including smooth  fluidization, bubbling  fluidization, turbulent fluidization and first  fluidization.  

Step 4: Drying:

The drying process takes place in three stages until the end point is reached (At the end point the solid particles moisture level is equal or less than 1%)

Step 5: Pre heating:

Preheating of granules is done to prevent the granules from adhering to the bowl and wet particles are suspended in hot and dry air stream. Moisture on the particles surface evaporates as heat flows through the body (conventional heating) the rate of drying slowly increases as the particles absorb more heat.

The moisture lost during preheating is still small but the temperature of the bed rises steadily.

Step 6: Filter bag shaking:

The blower continuously draws and excels air from Fluidized bed dryer. The airstream may contain very small particles called fines. The filter bags capture the fines in their pores but this cause the formation of a dust layer that clogs the filter bags causing a pressure drop.

Mechanical shaking is the best way to remove the dust layer and it is done by the pneumatic cylinder at the set intervals and seems we have two filtering chamber the shaking is alternated between the two.

Step 7: Discharging of dried material:

Discharging refers to the removal of dried materials from fluidized bed dryer. It can be done manually by unlocking and wheeling the product container on its trolley to the next process equipment.

Alternatively, vacuum conveying can be carried out by connecting the product container with a tube and creating negative pressure for suction using a vacuum transfer system. After drying, the next process is milling.

7. What Is MOC Of FBD :

All the direct product contact parts of the fluid bed dryer are made of stainless steel 316 or 316L.

8. Why Do We Use Finger Shape Cloth Filter In FBD :

The cloth filters used in FBD have finger shape or have pockets which help to increase surface area to reduce the drying time.

9. What Are critical process parameters (CPP) Of FBD :

CPP is Critical Process Parameters. The critical process parameters of FBD are as follows

Inlet Air temperature

Outlet Air temperature

Product Temperature

Air flow volume

10. What Are Other Names Of Cloth Filter In FBD :

The Cloth filter used in FBD is also known as,

Candle Filter

Finger Bag Filter

Pocket Filter

11. Which Type of Sensors are Installed In Fluid Bed Dryers :

Following type of sensors are installed in fluid bed dryer 

Inlet air temperature monitoring sensor

Outlet Air temperature monitoring sensor

Product Temperature monitoring sensor 

Differential pressure monitoring sensor 

Product trolley interlocking sensor 

12. What is Broken Bag Detector (BBD) or Solid Flow Monitor (SFM) :

BBD is a broken bag detector or  Solid Flow Monitor (SFM) which is installed in the return duct of FBD & detects the escape of powder due to rupturing of filters & shut down the fluid bed dryer to prevent product loss.

13. What Is The In Process Test Of Drying :

LOD or loss on drying is the In Process test which is performed during the product drying process.

14. Advantages of FBD:

Following are some main benefits of a fluid bed dryer.

• Uniform product drying.
• High product load can be dried in less time.
• Color migration or mottling defects are prevented.
• Easy to wash & clean.

15.  What Is a Dutch Woven Screen:

The mesh which is installed at the bottom of the FBD product trolley is known as Dutch Woven Screen. It is woven in such a way that it allows air to pass & prevent product leakage.

16. Pore Size Of FBD Mesh:

The pore size of fluid bed dryer mesh is usually 100 to 200 micrometers.

17. What Is Raking In FBD:

Raking is the manual activity which is performed by using spatula & gloved hands to break down the large lumps in the fluid bed dryer product trolley to ensure uniform lifting of the product.

18. Product Charging to FBD :

A pneumatic transfer system is used to transfer the sieved wet granules from high shear wet mill to the fluid bed dryer.

19. Product Discharging From FBD : 

Discharging of dried granules from the product trolley of fluid bed dryer to the co mill or containers is done by pneumatic transfer system.

20. What are the main disadvantages of using the fluid bed Dryer :

Not Ideal for Organic Solvents:

You cannot use the fluid bed dryer for reducing excess moisture in organic solvents or substances containing organic solvents.

This is because the organic solvents usually dissolve in the products thus making it very difficult to dry.

Risk of Fire Explosion:

Fluid bed dryers use high levels of hot gas and air thus making it difficult to dry toxic or flammable materials.

This may place the lives of the people operating the machine or around the machine in great danger.

Electrostatic Build-up:

When we use the fluid bed dryer there are high chances of electrostatic build up during the drying process.

It is a phenomenon that will happen especially when we are drying organic particles.

We should, therefore, go for the fluid bed dryers with electrical earthing elements to avoid this problem.

21. What is the Purpose of Drying of Material in Pharmaceutical using FBD:

Here are the main functions as to why you should perform solid drying.

• It increases the shelf life of the products
• It helps in the improvement of different product properties such as compressibility and flow ability.
• It will also make the materials more suitable for handling and it helps in proper preservation of the materials.

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