Principle and working of Fluidized Bed Dryer (FBD)


What is Fluid Bed Dryer :

FBD is used for drying of different pharmaceutical materials or products and it can easily achieve specific moisture content in granules and powders.

FBD is able to remove excess moisture from different materials and its working principle is so precise and focused on drying the materials without changing their physical attributes.

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

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.

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.

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

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:

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.

Refer Fluid Bed Dryer Filter Bag

https://pharmaceuticalupdates.com/2020/10/05/procedure-for-indent-receipt-usage-and-specifications-of-fluid-bed-drier-filter-bag/

 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.

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.

Difficulty in Drying Sticky Particles :

The main principle of drying using the fluid bed dryer is the movement of particles as it takes away excess moisture.

We will, therefore, experience a lot of problems when it comes to drying sticky materials as they don’t move freely.

Material of Construction of FBD:

For the contact parts of FBD we should use  AISI 316 and non-contact parts AISI 304.

Fluid Bed Dryer Quality Standards and Certifications:

The main quality standard and certification are

  • Current Good Manufacturing Practices (cGMP)
  • International Standards Organization (ISO) Quality Certification
  • Food and Drug Administration Quality Certifications
  • CE quality certification for the electrical appliances

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