Fluidized Bed Dryer -FBD: Principle, Working Process

What is Fluidized Bed Dryer (FBD)? or Principle of Fluidized Bed Dryer -FBD Machine:

FBD meaning is fluidized bed dryer (FBD)

  • In FBD, a hot air (gas) is passed through a perforated bottom of the container holding the product granules that need to be dried at high pressure.
  • From the bottom, the grains are raised and suspended in the airflow.
  • The term “fluidized state” refers to this situation.
  • Every grain is thoroughly dried by the hot gas that surrounds them. As a result, materials or granules are dried consistently

fluidized bed dryer diagram, Construction and working :


  • Two types of Fluid Bed Dryers are available in market
  • Vertical fluid bed dryer and
  • Horizontal fluid bed dryer.
  • Figure represents the design of a vertical fluidized bed dryer.
fluidized bed dryer (FBD) diagram
  • The dryer is constructed of plastic or stainless steel (SS). At the bottom of the dryer is a removable (detachable) bowl that is used for both charging and discharging.
  • For holding things to be dried, the bowl includes a wire mesh support and a perforated bottom.
  • To move hot air, a fan is attached in the upper section. To heat the air to the desired temperatures, a fresh air input, prefilter, and heat exchanger are linked in series.
  • Monitoring is done for hot air and exit air temperatures.
  • To recover particles, bag filters are positioned above the drying basin.

Components or Parts of FBD-Fluidized-bed dryer:

  1. Body Stainless steel
  2. Inlets Filters
  3. Air preparatory unit.
  4. Product container or Bowl.
  5. Expansion chamber 
  6. Exhaust Filter & Fan
  7. Control Panel
  8. FBD Bags
  9. Air Distribution Plates
  10. Gaskets
  11. Plenum

What is fluidized bed dryer ?

Working Procedure of Fluidizied Bed Dryer -FBD:

  • The principle behind a Fluidized Bed Dryer revolves around the concept of fluidization. Fluidization is a process in which solid particles are made to behave like a fluid by passing a gas or liquid through them. In the case of FBDs, a stream of hot air or gas is passed through a bed of solid particles, causing them to become suspended and act like a boiling fluid. This fluidized state allows for efficient heat transfer and uniform drying of the material.
  • The removable bowl on top of the retaining screen is filled with the wet granules that need to be dried. The bowl is pushed into the FBD.
  • Fresh air is allowed to pass through a prefilter before going through a heat exchanger to be heated. The bottom of the bowl is where the hot air passes through. Simultaneously fan is permitted to rotate. The air speed increased gradually.
  • The granules stay partially suspended in the gas stream when the air velocity is higher than the settling velocity of the granules. After some time, a pressure level is reached where the force of gravity and frictional drag on the particles are equal.
  • High velocity gas (moving at 1.5 to 7.5 metres per minute) causes the granules to float in the container before randomly falling again.
  • This state is referred to as fluidized state. Every granule is thoroughly dried by the as, which envelops them.
  • The bag filter is used to filter the air before it leaves the dryer.
  • The entrained particles continue to stick onto the inside surface of the bags. Intermittently the bags are shaken to eliminate the entrained particles.
  • Granules and hot gas are thoroughly mixed, resulting in consistent temperature, chemical composition, and particle size distribution. Drying is accomplished at a constant rate & the period of falling rate is quite brief. 
  • Any effort to increase the air velocity could result in entrainment.
  • The residence time for drying is about 40.0 min. The drying rate is 0.0 to 20.0 times higher than the time required during tray dryer.
  • The process parameters are conventional experimentally
    • Maximum, minimum, and optimal air velocities.
    • Air temperature,
    • Drying time,
    • Tendency to cake and channel.
  • The material is dried for a while to allow it to reach room temperature. For discharge, the bowl is removed. The finished product flows freely.

Lets Simplify with process to understand easy:

  1. Loading: The material to be dried is loaded onto the perforated plate or grid at the bottom of the drying chamber. The thickness of the bed is controlled to ensure efficient fluidization.
  2. Start-up: The FBD is started, and a stream of preheated air is introduced into the drying chamber from the bottom. The velocity of the air is carefully controlled to initiate fluidization without entraining too many particles.
  3. Fluidization: As the air flows upward, it passes through the bed of solid particles. The upward force of the air causes the particles to become suspended and behave like a fluid. This fluidization ensures that the entire bed is in motion, exposing all particles to the hot air.
  4. Heating: The hot air transfers its heat to the solid particles. This heat causes the moisture within the material to evaporate, changing from a liquid to a vapor state. The hot air also carries away the moisture vapor.
  5. Moisture Removal: The moisture-laden air rises through the fluidized bed, carrying the evaporated moisture with it. This continuous circulation of air through the bed ensures uniform drying.
  6. Temperature Control: The temperature of the incoming air is carefully controlled to maintain the desired drying temperature throughout the process.
  7. Monitoring: Various sensors and instruments are used to monitor parameters such as temperature, humidity, and airflow to ensure that the drying process is consistent and that the product reaches the desired moisture content.
  8. End of Drying: Once the material reaches the desired moisture content, the hot air supply is turned off. The bed of solid particles gradually settles as the airflow decreases.
  9. Product Collection: The dried product is collected from the bottom of the drying chamber. It can then be further processed, packaged, or stored as needed.

Uses or Application of Fluid bed drying :

  • Granules are frequently dried in fluidized bed dryers before being utilised to make tablets. Drying, granulating, and mixing are three processes that can be done with a fluidized bed dryer. It has been modified for granule coating.

Advantages and Disadvantages of Fluid Bed Dryer (FBD):

Advantages of Fluidized Bed Dryers (FBDs)::

  • Fluidized bed dryer (FBD) needs less time to finish the drying, i.e. 20 to 40 min compared to 24 hr required in a traditional tray dryer. Handling time is also less. It is overall 5 times faster than the tray dryer.
  • Excellent gas-particle constant results in high heat and mass transfer rates, which in turn lead to high rates of moisture removal.
  • It is offered in numerous sizes with a drying capacity ranging from 5 to 200 kg/hr.
  • Because the drying containers are portable, handling is easy and labor costs are decreased.
  • The thermal efficiency differs from tray dryer by a factor of 2 to 6.
  • It is also used to mix the materials, and it does so with excellent mixing effectiveness.
  • The dryer’s excellent mixing and drying capabilities stop the appearance of hot spots.
  • Hot spots are not detected in the dryer, since it works excellently for mixing and drying capacities.
  • Higher drying temperatures can be possibly used. But it is not possible in tray dryers and truck dryers.
  • Because the drying contact duration is brief, it makes drying of thermolabile materials easier.
  • It can be utilised in a batch or continuous fashion.
  • It produces a lot with little floor space.
  • Individual pat1icles can move freely, which reduces the possibility of soluble 1naterial migrating, as can happen in static beds.
  • Uniform Drying: FBDs provide uniform drying, ensuring that all particles are exposed to the hot air, resulting in consistent product quality.
  • Gentle Handling: The fluidized state of the particles reduces the risk of product degradation or damage during drying.
  • Efficiency: FBDs are energy-efficient due to their effective heat transfer and the recycling of hot air within the system.
  • Shorter Drying Times: The efficient heat transfer and uniform drying lead to shorter drying times compared to other drying methods.
  • Easy Scale-Up: FBDs are scalable, making them suitable for both laboratory and large-scale production.
  • Low Maintenance: They have relatively low maintenance requirements and are easy to clean.

Disadvantages of FBD:

  • During drying, electrostatic charges form in a lot of organic powders. Effective electrical earthing of the dryer is crucial to preventing this.
  • Some materials may attrite as a result of the fluidized state of granules’ turbulence, producing fines.
  • However, this issue can be resolved by employing an appropriate binding agent. Bag filters must be used to collect any entrained fine particles.
  • The necessity to suspend the entire bed in gas causes severe pressure drops, which also results in excessive energy usage.
  • Enhanced gas handling is needed because high thermal efficiency operation involves considerable exhaust gas recirculation.
  • Low flexibility and poor fluidization, particularly if the feed is overly wet.
  • Not the best piece of equipment to use when drying off organic liquids.
  • Non-uniform product quality for certain types of fluidized bed dryers.
  • Entertainment of fine particles.
  • High potential for attrition; in some circumstances, fine particle aggregation.
  • When working with poisonous or flammable substances, traditional hot air fluidized bed dryers are not the best option because there is a risk of fire or explosion if flammability.

Read More:


  • Book: Arun S. Mujumdar (2015). Handbook of Industrial Drying. CRC Press, Taylor and Francis Group, New York.
  • Book: PHARMACEUTICAL ENGINEERING-Principles and Practice Unit Operations Abridged with PCI Syllabus of B. Pharmacy by C.V.S. Subrahmanyam, J. Thimmasetty, Mrs Sarasija Suresh and Mrs V. Kusum Devi


  1. What is what is fbd or fbd meaning: Ans. FBD stands for fluidized bed dryer
  2. What is the Endpoint of FBD process: Ans. During the IPQC Product meet the Loss on Drying LOD that will be its endpoints.
  3. What is Full form of FBP: Ans. Fluid Bed Processor

Read More:

You cannot copy content of this page