Principle of FBD:
The equipment works on a principle of fluidization of the feed materials.
In the 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)
Construction of FBD:
The dryer is made up of stainless steel or plastic.
A detachable bowel is placed at the bottom of the dryer, which is used for charging and discharging.
The bowel has a perforated bottom with a wire mesh support for placing materials to be dried.
A fan is mounted in the upper part for circulating hot air.
Fresh air inlet, prefilter and heat exchanger are connected serially to heat the air to the required temperature.
The temperature of hot air and exit air are monitored.
Bag filters are placed above the drying bowl for the recovery of fines.
Working:
The wet granules to be dried are placed in a detachable bowl. The bowl is inserted in the drier.
Fresh air can pass through a prefilter, which is then heated when passing through a heat exchanger.
Hot air flows through the bottom of the bowl.
At the same time, fans start to rotate.
The air speed increases gradually.
When the velocity of air is greater than the sedimentation rate of the granules, the granules remain suspended in the gas stream.
After a specific time, a pressure point is reached in which the friction drag on a particle is equal to the force of gravity.
The granules rise in the container due to high gas velocity of 1.5 to 7.5 meter per minute and then fall back. This state is known as a fluidized state.
The gas surrounding each granule does dry them completely.
The air comes out of the dryer passing through the filters in the bag.
The entrained particles remain adhered to the interior surface of bags.
Periodically bags are shaken to remove entrained particles.
Uses:
It is used for drying granules in the production of tablets.
It is used for the coating of granules.
It can be used for three operations such as mixing, granulation and drying.
Advantages:
It takes less time to complete drying as compared to other dryers.
Drying is achieved at a constant rate.
Handling time is also short.
It is available at different sizes with different drying capacities.
The equipment is simple and requires less labor.
More thermal efficiency.
Drying capacity is more than other dryers.
It facilitates the drying of thermolabile substances since the contact time of drying is short.
It is a batch-type or continuous-type process.
Disadvantages:
Many organic powders develop electrostatic charge during drying. To avoid this, efficient electrical earthing of the dryer is essential.
Chances of attrition of some materials resulting in production of fines.
Commonly Asked Questions.
With a well labeled diagram describe construction and working of FBD.
Write a short note on the FBD.