1. Dhaneshwar Kumar Vishwakarma Kailash Institute of Pharmacy and Management GIDA, Gorakhpur DRYING FLUIDIZED BED DRYER DRYING FLUIDIZED BED DRYER

2. FLUIDIZED BED DRYER (fluid bed dryer) o It is an equipment used to reduce the moisture content of pharmaceutical powder and granules. Principle Particles are dry in fluidization condition (particles suspended in hot air) Let us consider a situation Where a bed of granules is placed over a perforated bottom container. Hot air is flown from bottom through the bed. Measure the pressure drop (  P) across the bed and Measure air velocity (V).  P is plotted against V then the following curve is observed.

3. Point A: When the air velocity is very low Air flow between the particles without causing any disturbance. Point B: When the velocity is increased to a certain value The frictional drag on the particles become equal the force of gravity of the particle. Point C: Rearrangement of the particles occurs to offer least resistance. Point D: Eventually the particles are suspended in the air and can move.  P decreases slightly because of greater porosity. Further increase in the air velocity causes the particles to separate and move freely (fluidized). In the D-E region the air flows through the bed in the form of bubbles – Boiling Bed Stage. Above point E the solid particles entrain into the gaseous phase and the particles float in the gas.

4. Construction Two types of fluidized bed dryers are there Vertical fluidized bed dryer – for batch process Horizontal fluidized dryer – for continuous process

5. The dryer consists of: 1.Air handler: This is a source of dry and hot air. 2.Product container: o This container holds the product that is to be dried. It is detachable (easy for loading and unloading) It has perforated bottom.

6. The dryer consists of: 3.Expansion chamber: This chamber is situated above the product container and holds the suspended material. 4.Filter: The upper part of the expansion chamber has bag filters. o It prevents fines from escaping into the atmosphere or collecting on the blades that pulls the air through the dryer.

7. Working

8. Applications It is used to dry the wet granules. It can be used for coating of granules (Wurster technique).  In fluidized condition the powder is coated by coating solution,sprayed from the nozzles.  As the particles are coated they become heavier.  When the mass developed becomes higher than the drag force given by the fixed air velocity the particles no longer float.  They fall back, which is then collected as product. It is also used for mixing

9. Advantages Heat and mass transfer coefficient high so require less drying time (20-40 sec). Suitable for thermolabile materials due to less holding time. Individual particles of the bed get dried in the fluidized state. Temperature can be controlled uniformly. A free-flowing product is obtained. Thermal efficiency is 2-6 time higher than tray dryer. Ease of control

10. Disadvantages Turbulence of fluidized state may produce fine particles due to attrition. Fine particles lead to segregation, so they must be collected by bag filters. Static charges may be produced due to vigorous movement of particles in hot dry air. Poor fluidization and low flexibility especially if the feed is too wet.

11. Email i.d- dkvpharmaguidance@gmail.com