Vibratory Fluid Bed Dryer (VFBD)

Vibratory Fluid Bed Dryer is an extension of fluidised bed techniques, by using vibrations as an external aid to fluidisation.

All materials cannot be fluidized because of one or more of the following reasons:
1. Excessive moisture
2. Strong surface forces
3. Wide particle size distribution
4. Fine Powder
5. Product characteristics

Some of the materials having such properties can also be fluidized well with the air of mechanical vibrations. Vibrations breakup the inter-particle forces of attraction and improve the quality of fluidization. Bubbling of hot air in a stationary fluid bed may cause violent agitation. When vibrations are used as air, gas velocities are reduced and the fluidisation is gentle. Particle attrition is reduced. Thus substances having low mechanical strength can be dried without damage.

There are two methods of imparting vibrations:
a) Constant Force System
b) Constant Displacement System.

Choice is exercised based on application.

Process Objective/Mechanism of Vibratory Fluid Bed Dryer

The following are the Process objectives of the Drying Process:

• To arrest the fermentation or oxidation process in the input leaves within a pre-determined time interval, from the time leaves would be fed into the drier.
• To remove a specific amount of moisture content at pre-determined rates w.r.t. time unit, from the input leaves. This, of course, is the main objective.
• To bring about certain desired specific changes in the physical and chemical properties of the input leaves like in color, density, flavor etc. by the end of the drying process.
• The drying work need to be a continuous process ensuring a specific output volume per unit time with preferably auto-controls of drying parameters in cases of  variations in feed, in the moisture contents of input leaves or in the heat content of the hot air etc.

For Moisture evaporation Thermal “Convection” drying system is chosen with Air being selected as the gaseous medium, due to system’s comparative overall advantages in the following areas over other thermal drying systems:

• Temperature measurement and control of both the in-process material and of the heating medium is easier and more accurate.
• Temperature of the in-process material can at no time exceed the temperature of the hot medium irrespective of any change in the feed volume or total heat content in the medium.
• Gaseous Medium chosen is available free of cost.

The Vibratory Fluid Bed technology with two temperature drying system (replacing the traditional six temperature one) had been adopted for the dryer model mainly leading to much better heat penetration and uniformity in heat distribution on all sides of the Particle, rotating on it’s axis due to the resultant angular excitation force acting on it.

• Considerable reduction in space requirement per kg of dry tea
• Improved appearance & gloss in dry tea due to the particles being moved in suspension in an air stream without any friction with bed.
• High thermal efficiency of the equipment.

The Equipment is designed appropriately with enough flexibility of performance & capacity to suit the customer’s requirement and specifications for drying the wet Fermented leaf.

Vibratory Fluid Bed Dryer is also commonly known as Fluid Bed Dryer in many industries.