Classification of fluid bed dryers and the significance of its work

Author: Vj Instruments

According To Process Applications :

Drying :

The fluidized bed dryers available for use in the Pharmaceutical industry are of two types,

1. Batch type Vertical Fluid Bed Dryer with Granulating option.

I. Reverse turning bed type

II. Rotating discharge type

2. Continuous type Horizontal Vibrating Conveyor Fluid Bed Dryer.

Granulation :

The fluidized bed dryers available for use in the Pharmaceutical industry are of two types,

  1. Top Spray Fluid Bed Granulator,
  2. Rotating disk Fluid Bed Granulator with Dryer option.

Coating :

The Fluid Bed Dryer available for use in the Pharmaceutical industry are of two types,

  1. Top Spray Pellet with Particle Coating option,
  2. Fluid Bed Bottom Spray Pellet with Particle Coating option,

According To Principle

  1. Spiral Granulator,
  2. Bottom spray coating,

Introduction

VJ Instruments Fluid Bed Dryer manufacturer is used in sample preparation and R&D departments. Drying is most widely used technique for drying pharmaceutical powders and granulation. The direct contact between particles and air/gas is possible in fluid bed system. Here any type of inert gas or air is used. They can be designed in either batch or continuous type fluid bed dryer. Various innovations in fluid bed drying are discussed in section 7.

The Rapid dryer operates under the principle of direct drying where direct contact between a heated gas/air and the product occur to effect heat and mass transfer. The hot air/gas used for drying can be generated by either steam coils or a combustion furnace. The holes in the perforated plate are covered with caps that prevent material form entering the plenum when the is not in operation. The fan equipped in the upper part of the apparatus induce fluidizing air stream. Hot air is fed in the material layer at rest from the bottom of gas straightening valve (e.g. perforated plate). The velocity of air is adjusted by means of a damper. When the velocity of hot air accelerates a bit, particle groups gradually come to make active movements gradually resulting in hot air pressure loss due to the material layers comes to be in proportion to the weight of material particles on the unit area of the The material later expands to 1.2 to 1.6 times in height that was at resting position. Product height in the fluid bed reaches between 100 to 500 mm (average 300 mm) depending on the application. The material layer behaves as it is liquid and shows an appearance as it is boiling. This state is termed as "fluid state". This type of fluid bed can be formed within a certain range of flow velocity depending upon particle size, specific gravity and other properties of the material. Uniform processing conditions are obtained by passing

hot air (or other inert gas) through a material layer under controlled velocity conditions to create a fluidized state. Air is filtered after drying in multi-cyclones and /or bag filters. However, the use of bag filter is troublesome if the dryer is often used for different products because careful cleaning of the dryer is required. The dry product overflows an adjustable weir plate and is discharged continuously through a rotary air lock. In fluid bed drying, airflow need not be the only source of heat. Heat can also be effectively introduced by heating surfaces (panels or tubes) immersed in fluidized layer. Fluid bed dryer can also be constructed with an integral cooling system thus avoiding the need for a separate cooler in those applications that require one. In fluid bed cooling usually ambient or conditioned air is used. Another option is cooling surfaces immersed in the fluidized layer. Conditioning of the air may be required to obtain sufficient product cooling in an economically sized plant and to prevent pick up of volatiles including moisture's.

Rapid dryer?is suitable for powders granules, agglomerates and pellets, having average particle size normally between 50 and 5000 micron.

The material containing very fine, light powder (low density) or highly elongated particles may require vibration for successful fluid bed drying.

Most fluid bed dryers are single pass system where the process gas passes through the bed only at once and is exhausted to atmosphere. Depending on the economic feasibility of the operation, some systems can be designed for re-circulation or recuperation. The larger particles that fall out of bed are introduced back into the bed or propelled along the length of dryer by vibrating action. Vibrating systems decrease power requirements for fluidization and thus reduce operating cost. In indirect fluid bed processing, a tube or series of plates are incorporated into the drying chamber. They are arranged in such a way that products remain in intimately contact with the heated surface. The heat energy is transferred by means of conduction. Here steam is used as a source of energy. The cost of operation is low because steam is low cost energy source.

A fluid bed dryer is capable to use almost any heat source. As the temperature of the process gas is increased, the volume of air required is small and the unit required is also small. With the correct design, fluid bed dryers can withstand at extremely high temperatures, providing the potential for calcining. Incorporation of refractory lining the box, drying chamber or expansion chamber is required with these designs. With independent control of airflow and temperature, the dryer can be divided into several different zones.