Pharmaceutical Industries: FLUID BED DRYER

A fluidized bed dryer (also called a fluid bed dryer) is a kind of equipment used extensively in the pharmaceutical industry to reduce the moisture content of pharmaceutical powder and granules. 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). Heat transfer is accomplished by direct contact between the wet solid and hot gases. The vaporized liquid is carried away by the drying gasses. Sometimes to save energy, the exit gas is partially recycled. VJ Instruments also has fluid bed processor for granulation.

A typical fluidized bed dryer also called as rapid dryer consists of the following components

Air preparatory unit.

Product container.

Exhaust filter.

Exhaust blower.

Control panel.

Air distribution plate.

Spray nozzle.

Solution delivers.

The choice of distributor used during and drying process apart from ensuring uniform and stable fluidization also prevents ·

Poor fluidization quality of solids in certain regions in the fluidized bed dryer. · Plugging of distributor –perforated holes. ·

Solids from dropping into the wind box or gas plenum located beneath the fluidized bed.

The pressure drops across the distributor must be high enough to ensure good and uniform fluidization.

Parameters to be controlled in fluidized bed dryers (system) To improve the operation, efficiency, and reproducibility of a fluidized bed dryer, some parameters need to be controlled. These parameters are categorized into

Apparatus parameters: Those controlled by the equipment.

Process parameters: Those controlled by the process.

Product parameters: Those controlled by the product.

Apparatus/Equipment Parameter

Position of the air distribution plate: This parameter influences the pattern.

The shape of the instrument: The annular-based design gives a better product.

Nozzle height: Nozzle height plays a vital role when a fluidized bed dryer is used as a coating machine. The atomized coating solution should not get dried before reaching the tablet surface.

Process/Operating Parameter

Temperature: Increased temperature leads to increased moisture diffusivity and hence increased drying rate and decreased drying time. The nature of the material plays an important role in choosing the operating temperature. Humidity: Faster drying is achieved when the moisture content of the inlet air is maintained at its minimum. Airflow rate/gas velocity: Increasing gas velocity increases the drying rate but should be maintained at an optimized rate (not too fast or too slow). Gas velocity does not affect particles with high internal resistance to moisture transfer.

Product Parameters

The moisture content of the feed material.

Feed rate/batch size.

Product moisture content.

Particle size, shape, and diameter.

Types of Fluidized-Bed Dryers

There are various types of fluidized bed dryers and an individual’s familiarity with the specific characteristics of these various types enables one to make a logical and cost-effective selection of fluidized bed dryers for a drying operation. In many instances, several different types may provide similar performance at the same cost. It should be noted also that not all modified fluidized bed dryers are necessarily better than conventional dryers in terms of product quality, energy efficiency, or drug performance.

Conventional Fluidized Bed Dryers

Conventional fluidized bed dryers include;

Batch fluidized bed dryers.

Semi-continuous fluidized bed dryers.

Well-mixed, continuous fluidized dryers.

Plug flow fluidized bed dryer.

Modified Fluidized Bed Dryers

Various types of modified fluidized bed dryers have been developed and are applied in many industrial processes to overcome some of the problems encountered while using conventional fluidized bed dryers and for a drying process. They include but are not limited to;

1. Hybrid fluidized bed dryers
2. Pulsating fluidized bed dryers
3. Fluidized bed dryer with immersed heat exchange.
4. Mechanically assisted fluidized bed dryer.
5. Vibrated fluidized bed dryer.

Pharmaceutical instruments which are mostly sed in food and many other industries.