Pelletizing Technology Liquid Layering of Pellets by Fluid Bed Processing

For maximum production flexibility, GEA can supply a single fluid bed unit, the PRECISION-COATER™, or a multi-purpose FlexStream­™ processor that combines granulation, drying and pellet coating in a single piece of equipment.

Liquid Layering of Pellets

Liquid Laying Portrait

GEA's multi-functional PRECISION-COATER™ and FlexStream™ systems can both be used to make pellets by layering the active material onto an inert core. Non-pareil starter pellets are sprayed with a solution or suspension of the active material and dried simultaneously.

Coating Quality

Coating products can be expensive and the volume of product needed is inversely proportional to the particle size of the material to be coated. Coating quality is, therefore, of paramount importance. 

The aim is to coat the particle with just enough coating material to achieve the desired result, but no more. In addition, when the coating is functional, it must also be evenly distributed over the entire surface of the product. An uneven application can seriously affect the performance (release profile) of the active. One cause of uneven coating can be the failure to generate sufficient rotation (spin) of the product during the process. Possibly resolved by increasing the airflow, this might, in turn, increase attrition losses owing to the generation of small, dust particles and reduce the yield.

 

Product Yield

In a traditional fluid bed coater, product can be lost as dust or by the agglomeration of larger, damp particles as they impact upon themselves or the equipment. Agglomeration is caused when the spray rate is too high and the product is still damp when it meets either another particle in the bed or the surface of the coater. 

In some systems, the spray nozzle can cause a ‘venturi’ effect, sucking particles into an area of high humidity around the nozzle where they can collide and agglomerate. An increased airflow rate may offer a solution, or lowering the humidity in the vicinity of the spray nozzle by reducing the spray rate; however, this might result in increased losses through attrition or longer processing times.

PRECISION-COATER™ Module

For smaller particles such as powders, granules, seeds, crystals, pellets and small tablets, the PRECISION-COATER™ offers a time- and cost-effective alternative to traditional bottom spray coating systems.

Features and Applications

The product is coated and partially dried by being blown upward through a central column with atomized liquid and drying air. The material falls into the outer part of the container where heated air completes the drying process.

On reaching the air distributor at the base of the module, the product flows into the central column for further coating. This process continues until the specified degree of coating is obtained.

Special features include high spray rates for short processes, highly controlled product movement and minimal agglomeration or granulation. 

The PRECISION-COATER™ provides higher yields by reducing agglomeration and attrition; it improves productivity by accelerating the coating and drying process; and it significantly improves product quality by ensuring that a coating of uniform thickness is applied, thus ensuring optimal clinical efficacy. It is ideal for coating applications involving particles from 50 microns to 3 mm in diameter.

GEA believes that no other currently available product is better suited to the industry’s need for a highly effective coating system (pellet production) with excellent scale-up characteristics.

 

FlexStream™ Fluid Bed Coater

The GEA FlexStream™ fluid bed processor is a multi-purpose unit that uses proven fluid bed technology to achieve granulation, drying and pellet coating (or tablet coating) in a single piece of equipment.

Process Description

The FlexStream™ comprises a fluid bed product bowl with several two-fluid atomization nozzles to distribute the granulation or coating liquid directly onto the fluidized powder or pellet layer.

A third low-pressure air stream comes directly from the fluid bed inlet plenum to create a particle-free area around the spray pattern of each nozzle. The low pressure results in much better control of the granulation and coating processes, fewer fines, less agglomeration when coating pellets and, as a result, significantly improved yields.

The FlexStream™ process is suitable for aqueous- and organic-based solvents. GEA offers a range of open- and closed-cycle systems to remove or recover organic solvents. Options include condensation, adsorption and wet scrubbing. 

Process and Design 

  • A number of nozzles and achieved spray rates for pellet coating comparable with high efficiency bottom-spray coating systems
  • Narrow particle size distribution for granulation Simple, cost-efficient design
  • Compressed air only for atomization gas 
  • Third air stream conditioned from fluid bed air inlet 
  • 10 bar pressure shock resistant fluid bed processor design
  • Existing GEA fluid bed equipment can be upgraded with the FlexStream™ process.