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Spray Granulation

Spray Granulation: Free Flowing Particles from Liquids

Precursors

The precursors are liquids, such as aqueous solutions, emulsions or suspensions beside this also waxes and other fusible raw materials can be processed as melts, melt emulsions or melt suspensions to produce granulates.

Many raw materials must first be converted into a suitable liquid, sprayable form: in our facilities we can mix, disperse, emulsify, heat, cool and, where appropriate, neutralise, or carry out simple chemical conversion reactions immediately before spraying. (Genthin site)

Process Technology: Spray Granulation

The liquid containing the solid substance (dissolved, emulsified or suspended) is sprayed through two-component nozzles as minute droplets with a diameter of around 20 – 50 µm into the warm/hot air flow in the fluidised bed unit. As a result of the large specific surface area of the droplets, the direct and intensive heat exchange dries them instantaneously. The initial effect here is, as in pure spray drying, to produce very small dry particles (seeds), which are held in suspension in the fluid bed (fluidisation) and form surfaces for further continuously atomised droplets to dry on. Thus, in the fluid bed spray granulation process, drying takes place coupled with the controllable growth of discrete particles. The dust-free granulate so formed can be continuously removed from the drying chamber through a classifying discharge without interrupting the drying process; this offers a flexible choice of particle sizes between 200 µm and 5,000 µm. The accompanying schematic illustrations show the principle of fluidised-bed technology, and how spray granulation develops over time.

This special type of granulation has decisive advantages! Depending on the physical properties of the precursor substances or solutions, and on the process and drying parameters, granules can be produced with specific particle morphologies (onion-skin and blackberry structures) with different properties and particle characteristics.

A variant of spray granulation is spray freezing. Here the melt, which contains the solids in molten form, as a melt emulsion, or a melt suspension, is sprayed into the fluid bed unit. The solidification of solid particles is achieved by the melt droplets losing heat to cold air in the fluid bed.

Product characteristics of spray granulation

  • Improved dissolution and redispersibility of the granules in water
  • Free-flowing, non-dusty particles
  • Easily dosable granulate, which is easy to work with
  • Defined particle size distribution
  • Granulate suitable for tablet pressing (direct compression)
  • Dense surface structure
  • Reduced wear
  • Reduced hygroscopicity