It is quite simple: The principle of spray granulation
Spray granulation combines convective drying/solidification and particle formation in a single process step. It generates compact particles (granulates) by spraying solid-containing liquids on a fluidized or spouted bed where the solvent (normally water but also organic solvents etc. are possible) evaporates and a particle growth takes place due to the remaining solid matters.
This process is often called granulation drying or layering as it starts with a granulation seed (also known core as or nuclei) which is typically from the same material as the solid matter sprayed by the liquid phase. The granulation seeds are generated either directly in the process itself by internal seed generation such as spray drying or abrasion, or by returning fine particles or grinding of oversized granulates from the sieving-milling circuit and thus there is no need to feed them as a solid raw material.
This simple basic process principle can be influenced to a great extent, which can be used for product design. To this end, diverse technical options and process-influencing parameters can be used to achieve desired granulate properties. These are:
- For the spray liquid: its solids content, its type (solution, suspension, melt, emulsion, etc.), its viscosity or tackiness, its composition (additives, binders, etc.).
- For the design of the spray system: the spray nozzle principle (two- or multicomponent nozzles, pressure nozzles, etc.), the nozzle orientation (top or bottom spray), the position and number of nozzles, the droplet size and droplet velocity.
- For the processing conditions: the temperature of the spray liquid (and atomization medium), the temperature in the process chamber (product temperature), the intensity of the particle movement (air velocity, air distribution, etc.), residence time, temperature gradient, drying or solidification velocity.
- For the machinery: Fluidized or spouted bed, batch or continuous operation of the process, internal seed generation or sieving-milling circuit.
Encapsulating of sensitive materials from the liquid
If different raw materials and actives are mixed as a liquid and are then spray-granulated, granulates will develop, in which the components are distributed very equally. In this way, also liquids can be enclosed in a solid matrix. Sensitive substances can be well protected by this. This encapsulation process is in particular used in the feed and food- industries. If required, the spray granulates can be coated with a protective film in an additional process step.
Beyond product and process development Glatt provides all the services from the idea, project development, research, implementation up to turn-key projects including aftersales-service. This single source approach allows a very efficient project execution and the use of synergies. For example, production cost can be reduced by integrated heat recovery or connected process steps including also the liquid production.
* The author is director of the plant and engineering division at Glatt Ingenieurtechnik GmbH, Weimar.