What is Powder Dispersion?
Powder dispersion is the mixing process that involves the introduction of dry material or powders into water or other liquids. A wealth of information exists on blending, solids suspension and gas dispersion, but powder dispersion is not as well understood.
The Application Challenge
Process engineers are fortunate if a solid material is “well behaved,” meaning the powders wet out and disperse readily. In this case, in-tank mixing is sufficient. However, well-behaved powders are a small percentage of applications; it’s more likely a process engineer faces “difficult” powder dispersion cases such as thickening agents like high-molecular weight hydrocolloids, cellulose gums, starches or proteins.
Two problems arise when dispersing difficult powders. First, the powders float, resisting efforts to wet or disperse them. Second, the powders clump into impenetrable sticky masses or “fish eyes” (powder lumps with a hydrated skin and dry core). Conventional in-tank mixing leads to long batch times, powder buildup and waste during tank cleanup. Traditional inline high shear rotor-stator mixers are problematic, too, due to inconsistent particle shear distribution, irreproducible results and air entrainment.
The Quadro® Solution
Inline processing addresses the issues summarized above. The answer lies in adding the powder phase into the liquid phase at some point in the piping, rather than in the process vessel itself. Direct application of powder to a process line has these advantages over in-tank mixing:
- No waiting for the wetting of floating powders
- No buildup on the tank wall, mixer shaft or baffles, which reduces cleaning time, lowers the risk of cross-contamination and eliminates powder loss
- Less air is entrained, eliminating the time required to de-aerate and/or the need to install expensive de-aerating equipment
A single-pass inline process allows not only for the controlled introduction of powders, but also for the controlled application of shear. This yields additional benefits:
- There is repeatable processing from batch to batch
- Overprocessing to eliminate lumps is eliminated, which is especially important with heat- or shear-sensitive products
- No energy is wasted on circulating multiple passes of fluid through an in-tank dispersing system
- Batch times are reduced
The Quadro Ytron® ZC Disperser is uniquely engineered to incorporate and disperse extremely difficult-to-wet powders into a liquid stream in a single pass. It intensely shears the powders prior to hydration, producing homogeneous dispersions that are completely free of lumps and “fish eyes.”
Because the powder is completely hydrated, yield is maximized and wastage is reduced or eliminated, translating into powder savings of up to 30%, compared to processing with in-tank or other inline high shear technologies. And overprocessing is entirely eliminated, preserving the rheological properties of shear-sensitive products.
Batch time reductions as high as 75% can be realized with the Quadro Ytron® ZC Disperser technology. Even with difficult products such as hydrocolloid gums, cellulose gums and carbomers, you achieve complete dispersion in a single pass.