Issue link: https://www.e-digitaleditions.com/i/1325722
28 / January 2021 powderbulk.com PBE AGGLOMERATION ADVISOR Using agglomeration to prevent agglomeration Greg Mehos, president Greg Mehos & Associates I frequently work on powder and bulk solids projects where the objective is to prevent the mate- rial from agglomerating or caking, which is what happens when pow- ders become cohesive due to being stored at rest for a period of time. Caking (unwanted agglomeration) can lead to misperceptions of mate- rial quality, customer dissatisfaction, and loss of sales. While this may sound counterintuitive, I often rec- ommend intentional agglomeration via particle size expansion to pre- vent unintentional agglomeration. Why agglomeration happens First, it's important to understand why unwanted agglomeration takes place. Caking results when the magnitude of interparticle adhesive forces — the tendency for particles to bond with each other — increases over time. The adhesive forces between particles are pri- marily polar interactions, van der Waals forces, and forces associated with liquid bridges (when moisture is present). Polar interactions (when a polar molecule's partially negative sec- tion and a polar molecule's partially positive section are attracted to each other) and van der Waals forces (the interparticle adhesive forces arising from the polar molecules' dipole moments) are both propor- tional to particle size. This means that as particle size increases, so does the strength of the polar inter- actions and van der Waals forces (the interparticle adhesive forces). The likelihood of caking, however, generally decreases when particle size increases due to the decrease in the powder's overall cohesive strength. This is why particle size enlargement is often used to reduce the likelihood of unwanted powder agglomeration. How particle size affects agglomeration To understand the effect of parti- cle size on powder agglomeration, consider the experiment illustrated in Figure 1. This figure shows a tensile strength (the maximum FIGURE 1 Tensile strength experiment A d σ T F H • Lean, dense phase, plug-flow conveying of powders & small particles • Gentle - segregation & damage free • Conveying rates up to 10,000 lbs/hr • Safe, explosion free • Quiet, hygienic, reliable • No tools assembly Simply the best vacuum conveyor 609-265-0101 www.volkmannUSA.com PUT US TO THE TEST