(222h) Dry Impregnation of Porous Particles with Different Levels of Cohesion in a Rotating Drum

In many industrial applications, such as the impregnation of granular materials, the behavior of particles is strongly influenced by their interactions with surfaces and other particles. In a rotating drum, particles often adhere to the walls as they absorb water, and this adherence can persist even when the particles are dry. This cohesion between particles and between particles and the vessel wall can have significant effects on the efficiency and uniformity of the impregnation process. The goal of this research is to investigate the role of cohesion in the impregnation of granular materials, which is particularly important for small support particles and powders under 100 microns in size. Cohesion is an often-overlooked factor in many impregnation systems, yet it plays a crucial role in dictating how particles behave within the system, especially in scenarios involving fine particles. Understanding how this cohesion impacts the overall process is essential for improving the design and performance of impregnation systems.

This study explores how particle cohesion influences the impregnation dynamics of granular materials in rotary drums by examining the effects of key parameters: surface energy and particle size. The surface energy governs particle adhesion both to other particles and to the drum walls, while particle size strongly influences how cohesion manifests in the system. These parameters help explain how cohesion affects the flow behavior and ultimately the water distribution within the particle bed. The Bond number is used to quantify cohesion, representing the ratio of adhesive forces to gravitational forces. Specifically, we focus on particle-to-particle cohesion (
$Bo_p$

) and particle-to-wall adhesion (
$Bo_w$

). When
$Bo \ll 1$

, surface tension dominates; when
$Bo \gg 1$

, gravity dominates; and when
$Bo \approx 1$

, both forces are comparable. This characterization is particularly important in processes involving small particles or droplets.

We performed a systematic study varying
$Bo_w$

to represent low, medium, and high adhesion with the wall, and
$Bo_p$

Bop for different cohesion levels between particles. We considered five Bond number values—0, 4, 12, 20, and 32—for both wall adhesion and particle cohesion. Simulations were carried out for particle sizes of 6 mm and 10 mm at a fixed pore volume of 0.6 cm³/g, fill level of 30%, and flow rate of 3.45 L/h in a 20 cm diameter drum. The results show that small adhesion to the wall has minimal impact on RSD for larger particles, even with strong interparticle cohesion. However, for smaller particles (6 mm), even low wall adhesion significantly increases RSD, indicating that small particles are more sensitive to cohesion effects. Moreover, higher cohesion between particles consistently leads to poorer RSD and slower impregnation.

Previous studies in bladed mixers demonstrated that particle systems with similar Bond numbers tend to mix in similar ways. We tested whether this principle applies to impregnation by performing simulations for particle diameters of 2 mm, 4 mm, 6 mm, and 10 mm, all at fixed
$Bo_p = 5$

along with other cohesion levels. We found that increasing particle-particle cohesion extends the time needed to reach uniformity, as higher cohesion slows water distribution throughout the bed. In contrast, increasing wall adhesion shortens the uniformity time by facilitating water transfer and reducing RSD. In cases with no adhesion to the wall and low interparticle cohesion (
$Bo_w = 0$

,
$Bo_p < 4$

, the system behaves similarly to one without cohesion, with RSD converging rapidly.

Interestingly, even when RSD values are similar, the underlying dynamics of the impregnation process differ markedly. Systems with small particles and low cohesion can show the same RSD as those with large particles and strong cohesion, but they reach uniformity through very different paths. This implies that using Bond number alone to predict behavior may not capture the full complexity of impregnation dynamics, particularly at higher cohesion levels. We also observed that particles with the same surface energy (
$γ_p = 0.2$

γp =0.2) may exhibit similar impregnation performance, though further studies are needed to confirm this trend.

Despite cases of similar RSD or similar impregnation time, the trajectory taken to reach uniformity—the actual dynamics of how water is distributed—is not the same. The kinetic pathways depend strongly on both particle size and cohesion levels. These findings suggest that optimizing impregnation systems requires not only matching bulk parameters like Bond number, but also understanding how these parameters interact with particle properties to influence dynamic behavior. In summary, the effective behavior of cohesive particles in an impregnation system is shaped by their adhesion forces, and while similar Bond numbers may lead to similar final outcomes, the dynamics can differ significantly depending on particle size and cohesion, with important implications for the design and scale-up of industrial processes.