Break

In flowing granular systems, such as conveying lines, fluidized beds, and hoppers, particles are subjected to different stresses which eventually lead to abrasion, or loss of small surface asperities. Abrasion impacts several key aspects of industrial operation, performance, and design, and often leads to environmental problems and the loss of valuable particle mass. In this study, particle abrasion is examined for three materials (pumice, bauxite, and FCC) in two different flowing granular systems. The first system is a FT4 shear cell in which the effects of increasing concentration of fines, as the particle abrades, and normal force are probed. When a normal force is applied at a constant shear rate, the generation of fines grows exponentially with time. However, if the fines in the shear cell are periodically removed, the abrasion rate is linear, indicating a cushioning effect of the fine particles on abrasion. The second system is a single-pass impact system in which a gas jet laden with particles impacts a flat plate, keeping the total solids loading for each pass constant. Single-pass systems allow for better assessment of the effect of fines, as the fines impact the plate the same number of times as the coarse material. In this system, the effect of fines concentration, gas velocity, particle size, and solids loading are investigated. Particle size distributions and microscopic images of the particles before and after abrasion, and high-speed video of particles in the near wall region, are also obtained. To isolate the effect of fines on particle abrasion, fine particles (under 44µm) are periodically removed after a given number of passes. Particle abrasion, as opposed to particle breakage, occurs below a critical gas velocity, and, without fines removal, the abrasion rate decreases as the number of passes increases.