Attrition Characters Of FCC Catalyst In A Fluidized BED

Recent years, as the development of fluidization technology, fluidized beds are widely used in plenty of production fields. However, solid particles in fluidized beds are blown by gas, and collide with other particles or walls of the reactors, which generates attrition. Attrition may cause severe consequences and have become one of serious problems of fluidized beds. Therefore, it is meaningful to research particle attrition in fluidized bed.In this paper, attrition characters of Fluid Catalytic Cracking (FCC) catalysts are investigated in a laboratory-scale ASTM fluidized bed. The effects of size, hardness, elastic modulus strength, surface roughness and other surface properties on attrition characters are taken into consideration. The correlation between attrition and gas velocity is also studied and a new model of bubble-induced attrition is introduced.To investigate the correlations between attrition and particle size, the results show the attrition extents in the steady-state stage decrease as the increase of particle sizes basically. Particles of 120-160 and 160-200 μm are the best attrition-resistant. Additionally, what is proved by the method of combination introduced in this paper is that interactions among various sized particles weaken attrition slightly. Therefore, the method of combination is effective.To study the relations between particle attrition and particle properties, the results indicate that particles with high hardness, elastic modulus and strength have better attrition resistances in fluidized beds, which proves these three factors have dominant effect on attrition extents. What’s more, abrasion often happens to the particles with high surface roughness in the whole attrition process, especially in the early period. Attrition mechanisms are related to the surface properties. Fragmentation often occurs to particles which have irregular shapes or adhering particles on surfaces in the nonsteady-state stage.To discuss the correlations between particle attrition and gas velocity, the results suggest the mass of particles remaining in the bed decreases linearly as the gas velocity increases. Then, a new model of bubble-induced attrition is introduced in this paper. In addition, the critical gas velocity is about 0.00347 m/s, and is far from generating bubble-induced attrition. The contribution of grid jet attrition increases remarkably as the gas velocity grows.