Authors:
Abstract: Particle attrition can be a major issue in using catalyst particles in fluidized beds and circulating fluidized beds. Particles tend to break down via two mechanisms – abrasion and fragmentation. Abrasion can be defined as constituent particles attriting off the surface of the parent particles. The resulting size distribution of parent particles shows almost no change in cut sizes under this abrasion attrition mechanism. With the fragmentation attrition mechanism, the parent particles are breaking down to intermediate cut sizes and also generating constituent particles. This results in a shift in the size distribution of parent particles in addition to producing finer constituent particles.
Several methods available in characterizing attrition characteristics of catalyst particles. Jet cup attrition testing is a common method for ranking relative particle attrition of several catalyst materials. An attrition index, calculated from jet cup data, is used to compare with one or more reference materials. However, this method is far from perfect despite its popularity. Results obtained at Particulate Solid Research, Inc. (PSRI) in different-sized jet cups and a 29-cm (11.5-in.)-diameter fluidized bed test unit did not provide the same ranking of catalyst with respect to particle attrition. To obtain a better understanding of attrition in a jet cup, both computational fluid dynamics (CFD) and cold flow studies were performed with a 2.5-cm (1-in.) diameter Davison-type jet cup and PSRI’s cylindrical 7.6-cm (3-in.) diameter jet cup. Results showed that a significant amount of material in the Davison and PSRI jet cup remained stagnant. Based on these results and additional CFD modeling, PSRI designed a new jet cup, where most of the material was hydrodynamically active. The new jet cup showed a 25% increase in attrition compared to PSRI’s cylindrical jet cup under similar conditions and run times. Results were also compared to cyclone attrition data for several materials at PSRI. The new jet cup provided data that correlated with attrition results from the 29-cm (11.5-in.)-diameter fluidized bed unit.