(28e) Particle Attrition: Mechanisms and Jet Cup Attrition Method

Particle attrition can be categorized into the two mechanisms of abrasion and fragmentation. In the abrasion attrition mechanism, particles are attriting off the surface of the parent particles. The resulting size distribution of parent particles shows almost no change in cut sizes, showing only a peak of finer constituent particles under this attrition mechanism. With the fragmentation attrition mechanism, the parent particles are breaking down to intermediate cut sizes as well as generating constituent particles. This results in a shift in the size distribution of parent particles in addition to producing finer constituent particles.

Several methods are available in characterizing attrition characteristics of catalyst particles. Jet cup attrition testing is a common method for ranking of relative attrition characteristics by comparing their attrition indices. PSRI jet cup attrition testing is a two-step process. The first step in jet cup attrition testing is to identify the threshold velocity and to determine the optimum jet velocity for evaluating particle attrition. The threshold velocity represents the gas jet velocity at which the transition of the attrition mechanism from abrasion to fragmentation takes place.

It is crucial to use a more reliable jet velocity in the jet cup attrition test since abrasion type attrition tends to be the dominant source of attrition for a well-designed process of fixed fluidized beds and circulating fluidized beds. PSRI jet cup data demonstrates how to determine the mechanisms of particle attrition purely by looking at the particle size distributions, and how the sizes of parent particles shift over the extended period for each relevant mechanism.