Catalyst attrition in FCC units has been a long-standing challenge, now with renewed concern due to tightening regulation of microfine particulate emissions. Further, reducing catalyst fines can reduce operability problems elsewhere in the unit. A variety of laboratory attrition test methods have been used for predicting relative rates of catalyst attrition, and these have not always given consistent catalyst rankings. Before improvements can be made to reduce catalyst-derived emissions, the relevance of these test methods in predicting catalyst attrition should first be understood. More importantly, the attrition mechanisms for generating fines in a commercial unit must be understood. Population balance models can be used to understand the pathway of fines generation in both the FCCU and the laboratory setting. Analogous to a reaction kinetic model, this technique can be used to distinguish the relative rates of attrition via particle fracture versus abrasion. After applying the model to commercial units, it was found that attrition can occur in varying proportions of fracture and abrasion, but in most of the units analyzed abrasion was most important. The model was subsequently applied to laboratory attrition tests commonly used in the industry, including the conical jet cup designed by Particulate Solid Research, Inc (PSRI). Using a single sample of equilibrium catalyst, it was found that attrition in the different tests ranged more dramatically, from predominantly fracture to mainly abrasion-based attrition. Air jet and conical jet cup testing proved to be the most representative of the commercial operations studied to date.
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