A review of attrition of fluid cracking catalyst particles

Catalyst particles used for fluid catalytic cracking (FCC) in oil refinerie s can undergo attrition, which can contribute to the production of fines. M ost FCC units thus have fines recovery systems (e.g. multi-stage cyclones) to control the loss of fines to the environment. However it is also necessa ry to ensure that the catalyst is sufficiently attrition resistant. This pa per reviews the attrition of FCC catalysts. Catalyst particles have a varie ty of features which may be implicated in fines production - surface burrs. cracks and shells formed during the production or ageing. The level of att rition in an FCC unit is thus a function of the interactions between these features, particle properties and structure, and the hydrodynamic regimes p revailing in the unit. The latter depends on the geometry, solids concentra tion, how rates and other operating conditions, and includes the fluidized state as well as dense and lean phase hows and impact of particle flows on stationary surfaces. A number of test methods exist, which have been very u seful in tackling design issues. Bulk test methods are often designed to re produce the hydrodynamic regimes in a unit on a smaller scale, so that a re lative assessment of the attrition propensity of the particles can be made quickly. However, the analysis of the experimental data for relating the tr end to the large-scale operation or particle properties is not straightforw ard. On the other hand, single-particle impact testing provides an unambigu ous method for assessing the attrition propensity of particulate solids. Fu rthermore, it allows various mechanisms of attrition to be investigated in detail. However, the application of this method for the prediction of parti cle attrition on large-scale operations requires reliable models of the hyd rodynamics of gas-solids how for various flow regimes, a feature which has not been fully developed. Nevertheless, this has been done for one case, i. e. the analysis of attrition in jets in fluidized beds, and that is reporte d here. It is shown that the results from the bulk tests may not be easily applicable to attrition occurring in large-scale operations. The source of this discrepancy is discussed in this paper.