(78a) Measuring Particle Attrition In a Jet Cup

Particle attrition is usually a detriment to product quality and process cost. It is an issue in virtually every solids processing unit operation. Thus, it is important to know how particle attrit under relevant operating conditions. Jet cup attrition test devices (such as the Davison Jet Cup) are typically used to ?infer? relative particle attrition for fluidized bed and riser operations. Jet cup attrition studies typically provide a relative comparison between two or more materials that can be used to generate a relative ranking of the material attrition indices. Ideally, the attrition rates measured in these laboratory units will provide a relative indication of how the materials will behave in the commercial unit. However, Particulate Solid Research, Inc. (PSRI) has found that a cylindrical jet cup attrition measurement may not be effective in providing accurate attrition rankings. Attrition index rankings from a cylindrical jet cup and a 12-inch (0.3-meter) diameter, pilot-plant fluidized bed unit did not correlate with each other.

Barracuda? computational fluid dynamics (CFD) simulations of a traditional cylindrical jet cup suggest that the results from a cylindrical jet cup design may not be completely accurate. CFD studies show that 30 to 50% of the particle sample will not be exposed to the solid stresses needed for accurate particle attrition measurements. This is because many of the solids are nearly stagnant, even at high jet velocities. This was subsequently confirmed with cold flow studies at PSRI in Plexiglas jet cup models. As a results, it is unlikely that relevant attrition rankings can be determined from traditional jet cup studies as a significant portion of the particle sample is not exposed to sufficient solid stresses to cause attrition. Only by insuring that the entire sample is under similar amount of stresses can attrition be accurately linked to inlet jet velocity and directly compared with different materials.

This paper discusses the development of a jet cup device that allows all of the sample particles to experience similar amounts of solids stresses. The rankings of the attrition indices from the new jet cup were found to correspond to the same rankings observed from pilot-plant attrition tests. The agreement in rankings obtained with the new cup was not observed with the traditional cylindrical jet cup.