May 5, 2010

R. Cocco, S.B.R. Karri, Y. Arrington, R. Hays, J. Findlay, T.M. Knowlton, in “Fluidization XIII” (S.D. Kim, Y. Kang, J.K. Lee, Y.C. Seo, eds.) Engineering Conferences International, Gyeong ju, Korea, p. 89.

 

Particle attrition is usually detrimental since it negatively affects product quality and process cost. Thus, it is important to know how particles attrit under relevant operating conditions.  Small jet cup attrition test devices (such as the Davison Jet Cup) are typically used to measure relative particle attrition for fluidized beds and risers. Ideally, the attrition rates measured in these laboratory units provide a relative indication of how the materials will behave in the commercial unit.  Most jet cup devices have a cylindrical configuration.  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 agree with each other.  Computational Fluid Dynamics (CFD) results show that 30 to 50% of the particle sample in a cylindrical jet cup 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 inlet jet velocities.  This was subsequently confirmed with cold flow studies at PSRI in Plexiglas™ jet cup models.  As a result, it is unlikely that relevant attrition rankings can be reliably determined from traditional jet cup studies because 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 a similar amount of stress can attrition be accurately linked to inlet jet velocity and directly compared with different materials.

 

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