Small scale tests for attrition resistance of solids in slurry systems

In many present day solids‐liquid contacting processes and slurry transport systems, the attrition rate of the solid particles is of primary technical and economic concern. Particle size degradation in a transport pipeline may make the delivered solids entirely unsatisfactory for the intended use, or separation of fines from the liquid phase and makeup of attrited solids may be so costly that an otherwise attractive process becomes unacceptable. Pilot scale tests to measure attrition in a slurry system are often costly and very time consuming. For this reason small scale tests have been developed for screening candidate systems prior to pragmatic pipe‐loop or pilot‐plant tests. Two of these test methods, crushing tests on individual particles, and annulus flow in a rotating cup apparatus, appear to give useful data on the relative attrition resistance of various solids and to provide a basis for estimating the attrition rate to be expected in a flowing system. Results obtained by using these test methods with silica gel in hexane and with molecular sieve particles in kerosene yielded some information as to the predominant mechanisms of attrition for these two types of solids. The brittle, glasslike silica gel appears to fail through impact fracture of small to medium size chips from the large particles, while attrition of molecular sieves results from surface abrasion, probably due to failure of the binder material, and yields only extremely fine products of attrition. This paper, which is based on a rather limited amount of preliminary experimentation, has been prepared in the hope that it may stimulate additional work on the development of useful standardized procedures for evaluating attrition resistance of solids.