The influence of air counter-flow through powder materials as a means of reducing cohesive flow problems

The cohesive behavior of aerated solids controls fluidization behavior of bulk materials. Very cohesive materials cannot be easily fluidized. However, aeration is often used in contact bed situations to help maintain some cohesive materials in flowable conditions. The cohesive properties of aerated materials are not well understood. This paper presents a new test method to measure the effect of aeration on cohesive flow properties. These measurements could be used along with new design equations to predict arching and stable rathole formation of cohesive materials in aerated process equipment. Experimental results on fine silica powder and fluid catalytic cracking (FCC) catalyst show the evolution of the yield locus shape and the effective yield locus shape as a function of the degree of aeration. It was found that both the cohesion intercept and the yield locus slope are functions of the degree of aeration.