(362d) Developing a Cohesive Model to Describe Channeling in Fluidized Behavior

Fluidization is an important unit operation critical to drying processes, catalyst cracking processes, and coating processes.  In many instances fluidization of cohesive materials is difficult to obtain and control.  Models have been developed in an attempt to introduce cohesive effects into fluidization models, but these have been largely semi-empirical in nature.    This paper describes a more fundamental approach; it uses a limiting state analysis similar to the limiting state rathole analysis used by Jenike to describe the stability of channels where gas pressure gradients and cohesive flow properties control the stability of channels.  The methodology sets allowable size ranges on the channels based on measureable cohesive effects.  The cohesive effects are measured at very low solids consolidation stress values, comparable to those expected in fluid bed operation.  These cohesive measurements are conducted utilizing a new tester that measures the bulk strength of powder material at consolidation stresses as low as 30 Pa.  An energy minimization principle is applied to gas flow through channeling bulk samples to determine the size, number, and spacing of channels in the material as a function of total gas flow.   Fluidization data using typical FCC catalyst material, coupled with strength data measured with this new tester, is presented to validate the cohesive model describing channeling behavior.   It is expected that this new model will find applicability in fluidization unit operations as well as prediction of de-aeration times for cohesive material in processes where gas is injected to induce flow.