(577d) Is Mass Flow Always the Solution to Segregation Problems in Processes Equipment

Literature is full of claims that achieving simple mass flow in a process is the means of segregation control.  This paper examines that claim.  Segregation is a mechanistic behavior.  A particular mechanism will induce a characteristic segregation pattern.  For example, sifting will generally produce a radial segregation pattern with the finer components at the top of pile.  However, sifting can sometimes produce top to bottom segregation patterns resulting from external forces causing inter-particle motion.  Entrainment of fines will cause the fines carried by air currents to deposit close to the container wall.  Fluidization segregation results in top to bottom segregation patterns.  Can mass flow be used to solve all these segregation issues, or is something more required besides just flow along the walls to solve segregation?  This paper examines the influence of “mass flow” velocity profiles on the segregation of materials exiting a piece of process equipment.   The analysis will show that the solution to a segregation issue in a process is not by achieving mass flow, but rather to attaining velocity control.  The velocity in process equipment must match the segregation pattern and mechanism to be an effective control.  We have examined the effect of theoretical velocity profiles on measured segregation patterns of key materials.  These segregation patterns were superimposed onto the geometry of the process vessels and the computed velocity profiles were used to determine the concentration of key components leaving the system as a function of time.  These results were compared to actual experimental results showing good agreement with the theoretical models.  There is a relationship between the velocity profile in the process equipment and the degree of segregation leaving the system.  Thus, it is velocity control and not simple mass flow that really controls segregation in process vessels.