Bed Segregation Model

The mechanism of segregation as observed in rotary kilns indicates that percolation is the primary cause of driving smaller size particles to the core of the bed. To model the phenomenon, several 

From a condition of uniform mixing of particles within the bed, radial segregation proceeds very rapidly and is fully implemented within 2 to 10 kiln revolutions (Rogers and Clements, 1971 Pollard and Henein, 1989). The mechanism of segregation can therefore be considered as a steady-state problem. 

The segregation process is continuous and there is a constant discharge of fines from the plug flow region into the active layer. This discharge of fines occurs in the upper part of the bed toward the apex and is followed by percolation normal to the bed surface as material is sheared in the active layer. 

The resultant segregated core, popularly known in the industry as the kidney (or tongue ) does not consist entirely of fine particles but also contains a small amount of coarse particles (i.e., there are concentration gradients even in the core). 

The bulk velocity distribution in the active layer does not change with addition of fines and the bed behavior (e.g., rolling, slumping, etc.) remains unchanged with fines (Henein, 1980). 

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