(114a) Role of Aeration with Standpipe Flow

Standpipes provide the pressure balance in a circulating fluidized bed and thereby dictate the solid flux into the riser.  A higher pressure build in a standpipe provides the higher pressure needed to move more solids in the riser.  Thus, in today’s FCC units with Geldart Group A catalyst powder, the standpipe is most likely the bottleneck in increasing plant capacity.  Aeration can help with this pressure build, but how it helps is somewhat contentious. For small-scale standpipes, aeration appears to provide fluidization of the standpipe core, especially at high aeration rates [1].  Pressure drop is translated from shear and wall stresses to increasing the pressure build in the standpipe.  However, this may not be the mechanism for large-scale standpipes.  It seems unlikely that aeration jets can penetration deep into a one-meter diameter standpipe,  a size typically used in industry.

Several CFD models were developed using Barracuda® to understand the role of aeration in large-scale standpipes.  Modeling results suggest that jet penetration from the aeration ports does not provide sufficient aeration of the standpipe core.  Aeration appeared to be providing a “lubricating” effect for wall shear.  Hence, having more aeration around the perimeter of the standpipe may be equally important as the axial aeration position for these commercial-scale standpipes.

[1] A. Srivastava, S. Sundaresan, K. Agrawal, S. R. Karri, and T. Knowlton, “Dynamics of gas-particle flow in circulating fluidized beds,” Powder Technology, vol. 100, no. 2, pp. 173–182, 1998.