(114a) Role of Aeration with Standpipe Flow
AIChE Annual Meeting
2012
2012 AIChE Annual Meeting
Particle Technology Forum
Special Session to Celebrate Tom O'Brien's Career Long Accomplishments II
Monday, October 29, 2012 - 12:30pm to 12:55pm
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.
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