Authors: Knowlton T.
Particulate Solid Research, Inc. (PSRI)
Abstract: 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.