Past experiences of commercial FCC units indicate that hydrodynamics have a pronounced effect on the riser performance. For example, an increase of lift steam velocity has been shown to result in increased gasoline selectivity in many units. For a large FCC unit in Asia the installation of dual-radii feed distributors improved feed-catalyst contacting in the lower riser and also led to better gasoline yields.
A study of FCC riser hydrodynamics was undertaken to understand the phenomena observed in the field. It encompassed computational fluid dynamics (CFD), cold flow modeling, radioactive tracer studies, kinetic modeling and yield estimation. The ultimate goal of the study was to isolate the effects of riser diameter, lift steam velocity, and solids flux on the hydrodynamic behavior and yield performance of FCC risers.
Our CFD approach was successfully validated by cold flow results and applied to several commercial FCC units. The general trends of riser hydrodynamics were identified as follows. Lower vapor velocity, larger riser diameter and higher solids flux through the riser all contribute to hydrodynamic “pathologies”, such as catalyst downflow at the wall and vapor channeling through the core of the riser. In practice, these “non-idealities” lead to “under-conversion” of feed in the core of the riser and overcracking of products in the annulus of the riser.
Would you like to access this content?
No problem. You just have to complete the following steps.
You have completed 0 of 2 steps.
You must be logged in to view this content. Log in now.
Purchase Technical Presentation
You must purchase this technical presentation using one of the options below.
If you already purchased this content recently, please click here to refresh the system's record of ownerships.
|Credits||0.5 Use credits|
|List Price||$25.00 Buy now|
|AIChE Members||$15.00 Buy now|
|AIChE Fuels and Petrochemicals Division Members||Free Free access|
|AIChE Undergraduate Student Members||Free Free access|
|AIChE Graduate Student Members||Free Free access|