A Three-dimensional CFD Study on Multiphase Flow in an FCC Regenerator Integrated with Oxy-combustion

Abstract

A vital process for converting heavy petroleum productions is Fluid Catalytic Cracking (FCC). As a major source of CO 2 emissions, the regenerator reactor in the FCC unit accounts for about 20-35% of the refinery's total emissions. A common method for reducing CO 2 emissions from the FCC regenerator is oxy-combustion, which has different advantages with regard to reducing energy penalties and associated costs. In this study, a computational fluid dynamic (CFD) study was used to examine the hydrodynamic characteristics of solid particles and gas inside the FCC regenerator, allowing CO 2 to be captured more efficiently. Utilizing Ansys Fluent platform, the Eulerian-Eulerian model was applied with granular flow kinetic theory. In the simulations, different mesh sizes were tested, and the hydrodynamics of the oxy-combustion regenerator were evaluated by adjusting CO 2 flow rates to achieve similar fluidization behaviors. The CFD results indicated that the conventional drag model accurately predicted the density phases within the bed. In oxy-combustion, CO 2 , due to its density, naturally creates a smaller dense phase compared to air-combustion. Moreover, optimizing the fluidizing gas velocities resulted in enhanced particle mixing, resulting in a distributed flow with vortices within the dense phases due to a reduction in gas velocity. To improve the environmental performance of the FCC unit, this research provides valuable insight into the hydrodynamics of solid catalysts used in the oxy-combustion process.