Numerical study of a fluid catalytic cracking regenerator hydrodynamics

Abstract

Fluid catalytic cracking (FCC) is one of the most important conversion processes in petroleum refineries, and FCC regenerator is a key component of an FCC unit to recover the solid catalyst reactivity by burning off the deposited coke on the catalyst. In this paper, a three-dimensional multi-phase flow computational fluid dynamics (CFD) model was established to simulate the flow inside a commercial FCC regenerator. The two phases involved in the flow are gas phase and solid phase. The Eulerian-Eulerian approach, where the two phases are considered to be continuous and fully inter-penetrating, was employed. The effects of different drag models on the flow characteristics were firstly investigated. A modified drag force model was applied by using user define function (UDF) in ANSYS Fluent, which provides a better prediction on the solid volume fraction profile along the regenerator height. Particle clustering phenomena was taken into consideration through the adjustment of effective particle cluster diameters. The appropriate effective cluster diameters in the dense bed and the dilute phase are 300μm and 200μm, respectively. Catalyst solid volume fraction profile indicates that there are four zones in the computational domain: dense zone, sub-dense zone, dilute zone and sub-dilute zone. The developed CFD model was validated by plant data. The effect of air superficial velocity on the fluidization was also investigated and the results shown that the total flow rate of catalysts goes through the cyclone increases linearly with increasing air superficial velocity from a range of 0.6 to 1.03.