Hydrodynamic study of fluid catalytic cracker unit stripper

Abstract

This paper reports a three-dimensional (3D) computational fluid dynamics (CFD) simulation of a laboratory scale fluid catalytic cracking unit (FCCU) stripper. Solid holdup and solid mixing were studied in a geometrically and dynamically scaled down cold model FCCU stripper fitted with disk and donut baffles. The solid holdup was measured using a gamma-ray densitometry technique with a 3 micro-Ci strength 137Cs radioactive source. Measurements were taken at different axial levels, for different chordal positions. An Eulerian-Eulerian approach was used to simulate the gas-solid flow in the stripper column. The CFD simulations predicted asymmetric solid holdup profiles emphasizing the importance of 3D simulations. The CFD model predictions matched well with the solid holdup data from experiments. The CFD model also clearly predicted the recirculation and dead zones as noticed in the experimental analysis. Local defluidization zones were also noticed near the donut baffle wall regions. The particle axial velocity was low near the baffle walls, indicating that the particles slide down on the baffle walls. The radial and axial variations of solid holdup are discussed in this work, giving new knowledge in the complex countercurrent operation. This work is first of its kind to report detailed 3D study on the hydrodynamics of stripper operation both in cold flow and in the CFD model.