Hydrodynamics of Riser Units and Their Impact on FCC Operation

Abstract

The hydrodynamic characteristics of the riser of a FCC plant are investigated in a cold pilot plant. The results are checked and completed with measurements made in real operating FCC units. In both cases, tracing of the gas, sampling probes, and γ-tomography were used. The gas and solid velocity profiles are described by using a plug-flow model with radial dispersion. The gas velocity profile is formally represented by an Ostwald−de Waele type equation. The axial solid concentration profile is fitted to data obtained in a commercial FCC unit. The radial dispersion coefficient of the gas is directly measured in the plant. The kinetics of the reactions occurring during catalytic cracking are investigated in a microreactor and are represented by a 19-lump model including deactivation by coking of the catalyst. A combination of this reaction model with the hydrodynamic model is able to predict with a good precision the yields of the different product families obtained in an industrial FCC unit. It is checked by comparison with sampling data in the plant, and it yields useful information on the influence of riser hydrodynamics on yields and products quality.