HYDRODYNAMICS OF RISER UNITS AND THEIR IMPACT ON FCC OPERATION

The hydrodynamic characteristics of the riser of a FCC plant are inves tigated in a cold pilot plant. The results are checked and completed w ith measurements made in real operating FCC units. In both cases, trac ing of the gas, sampling-probes, and gamma-tomography were used, The g as and solid velocity profiles are described by using a plug-flow mode l with radial dispersion. The gas velocity profile is formally represe nted by an Ostwald-de Waele type equation. The axial solid concentrati on profile is fitted to data obtained in a commercial FCC unit. The ra dial dispersion coefficient of the gas is directly measured in the pla nt. The kinetics of the reactions occurring during catalytic cracking are investigated in a microreactor and are represented by a 19-lump mo del including deactivation by coking of the catalyst, A combination of this reaction model with the hydrodynamic model is able to predict wi th a good precision the yields of the different product; families obta ined, in an industrial FCC unit. It is checked by comparison with samp ling data in the plant, and it yields useful information on the influe nce of riser hydrodynamics on yields and products quality.