Development of a Two‐Fluid Hydrodynamic Model for a Riser Reactor

Abstract

ANSYS Fluent is used to examine the mixing of catalyst zeolite particles with petroleum feedstock and water vapor in a fluid catalytic cracking (FCC) riser. A two-fluid model is developed for tracking catalyst particles and gas mixture in a riser, modeling the granular and gaseous phases as two interpenetrating continua. The hydrodynamic flows are analyzed with the aim to single out the principal physical effects that determine the distribution of particles. The results are compared with a study that is based on a non-isothermal reactive model. It is demonstrated that the simplistic purely hydrodynamic model generates similar flow fields. The developed model is valuable for improvements of modern FCC risers. The model is applied for understanding the hydrodynamics of an S-200 KT-1/1 industrial unit.

Simple Model of an Industrial Catalytic Cracking Riser Reactor

“…Much stronger fluidization is achieved by the feedstock injection, which is so intensive that the catalyst fraction decreases to 0.05–0.03 in the upper zones of the reactor. The reported changes in the volume fractions well agree with the results of other numerical studies, e.g., with the results reported by Lee et al Also, as noted in the study by Vorobev et al, these flow fields are solely defined by the hydrodynamic model, and chemistry adds very minor differences to these results.…”

“…We developed a two-fluid model for tracking of nonisothermal reactive mixing of solid and gas phases in an industrial riser. The work extends our earlier study, 26 in which we reported the results of hydrodynamic modeling of a nonreactive isothermal We conduct nonsteady numerical simulations showing that, if input or operation parameters of the reactor are altered, it takes about 1 min for a new steady-state operation mode to be reached. The major attention in our work is given to the details of the steady-state (normal) operation of the reactor.…”

“…In the study by Vorobev et al, we found that for the studied flows the gas molecular viscosity and the granular viscosity are always overpowered by the gas turbulent viscosity, μ g,t , and by the turbulent granular viscosity, μ s,t . That is why the viscous terms in eqs and are solely defined by the turbulent viscous stresses, which are given by the following equations: τ g , t = μ g , t false( normal∇ true v → normalg + false( normal∇ true v → normalg false) T false) − 2 3 false( ρ normalg k + μ normalg , normalt ( ∇ · v → g ) false) I τ s , t = μ s , t false( normal∇ true v → normals + false( normal∇ true v → normals false) T false) − 2 …”

“…In fact, in a study by Vorobev et al, 26 we found that the granular temperature always remains very low almost in the entire flow domain (see Figure 6 in work 26 ). Low (near zero) values of the granular temperature make other parameters that characterize the granular phase close to zero.…”

“…Geometry Numerical approach. For numerical computations, we employ the 3D geometry of the catalytic cracking riser developed in our earlier work 26 (see Figure 3). The dimensions of the model are summarized in Table 4.…”