Parametric study of particles homogenization in cold-flow riser reactors

Fluid Catalytic cracking (FCC) process are frequently used for the upgrading of heavy crude oil into more valuable products. Traditionally, the FCC process occurs in a riser reactor, where both vaporised hydrocarbon feed-stock and solid catalyst flow in the direction against gravity. This kind of reactor presents heterogeneous flow distributions that affect the axial and radial flow structures, as well as the product quality. To understand the effect of operational variables over riser flow distribution, a numerical study of the two-phase cold-flow in the pre-acceleration zone of a riser reactor fed with catalyst particles used in this kind of reactors is presented in this work considering a two-dimensional model. The Computational Fluids Dynamics (CFD) software ANSYS® Fluent® is used to study two-dimensional gas (air) and solid (catalyst particle) flow in a riser section of a cold-flow Circulation Fluidized Bed (CFB) system under different flow inlet conditions (i.e., either for the gas and solid flux), as well the particle diameter size. An Eulerian-Eulerian approach, including the turbulence (κ−ε model) and the Kinetic Theory of Granular Flow (KTGF) models, are solved for the gas phase and the solid particles treated as a dispersed phase. The implemented computational model is validated by comparing numerical results for solid velocity and volume fraction distribution to values reported by peers. As expected, a higher concentration towards the axis of the reactor is obtained for the solid volume fraction values. The RNI index estimated for gas velocities of 3 m/s and 4 m/s are significantly lower than the others, indicating that as the inlet gas velocity is reduced, a more homogeneous profile is obtained. Finally, the numerical results obtained shown closer to the experimental data used for the validation as the steady-state is attained.