轻质油催化裂解耦合流化床反应器过渡段数值模拟OA

Light oil catalytic cracking is an important process in petrochemical industry.The new type of riser-turbulent bed-dense phase bed catalytic cracking coupled reactor can optimize the mass transfer,heat transfer performance and reaction efficiency during the catalytic cracking process.Compared with traditional reactors,the coupled reactor has higher reaction rate,better temperature control capability and longer catalyst service life,thereby improving the product selectivity and yield.Among them,the transition section of the coupled fluidized bed,as an important structure connecting the riser and the fluidized bed,has significant advantages in optimizing gas-solid flow and improving reaction efficiency.The focus of this study was to analyze the gas-solid two-phase flow characteristics in the transition section of a coupled fluidized bed.Furthermore,the orifice arrangement of the large-orifice distributor was modified to investigate its effects on the flow characteristics.Based on the Euler-Euler two-fluid model and the energy-minimization multi-scale(EMMS)drag model,numerical simulation studies were carried out for the transition section of the reactor.Through grid independence verification,combined with the reasonable selection of the specular reflection coefficient and the optimization of the viscosity model,a numerical model with good agreement with the experimental data was established.The simulation results showed that with the increase of gas velocity in the variable-diameter section,the solid holdup in the wall region increased accordingly,and the movement of particles from the central region to the wall became more intense;the main reason for the formation of backmixing was that the gas velocity in the central region was higher than the entrainment velocity.Increasing the orifice spacing near the center of the large-orifice distributor could improve the backmixing velocity of the variable-diameter section wall and the particle accumulation on the wall,while reducing the gas backmixing range.Further balancing the fluid distribution between the inner and outer layers could effectively reduce particle retention at the angle between the large-orifice distributor and the variable-diameter section wall,and significantly improve the uniformity of gas-solid two-phase distribution.