Numerical Simulation And Structure Optimization Of Annular Swirling Quench Box

Gasoline hydrotreating reactor is a key component of gasoline hydrotreating process and quench system is an important component of the hydrotreating reactor,so it is important to enhance the performance of quench system.Quench system comprises a quench box and quench pipes,mainly used to cool reacting gasoline by cold hydrogen.Existed quench systems present mixing insufficient problems,leading to the large temperature difference,reduced product quality and increased plant operation time.By integrating an annular quench pipe close to the outer wall of quench box,an annular swirling quench box was designed in our laboratory.In this paper,the annular swirling quench box was simulated by CFD,and the structure was further optimized.For CFD simulation,it is mostly important to select the turbulent model.And previous works usually select the turbulent model by experience without carefully considering the flow characteristics,which greatly reduced the accuracy of the simulation results.Therefore,the application scope,the advantages and disadvantages of common turbulence models were compared,optimal turbulence models for modelling the fluid flow in the annular swirling quench box were selected.The models were verified through comparison of CFD simulation results and experimental results.To better understand the mechanism of swirling mixing of reacting gasoline and hydrogen in the quench box,the distribution of fluid flow parameters such as turbulent kinetic energy,turbulent kinetic energy dissipation rate,turbulent viscosity ratio,vorticity and Kolmogorov scale at different fluid mixing degrees were studied.The results showed that the fluid turbulent kinetic energy,turbulent kinetic energy dissipation rate,turbulent viscosity ratio are proportional to the fluid turbulent intensity.Fluid turbulent intensity is greater,the mixing of materials is more uniform.The vorticity and mixing of materials are positive correlation.Under the same conditions,the fluid vorticity is greater,the mixing of materials is more uniform.Kolmogorov scale can be used as the basis to measure whether the fluid can generate eddy.Under the same conditions,the fluid flow with eddy can obtain better materials mixing than flow with no eddy.The previous design of the annular swirling quench box has shortcomings such as large occupying space and relatively complex structures.In this paper,the design of the quench box was optimized by CFD simulation,including simplify the structure of quench box by reducing the number of baffles,increasing the width of the inlet baffles,and reducing the height of the quench box.The operating flexibility of the quench box was investigated and the results showed that the operation performance of the quench box remained unchanged for processing capacity changes in the range of 50%-200%,The above work laid a reference for improving existing quench system in FCC gasoline hydrotreating reactor.