Computational Particle Fluid Dynamics Modeling Of Particles Mixing In FCC Pre-mixer

Fluid Catalytic Cracking(FCC)technology plays a crucial role in China's oil refining industry and contributes a lot to the economic benefits of petrochemical enterprises.With the raw oil becoming increasingly heavy and poor in quality,researchers have paid much attention on how to make full use of oil resources to improve the yield of light products.Under this trend,SINOPEC Research Institute of Petroleum Processing(RIPP)develops the MIP-DCR technology on the basis of the MIP process,aiming to reduce the yield of dry gas and coke for the FCC process.The notable feature of this technology is the introduction of the pre-mixer.Part of the hot regenerated catalysts are cooled down in an external heat remover and mixed well with the other part of the hot regenerated catalysts in the pre-mixer before they are fed into the riser.This technology has achieved the operation condition of low temperature contact between the raw oil and the catalyst and large catalyst-oil ratio.Since many large domestic petrochemical enterprises have introduced this technology,it becomes increasingly important to explore the flow and heat transfer behaviors and to obtain deep analysis of particle mixing between the hot and the cold catalysts in the pre-mixer in order to guide industrial applications of MIP-DCR technology.First,a Computational Particle Fluid Dynamics(CPFD)model of gas-solid flow for the bubbling bed containing Geldart A particles was developed.The influence of the drag force model,the mesh size,the number of particle packing and the wall boundary conditions were investigated.The feasibility of using modified Gibilaro drag correlation to correct the traditional drag force model for FCC particles was confirmed and reasonable model parameters were chosen based on the experimental data.With the above developed model,the CPFD model of FCC pre-mixer was further established.A detailed analysis of mixing process between the cold and the hot catalysts in the pre-mixer was performed by studying the gas-solid flow characteristics,heat transfer and particle mixing behaviors.It was found that the rise and break of bubbles in the pre-mixer promoted the axial and radial mixing between the cold and the hot catalyst.Compared to the catalyst particles in the near wall region and in the transition region,the particles in the central region were better mixed with the assistance of large amounts of bubbles generated.From the perspective of overall mixing effect,it is more difficult to achieve a well-mixed result for solid temperature than for solid concentration.Finally,the impact of the gas velocity,the ratio of the cold catalyst to the hot catalyst,the solids inventory and the particle size distribution on the degree of particle mixing were investigated.The modeling results showed that higher gas velocity,smaller ratio of the cold catalyst to the hot catalyst,lesser solids inventory and wider particle size distribution could enhance the effectiveness of particles mixing.The greater difference between the times required for uniform mixing state on concentration and temperature achieved at larger ratio of the cold catalyst to the hot catalyst and lower gas velocity.For large solids inventory,the decrease of gas velocity could bring more negative effects for particle mixing.