Simulation And Structure Optimization Of Catalytic Cracking Risers Based On Single Particulate Reaction Kinetics

The riser reactor is widely used in heavy oil catalytic cracking processes,and the internal catalytic reaction and flow process have an important impact on process performance.In this paper,the computational fluid dynamics(CFD)method was used to study the reaction characteristics of single catalyst particles in riser,combined with the 12 lumped reaction kinetics models.The kinetics of coupled catalyst deactivation was studied to simulate the catalytic reaction flow process in an industrial riser reactor,and influence of reactor structure on catalytic cracking performance was analyzed.The main contents of the paper are as follows:1.The reaction process in a single catalyst particle was simulated based on the porous medium model,and the effect of gas-solid relative speed,particle size,and environmental atmosphere on the component distribution and reaction rates in the catalyst particle were investigated.The results showed that the closer to the center,the higher the olefin content,while the the distribution law of the raw material is just the opposite;the raction rate of coke and olefins are increased as the gas-solid relative speed is increased;the reaction rate of coke and olefins are reduced as the diameter of the catalyst particles.That is,high gas-solid relative velocity and small catalyst particle size are beneficial to olefin formation.The reaction rate of the catalyst particles in the lower portion of the riser is higher than the upper space.2.A integrated model containing Euler-Euler multiphase flow model,12 lump kinetic model and catalyst inactivation kinetic model was used to simulate multiphase catalytic reaction flow in industrial scale catalytic cracking riser reactor,and compared with industrial data.The effects of operation parameters on the performance of the riser were investigated.The simulation results of the outlet gas composition were coincident with the industrial data,which verifies the reliability of the model.The catalyst is enriched near the riser wall,which is beneficial to the catalytic cracking reaction.With the increase of operating load,the conversion of heavy oil and the yield of olefins decrease the yields of diesel and gasoline increase first and then decrease,while the yield of coke has little impact.The higher the CTO,the higher the mass fraction of propylene and butene,and the lower the mass fraction of diesel and coke;The asphaltene content in the raw material has little effect on the product;With the increase of steam flow rate,the mass fraction of coke and olefin decreases,while the mass fraction of diesel and gasoline increases.3.The structure optimization of riser reactor was carried out,and the effects of the diameter ratio,position,length and structure of the expanding section on the performance of reactor were analyzed.The results show that with the increase of the diameter ratio(D/d)of the expanding section,the conversion of feedstock and the yield of olefin first increase and then decrease,while the yields of diesel,gasoline and coke first decrease and then increase.The optimum expanding ratio(D/d)is about 2;With the increase of the height of the expanding section,the conversion of feedstock and olefin yield decrease,while the yields of diesel,gasoline and coke increase.With the increase of the expanding length,the conversion of feedstock and the yields of olefins and coke increase,while the yields of diesel and gasoline decrease.The structure of the gradual expansion catalytic cracking reactor is more favorable for the formation of olefins.