Modeling and Simulation of Cluster Formation Effects in Riser Section of Fluid Catalytic Cracking Unit

The riser reactor is a highly effective reactor for fast gas-solid reaction systems. In spite of extensive research in this area, the degree of understanding of these types of reactors is different. In this work, mathematical model for riser reactor is developed based on the conservation equations for non-isothermal riser reactor linked with hydrodynamics. The cracking reaction is described based on four lump kinetic models and the hydrodynamic is based on cluster based approaches. The advantage of this work is the model developed based on the concept of cluster formation. Resulting riser FCC models calculate flow and reaction parameters including conversion rates and product yields to determine performance. The resulting riser model is simulated using numerical method of Dormand-Prince, a member of Runge-Kutta family of ordinary differential equation (ODE) solvers, via MATLAB Environment. Simulation results of the base case riser model agree with plant data sufficiently well with majority of the data deviation lies between 1 and 5%. Simulation studies were also performed using the model to encompass the effect of inlet catalyst temperature, and catalyst-to-oil (CTO) ratio on reactor performance. The gasoline yield did not show direct relation with inlet catalyst temperature due to secondary reaction. Increasing CTO ratio increases conversion and other products. Further increase of CTO ratio beyond 10 did not increase the conversion and yield of gasoline due to increase in coking. These findings are useful to determine coking limit for CTO ratio and its cost. Finally, the effect of cluster formation on riser performance was investigated. Conversion was increased by 9% with the formation of cluster and an additional densification by 25% due to residence time of cluster increased. The reason for higher conversion may be explained by the formation of cluster which increases the residence time of catalyst inside the reactor. However, the formations of cluster had inverse effect on the production of gasoline, which drops by 5%, due to high temperature drop attained and higher residence time of catalyst. In summary, the objectives of this study, which are to develop mathematical model and build understanding on the parameters that influence the performance of riser reactor, have been achieved.