MODELING AND SIMULATION OF FLUID CATALYTIC CRACKING UNIT

Abstract

In the present work, a new approach of kinetic scheme for the FCC riser is introduced which considers cracking of one lump (pseudo component) giving two other lumps in one single reaction step. The proposed model falls under the category of models in which lumps are formed on the basis of boiling point. In this approach, each individual lump is considered as a pure component with known physico-chemical properties. This scheme facilitates the consideration of cracking reactions’ stoichiometry. Since a new cracking reaction mechanism is introduced, a new semi empirical approach based on normal probability distribution is developed to estimate the cracking reactions’ rate constants. This approach makes the kinetic model more versatile. Six tunable parameters have been introduced to adjust more than ten thousand reaction rate constants needed to explain complete reaction mechanism in a typical FCC riser reactor. The model also incorporates two phase flow and catalyst deactivation. The various products’ yields, catalyst activity, and riser temperature are predicted all along the riser height. Plant data reported in the literature is used for the validation of the developed model. A sensitivity analysis of the proposed tuning parameters is done which suggested that the products’ yields were insensitive to one tuning parameter out of the proposed six tuning parameters. Also, the value obtained for one of the tuning parameter out of the proposed six tuning parameters was zero. These two tuning parameters were than dropped for the subsequent case studies for the simulation of the riser reactor and FCC unit. A regenerator model adopted from the literature is integrated with the proposed riser model to simulate the entire FCC unit. The steady state simulation of the FCC unit is then done to study the effect of operating parameters on the performance of this unit.