Modeling and simulation of fluid catalytic cracking unit

Abstract

Fluid catalytic cracking unit (FCCU) plays most important role in the economy of a modern refinery as it is used for value addition to the refinery products. Crude oil, as produced from the ground, contains hydrocarbons ranging from light gases and LPG to residues boiling above 343 0C (650 0F). Products of various boiling ranges can be obtained by distillation. Compared to the products demand, crude oil is short of lighter material in the boiling range of the transportation fuel (gasoline and diesel) and long on heavier material. Fluid catalytic cracking (FCC) units convert a portion of this heavy material into lighter products, chiefly gasoline and middle distillates. Because of the importance of FCCU in refining, considerable effort has been done on the modeling of this unit for better understanding and improved productivity. In last fifty years, the mathematical modeling of FCC unit have matured in many ways but the modeling continues to evolve to improve the closeness of models predictions with the real process whose hardware is ever-changing to meet the needs of petroleum refining. The FCC unit comprise of three stages: a riser reactor, a catalyst stripper, and a regenerator (along with other accessories). From modeling point of view, the riser reactor is of prime importance amongst these stages. Detailed modeling of the riser reactor is a challenging task for theoretical investigators not only due to complex hydrodynamics and the fact that there are thousands of unknown hydrocarbons in the FCC feed but also because of the involvement of different types of reactions taking place simultaneously. In the present work a new kinetic model of the riser reactor is developed using the common assumptions made by various researchers on various aspects of the riser modeling. The traditional and global approach of cracking kinetics is lumping. Mathematical models dealing with riser kinetics can be categorized into two main types.