PREDICTION OF VELOCITY & MASS FRACTION PROFILES OF SOLID (CATALYST), LIQUID & GAS IN FLUID CATALYTIC CRACKING (FCC) RISER

Abstract

Fluid Catalytic Cracking (FCC) is an important process in oil refinery used to increase the gasoline (petrol) production from the crude oil. The bottom end heavier (long chain hydrocarbons- C12 or more) products from fractionating distillation column are fed into the riser where long chain molecules are broken into the desired product (i.e. Gasoline) in the presence of catalyst such as Alumina particles . The FCC process involves hot regenerated catalyst supplying the net heat demand required for the reaction to occur. Finely sized solid catalyst continuously circulates in a closed loop between the reaction riser column and catalyst regeneration system. The feed and Catalyst are directly contacted in the riser reactor, in a proper ratio having proper residence time and temperature to achieve the desired level of conversion. The reaction riser presents a rather complex physical scenario as it contains three phases (solid, liquid, & gas) and not less than a double figure even more number of intermediate products such as LPG, coke & others. The project will be an attempt to model the phenomenon theoretically using commercial code (e.g. ANSYS FLUENT) 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. Fluid Catalytic Cracking (FCC) is an application of fluidized bed. Fluidized beds are used in processes where gas/solid mass transfer is of importance. The cracking of heavy hydrocarbon, using particles as a catalyst, creates a suitable low-temperature environment for mass transfer. This research work a gas/solid flow with a cracking reaction in a fluidized bed. This project is designed to implement and predict the following:  Use the granular Eulerian multiphase model with species transport.  Define the rate of reaction with a pre exponential factor and activation energy.  Define the Syamlal O' Brian drag correlation with different functions using appropriate parameters.  Set boundary conditions for internal flow.  Define the fluid and solid phases.  Calculate a solution using 2D planar geometry in conjunction with the pressure-based solver  Solve a time accurate transient problem with the prediction of pressure, velocity, temperature and mass fraction profiles. The output curves demonstrate the breaking of heavy hydrocarbon in the presence of Alumina (Al2O3) catalyst. The work done in this study is organized into five chapters. The introduction of the fluid catalytic cracking (FCC) process/unit is presented in the first chapter, a literature review on the modeling and simulation of FCC unit follows in the second chapter. Chapter 3 deals with the riser model development. In the last section the riser model and regenerator model are integrated to simulate the FCC unit. Results of the riser simulation are presented and discussed in Chapter 4. Conclusions drawn from the study are summarizes in Chapter 5