(690a) Three-Dimensional Modeling of Fluid Catalytic Cracking Industrial Riser Flow and Reactions

Fluid Catalytic Cracking (FCC) is one of the most important operation in a petroleum refining industry, converting low-value heavy oils into more valuable products (like gasoline, for example). Computational simulations have been widely used to predict and analyze the dynamic behavior of this process. However, to simplify the numerical solution and reduce computational time, most of research groups assumed some hypothesis in which the final results may not represent the real process conditions. FCC is a complex process, where the gas-solid flow involves several physical and chemical phenomena. Inside the FCC reactor, fine particles are fluidized at high gas flow rates, causing particle aggregation (clustering) and gas voids unevenly distributed, characterizing the domain as a turbulent fluidized bed. The dynamic behavior of the two-phase fluidized bed has different trends in radial and axial directions, due to complex interactions between the phases. Furthermore, the catalyst is accelerated after the feed vaporization, in the inlet section of the riser. Thus the inlet zone is considered the most complex part of the reactor, where intense turbulence and flow inhomogeneities result in high temperature and concentration gradients.

Studies involving fast transport of solids are very common in literature, but there is contradictions about some aspects. Several correlations are recommended, although most of them do not unify the theory. Moreover most experiments are performed in laboratory scale, which, when extrapolated to industry scale, can lead to failure projects. The interaction between the hydrodynamics and the cracking kinetics is another characteristic a little explored. Most part of studies which use models to predict heat transfer and chemical reactions, does not emphasize the fluidodynamic development of the process, using, thereby, one-dimensional fluidodynamic models. However, experimental studies have shown that when a gas drags solid particles in a vertical riser, these are not uniformly distributed in the cross section of the reactor. Then, temperature and concentration gradients are established there, strongly affecting chemical conversion of the species involved in the catalytic cracking. Thus, it is evident the need to unify the study of these phenomena.

The present study aims, therefore, developing a three-dimensional and two-phase model, which takes into account heat transfer and chemical reactions, to predict the industrial riser FCC process. A four-lump model is proposed to represent the catalytic cracking reactions, in which the heavy oil (gasoil) is converted into gasoline and light gases hydrocarbon groups. A model to describe the undesirable catalyst deactivation by coke deposition in particle surface is considered. The fluidodynamic model is based on Eulerian description of the phases, which treats both phases as interpenetrating fluids with interfacial momentum, energy and mass transfer terms between the phases. Finally, the results obtained using the three-dimensional model were compared to those obtained with a one-dimensional model, showing the importance of hydrodynamic effects on the the kinetic cracking of petroleum.