%0 Journal Article %T CFD Study of Industrial FCC Risers: The Effect of Outlet Configurations on Hydrodynamics and Reactions %A Gabriela C. Lopes %A Leonardo M. Rosa %A Milton Mori %A Jos¨¦ R. Nunhez %A Waldir P. Martignoni %J International Journal of Chemical Engineering %D 2012 %I Hindawi Publishing Corporation %R 10.1155/2012/193639 %X Fluid catalytic cracking (FCC) riser reactors have complex hydrodynamics, which depend not only on operating conditions, feedstock quality, and catalyst particles characteristics, but also on the geometric configurations of the reactor. This paper presents a numerical study of the influence of different riser outlet designs on the dynamic of the flow and reactor efficiency. A three-dimensional, three-phase flow model and a four-lump kinetic scheme were used to predict the performance of the reactor. The phenomenon of vaporization of the liquid oil droplets was also analyzed. Results showed that small changes in the outlet configuration had a significant effect on the flow patterns and consequently, on the reaction yields. 1. Introduction Although commercially established for over half a century, the fluid catalytic cracking (FCC) process is still widely studied nowadays. Since it is a very profitable£¿£¿ operation, any improvement in it can result in large savings for the refinery. In the FCC process, preheated high-boiling liquid oil is injected into the riser reactor, where it is vaporized and cracked into smaller molecules by contact and mixing with the very hot catalyst particles coming from the regenerator. These phenomena cause a gas expansion, which drags the catalyst to the top of the reactor. Since catalytic cracking reactions can only occur after the vaporization of liquid feedstock, mixing of hydrocarbon droplets with catalyst must take place in the riser as soon as possible. It is known that riser reactors have complex hydrodynamics. They present a high solids concentration near the walls and are also axially divided into dense and dilute regions. In addition, different riser configurations such as the inlet and outlet structures can have a profound effect on the flow patterns mentioned above. The influence of riser exit geometry on the hydrodynamics of gas-solid circulating fluidized beds (CFB) has been investigated in many studies [1¨C6]. Although the results reported in these studies apparently conflict quantitatively concerning the influence of riser exit, some common aspects can be observed: the design of the exit has a large effect upon the reflux of solids; abrupt exits cause an increase in the solids holdup and a large backmixing at the top of the riser; increasing the refluxing effect of the exit has proved to increase the mean particle residence time; larger and denser clusters are formed at the walls in the risers with abrupt exits. In an experimental work, Lim et al. [7] investigated a cold model of a circulating fluidized bed, in a %U http://www.hindawi.com/journals/ijce/2012/193639/