Diffusion of feed spray in fluid catalytic cracker riser

Abstract

For fluid catalytic cracker (FCC) riser reactor, the diffusion pattern of feed spray and the flow features of catalysts in the feed injection zone were investigated in a cold-riser model that is made of 186-mm ID plexiglass pipe. In the feed injection zone, when a feed spray is introduced into the riser, a secondary flow of spray will occur. The secondary flow extends at first and then merges into the mainstream of spray. The occurrence of the secondary flow enhances the mixing of catalysts with feed. However, the extension of the secondary flow causes a violent catalyst backmixing; it is believed to be harmful to FCC reaction. The generation of the secondary flow of feed spray was theoretically analyzed by using the Kutta-Joukowski Lift Theorem. Furthermore, a FCC feed nozzle, which can control/utilize the secondary flow in riser, was proposed. The effects of the nozzle used in some commercial FCC units are quite desirable.

CFD simulation of gas–solid two-phase flow and mixing in a FCC riser with feedstock injection

“…The appearance of secondary flow is in agreement with the experimental finding of Fan et al [17]. In their work, Fan et al [17] indicated that the secondary flow in the feedstock injection zone closely relates to a transverse lift force in the riser.…”

“…In their work, Fan et al [17] indicated that the secondary flow in the feedstock injection zone closely relates to a transverse lift force in the riser. According to the Kutta-Joukowski lift theorem [21], when a steady, irrotational 2-D flow with velocity (U r ) and density (ρ) passes around a closed body with a velocity circulation (Г), the lift per unit span of the body is given by:…”

“…Indeed the back-mixing was attributed to the coupling of the wall effect and the entrainment of high-speed jets in the feedstock injection zone [14,15]. Fan et al [17] indicated when the prelifted particles shear with the high-speed feed spray, there will be a transverse force (i.e., Kutta-Joukowski lift by Anderson [21]) that makes the feed spray separated into two parts,…”

“…Aside from the atomization effects on the coke deposition that have been extensively discussed, in this study, we put emphasis on the effects of uneven oil-catalyst contacting and severe back-mixing near riser wall on the coke problem. Uneven gas/solid distribution was widely found in the vicinity of the feedstock nozzle exit in experiments [16][17][18][19][20]. Indeed the back-mixing was attributed to the coupling of the wall effect and the entrainment of high-speed jets in the feedstock injection zone [14,15].…”

Study of Feedstock Injection to Improve Catalyst Homogenization in the Riser of a FCC

“…In this respect, the works of Fan et al (2002) and Fan et al (2010) focused on the lift region and injection zone, and Gupta and Berruti (2000) and Harris et al (2003) investigated the effects of riser outlet geometry. Despite using cold-riser models, these experiments generated important data about the boundary and initial conditions, which were essential for numerical models.…”