Feedstock atomization effects on FCC riser reactors selectivity

Feedstock atomization affects catalytic cracking reactions that take place in an FCC riser reactor, and is considered a critical parameter especially when processing heavy fuels. A finely atomized feed allows instantaneous fl ash vaporization and quick quenching of the catalyst, conditions that allow the feed components to be subjected to an ideal mixing temperature. Mixing conditions at the inlet of the riser reactor also affect cracking reaction s selectivity. An atomization modeling scheme has been incorporated into a CFD model devel oped by Theologos & Markatos (1993, A.I.Ch.E. Journal, 39(6), 1001.) and Th eologos, Nikou, Lygeros & Markatos (1997, A.I.Ch.E. Journal, 43(2), 486) an d has been used to evaluate atomization effects on feedstock vaporization r ates, cracking reactions initiation, reactor selectivity and overall reacto r performance. Cracking reactions are simulated using a simplified 3-lump m odel. The atomization modeling scheme takes into account the initial feed d roplet size at nozzle's exit, as well as droplet size reduction along with vaporization. Droplet vaporization parameters from the literature have been considered. To evaluate the degree of feedstock atomization effects on rea ctor performance, a parametric study is carried out considering three diffe rent initial feed droplet sizes, namely 30, 100, and 500 mu m. The area whe re feedstock vaporization takes place inside the reactor is predicted and t he evolution of atomized droplet size is illustrated. The effect of the ini tial degree of atomization on cracking reactions selectivity is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.