A numerical study of multicomponent vaporization effects in FCC riser reactors

The petroleum refining industry uses fluidized catalytic cracking (FCC) to convert heavy feed oil into lighter molecular weight, more valuable components such as olefins, gasoline, and diesel fuel. Hot catalyst particles are used for the conversion, which occurs in a riser reactor. The interphase mixing, vaporization, and chemical reactions are the controlling processes inside the FCC riser. The interactions between the feed oil spray and the gas/solid flow determine the final products of the cracking process, and ultimately the profitability of the FCC unit. The complex nature of the multiphase interactions and chemical reactions that occur in the riser reactor presents a huge challenge for analysis. Numerical simulation provides the means to facilitate and reduce the design time of new units, and also optimize existing units. A new vaporization model is incorporated into an existing three-phase reacting flow computational fluid dynamics (CFD) code developed at Argonne National Laboratory. In this study, ICRKFLO is used to simulate a low profile FCC riser. A low profile riser has a shorter residence time than standard FCC risers, and the modeling of the droplet vaporization process is of great importance. Because feed oil droplets are composed of many hydrocarbon components, each of which vaporizes at a different temperature, a new vaporization model is developed to include multicomponent vaporization of a droplet. The model allows the boiling point temperature of the droplets to vary as the vaporizing droplet loses mass to the gaseous phase. Comparison between vaporization models indicates a significant change in predicted product yields.