Effect of thermolysis on resid droplet vaporization in fluid catalytic cracking

Abstract

Heavy feed cracking is certain to play an increasingly important role in oil refining. Against this backdrop, this work aims to gain some understanding of how thermolysis affects the manner in which a heavy Arabian vacuum resid droplet vaporizes in fluid catalytic cracking (FCC). Specifically, we study the vaporization history of the droplet under two limiting conditions that bracket the actual vaporization process. One is a high-temperature environment in which the catalyst heats up only the resid droplet. Another is a low-temperature environment in which the catalyst vaporizes a gas oil before heating the resid droplet. Key findings are as follows: (1) Droplet life can go through one, two, or three stages, depending on the drop size and environment. A large droplet in the high-temperature environment goes through the heat-up, thermolysis and evaporation stages. A small droplet at low temperatures goes through only the heat-up stage. (2) The effect of thermolysis increases with temperature and the initial drop size. (3) Thermolysis can significantly lower the drop’s steady-state temperature—the larger the drop, the greater the effect and, hence, the longer the drop lifetime and (4). During the evaporation stage, the drop’s surface area decrease can be approximated by the classical D 2-law.