(194b) CFD Modeling and Liquid Vaporization: Industrial FCC Riser Feed Injection Application

Computational fluid dynamics (CFD) modeling has been used to simulate FCC risers for more than a decade. Riser simulation has been performed with a variety of commercial CFD tools including Barracuda Virtual Reactor.

Historically, for CFD modeling with reactions, the hydrocarbon feed to the FCC riser is assumed to be instantly vaporized, or very simple approximations are made to close the mass balance between phases. However, the liquid injection, liquid penetration, spray angle, droplet size distribution, liquid-solid contacts, vaporization and therefore gas-phase expansion are some of the important parameters that can only be captured if the feed is injected as liquid. Therefore, liquid feed injection, as opposed to injecting the feed in gas phase, is far closer to reality, and critical to typical phenomena of interest for risers.

In this work, we have used Virtual Reactor to simulate an industrial scale FCC riser for a Gulf Coast refinery. The feed is injected to the riser as discrete liquid droplets. Part of the liquid feed directly vaporizes into gas phase while some of the liquid forms a liquid film on the catalyst particles. This film, then vaporizes into gas-phase using the heat from both the gas and the particles. This mechanism is similar to that of real-life liquid feed injection and vaporization in FCC risers.

For this application, the liquid feed injection is characterized by features such as droplet size distribution, spray angle, momentum flux distribution, etc. Liquid penetration, liquid film transfer from droplets to catalyst particles and vaporization are captured with the model. Overall vaporization times obtained from the model agree with commercial riser design criteria. We also demonstrate in this work that liquid feeds, consisting of multiple components with different boiling points, show vaporization profiles agreeing with expectations for such multi-component hydrocarbon feed vaporization.