Downer‐to‐Riser Coupling Technique for Petroleum Refining

Many recent developments in the fluid catalytic cracking (FCC) technique have focused on achieving cleaner gasoline with less olefins and maximizing light olefins such as propylene. A coupled high-density downer-to-riser reactor was proposed to utilize the advantages of both downer and riser to improve the gasoline quality and to efficiently control the product distribution. The basic idea is to decompose the complex FCC reactions into two reaction zones with distinct operating conditions. The downer accommodates high-severity operation at the initial stage with the benefit of near plug-flow while the riser is operated at a lower temperature with longer contacting time to promote hydrogen shift reactions. A comprehensive 2D reactor model is presented to predict the reactor performances for different reactor designs. The coupled downer-to-riser reactor design was found to have more light olefins and cleaner gasoline than the conventional riser and the coupled riser-to-riser reactor design.