FCC "Downer" Pilot Plant at KFUPM: A First Experience

The High-Severity FCC (HS-FCC) is a novel process that combines short contact time, downer reactor, and high temperature to increase production of light olefins while keeping the gasoline yield fairly unchanged. In a joint project, KFUPM and JCCP demonstrated that HS-FCC reduced dry gas formation and coke yields as a result of increasing gasoline yield. The light olefins in downer configuration were lower than the same from riser, mainly due to the reduced overcracking of gasoline. The overcracking of gasoline resulted in more LPG (containing some light olefins) and dry gas. The yield of 1,3 butadiene, a product due to thermal cracking only, decreased as conversion increased (when C/O was increased). Increased C/O increased the contribution of catalytic cracking over thermal cracking. A low activity base catalyst with low hydrogen transfer activity was the most suitable with ZSM-5 additive to maximize light olefins. With paraffinic crude based virgin VGO, propylene yield of 25 wt % and total butylenes yield of 19.5 wt % was obtained under HS-FCC conditions.