Rama Rao Marri - CB&I
Global propylene demand is projected to increase at a much higher rate compared with the gasoline demand increase. The cheap gas feed stock option to ethylene crackers also increase the difference between supply and demand for propylene. In certain parts of the world, gasoline demand is projected to decline or be flat. This shift in the marketplace has resulted in the lowering of throughput or idling of some FCC units.
In United States, the refineries processing Shale Oil/ Tight Oils result in lower octane components to gasoline pool due to paraffinic nature of gasoline from these crude sources. Therefore, it is important to produce incremental alky feed from FCC unit that helps in effective utilization of existing alky units and maximizing refinery gasoline pool volumes or provide flexibility for gasoline blending options. Thus, reorienting or using the idle or spare Fluid Catalytic Cracking (FCC) unit capacity available due to either lower gasoline demand or naphtha streams with lower octane can be used to produce propylene and improve gasoline blending capabilities. This paper examines maximizing propylene yield and alky feed from existing FCC units under various throughput and yield scenarios.
All presented scenarios can be implemented with relatively low cost modifications and/or technology upgrades to the reaction section, without modifications to any major equipment in the product recovery section, commonly known as Vapor Recovery/Gas Concentration Unit (VRU). This excess capacity can be used to make propylene and additional alky feed, thereby improving refinery margins and adding to the supply of propylene in the market.
Operating the existing FCC at lower throughput and with low cost technology upgrades, along with optimization of the catalyst formulation and operating conditions will boost the propylene production as well as alky feed significantly with minimal investment. Existing FCC units are “paid-off” assets, and the price premium commanded by propylene compared with other products may be enough incentive for refiners worldwide to consider operating FCC units in propylene mode as described in this paper.
In addition, incremental alky feed helps in maximizing refinery gasoline pool blending options especially in refineries processing Shale Oil/ Tight Oils that otherwise result in lower octane gasoline.