Refiners increasing shale crude and LTO processing are initiating “mid-course” corrections, such as shutting down the crude vacuum unit due to lack of heavy ends in those streams, resulting in VGO deficits for conversion in the FCCU. According to information provided by Gary Hawkins, Senior Refining Consultant, Emerson Process Management – Refining Industry Solutions Group, firstname.lastname@example.org, he explained that refiners primarily processing LTO can shut down the vacuum unit, as previously noted, and send the atmospherhic gas oil (AGO) and atmospheric residuum from the crude unit to the FCC (to compensate for the VGO deficit). “For mid-course corrections, the objective should be targeted towards obtaining consistent feed properties (API gravity, H2S removal without excess amine scavengers used, and solids removal),” noted Hawkins.
Hawkins was also queried how the yield shift toward production and exportation of specialized products, such as Euro-5 diesel and polymer grade propylene (PGP) affect refiner’s selection of certain shale-based resources, he noted, “refiners are always on the lookout to create and sell the highest margin products, and minimize production of lower valued products [i.e., Bunker C fuel].” Hawkins also noted the value for petrochemical producers, noting that “in the U.S., the current economics favor converting ethane to ethylene, as ethane from shale gas has softened ethane prices. Naphtha feed is more expensive than ethane, but it gives petrochemical producers a wide variety of co-product options, whereas ethane crackers are essentially limited to ethylene production.” He also pointed out that propylene shortages and changing economics may influence the use of naphtha crackers — and potentially the refinery FCC product slate priority towards petrochemicals rather than fuels.
Regardless of the plant-specific (case-by-case) challenges with unconventional crude blends, by 2020 LTO volumes are expected to increase to more than half of total crude processed by U.S. Gulf Coast refiners, predicating the de-bottlenecking of the light-ends sections of their distillation assets, including adding new distillation capacity particularly suited to LTO processing. According to Hawkins, one solution to these distillation system bottlenecks is to obtain bigger pumps, while adding distillation column capacity is another potential solution. Hawkins said, “perhaps retrofitting internals with higher capacity trays can be part of the solution. If the refinery wants to run with the same or more barrel per day capacity going through the crude pumps, then they need to consider that “de-bottlenecking” can be a considerable expense – not just to the top of the crude column but the downstream hydroprocessing units as well. One refiner is considering a separate crude unit specifically designed for 100% LTO to avoid crude blending incompatibilities and typical bottlenecks (as expected) on older units designed for medium-heavy crude slates.”
Hawkins also noted that if the crude feed continues to be light(er), then the energy balance around the pre-heat exchangers will not be sufficient to accommodate the expected throughput. “However, there may be consideration to operate the crude fractionator bottoms colder since there is less bottoms component. In addition, the top of the crude fractionator could get bottlenecked enough to limit refinery-wide throughput, whereas bottoms production is not sufficient to economically operate bottom of the barrel processing units like a delayed coker,” noted Hawkins.