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Nasty stuff

Heavy crudes are here to stay. As longs as oil prices remain high, Canadian, Venezuelan, Deep Water Gulf of Mexico, Mexican and other low API gravity crude oils will play an ever more important role in supplying world refineries. And prices promise to remain high because gainsayers notwithstanding, Hubbert was right.

A big question is how to handle best these nasty crudes? Do you revamp existing units or invest in new capacity? With refineries now running flat out, the balance might seem to favor grass roots expansion, but given the substantial cost multiplier over revamps, this could be questioned.

Whichever the case, however, an inescapable fact is that the process design of the project will prove crucial. Between the charge pump and the desalter and the units’ distillation columns there are many places where miscalculations in the process design could wreck the entire project.

Can you really be sure of attaining desired crude rates? Desalting viscous crude is extremely difficult. Minimizing coking or asphaltene precipitation in the heaters demands extreme care. Can you reasonably expect high diesel and HVGO recoveries, acceptable levels of nickel, vanadium, and microcarbon residue (MCR)? Refiners who cut deep should not be surprised when the HVGO product MCR is over 2 wt% and the vanadium content is in excess of 10 ppmw. Any one of such difficulties can result in lower revenue, unstable operation or even an inoperable unit. It is critical to understand that the inherent properties of these low API gravity crudes dictate that exact process design is of paramount importance.

The point of this litany of possible problems is to remind you not to skimp in the early phases of engineering. From the start of the LP work through the completion of front-end process engineering, actual product yield and product qualities depend on the process design.

The message is clear. Nasty crudes will continue to make up an increasing proportion of refineries’ crude slates. But time is precious. The sooner we face this fact, unwelcome as it may be, the more expeditiously we can adapt.

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