What processing capabilities should refiners have in place if they plan to process heavy sour Canadian crudes?
Answers
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24/07/2007
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A:
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
If a refiner elects to purchase a "premium/low-sulphur bottomless synthetic crude oil, this can generally be substituted for one-third or so conventional low-sulphur waxy crudes (API = 40 and S = <0.5 wt%) via distilling this in a separate crude topping tower.
The naphtha fraction goes to either (a) existing debutaniser + naphtha splitter + heavy naphtha hydrotreater + catalytic reformer or (b) bulk naphtha hydrotreater + downstream sat gas plant + naphtha splitter + catalytic reformer.
Kerosene cut is likely to be already at S = <10wppm and thus suitable for direct blending into the ULSD pool. Cetane values may be somewhat low, so that kerosene from conventional crude slate and hydrotreated coker kerosene may need to offset. Cat kerosene (ie, front one-third of FCC LCO) may need to be diverted out of the ULSD pool.
Heavy diesel cut might contain too much sulphur to be directly blendable, so re-running through the light distillate hydrotreater is likely to be required. Cetane values may be somewhat lower than desirable, so hydrotreated heavy diesel derivatives from conventional crude slate and medium coker gas oil and medium cycle oil may need to offset.
Collective of kerosene and heavy diesel from synthetic crude oil, hydrotreated FCC medium cycle oil, hydrotreated light coker gas oil and hydrotreated heavy straight-run diesel should meet Cetane Index (ASTM D976) = >40 and Cetane Index (ASTM D4737) = >40, or >42.5 before the addition of cetane-booster additives. This assumes that most of the straight-run kerosene from the conventional crudes is partitioned into making Jet A aviation jet fuel.
VGO is usually suitable or desirable as supplemental cat feed. Desirability is enhanced when sulphur is less than 1000wppm in cat feed VGO; organic hydrogen is better than 12.4 wt%; and residual hydrocarbon polynuclear aromatics are less than, say, 15-20 wt%. For most offtaker refiners, relatively high contents of 1050F+ components (20-30 wt%) can be acceptable as long as MCR = <1.0 wt% and Ni + V = <1 wppm.
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