Are there any rules of thumb for the upper limit for basic nitrogen content and/or feed density in the VGO before hydrotreating is recommended/necessary when the VGO is going to be used as FCC feed ?
Answers
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26/10/2011
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A:
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Steven Kalota, ECI, steve@fluidcatcracker.com
The general rule is FCC feed basic nitrogen begins to impact conversion and yield selectivity at 750 wppm; roughly equivalent to 2,000 wppm total nitrogen. Above this concentration, catalyst activtiy in the Riser is decreased by ammonia species, which serve to partially neutralize the acidic activity of the regenerated catalyst. The decision to hydrotreat is dependent on the degradation in FCC product quality and yield in relation to the refinery blending balance. Gasoline octane will be increased as feed nitrogen increases at lower yield but this is driven by increased olefinicity, whose species are not ideal for gasoline bromine number specifications or alkylation iso/olefin ratio balance. The upper limit would be defined as the point where the decrease in product quality and quantity decrease the profit margin to a value justifying hydrotreating benefits, including desulfurization and aromatic saturation.
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