Q & A > Question Details
What factors affect aromatic saturation in hydroprocessing of coker heavy gas oil? How can the aromatic saturation be minimized for heat balance benefits in the downstream FCC unit?
15/09/2016 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
In another direction, if we can reduce the H2 partial pressure, there will be reduction atomatic saturation.. S conversion up to 500 ppm is not a strong function of pressure. I hope you are targeting S in FCC feed above 500ppm. We may need high H2 partial pressure for converting difficult sulfur involving aromatic rings. Try to H2 partial pressure in your case bu reducing Makeup H2 purity which may help up to some extent. Reducing reactor pressure may constrain unit hydraulics as gas volumetric flow increases.
13/09/2016 A: utkarsh mishra, Ingenero Technologies, utkarsh1612mishra@gmail.com
Just to add to what has been already discussed about thermodynamic limit of aromatic saturation. If you choose a specific catalyst & a specific reactor operating pressure (i.e rather a specific H2 purity in H2 gas) then you can play with your operating temperature till thermodynamic limit of aromatic saturation is reached (typically it is ~ 385 °C). In this case whether you will get desired aromatic saturation or not, becomes strictly a function of amount & type of aromatics (i.e. mono,di & tri aromatics) present in feed stream. In case you still want to achieve same aromatic saturation in spite of high aromatic feed, then option of more advanced catalyst can be thought of.
11/09/2016 A: Sankar Gunasekaran, Indian Oil Corporation Limited, sankarg.eng@gmail.com
The aromatic saturation reaction is strongly favored by high hydrogen partial pressure. The amount of conversion of aromatics becomes equilibrium limited at higher operating temperatures as the naphthene dehydrogenation reverse reaction becomes favored. The optimum temperature for maximum aromatic saturation depends on LHSV, hydrogen partial pressure, and catalyst type but typically lies in the range of 355–388 C. Complete saturation of aromatics requires the application of noble metal catalysts in a sulfur- and H2S-free environment, which is not the usual case with Base Metal sulfide catalyst.
For a given catalyst system by adjusting the temperature and hydrogen partial pressure one can fine tune the aromatic saturation in Hydrotreating reactor.
02/08/2016 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The level of aromatics saturation is a function of kinetics and equilibrium. For a given temperature there is a maximum possible level of saturation that is achievable. The kinetics, reactor design, and catalyst determine how close you get to equilibrium. As temperature increases the equilibrium level of saturation decreases while the kinetic reaction rate increases (theoretical max decreases while the approach to that max gets closer due to kinetics). That means there is an optimum set of reactor conditions to maximize aromatic saturation that strikes the best possible balance between equilibrium and kinetics. That optimum may not coincide, however, with optimum conditions for HDN or HDS reactions. H2 consumption can also be a consideration in plants with limited hydrogen supply.
Generally speaking, the more severe the hydrotreating operation, the lower the delta coke make will be in the FCC. The optimum level of hydrotreating will depend on your FCC objectives. Delta coke yield is part of the equation as are sulfur and nitrogen levels in the feed.
Finally you also need to consider hydrotreater runlegth objectives and the impact of optimum operation from an FCC yield standpoint on hydrotreater catalyst life. If "optimum" operation causes you to miss runlength objectives you may discover that you were at a false optimum. As you can see there are a lot of factors to consider which makes it difficult task to truly optimize this aspect of operation.
02/08/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
As you know, increased aromatics saturation occurs when more sulfur removal is needed, and severity is increased to achieve that objective. You can lower the hydrotreating severity, which will reduce aromatics saturation, but that would increase the sulfur in the products. I doubt that is what you want to do. Catalyst selection choices (boutique catalysts) can directionally minimize saturation at a specific sulfur removal level.
27/07/2016 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Factors which can affect aromatic saturation during hydroprocessing of heavy coker gas oil will be high hydrogen consumption, presence of high coke precursors in heavy coker gas oil .