Ultra Low Desulfurization impact on Hydrogen consumption

[spappu]

Would anyone be able to guide me towards any studies or reports on understanding how ULSD requirements impact Hydrogen consumption. More specifically, how much extra hydrogen would be needed to move from 500ppm to 15ppm sulfur. I understand that the relationship is nonlinear - but the specifics evade me

thanks for your help

 

[epoisses]

spappu,

Theoretically (chemically speaking) you would need
485 wppm S * ( 2 g/mol H2 / 32 g/mol S ) = 30.3 wppm H2
i.e. 30.3 kg/h H2 on 1000 tons/h feed. This relation is perfectly linear.

But that is not how things go - unfortunately.

If you increase severity, you increase parasite reactions like hydrogenation, and you will end up with a significantly higher hydrogen consumption than the theoretical one required to just convert sulfur species to H2S, the difference being dependent on your operating conditions, type of feed and type of catalyst (e.g. NiMo vs CoMo). Catalyst vendors can give you further (quantitative) details. This relation is very non-linear... I guess.

And that is not all... because your operational changes to go from 500 to 15 ppm will probably require increased treatgas flow rate and/or hydrogen partial pressure, so will lead to higher losses of hydrogen losses toward fuel gas. This is obviously site-specific. I have a feeling that this may actually be the most important factor.

There must be lots of studies on H2 consumption available by now, not sure how much valuable information you can google up for free but you could give it a try.

 

[spappu]

thanks for the info epoisses,

i did do a whole lot of googling, but couldnt come up with anything specific - the EIA no less, has this on its site

"The amount of hydrogen required for desulfurization is also uncertain, because the industry has no experience with widespread desulfurization at ultra-low levels"

 

[JLSeagull]

Several refiners have already built and started hydrotreaters for ULSD. However I would not expect those refiners to publishing much about their experience to help other refiners.

 

[25362]

Spappu, the quotation on the experience of industry on ultra low-level desulfurization is not entirely true since catalytic reformer feeds are being desulfurized to levels lower than 0.5 ppm by hydrotreating, and there are also proprietary absorption techniques that claim reducing sulfur levels further down to 0.1 ppm.

The stoichiometry mentioned by epoisses could be complemented with the need to saturate with hydrogen the bonds left opened by removing sulfur, as in

R₁SR₂ + H₂ [→] R₁H + R₂H + H₂S​

With higher-boiling more refractory thiophenes and benzothiophenes, there is also opening and saturating of the thiophene ring.

These reactions need more moles of hydrogen than would be required by making one mole of H₂S.

As a result larger amounts of lower boiling hydrocarbons are produced which require stripping of the product to preserve flash point and boiling range.

Side reactions such as hydrocracking, dehydrogenation, and dearomatization, as well as those leading to carbon laydown, are minimized by chosing the right catalyst (and support) and operating conditions.

The selection of the latter (in particular space velocities which are about proportional to residual sulfur content) may affect also the removal of nitrogen (as ammonia) and oxygen (as water), and in the heavier fractions, such as distillation residues, the removal of metal compounds.

 

[epoisses]

Err... you are right as usual, 25362, my calc is only applicable to mercaptans, conversion of species like thiophene require more hydrogen moleules (1 thiophene actually requires 4 H2). This additional consumption is indeed inherent, not from parasite reaction.

There ARE lots of studies available, from catalyst manufacturers, hydrogen producers, governmental bodies... I have not spent much time (10 mins I believe) and have not found the magic link that provides you with everything you need, but articles and reports like the following:

http://www.albemarle.com/Products_and_services/Catalysts/Courier/C62_art08_ULSD_technology.pdf

https://portal.mustangeng.com/pls/p...CHNICAL_ARTICLES_CONTENT/USDLHYDROTREATER.PDF

http://ec.europa.eu/environment/sulphur/uls.pdf

are readily available. I hope you will find similar ones with further numbers that will give you a good idea.

 

[25362]

You may add to the list:

http://www.exxonmobil.com/refiningtechnologies/pdf/AbuDhabideliveredpaper03.pdf