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Planning a New Hydrotreater (HDS) Unit to remove Sulfur from Heavy Cracked Naphtha stream ex.FCC Unit. To achieve Ultra-low Sulfur Gasoline specs. (<10ppm), and also to meet Gasoline production, other two Naphtha streams are planned to be treated in the above new Hydrotreater. Naphtha ex. Merox Unit having about 375ppm Sulfur is one of them. My query to subject matter experts are as under:
a) Is it recommended to treat Merox treated Naphtha in the above new Hydrotreater? OR
b) Bypass the Merox Unit; Only treat the Naphtha stream with aq. caustic (Pre-wash only for H2S removel); No conversion to Disulfides by 2nd stage Oxidation process in the existing Merox Unit. Feed the untreated Naphtha stream directly to the New Hydrotreater.
Would appreciate pros and cons of treating the straight run-Naphtha, by-passing Merox Unit and treating it in the New HDS Unit. Many thanks for any useful advise from SME.
 
Answers
29/01/2013 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
No easy answer on the several questions. There are advantages and disadvantages of the options. A Merox unit does not have a high operating cost, but it normally does not remove sulphur components. It does on LPG streams. LPG streams have some other problems which are not well understood. LPG streams from FCC units tend to have more sulphur and nitrogen than is normally measured.
27/01/2013 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
There are no significant advantages in continuing to operate any part of the Merox sweetener. One could compare the operating costs of removing just the H2S from the FCC gasoline, but it makes more sense to eliminate the operating and maintenance costs of the Merox unit entirely. If you do elect to run the caustic or amine sections of the Merox unit, go through tankage to allow caustic carryover to settle out and not go to the hydrotreater.
27/01/2013 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
You really should consider a purpose designed "Two Stage" Cat Gasoline Desulfurizer Unit to process full-range FCC Gasoline and idle the catalyzed caustic treater. First stage is selective hydrogenation reactor train and this is followed by cat gasoline splitter to partition out 'sulphur-free' FCC C5 Cut. C6+ FCC Gasoline goes to sophisticated desulfurizer stage. FCC C5 Cut can be reblended with desulfurized heavy cat gasoline for convenient storage or kept in separate storage for mogas blending flexibility.
Straight-run naphtha containing significant sulphur can be spiked into the full-range FCC gasoline.