Q & A > Question Details
We need to revamp our NHT. Before revamp: 23500 bpd SR Naphtha 100ppm S, Naphtha product for CCR feed has 0.5 wt ppm. After revamp: 30 000 bpd (90% vol SR Naphtha, 10 % coker Naphtha) with 0.1 wt ppm in product for our new regulation. We have 1 reactor (R1) with 1 bed of catalyst (18m3 catalyst in 27m3 reactor). I think we should install one more reactor. But I don't know which case is better between: Case 1: Feed-R1-R2-Stripper-splitter and Case 2: Feed-R1-Stripper-Splitter-R2 (recycle bottom product from splitter to R2)-R1. May you have any advice for our revamp?

Additional info:
Of course that Case 1 is traditional process revamp. But I have just read an article from Chevron, about their process revamp as Case 2. It called SSRS Isocraking (single stage reverse sequencing), licensed by Chevron Lummus Global. In that article, they said that the revamped unit can run at 133% of original design capacity with the existing recycle gas compressor. I think in case 2, R2 is existent reactor and R1 is new one (because R1's volume needs to be bigger than R2) This article named "Hydroprocessing upgrades to meet changing fuels requirement", Jay Parekh and Harjeet Virdi. Unfortunately, It's not for NHT, It's Hydrocracking. Is it O.K if I use Case 2 for my NHT revamp?
05/07/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
For hydrotreating, the reactors should be together, as suggested by others, either in series or parallel, depending on the hydraulics and maximum vessel diameter. Bottoms recycle is unnecessary. I believe this to be the optimum revamp design.
02/07/2011 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Aim of the Hydrocracker is to convert heavy stocks such as VGO to lighter stocks such as Diesel and lighter ones like Naphtha. To achieve very high conversion of VGO, process design may require two stages with number of reactors.
However in NHDT, the objective is only HDS. HDN. With coker streams olefins saturation is also needed and no cracking is required is required.
There is need to have minimum partial pressure of Hydrogen, required type and amount of catalyst and suitable choice of reactors but not the two stages.
27/06/2011 A: carlos hugo mendiondo, ypf sa, cmendiondoc@ypf.com
Normally you have in Hydrocracking one trought or two stages with recycle according with depth in the conversion level to be achieved . The bottom of fractionator you mention is call UCO ( unconverted Oil ) and so has sense to send this fraction to a second reactor ( traditional or SSRS) from bottom of fractionator . while conversion of heaviest compounds is increased , the Lighter productos ( N,K, diesel) are extracted as side cuts of the same column .
In HTN there is not conversion to lights compounds as in Hydrocracking process so that all heavy naphtha is extracted on specification from bottom of the splitter . In my opinion only case 1 has sense and will be more efficient too
24/06/2011 A: Randy Alexander, EURECAT, randy.alexander@eurecat.com
Another note - You will typically need to delay the introduction of CGO to the reactor for 3 days due to hyperactivity of the catalyst after sulfiding. If this creates a problem due to tankage issues or SR feed availability, you should consider is preactivation of the catalyst prior to loading with Totsucat CFP. CFP (Cracked Feed Protection) allows startup with CGO containing feed without the three day delay. This process is offered by the Eurecat Group.
24/06/2011 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Large number of units are there which hydrotreat blend of coker plus straight run naphtha (SRN). For coker naphtha there is need to have one bed of catalyst different to that for SRN . This catalyst is appropriate for silicon contamination, greater amount of unsaturates and high nitrogen in blend of Coker plus SRN This bed is located before the normal bed having Ni- Mo / Co-Mo This bed is more effective for coker stream blend relative to SRN catalyst. To avoid the delta P build up, a better temperature management is needed.
23/06/2011 A: carlos hugo mendiondo, ypf sa, cmendiondoc@ypf.com
I guess you have full range naphtha Feed and the splitter is to divide it two cuts. I think the Case 2 will not work with NHT process .It is good for hydrocracking cause you have cracking of long molecules to shorter .The UCO (unconverted Oil) is the fraction which has not converted in a first pass so that you have the opportunity to recycle it from the bottom of fractionator ( in your case would be the splitter ....???) in order increasing the conversion in a second or in the only reactor while its cracking products (N , K, Diesel ) leave the fractionator from differents levels above the bottom. In the naphtha case it has not sense for me.
22/06/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
I can't comment on proposed reactor set up, that should be something you discuss with NHT licensor & catalyst supplier, however a few things spring to mind with regard to this revamp and capacity increase from a filtrations & separations standpoint that should be considered.
i) As the proposed feed will have 10% CGO you need to probably upgrade or install a NHT feed filter. CGO will be typically having much higher content of hard particulate contaminants (i.e.coke fines & corrosion prodducts) so NHT feed filter upgrade should be considered to prevent premature plugging of reactor and fouling feed exchanger. A feed contamination study should be undertaken to determine correct feed filter sizing and filter equipment selection. This would usually be a suitable sized disposable filter but may be an automatic backwash filter too depending on the Total Suspended Solids loading in the feed.
ii) Proposed increased throughput may mean the separator after thre reactor may be now be undersized and naphtha carryover back to recycle gas compressor (if you have one) may result. So you may need to consider replacement of the separator with a bigger one to maintain suitable residence time , or alternatively keep the existing separator & install a SepraSolTM LG coalescer to catch expected carried over naphtha in the recycle hydrogen stream coming from the separator. Where recycle gas compressor is installed, this can provide significant reliability improvements to the H2 recycle gas compressor reliability.
iii) For the extra 27% new capacity, you may well require a new larger furnace. If the new furnace has low NOX or ultra low NOX burners installed, you should consider having high efficiency SepraSolTM LG coalescer on fuel gas treatment to protect the low NOX buners from fouling to reduce maintenance and reduce or eliminate a burner cleaning program. These low NOX and ultra low NOX burners have a smaller orifice than conventional burners and are much more prone to fouling which can put NOX emission off spec and can require increased burner maintenance.
21/06/2011 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
I think Case 2 sounds too complicated. This will require a second set of HP charge pumps. Further, recycling material through R1 again will reduce the ultimate capacity, because the pressure drop therein will limit throughput. Case 1 is a more traditional configuration for similar revamps.
A detailed study should be done by yourselves or your engineering contractor or licensor.
21/06/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
case 2 provides a much better probability of long runs meeting the sulfur specification with the much more refractory coker naphtha. You really need to have this re-vamp designed by a Licensor to optimize the capital and operating cost -including catalyst life.
There are several 'trade-offs' to be evaluated and the best overall revamp is not obvious from the very limited information provided. The 30% increase in feed rate probably requires additional heat exchange, fired heater, pumps, piping,etc. While existing equipment may be adequate (hydraulically) in some instances, end-of-run catalyst condition may require more heat exchange capacity. Throwing in the coker naphtha along with much more stringent product sulfur specification vastly raises the needed reaction severity. The nitrogen contained in coker naphtha will adversely impact catalyst activity in R-1 (and R-2 if not stripped out).
See your preferred catalyst licensor for case studies. If you have not already settled on a process licensor, have a qualified Consultant/ Engineer perform technology +revamp technology selection evaluations.