Q & A > Question Details
We have a SR type reformer. The HDT catalyst (HR 306) was replaced by HR 506 after operating for 12 years and still getting DSN sulphur at about 0.1-0.2 ppm as reformer feed. After replacement of catalyst in April, 2009, the pressure drop was found to be increasing alarmingly and needed opening the reactors in Feb, 2010. On opening the reactor, a thick layer of about 1 ft of Fe dust was observed at the top of the reactor. We are planning to install a magnetic filter now to trap the Fe dust.
My query is with the same kind of feed and same type of loading (Sock) why the Fe dust deposition rate has increased to such an extent which was never experienced in the 12 years of operation from 1997 to 2009. The only process is that we are continuously dosing DMDS at the HDT to keep H2S at about 150-200ppm at HDT separator off gas as our Naphtha is very sweet in nature.
1. Can DMDS be the culprit for enhanced Fe deposit at the NHDT reactor?
2. In the latest catalyst loading, grading material was used which was not done in the previous loading. Has the new grading material caused the entire Fe-dust to be trapped at the reactor top.
3. What is the best location for installing a Magnetic filter?
4. Has the Fe-dust has increased due to the ageing Unit which was also observed during the last reformer section catalyst unloading in 2009.
 
Answers
23/02/2010 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Proper Grading helps in suitable retention of dust at the top and prevents it to go deeper into the bed. Trash baskets are helpful too. DMDS dosing is commonly recommended practice for low sulfur sweet stocks. Magnetic filter downstream of surge drum have done well.
15/02/2010 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
I agree it's unusual to see that much corrosion products (iron sulphides?) in reformer feed. When reformer feed is contaminated with high solids loading & plugging the reformer catalyst bed, normally such feed would be imported or coming from storage tanks and not directly from HDT unit. Can you advise if feed is routed directly from HDT unit or via tanks?
A feed filter similar to what we supply as feed filters to HDT (Prime G+or other HDT) , HDS or MRU to protect fixed bed reactors or absorbent beds from plugging may be warranted here. I would caution you on the use of magnetic filters. While Pall supply magnetic filters also using rare earth magnets, these will be only partially effective in protecting something critical like reformer reactor bed and will need frequent maintenance (cleaning). The iron solids you report is likely to be corrosion products and this is typically 80-90% sub 15um in size and much of it can be 1-5um size range. Magnetic type filters alone are not very effective removing fine particles like corrosion products plus are difficult to monitor as to when external cleaning is needed. A properly sized disposable feed filter would be a better choice. If the solids loading is high, and you are concerned about short feed filter life, a magnetic filter can be incorporated into the feed filter design which does increase the feed filter run time. Should the solids loading be extreme, an automatic backwash filter could be offered however this would involve an order of magnitude higher capital cost and would not normally be warranted on a duty like reformer feed. (a properly sized disposable feed filter being more likely to be the right equipment selection).
We would also recommend a feed characterisation study to measure solids loading (TSS) and particle size distribution (PSD) if this has not been already done. This will ensure appropriate feed filter sizing is made. This can be useful as the solids loading can vary a lot and it sounds like the solids loading in your heavy naphtha feed is fairly high. We offer such consultancy services.
15/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Example bypass bed: Patent No. 4313908, Feb 2, 1982, by Ramesh Gupta at ER&E, written for 2-phase reactors, but works for single phase as well. Consists of a bed of catalyst with vertical tubes that allow flow when bed pressure drop reaches a pre-designed level. Extends run length limited by a target overall reactor pressure drop.
14/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Inspection/measurements of the furnace tubes during each TAR should disclose if there is increased corrosion of the tubes. Did you replace baskets with graded catalyst this time? If so, maybe the baskets were more effective. Can't comment on magnetic filter. Have you considered a "bypass bed", developed (I think) by Shell?