Q&A

(2008) Question 93: On a CCR, what causes the regenerator chlorination zone to plug off before the regeneration zone?

Question 93: On a CCR, what causes the regenerator chlorination zone to plug off before the regeneration zone? Ka Lok/Joe Zmich (UOP LLC) Assuming that the question relates to the inner screen of the chlorination zone of a UOP Atmospheric CCR regeneration section relative to the burn zone, the most likely cause of this is failing to operate the CCR regeneration section burn zone per the UOP General Operating Curve. If the catalyst circulation rate for given oxygen concentration exceeds the maximum indicated by the curve, it’s likely that catalyst with higher than desired coke will enter to the chlorination zone leading to catalyst damage. The damaged catalyst can be smaller and fracture into dust and chips in the chlorination zone leading to plugging of the chlorination zone screen. Some licensees have observed an increased slot width in the chlorination zone after a long time in operation. An increase in slot width increases the tendency of the screen to foul with catalyst chips or smaller diameter catalyst.

(2008) Question 94: In monitoring catalytic reformer operation, how often do you perform a feed/product analysis and what analytical methods do you use? How often do you perform a mass balance and what is the acceptable mass balance closure? What is a typical mass balance closure?

Question 94: In monitoring catalytic reformer operation, how often do you perform a feed/product analysis and what analytical methods do you use? How often do you perform a mass balance and what is the acceptable mass balance closure? What is a typical mass balance closure? Michael Newton (Roddey Engineering) Units were the feed properties are relatively constant need to be monitored much less than those were the properties change often. For material balances during performance evaluation, accuracy should be within +/-1%. For daily monitoring, +/-2% is acceptable. All balances and monitoring require good data from the lab and making sure that meter data is input and calculations performed correctly.

(2008) Question 95: How often do you perform CCR and cyclic reformer turnarounds? What determines the turnaround interval? What actions can you take to extend the turnaround cycle?

Question 95: How often do you perform CCR and cyclic reformer turnarounds? What determines the turnaround interval? What actions can you take to extend the turnaround cycle? Javier Quintana (Valero Energy) Valero’s best practice guideline for reformer turnarounds is currently 4-6 years, but eventually we will target 10 years. With the longer turnaround horizon, catalyst condition in a CCR unit can be managed with on-the-fly change out, which has been demonstrated several times in practice, while in cyclic units, a reactor can be changed out while the remainder of the unit is operating.

(2008) Question 96: How do you manage sulfur in the feed to a catalytic reformer? What is the minimum allowable sulfur for CCR, semi-regen, and cyclic reformer feeds? What are your sampling frequencies and allowable ranges? What is your experience with carburization and/or metal-catalyzed coking?

Question 96: How do you manage sulfur in the feed to a catalytic reformer? What is the minimum allowable sulfur for CCR, semi-regen, and cyclic reformer feeds? What are your sampling frequencies and allowable ranges? What is your experience with carburization and/or metal-catalyzed coking? Joe Zmich (UOP LLC) UOP has extensively researched the tendency of metal surfaces to promote coke formation. UOP will provide specific recommendations on operating guidelines based on unit design and operating conditions. We are aware of two fixed bed units that have each operated with feed sulfur below 0.05 wppm and experienced coke growth in the reactors. Subsequent operation with a target of 0.15 wppm S successfully prevented repeat coke growth. Most fixed bed reforming catalyst systems must be properly sulfided following regeneration to attenuate the catalyst metal function.

(2008) Question 97: What technologies and adsorbents are you using for net hydrogen off gas chloride traps and what operating problems have you experienced? What are the criteria for changing out the adsorbents and how often are the beds changed?

Question 97: What technologies and adsorbents are you using for net hydrogen off gas chloride traps and what operating problems have you experienced? What are the criteria for changing out the adsorbents and how often are the beds changed? Javier Quintana (Valero Energy) There are various adsorbents available for effective chloride treating of the hydrogen-rich net gas stream, including activated aluminas, promoted aluminas, and zeolites. Valero has moved away from the alumina products towards a best practice of using the zeolite products, not only for reasons of cost per quantity of chloride removed, but also for ease of changeout and completeness of chloride removal.

(2008) Question 98: What metallurgy are you using for mesh pads in reformer compressor suction knockout drums? How often are the mesh pads inspected and how often are they replaced? Are the same criteria used for mesh pads in product separators?

Question 98 What metallurgy are you using for mesh pads in reformer compressor suction knockout drums? How often are the mesh pads inspected and how often are they replaced? Are the same criteria used for mesh pads in product separators? Rick Grubb (Chevron USA) We typically use 304 SS demister pads in the refinery and inspect them every 10 years. In reforming service we have been using Tefzel demister pads and have been replacing them approximately every dump and screen due to separator internal inspections. If we go into the vessel we go ahead and inspect the mesh pad, but assume before opening the vessel that the pad will need replacing. The Tefzel pads have greatly increased the reliability such that we don’t find mesh pad pieces in the compressors anymore. We have been contemplating using co-knit pads (synthetic fiber inter-woven with a SS fiber), but have not done so yet.

(2008) Question 76 The regeneration of feed dryers/sulfur guard beds on butane isomerization units generates a butane slop stream. Will processing this butane slop stream in an HF or sulfuric acid alkylation unit cause any problems? If so, what else may be done with this slop stream?

QUINTANA (Valero Energy Corporation) The spent Isom regenerant will contain butanes that are attractive to recover. They can come from generally any of three sources: either the treated normal butane feed downstream of the on-stream dryer, the fractionated isobutene from the Deisobutanizer fractionator overhead, or the isomerate product is used as the regenerant source. The spent regenerant also contains all of the sulfur and oxygenate impurities that were previously accumulated on the sieve; and after the spent regenerant coalescer, it will also be saturated with water.

(2008) Question 77 What is your experience with cooling water exchangers in an HF alkylation unit? How long do you go between cleanings? Do you have a special water treatment program for cooling towers dedicated to the alkylation unit?

KAISER (Delek Refining Ltd.) In my experience, the cooling water exchangers in an HF alkylation unit are really no more problematic than any other exchanger in the refinery when you’re looking at the waterside only. If you have an exchanger in the HF alkylation unit that suffers from low flow or it’s at the end of a header, trapped scale, and there are certainly critical exchangers inside the alkylation unit that you want to keep clean, it’s really no different if it’s in the alkylation unit or in some other unit in the refinery. You’re going to have water problems and that’s going to generate issues for you.

(2008) Question 78 For HF alkylation units, have you changed your criteria for materials given the low availability of low carbon/non-recycled steel? Are you heat treating welds? Can you control Brinell Hardness with welding procedures? For small bore pipe, do you recommend using flanges or threaded pipe?

KAISER (Delek Refining Ltd.) Again, just to re-emphasize, I’m not currently on an HF unit so part of this response will rely on some former colleagues of mine. I would not make a blanket recommendation to change the material specification for carbon steel in HF alkylation units. To me, the risk is too great. I understand that there are certain times when things are tight and you might need immediate material delivery and there’s no other option, but I would not make a blanket relaxation in the material specifications.

(2008) Question 79 It has been reported that diisobutylene (isooctene) causes a stability problem when blended in gasoline. Do you have experience blending diisobutylene in gasoline? And if so, were there stability or other problems?

GRUBB (Chevron USA, Inc.) I consulted our corporate experts for this, Shingou Lou and Dave Kohler. We built one in Pascagoula and their basic response was that there’s really no reason to expect any more instability problems than you would have with normal olefins. And as with the other olefins, if you let them go unchecked, they could lead to an insoluble gum residue. These can be mitigated effectively with some antioxidants—the phenylenediamine-hindered phenol. They do recommend that you inject them very close to the source unit. Like I said, Pascagoula converted an MTBE plant and we had no instability issues at our plant. Corporate-wide, we actually have experience with two ion exchange resin-type catalyst units, two solid phosphoric acids distributed on solid support-type catalyst units, and we have experience with Dimersol-type units.

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