Q&A

Question 2: Which type of valve technology or design is typically utilized in units with high catalyst withdrawal rates? Do you continuously withdraw catalyst? From a reliability and safety perspective, what type of hardware are you using for control? What is the best withdrawal line design?

Valve selection for FCC catalyst withdrawal services is dictated by temperature and erosion considerations.

Question 3: Carbonate stress corrosion cracking (CSCC) has been identified as a cause of failure in FCC main fractionator overhead systems. What changes in feed quality, unit operation, or configuration would lead to increased risk of CSCC? What parameters do you monitor to determine whether a system is susceptible to CSCC? Has the problem been significant enough to warrant either comprehensive PWHT in potentially affected areas or localized PWHT when problem areas are identified?

Carbonate stress corrosion cracking, CSCC, is characterized by inter-granular, sometimes branchy, scale-filled cracks. It is believed that ammonium carbonate is the main contributor to the cracking mechanism.

Question 4: Does your refinery/company adopt a time-based rather than inspection-based replacement strategy for FCC reactor and regenerator hardware such as feed nozzles, air distributor, cyclones, cyclone support systems, and flue gas expansion joint bellows? If so, what is the planned service life for this equipment?

Service life of each component is highly dependent on the application and varies from unit to unit. We have generally found that inspection-based replacement frequency is used as opposed to time-based. We use the results of the last unit inspection, coupled with a run history, to determine whether we need to replace a particular component.

Question 5: What is the shortest possible time between oil out and entry for maintenance on large inventory, high capacity FCC units? How is this achieved?

With FCCs at 27,000 bpd and 9,000 bpd capacity, neither of our units really qualifies for high throughput or large capacity. However, in discussions amongst the members of the panel, we found that throughput and inventory are not necessarily good indicators of how quickly you can move oil-out to maintenance-in.

Question 6: Some CO and waste heat boilers operate with bypass stacks separated by seal pots or isolation valves. Maintenance of these seal systems can be expensive and these seal systems can be sources of poor reliability. What design upgrades and operating practices have enabled you to eliminate these bypass systems?

Holly Refining continues to use bypass stacks with diversion valves at both of our refineries. Those stacks and diversion valves are allowed by permit and we use them during startup/shutdown manning upset conditions. Both our Operations and Maintenance groups are assigned weekly preventative maintenance tasks to ensure operability when we do have to throw these valves.

Question 10: What is your recent experience regarding the maximum level of equilibrium catalyst metals (Ni, V, Na, Fe, Ca) in FCC units processing residual feedstocks? Have there been any recent improvements in vanadium passivation technologies? At nickel levels approaching 10,000 ppm, have you experienced increased catalyst deactivation as evidenced by lower equilibrium zeolite surface area?

Here we see data regarding one of our FCCUs that operates at e-cat nickel levels exceeding 10,000 ppm. We observe that the MAT generally remains within the same range until high e-cat nickel concentrations are approached.

(2008) Question 72 What feed contaminants can lead to metal corrosion in both sulfuric acid and HF alkylation units? What operating conditions promote corrosion? What do you do to reduce corrosion and/or remove contaminants?

GRUBB (Chevron USA, Inc.) I’ve consulted Gary Ash, the Pascagoula local expert, and Steve Mather, who is the corporate expert. They relayed to me that acid is still the biggest problem and not really necessarily the contaminants; but where the feed contaminants come in, they can make the acid more

(2008) Question 73: Does alkylate volume yield decrease if T90 increases? Have you quantified the costs and benefits of reducing T90 by changing reaction conditions?

KAISER (Delek Refining Ltd.) With respect to alkylate yield and T90, the short answer to the question is, yes. When T90 increases, your alkylate yield is going to go down. And if that’s all you care about alkylation, you can go to sleep for the next five minutes and Jeff will wake you up when we get

(2008) Question 75: The butane stream from a catalytic polymerization (cat poly) unit, which contains 69% isobutene, 14% butylenes, and 17% normal butane, would appear to be an excellent alkylation unit feedstock, especially if isobutene is i

METKA (Sunoco, Inc.) We operate a cat poly and sulfuric alkylation unit within the same refinery. The configuration offers flexibility and synergies that allow various operating and business demands to be met. In our configuration, the cat poly debutanizer overhead feeds the alkylation unit to

(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.

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