Q&A

(2015) Question 22: How frequently do you change [or changeout?] the catalyst in reforming units? What are the appropriate economic criteria to evaluate?

For semi-regenerative reformers, catalyst life is often dependent on contamination or upset-related issues. Lead reactors can become contaminated with iron, which ultimately affects the product yields. Skimming or possible replacement to prevent downstream contamination is a common practice.

(2015) Question 23: In continuously regenerated reforming units, are there valves in cyclic service that have demonstrated superior performance compared to the originally installed valves? How can maintenance of these valves have an impact on their longterm performance and reliability?

From the question, it is not clear which style of valve in cyclic service is of the highest interest. There are two types of cyclic services that are specific to the CCR process, each with different requirements and potential pitfalls. There are on/off valves in vapor service with catalyst dust, such as those that vent the lock hoppers, and the on/off valves in flowing catalyst service, such as those used for catalyst flowing in and out of the lock hoppers.

(2015) Question 24: During the oxidation step in the regeneration of fixed-bed catalytic reformers, how does varying the length and oxygen concentration affect the unit performance?

The length of the oxidation period will vary from a minimum of 11 hours up to 24 hours. The timeframe will depend on the amount of platinum agglomeration, surface area, oxygen content, and chloride injection rate. Minimizing the burn temperature during the primary burn will minimize agglomeration.

(2015) Question 25: Have you detected any hydrogen chloride slip in the stabilizer bottoms for any gasoline units (isomerization or reformer)? What are your Best Practices to prevent downstream unit corrosion?

Occasionally, isomerization units will slip some HCl or organic chlorides at the bottom of the stabilizer. The key here is having the proper reflux ratio on that tower because you need to keep the partial pressure of the HCl low enough that it will not overheat.

(2015) Question 26: What is your Best Practice for packing (material and shape) in isomerization unit off gas caustic scrubbers?

UOP recommends carbon Raschig rings. The key here is to specify to the vendor that this be used for caustic service so that the rings will be formed with the proper binder. If you get the wrong binder, the rings will dissolve. We have a similar service in HF alky units where we use carbon Raschig rings; and there, you have to make sure that the binder is resistant to acid.

(2015) Question 27: What is your experience with processing benzene in C5/C6 isomerization units? Have there been any issues with higher reactor exotherms associated with benzene saturation?

UOP’s general guideline is to limit the lead reactor ΔT to 100°F (55°C). This limit is based on our design margins or the heat exchangers around the reactors. That 100-degree limit corresponds to above 5 to 8% benzene in the feed. So, one way to get around that is to recycle or add something to dilute the benzene.

(2015) Question 28: What are your Best Practices for measuring chlorides in LPG streams? What criteria do you use to determine when to change LPG chloride treater media?

There are three methods for measuring chlorides in LPG streams: UOP 910, UOP 930, and Dräger 2.0.2/A.

(2015) Question 29: What are the likely causes for temperature excursion events in a hydrogen plant?

Hydrogen plant temperature excursions are possible in several of the catalyst vessels and are usually observed in association with the water/gas shift reaction. During normal operation, the high, medium, and low temperature shift reactors display an exothermic reaction.

(2015) Question 30: What factors influence your decision to conduct air versus inert reactor entry for catalyst changeout? For, what methods do you use to avoid stress corrosion cracking?

For us to enter a reactor that is under an inert atmosphere, the conditions need to warrant it, such as when there are large amounts of pyrophoric material still present, when a specific job is required, an old catalyst needs to be vacuumed out for sampling purposes, or if there is filtration material on top that requires removal in order to allow the catalyst below to dump freely.

(2015) Question 31: What are your current safe practices for sour water monitoring? What are your preferred analytical methods/sampling frequency used to measure NH3/NH4HS (ammonia/ammonium bisulfide)?

The primary concern with sour water sampling is exposing operators to H2S and ammonia, which will evolve off the liquid as it is collected into the sample bottle. Typically, most of our plants would take an approach of ensuring that the operator pulling the sample was in supplied air.

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