Q&A

(2010) Question 53: During the coking cycle, how are drum skin temperatures used to monitor drum wall condition?

Monitoring drum wall conditions during the drum cycle is best performed using strain gauges. Each strain gauge location will typically be fitted with gauges in both the axial and hoop directions and have an associated skin thermocouple.

(2010) Question 61: In your experience, what is the effect of crude oil compatibility on crude unit preheat exchanger fouling? Are there any correlations used to predict fouling?

Since there are only isolated instances of fouling in the “cold train” exchangers prior to the desalter(s), we will assume this question is directed more towards the “hot train” exchangers.

(2010) Question 62: What are the refiners experiences using static mixers in place of, or in conjunction with, traditional mixing valves at the desalter?

Years ago, many refiners installed static mixers in desalters, as opposed to traditional mix valves, to improve contacting of water and oil at a lower pressure drop. In theory, this was a good idea, but in practice it has not worked well.

(2010) Question 63: Certain crudes are treated with H2S scavenger to meet a 10 ppm or less specification in the vapor space. In your experience, what is the disposition of the reacted and unreacted scavenger additive through the crude unit? Will this product and/or associated byproducts create corrosion or product quality issues in the crude unit or downstream units?

The majority of H2S scavengers used today are water-soluble, cyclic amines which can quickly react with H2S, forming a water-soluble reaction product. However, these amine-based scavengers are not without potential problems. As formulated, these scavengers often contain un-reacted amines.

(2010) Question 67: Have you experienced coking or other fouling of reboilers in naphtha distillation service (splitter, debutanizer, etc.)? If so, what operational or design changes did you implement to eliminate this problem?

Two types of fouling are common in naphtha reboilers. The first type of fouling is generated as a result of the more reactive cracked stock hydrocarbons and is typically seen only in units like Cokers or FCCUs with a cracking process. The second type of fouling is a more complicated issue related to the presence of sulfides in the naphtha and can be seen in straight run units like the Atmospheric Crude.

(2019) Question 38: What are your guidelines for cleanliness of reactor vessel and overhead lines during Turnaround?  Do you have limits on reactor temperatures during dry-out to prevent the ignition of coke in the reactor?  What actions do you take if coke starts to burn?

What are your guidelines for cleanliness of reactor vessel and overhead lines during Turnaround?  Do you have limits on reactor temperatures during dry-out to prevent the ignition of coke in the reactor?  What actions do you take if coke starts to burn?

(2019) Question 39: What are your best practices for transferring FCC catalyst into/from pneumatic trailers and rail cars to ensure personnel safety and catalyst containment?

These trailers are often referred to as pneumatic, dry bulk, or pressure differential (PD) trailers. On-road trailers and railcars have similar functionality although railcars are not usually rated for vacuum, nor do they usually have a filter system. Both types of transport vessels have multiple hoppers.

(2019) Question 43: What are your best practices when shipping ecat, fines, feed, and slurry to suppliers for testing?  Please also comment on some best practices for sampling equilibrium catalyst.

When shipping ecat or fines, an appropriate sample container should be used. Catalyst suppliers will typically provide refiners with sample containers if needed. Catalyst shipping containers should be made of plastic or metal.

(2019) Question 44: What is your recommended back up options for slide valve / plug valve Hydraulic Power Units? Are electric actuators an option? What are the response times?

What is your recommended back up options for slide valve / plug valve Hydraulic Power Units? Are electric actuators an option? What are the response times?

(2018) Question 4: What are the requirements for a unit depressurization valve in isom unit using a chlorided alumina catalyst based? Do you require the depressurization valve to be operable from the console and/or emergency shutdown device (ESD) panel?

Axens recommends that in cases of emergency depressurization of the reactor circuit, the circuit fluid is depressurized into the product stabilizer with the light gases still being treated in the off-gas caustic scrubber before being sent to flare.

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