Q&A

(2010) Question 6: The use of infrared pyrometers for monitoring tube temperatures in steam reformers is a well known practice. What is your recommended frequency for use of these devices ( how many times per week)? Can you offer any recommended alternate devices or methods available such as fixed infrared pyrometer skin thermocouples or infrared imaging?

CITGO’s operating philosophy is to monitor our tubes with an optical pyrometer every shift. We monitor the tubes from multiple locations on each level of our terraced wall furnace. This method has been extremely effective in extending the life of the furnace tubes and catalyst.

(2010) Question 7: What is your experience with reusing molecular sieves in pressure swing adsorption hydrogen purification? What is your recommended inspection criteria for the molecular sieve to be reloaded?

CITGO has successfully reloaded the same PSA adsorbents multiple times in the same PSA skid. We review operating history to ensure the system was not exposed to a significant amount of liquid water carry over. We monitor the hydrogen recovery from the PSA and ensure the system is operating within the design parameters to determine if the adsorbent is worth retaining.

(2010) Question 8: With respect to hydrogen purification pressure swing adsorption vessels, what are the best practices regarding inspection? Can their working life be extended beyond design with vessel inspection?

The intent of a thorough vessel inspection would be to assure that the effects of corrosion, fatigue service, or other operating conditions have not deteriorated the integrity of the vessel. The inspection would determine if the vessel wall thickness has been reduced below the minimum required, or if cracks have developed in any vessel parts.

(2010) Question 9: What experience do refiners have regarding fired heater stainless steel tubes OD/external polythionic acid attacks due to sulfur in fuel gas such as the ones in hydroprocessing units? What criteria are refiners using to decide when to neutralize the external side of the tubes with soda ash during turnarounds?

If it has been determined that sulfide scale is present, then the heater tubes can best be protected by maintaining a balanced set of small fires (or pilots, as applicable) in the heater box at all times, even when there is no process circulation

(2010) Question 10: What are refiners' experience with respect to unit availability, catalyst performance and product quality when co-processing "renewable" feedstocks in a ULSD unit? Is there a big variation in operability with different sources of renewable feedstocks?

The co-processing of renewable feedstocks in a ULSD unit means introduction of feed components that are completely foreign to a diesel hydrotreater. These oxygenates will react quite readily with hydrogen to form normal paraffins in the diesel range but in doing so consume high amounts of hydrogen and cause high heat release.

(2010) Question 11: Are any operators still using salt dryers for ULSD or Jet? If so, do you have any related product quality or corrosion issues?

Sunoco has a few ULSD units that employ salt drying of their ULSD rundown product. These units produce an on-specification product that meets the D4176 Haze spec of 2. As far as corrosion, no major issues have been identified to date

(2010) Question 12: Now that ULSD production has seen several cycles, what are the SOR and EOR operating conditions? What catalyst formulations are you using (NiMo, CoMo, regen, various blends)?

The operating conditions for ULSD vary and will depend on the feed to be processed as well as specific requirements to the product quality. This is apart from the typical US and European standards for ULSD, such as low aromatics, color, cold flow properties or other additional specifications.

(2010) Question 13: Severe fouling of diesel and gas oil hydrotreating preheat exchangers has been a growing problem. In your experience, what are the causes and how can these be prevented? Have you tried antifoulant injection in this service?

Fouling of the heat exchanger train is sometimes a problem particularly when processing cracked feed stocks. The fouling is often caused by polymer like compounds (gums) that form when petroleum distillates come in contact with air.

Question 14: How do you ensure that the reactor effluent stream is evenly divided when going to parallel exchangers?

Two phase reactor effluent flow to parallel exchanger trains need to be addressed during the design and initial piping layout phase. Once the system is installed very little can be done to evenly distribute the liquid and vapor.

Question 15: ULSD reactor feed/effluent heat exchanger leaks can be a big problem meeting product specifications. What are best practices for detecting and preventing leaks? Are there new technologies or mechanical specifications to prevent cross contamination?

With regard to feed/effluent exchanger leaks there are a number of actions that can be taken during the initial design phase of the unit.

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