Q&A

(2010) Question 1: What is your experience with emergency isolation equipment (such as a check valve or actuated valve) on the outlet of reactor charge heaters to prevent loss of containment of the reactor loop in a tube rupture scenario? What are the advantages and disadvantages of having this type of equipment?

Sunoco typically looks at the use of isolation equipment on the reactor charge heaters on a case by case basis. The need for these devices is driven by the design configuration of the unit, the process stream being charged to the heater, the emergency depressuring capabilities installed on the unit, and LOPA/HAZOP analysis.

(2010) Question 2: Please discuss your experience regarding the need to add an emergency shutdown (ESD) valve between the cold high pressure separator and the product stripper. The typical design for vapor blow through is to size the stripper relief valve for this case.

Vern Mallett (UOP) UOP considers that an ESD valve between the cold separator and product stripper is not required and not recommended. The design philosophy behind this practice is to prevent liquid from filling the cold high pressure separator and carrying over into the auto depressuring system and filling the relief header.

Question 3: Please discuss your best strategies to prevent overheating of steam reforming furnaces?

The question is general; however, there are a variety of steam reformer designs with different operating and control strategies used industrially so a general answer is provided. Operators are urged to consult with their technology providers or qualified engineering contractors for specific guidance on this issue.

Question 5: Does anyone have proven experience using promoted zinc oxide products for sulfur removal upstream of the reforming section? What improvement have you measured in the downstream catalyst performance?

Topsoe has installed our new promoted zinc oxide product HTZ-51 upstream the reformer section in a number of Ammonia, Hydrogen and Methanol plants. Topsoe’s promoted zinc oxide is also used as a purification absorbent upstream methanator units.

(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

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