Q&A

(2019) Question 20A: What are the recommended guidelines for operating temperature and temperature rise in reactor beds during the initial month of operation? What determines these limits?

Recommended guidelines for operating temperature and temperature rise in reactor beds during the initial month of operation

(2019) Question 21: We are observing fouling of our feed/effluent exchangers that has impacted heat transfer and restricted feed. What are potential contributing causes and how can we mitigate?

ROBERT STEINBERG (Motiva Enterprises)
There are many things that can contribute to fouling of feed/effluent exchangers. Fouling can occur on either the feed or product side of the exchangers.

Possibilities sources of fouling on the feed side include:

• Dissolved O2. Oxygen can get into feeds

(2019) Question 22: What sets the endpoint limit for feed to an Ultra-Low Sulfur Diesel unit? Should 90%, 95%, 98% or Final Boiling Point be monitored and what is an acceptable tail for amount of feed greater than the cutpoint spec? Is the answer different for straight-run diesel vs coker diesel vs Light Cycle Oil feed components?

AMIT KELKAR (Shell Catalysts & Technologies)
There is limited boiling point shift from feed to product in a typical diesel hydrotreater. The boiling point shift correlates strongly with H2 consumption which is dependent on feed properties and unit conditions. In our experience, boiling point shift

(2019) Question 25: What are your key factors around amine contactor operation in hydrotreating units?

JOE RYDBERG (CITGO)
The biggest key factor in amine contactor operation in hydroprocessing units is controlling the lean amine flow and the lean and rich amine loading. We have seen corrosion in rich amine piping likely due to elevated H2S loadings and higher velocities (both lean and rich)

(2019) Question 26: What do you do to predict Silicon breakthrough in a naphtha hydrotreater? What are the consequences to the downstream units if breakthrough occurs?

AMIT KELKAR (Shell Catalysts & Technologies)
The primary source of Silicon is the anti-foam injection at the coker. Silicon is also present in a wide variety of crudes including Maya, Canadian syncrudes and Venezuelan. It may show up in straight run naphtha due to use of Silicon based additives in

(2019) Question 27: What do you do to predict Silicon breakthrough in a naphtha hydrotreater? What are the consequences to the downstream units if breakthrough occurs?

JOE RYDBERG (CITGO)
CITGO refineries basically operate in the full coking mode which means that on our usual crude blends we do no net VTB for outside sales nor we are a player in the Bunker fuels supply market. Having said that, we have to be watchful of the demand shift that will follow with the

(2019) Question 28: In light of IMO (International Maritime Organization) 2020 and the potential for shipping intermediate streams from refinery to refinery, what are your plans to ensure H2S specification in the vapor space is met, either at the shipping or receiving point?

STEVE WILLIAMS (Marathon Petroleum Corporation)

• Movement of intermediate streams from refinery to refinery has been a common practice, including movement of heavy oils. This activity is expected to increase following implementation of the IMO 2020 rules reducing the sulfur content in maritime

(2019) Question 31: Is intermittent or continuous mud washing considered your best practice and why?

STEVE WILLIAMS (Marathon Petroleum Corporation)
• Mud wash is utilized to help keep the bottoms of a desalter vessel relative free of solids build up.
• Utilizes a distribution header with nozzles located near the bottom of the desalter to create a liquid disturbance at the bottom to preclude

(2019) Question 32: Where are ammonium chloride and amine hydrochloride salt found in your crude unit? What is your best practice to monitor and mitigate the resulting corrosion and fouling?

Ammonium chloride and amine hydrochloride salts can form in the top section of the Atmospheric and Vacuum Towers, and the overhead exchangers of the tower. The formation of these salts is a function of partial pressures which dictated by the concentrations of ammonia, amines, chlorides in addition to operating conditions such as overhead temperature, pressure, steam flow rate and hydrocarbon flow rate.

Question 1: Historically, instrument air was used to purge FCC reactor instruments. More recently, dry gas or nitrogen is typically used for this service. Please explain the reasons for moving away from air and provide examples of operating upsets that have occurred when using air to purge instruments.

Gas purge streams for instrumentation in FCCU reactor-regenerator service are required to ensure their functionality. For example, the reliability of level- and pressure-measuring devices relies on clear impulse lines. The utilization of a continuous-purge gas stream ensures that catalyst particles are prevented from entering or are swept from impulse lines to keep them clear and reliable.

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