Q&A

(2014) Question 25: What factors contribute to your decision to place the regeneration section of a CCR in standby mode when the unit is operating in a low-coke mode? Discuss the advantages and disadvantages of the different standby modes (black-catalyst circulation, hot-shutdown, cold-shutdown, etc.).

If the coke content is very low in comparison with the coke burn capacity of the CCR unit, the operation can be limited in one of a few ways. A minimum gas flow is required to ensure the catalyst is properly dried before leaving the regenerator and returning for reduction.

(2014) Question 26: What are options for disposition of the caustic regeneration outgas stream associated with an LPG or gasoline caustic treater? What measures have you successfully used to prevent fouling, pluggage, and corrosion in this line?

The caustic treating off gas stream is primarily air that has been partially depleted of oxygen during the oxidation of mercaptides to disulfides in the caustic regeneration step.

(2014) Question 27: What impacts are you seeing in naphtha processing units from contaminants suspected to come from shale crudes (e.g. tramp amines, chlorides, fouling)? What are you doing to mitigate these impacts?

Tramp amines, chlorides, and fouling related to processing of Shale Crudes (or more specifically, Tight Oils) are issues that are of concern on the Crude Unit. I am not aware of issues specific to the gasoline pool and blending downstream of the crude unit.

(2014) Question 28: What is your best practice for determining the maximum allowable temperature rise in hydrotreating beds? What solutions do you have for managing temperature rise?

Operating philosophy regarding the maximum allowable temperature rise in hydrotreating beds from a design perspective is determined by several factors.

(2014) Question 29: What are your current best practices for protecting the charge heater from backflow?

Our design practice for a gas only heater uses a check valve at the outlet of the heater mainly to cut down on the chance of liquid flowing back into the heater during a compressor trip.

(2014) Question 30: What is your minimum charge heater firing limit, especially when highly heat integrated or when processing cracked stocks? Do you have any hydroprocessing units run without firing the charge heater?

The low firing limit is caused by burner instability. Heaters can be turned down by completely shutting off some burners; but there is also a firebox temperature component. Burner instability would be noticed visually – examples being flickering, irregular flame pattern plus increased CO emission.

(2014) Question 31: As more and more refiners consider installing zeolite catalyst in their hydrotreating units, what are your recommendations for a depressuring system?

Though many hydrotreating units operate at lower pressures than most hydrocracking units, loading zeolite catalysts poses a risk of temperature excursion which should be mitigated. Reactor thermometry, depressuring system capacity, and automating depressuring based on indication of excursion must be evaluated when cracking catalyst is loaded in a hydrotreating unit.

(2014) Question 32: How does catalyst activity, run length, H2 uptake, volume swell, reactor temperatures, price of the catalyst and product quality impact optimizing the business case for a catalyst selection? Compare a regen catalyst, moderate activity and next generation catalysts in a cheap H2 available market.

Refinery Process Engineers are often confronted with a complex and time-consuming process when it comes to choosing a catalyst for their hydrotreating units.

(2014) Question 33: What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

Color chemistry is very complex and strongly influenced by the feed molecules and the unit operating conditions. Dehydrogenation of saturated aromatics (condensation) and/or insufficient removal of nitrogen containing molecules can both result in off spec product color issues. Dehydrogenation or condensation reactions are favored by low H2pp and high temperatures.

(2014) Question 34: What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

What solutions do you have for extending cycle length in distillate hydrotreating units limited by product color?

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