Q&A

(2017) Question 14: For units that feed hydrocracked naphtha directly to the reforming unit, what is the typical concentration of sulfur in the feed? How does the concentration change over the hydrocracker catalyst cycle, and what are the impacts to the operation of the reformer?

At start-of-run conditions in a hydrocracking unit, the sulfur in hydrocracked naphtha can be between 2 and 5 ppmw. At end-of-run conditions, the sulfur can be between 10 and 20 ppmw. As high 40 ppmw has been observed at end-of-run conditions for one customer.

(2017) Question 15: For units that feed hydrocracked naphtha directly to the reforming unit, what is the typical concentration of olefins in the feed? How does the concentration change over the hydrocracker catalyst cycle, and what are the impacts to the operation of the reformer?

Olefins are expected to be saturated in the first bed of the hydrocracking unit. At start-of-run conditions, olefins are not expected to be found in hydrocracked naphtha.

(2017) Question 16: HCl concentration in the reformer net off-gas is being actively measured using hand-held detector tubes. Despite routinely measuring near-zero ppm (parts per million), chloride corrosion occurs downstream. What is the source of this corrosion, and what can be done to better measure and manage the source?

Organic chlorides can be invisible to simple HCl- detecting tubes. There are alternative measuring devices from which to choose to detect organic chlorides. It is well known that organic chlorides can be created from an alumina guard bed and cause green oil, chloride salt formation, and corrosion downstream.

(2017) Question 17: What is the importance of water content in reformer feed and recycle gas on the performance of the catalyst? What are your desired water concentrations in each of these streams?

Managing the water content in the reactive environment is critical for the overall performance of the reformer unit and catalyst. The content of water (H2O) must be controlled to allow for a sufficient quantity of hydroxyl [AlOH (aluminum hydroxide)] sites while simultaneously controlling the hydrogen chloride (HCl) levels to have the right balance of H2O/HCl to set the catalyst HCl content (Al-Cl).

(2017) Question 18: In a fixed-bed reformer regeneration, caustic is used to neutralize the combustion and chlorination gasses. How do you dispose of caustic after the regeneration is complete?

During the regeneration step of fixed-bed reformers, caustic is typically used to neutralize the regeneration effluent. Additional use of sodium bicarbonate to maintain the pH of the neutralization solution has also been utilized and is included for disposal.

(2017) Question 19: What are your Best Practices for recovering from high coke on spent catalyst in continuously regenerating reforming units?

The Honeywell UOP Platforming™ CCR regenerator is designed to burn 5 wt% (weight percent) carbon off catalyst circulating at 100% of the design rate. Most units can successfully burn off significantly more coke than design at normal operating conditions when the screens are clean and regeneration gas flow is uniform. Note that if there is screen fouling or some other condition leading to non-uniform or reduced flow, the coke-burning capacity would be reduced.

(2017) Question 20: What is your Best Practice for handling temperature excursions for hydrocrackers? Is a manual or automatic control system best?

Automatic depressuring on a “defined” temperature excursion is the procedure considered to be Best Practice and can be used to prevent the potential failure of the reactor outlet elbow or line. Automatic depressuring retrofits to existing units continues in industry.

(2017) Question 21: What are some of your typical examples of integrity operating window (IOW) types which are specific to hydroprocessing? What technique do you use to determine severity level of IOW alarms? How do you coordinate operator response to IOW alarms?

Hydroprocessing is an area that is somewhat unique in refining in the sense that it has everything that you do not want for mechanical integrity: high temperature, high pressure, and a process that can run away at both, as well as high concentrations of hydrogen sulfide and hydrogen; and just to make things fun, injection of water into the process.

(2017) Question 22: A) What has been your experience with hydrogen leaks to cooling water systems and the resulting impacts? B) What are your findings and recommendations from major associated incidents?

I have seen an instance where hydrogen leaking to a cooling water system was detected by a local VOC monitor at the cooling tower. The source was isolated as a pinhole leak at the hydrocracker unit’s makeup hydrogen cooler.

(2017) Question 23: When shutting down a reactor, what is your current Best Practice for measuring CO (carbon monoxide) in a mostly hydrogen/nitrogen atmosphere to assess the carbonyl concentration? Is the steel a potential source of zero-valence metal necessary for carbonyl formation? If so, does that cause a corrosion concern for equipment that normally operates in the temperature range favorable for carbonyl formation?

When shutting down a reactor, what is your current Best Practice for measuring CO (carbon monoxide) in a mostly hydrogen/nitrogen atmosphere to assess the carbonyl concentration? Is the steel a potential source of zero-valence metal necessary for carbonyl formation? If so, does that cause a corrosion concern for equipment that normally operates in the temperature range favorable for carbonyl formation?

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