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.

(2010) Question 26: What are the best practices for entering the vapor space above an internal floating roof in a gasoline tank

Entering the vapor space above an internal floating roof tank creates a set of somewhat unique safety concerns that must be addressed in a facility’s safe work procedures. The primary hazard is entry into an air atmosphere with some level of hydrocarbon vapor or toxics, and liquid hydrocarbon (gasoline for this discussion) beneath the floor, with wiper seals, pontoons, etc. creating a barrier to prevent conditions within the confined space from changing.

(2010) Question 27: It has become increasingly common to chemically neutralize / passivate refinery towers and vessels prior to entry. What are the recommended practices for implementing these tasks? In your experience, what conditions trigger the need for chemical treatment?

Although this list is not “all-inclusive”, here are some general recommended practices when chemical cleaning and/or neutralizing towers and vessels. First, there needs to be a single point of contact for the chemical cleaning vendor. This person is responsible for the planning, preparation and execution of the chemical cleaning process. Prior to cleaning, P&ID’s need to be marked up to identify all injection points, steam and chemical flows and even line ups for the chemical cleaning.

(2010) Question 35: What experiences do the panelists have with naphtha hydrotreater combined feed exchanger fouling? How do you monitor fouling in this exchanger service?

Feed side fouling of the NHT feed/effluent exchanger can be attributable to polymerization of olefins or diolefins. Storage of unsaturated materials from the Coker/FCC/Visbreaker may exacerbate the problem with the introduction of oxygen as a free radical that can promote polymerization.

(2010) Question 36: What are the best practices for maximizing catalyst run length in NHT units that are limited by reactor pressure drop?

Marathon’s experience with NHT fouling has been primarily corrosion products from upstream units and oxygen related polymerization of the naphtha. The use of feed filters can help minimize the effects of corrosion products. Oxygen related polymerization has impacted our NHT units from air leakage across intermediate naphtha storage tank seals and in purchased naphtha.

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