Marathon Petroleum Company has adopted the philosophy of optimizing the hydrotreater and hydrocracking catalyst together as one unit. We do not measure nitrogen slip from the hydrotreater section, but rather allow the hydrocracker apparent conversion dictate adjustments to the pretreat section.

In nearly all hydroprocessing heaters, MPC has installed tubeskin thermocouples in order to provide continuous monitoring of tube metal temperatures to the DCS (distributed control system) operator. These thermocouples are strategically located in the heater at the areas with the highest estimated maximum heat flux.

Austenitic stainless steels (200-and 300-series steel) are the most common type of stainless steels. Austenite refers specifically to the geometry of the steel (face-centered cubic crystal). These types of steel are most typically recognized as non-magnetic. Austenitic steels are widely used in the industry because they have very desirable mechanical properties. Their austenitic structure is very tough and ductile down to absolute zero. They also do not lose their strength at elevated temperatures as rapidly as ferritic iron base alloys.

The sulfur target for hydrotreated FCC gasoline is very site dependent. But where possible, it is desirable to hydrotreat all other gasoline streams fully so that the FCC naphtha can be treated as mildly as possible. Deeper desulfurization for FCC naphtha results in increased olefin saturation with the resultant octane loss.

Tier 3 drives hydrotreating of essentially all light naphtha streams. Since most United States refineries have FCCs, it is usually desirable to hydrotreat other gasoline streams more completely to minimize the FCC naphtha olefin saturation and the associated octane loss

It is desirable to have a small amount of sulfur in the feed for CCR reforming units in order to reduce the risk of metal catalyzed coke (MCC) formation and heater-tube carburization and dusting. The sulfur interacts with the chromium and the iron to form a protective layer that reduces the penetration of carbon into the metal.

In CCR Platforming™ units, the movement of catalyst through the lift pipe results in contact between the catalyst pills and the inner surface of the lift pipe.

Catalyst unloading from a CCR Platforming™ reactor stack is done under nitrogen atmosphere using the normal catalyst transfer line under the catalyst collector. Typically, the last 10 to 15% of the catalyst unloaded will be contaminated with heel catalyst. This percentage may be higher if there has been damage to internals or blockage of catalyst transfer lines.

The most common situation that results in the contamination of a catalyst load with heel catalyst occurs during a turnaround as a result of accidentally reloading drums of used catalyst that contain heel catalyst back into the reactors. This type of contamination occurs in one or two units every year.

There are two broad scenarios which might result in the catalyst circulation of a CCR Platforming™ unit being stopped for an extended period of time. The first is that there is maintenance being performed that requires the regenerator to be taken off-line for several days.