Q&A

(2015) Question 72: The FCC is LPG-constrained, and the refinery is octane short. What are your suggested options to increase FCC gasoline octane while minimizing any associated increase in LPG yield?

When the FCC is constrained in LPG and short on octane, the feed is one of the most important parameters for yields and quality of the yields. So, if you can, blend in more aromatic feeds. Or if you have feed pretreat, backing off from it will help improve your gasoline octane.

(2015) Question 73: Octane may become an issue as refiners increase severity on the FCC gasoline post-treatment units. What are your options available to address octane debits?

When you want to reduce the sulfur in gasoline, one of the first options you can do is undercut the gasoline. The sulfur distribution in gasoline is typically exponential. If you reduce the cutpoint of your gasoline, you will reduce the amount of sulfur in your gasoline. Sulfur exhibits an exponential distribution.

(2015) Question 74: For a unit targeting low vapor pressure gasoline, which variables have the greatest impact on isopentane production?

While the question asks specifically about isopentane production, other C5 hydrocarbons also have significant vapor pressure. Isopentane has a Reid Vapor Pressure (RVP) of 20 psi (pounds per square inch); n-pentane has an RVP of 16 psi; and, the C5 olefins have RVPs between 14 and 26 psi9. For refineries desiring to minimize RVP, it is also important to minimize the quantity of C4s in the gasoline pool since C4s have even higher vapor pressures than C5s.

(2015) Question 75: What do you recommend to either prevent the formation of carbonyl sulfide or remove it from the propylene stream? At what level does this become a concern?

Carbonyl sulfide is produced during the cracking reaction and boils slightly below propane at -50°C (-58°F). Upon post-fractionation, it concentrates predominantly in propylene. COS (carbonyl sulfide) level in FCC LPG most strongly corresponds to the sulfur in the feed.

(2015) Question 76: What has been your experience with respect to FCC flue gas analyzers using tunable diode lasers or alternatives? Any specific advantages of tunable diode laser (TDL) analyzers with respect to installation, operational service requirements, and/or reliability?

MPC does not have any TDL analyzers in FCC flue gas service. However, we do have a few installed-on process heaters that are used to measure O2, and we are happy with their performance. In FCC flue gas service, MPC has one unit that utilizes an extractive system.

(2015) Question 77: When relying primarily on FCC feed pretreating to meet FCC gasoline sulfur specifications (current or future Tier 3), how do you manage feed pretreater outages?

Marathon relies on feed pretreating for three of our FCCs, which will all continue post-Tier 3 regulation implementation. Looking at the difference between Tier 2 and Tier 3, we see that when the annual average ppm in gasoline goes down from 30 to 10, the maximum per gallon, I believe, does not change from 80.

(2015) Question 78: Under what conditions do gasoline sulfur reduction additives and catalysts reduce sulfur in gasoline, and by how much? What is the lowest gasoline sulfur level for which the gasoline sulfur reduction products are effective? At this gasoline sulfur level, please quantify the gasoline sulfur reduction and the amount of additive/catalyst required.

That is a very long breath of a question. [Laughter] I will summarize some of the Marathon’s findings on gasoline sulfur reduction additives. We have done a lot of testing in our pilot plant in the past. Some of that has already been presented.

(2015) Question 79: For units that have experienced elevated losses leading to coarse inventory, what options exist to improve catalyst properties during turnaround? Describe your experience with purchasing external or classifying spent catalyst.

We get fixed on how much 0-to-40 micron catalyst is in the inventory. You need 10% to run the unit well. And as Bob Flanders used to say, “Purgatory was trying to run a Model IV with less than 10% fines in it.” What I would suggest is certainly nothing smaller than 20 microns.

(2015) Question 80: What are your Best Practices to address increased levels of conventional and “new” metals (V, Ni, Fe, Ca, Cu etc.) in the FCC that come from tight oil processing in the refinery?

The first consideration should be removal or minimization of the contaminant metals upstream of the FCC. Since removing or limiting these contaminants may not be an option, other methods must be considered to address their negative impacts.

(2015) Question 81: Under what conditions is iron on FCC catalyst mobile, and how does this affect catalyst performance?

The first reports of FCC iron poisoning on a large-scale date from the 1990s. Iron was used in drilling liquids for oil recovery. Iron poisoning results in a loss of activity and an increase in slurry yield. The apparent bulk density of the catalyst decreases, which causes a drop in pressure differential over the standpipes and can lead to erratic catalyst circulation.

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