Q&A

(2012) Question 30: How are water drains routed in alkylation units; for instance, in waterwash or propane drying services? What options exist for separation of the water and entrained light hydrocarbons? How can enclosed systems be monitored?

In many units, including both HF (hydrogen fluoride) and sulfuric acid alkylation units, there may be opportunity to drain water from vessels that contain hydrocarbon.

(2012) Question 31: What is the panel’s experience with temperature excursions (regeneration and otherwise) leading to the catalyst or equipment damage in reforming and isomerization units?

In a refinery where I used to work, our moving-bed reformer experienced a severe temperature excursion in the chlorination zone of the regenerator. After a prolonged outage on the regenerator, the unit was put back into white burns sooner than would have been recommended.

(2012) Question 32: What are the impacts of the presence of acetone in the alkylation unit feed? How is this formed in the FCC? Comment on both HF and sulfuric units.

In both HF and sulfuric acid units, acetone will consume acid, resulting in a reduced acid strength. Regarding sulfuric acid units, some documentation that I got from DuPont STRATCO indicated that one pound of acetone will consume about 10.5 pounds of acid.

(2012) Question 33: Increased feed sulfur increases acid consumption. How does it affect alkylate yield and/or alkylate properties?

In HF units, when sulfur is in the feed, it produces acid-soluble oil (ASO), organic fluorides, and polymers, which then have to be removed through the regeneration process. The light ends that are contained in this ASO can put more pressure on the regeneration system and lead to the higher acid losses. So that is the mechanism there.

(2012) Question 34: Fresh sulfuric acid fed to an alkylation unit can contain niter (nitrosylsulfuric acid) which may lead to excessive corrosion. What is niter; what does it do; can we test for it; and how can we reduce the levels in our fresh acid?

“Niter” is actually a common term referring to the amount of NOx (nitrogen oxide) or nitrates in the sulfuric acid. It is actually generated in the sulfuric acid regeneration process. One of the first steps you go through in acid regeneration is a combustion furnace. In that combustion furnace, you can generate NOx, which is really a function of your peak flame temperature and excess oxygen: the normal NOx contributors.

(2012) Question 35: Does the panel have any experience intentionally producing a ‘heavy’ alkylate stream? What are the disposition options for this stream?

Phillips 66 has one location that makes odorless mineral spirits (OMS), starting with the raw alkylate off of the deisobutanizer column. We take those bottoms through a rerun where we drive off to 340ºF, and then that stream goes right back into alkylation unit storage.

(2012) Question 36: What is the panel’s experience with the latest technologies used to control the bromine index (BI) in aromatic streams, other than clay treatment? How many units are operational, and how were these justified?

The most prevalent technologies for bromine index control are clay treating and selective hydrogenation of the olefins. At Axens, we recommend the selective hydrogenation route to control the olefins and trace diolefins that may appear in your aromatic streams. Last year at the NPRA Q&A, there was a similar question about the different reactive mechanisms between clay and selective hydrogenation.

(2012) Question 37: What is the panel's experience in operating chlorided isomerization units, which were not designed specifically for benzene saturation, in a benzene saturation mode? How are operational parameters adjusted for the different operation?

This is a good question; because as we blend more ethanol into the gasoline pool, a lot of refineries become octane-long and RVP (Reid Vapor Pressure)-long as well. So, the incentives to isomerize are diminishing as you blend more ethanol. Within Valero, we looked at one of our isomerization units and did a project to convert it into a benzene saturation unit but without capital improvements.

(2012) Question 38: Does the panel have experience with mercury contamination of feedstocks to gasoline processing units? What are the typical crude sources that can potentially contain mercury? What units are likely to be most impacted, and how?

Mercury is an ever-increasing problem that we see. It is coming in higher quantities and in more various crudes. Crudes from the East Asia region have historically been known to contain quite a bit of mercury.

(2012) Question 39: What options are available for managing blend stream Reid Vapor Pressure (RVP) and pentane content during the summer blend season? Discuss operational changes in existing equipment, simple modifications, and large capital projects.

Each refinery configuration will obviously be very different, so there is never going to be a one-size-fits-all solution for managing gasoline component RVP or dealing with pentane streams. However, there are certainly many common elements that can be explored.

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