Q&A

(2015) Question 52: What approaches are effective for you to reduce aromatic levels in the ULSD product streams?

To reduce aromatic levels, we definitely need to assess the unit’s capabilities. Is it a high hydrogen partial pressure unit with psig greater than 800, and does it have a higher than 4.0 hydrogen availability ratio (HAR)? If both answers are greater than those reference points, then full loading of NiMo catalyst can be employed to give higher hydrogenation and very good aromatic saturation results.

(2015) Question 53: What are your Best Practices used to minimize the time needed to prepare a crude storage tank for safe entry?

The biggest obstacle, in my mind, to gain entry a crude tank is the accumulated sludge and solids. There are several strategies operators can use to attack that issue. The first strategy is to keep the sludge from accumulating during normal operation. For most MPC refineries, we try to keep our crude tank mixers running as much as possible.

(2015) Question 54: What are your options and Best Practices for routing liquids in a desalter pressure relief scenario if routed to crude fractionator? If routed to crude fractionator, how should one avoid damage caused by water?

The discussion of where to route the discharge of relief valves is always a great conversation, and we are going to talk a lot about what happens in the crude preheat train; and specifically, with desalter PSVs (pressure safety valves). We want to minimize the amount of liquids (especially water) sent to the fractionator whenever possible.

(2015) Question 55: What strategies do you employ to purge solids from recovered oil at the wastewater treatment plant (WWTP) to avoid recycling solids back to the crude unit?

The crude unit wants them out of the crude oil, and the wastewater treatment plant would prefer not to have them. So essentially, we are talking about wastewater treatment solids. Some people call it recovered oil; some people call it slop oil; and some people call it skimmed oil. So, if I interchange these definitions, what I mean is recovered oil from the wastewater treatment plant.

(2015) Question 56: Light slop oils are frequently collected and routed back to the crude unit with fresh crude. In a capacity limited crude unit, this results in backing down crude rate. What are your considerations for injecting slop/recovered oils into process units that avoid backing out crude feed?

This question is a compilation of several that were originally submitted. One of those questions focused on being able to put slop into a pumparound, so we are going to address that as well. But of course, the most important factor about running slops is knowing what it is: understanding whether it is wet or not, whether the quality is known, and whether the quality is consistent.

(2015) Question 57: What are the desalter conditions that may require acidification? If needed, what types of acids do you use and what issues arise downstream?

Under normal operations, having a consistent crude slate and a washwater pH between the 5 and 9, acid addition is not normally required, despite what gravity of crude the refinery is using. There are three situations for having a good conversation with your chemical vendor, if you think you need acid addition. One is removal of tramp amines. The second is metal removal; specifically, calcium or iron.

(2015) Question 58: What issues have you seen in your wastewater treatment plant caused by crudes containing biocides? If so, what parameters have you established to control these effects?

Biocides: Typically, the upstream group wants to kill bugs and the downstream wastewater treatment plant wants to keep them alive. So, you have bacteria in light tight oils, as well as in the oil sands, during crude oil production. The upstream group uses a biocide to prevent the sulfide-reducing bacteria to produce H2S, and the dosage is usually between 25 to 500 parts per million.

(2015) Question 59: What is your experience with hot preheat train and heater fouling attributed to waxy crudes? What methods can be used to identify fouling that is specific to wax in crudes?

For the black and yellow wax, really the biggest issues we have seen are actually from what looks like upstream additives – bromides, in particular – that are coming out in the hydroprocessing area as bromic chloride salts. So that is a little different. Typically, we worry about ammonium chloride. Those two crudes tend to have bromine-type contamination, so you do see some issues with them.

(2015) Question 60: Please describe your experience with the occurrence of phosphorus and barium fouling in the distillate section of the crude tower. What steps have you taken to identify and mitigate the problem?

I know this topic generated a lot of discussion in our Hydrotreating session yesterday. I am mainly, obviously, going to focus on the crude side of it. I will start by saying that basically, it starts with a process to analyze processed crudes for impurities to manage and minimize fouling coming from salts, asphaltene precipitation, and other impurities.

(2015) Question 61: What are the advantages and disadvantages of preflash/pre-topping columns in crude units in terms of operational flexibility to process different API crudes? Please comment on overall energy efficiency and reliability (corrosion).

Preflash drums are useful for removing the vapor from the feed to the atmospheric tower, but there is a lot of debate about its purpose. Many people believe that this is done for energy purposes, but I think those who really study this come to the realization that it is not for energy.

Find the answer to your technical question in AFPM's extensive Q&A database.

Q&A