| American Fuel & Petrochemical Manufacturers

Question 61: Extensive use of upstream H2S scavengers in crude oils can cause salt deposition in atmospheric tower overhead systems, as well as on atmospheric tower trays, particularly when trying to operate at lower naphtha endpoints. What adjustments in desalter operation are used to mitigate amine salt deposition?

H2S scavengers may cause salt deposition in atmospheric towers. Triazine, the most common scavenger, is made by reacting formaldehyde with an amine, such as MEA (monoethanolamine), and creates an MEA-based triazine; similarly with methylamine-based triazine.

Question 60: With an increasingly varied crude slate, how are you managing substantial variability in salt levels in desalted crude and overhead neutralizer rates? How can this impact the amount and location of amine salt and other deposition in the atmospheric tower and overhead system?

The salt loading in the overhead is set by the salt loading leaving the desalters. Two key factors are the salt content of the oil and the salt coming in with the entrained water.

Question 59: What challenges have you faced from processing crudes that contain elevated levels of wax crystal modifiers or flow improver chemicals?

This is a complex question. There are many different chemical families that can be employed as either wax crystal modifiers or flow improvers. Flow improvers can be dragging reducers or pour point depressants. I recommend empirically measuring its impact.

Question 58: Does your site/company require the use of a chemical wash to mitigate possible pyrophoric scale hazards in columns with structured packed beds?

We currently have an Advisory Policy requiring an oxidative chemical wash to help preclude any event from pyrophoric scale accumulation when the towers utilize structured packed beds. This policy is currently being progressed to a Mandatory Process Safety Policy.

Question 57: Do your CDUs/VDUs (crude distillation units/vacuum distillation units) employ automatic trip systems to mitigate tower level overfills? What is considered the Best Practice for high level detection and response?

We do have a High Integrity Pressure Protection System, or a HIPPS, that is going to be installed on a crude unit vacuum tower at our Detroit refinery this fall.

Question 56: Startup, shutdown, and upset conditions can result in abnormal pressure conditions in process equipment and connected utilities. What are the panel's experiences with reverse flow of hydrocarbon into the connected steam systems? What designs and practices are employed to prevent this?

In terms of hydrocarbon reversing to steam systems, there are several ways to go about it. The best and most effective approach is design.

Question 55: Leaks in a vacuum system can result in oxygen ingress into the process. What are the panelists’ experiences/practices with respect to safe sampling and monitoring of vacuum system off gas quality?

Oxygen ingress is a serious concern. For the vacuum units which route the tail gas for processing into a fuel gas header or to downstream LPG (liquefied petroleum gas) recovery unit, we require them to have an online O2 analyzer on the tail gas stream.

Question 54: Does the panel have experience chemically cleaning their reforming unit reactor circuit to minimize the lower explosive limit (LEL) when opening up equipment to the atmosphere in an effort to comply with environmental regulation? If so, is the chemical compatible with the catalyst?

HollyFrontier does not have experience using a chemical in this case. Our normal procedure involves coke burning prior to opening the reactor, and there has not been a problem with LEL in the system after that.

Question 53: What is the panel’s experience with addressing reforming unit stabilizer salting?

I actually have three examples that all apply to a reformer stabilizer. The first slide shows what we call our hot wash. By that, I mean we do not lower the temperatures. We will keep the bottoms re-boil temp in the 440°F to 480°F range. We then have two options on this hot wash. If we just see a high differential pressure on the overhead cooler, then we will put the water in front of that air cooler.

Question 52: What is your recommended method for mitigating fouling in reforming unit recycle compressors? Has any technique proven successful? Is anyone using reformate to clean the compressor online?

The best method for reducing fouling in the compressor is to take the nitrogen out of the feed. In Valero, we have recently reviewed our naphtha hydrotreater performance. In a lot of cases, we found that the naphtha hydrotreaters can actually be pressure drop-limited versus activity-limited.