Q&A

(2012) 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.

(2012) 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.

(2012) 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.

(2012) 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.

(2012) 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.

(2012) 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.

(2012) 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.

(2012) Question 62: What are causes of foaming in crude pre-flash drums and towers, and what options are available to mitigate foaming?

Surfactants cause foaming. Mike will discuss surfactants and amines that should not be in the crude. Sodium naphthenate is a common surfactant produced by the reaction of caustic injected at the desalter effluent and naphthenic hydrocarbons.

(2012) Question 63: Crude and vacuum tower off gas production from bitumen crudes can be quite variable depending on feedstock quality. Please comment on observed off gas production when processing bitumen crudes.

Our response to this particular question is based on the presumption that bitumen crudes include the conventional Canadian heavy supply of crudes such as Lloydminster and Cold Lake. There has not been much Canadian tar sands bitumen actually processed within BP, either as a synbit (bitumen diluted with synthetic crude) or a dilbit (bitumen diluted with condensate) as of yet. Some of this new bitumen supply includes supplies such as Christina Lake, Sunrise, and Firebag bitumen.

(2012) Question 64: Based on your experience, what are causes of fouling in the diesel/distillate draws of crude, vacuum, and coker fractionation towers? Does this migrate to downstream diesel hydrotreating units? What mitigation strategies are being employed to overcome these issues?

We have been concerned with potential phosphorous fouling on units processing Canadian heavy crude oil. We are aware that some refiners have experienced and reported on significant phosphorus fouling issues in the light diesel or jet draw section of the crude tower, as well as in the crude furnace. While we are concerned with the issue and monitor for it, we have not had any particular callout issues with CDU phosphorus fouling.

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