Q&A

These digital transcripts are meant to share information on process safety practices in order to help improve process safety performance and awareness throughout industry. The goal is to capture and share knowledge that could be used by other companies or sites when developing new process safety practices or improving existing ones. The documents being shared have been used by an industry member, but this does not mean it should be used or that it will produce similar results at any other site. Rather, it is an option to consider when implementing or adjusting programs and practices at a site.

BY THEMSELVES, THESE DIGITAL TRANSCRIPTS ARE NOT STANDARDS OR RECOMMENDED PRACTICES. THEY ARE NOT INTENDED TO REPLACE SOUND ENGINEERING JUDGMENT. THEY DO NOT PRECLUDE THE USE OF ALTERNATIVE METHODS THAT COMPLY WITH LEGAL REQUIREMENTS. A SUBJECT MATTER EXPERT SHOULD BE CONSULTED PRIOR TO DETERMINING WHETHER A PRACTICE CAN BE USED IN ANY SPECIFIC SITUATION.

(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.

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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?

(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?

(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?

(2012) Question 59: What challenges have you faced from processing crudes that contain elevated levels of wax crystal modifiers or flow improver chemicals?