August US Nitrogen Incident Reported

By Walter F. Roche Jr.

Officials of US Nitrogen have filed a report with the state disclosing that an early August incident forced a shutdown of its Green County ammonia plant.
Calling it a "process upset," US Nitrogen's manager Andrew Velo wrote that the incident resulted in three abnormal flare events "which led to an operating shutdown."
In a letter to Michelle Owenby, the manager of air pollution programs at the Tennessee Department of Environment and Conservation, Velo said that the incident triggered an internal investigation to determine the root cause.
According to the letter, as a result of the investigation some equipment had to be replaced and extensive staff training was implemented. Still further training may yet be required.
The incident is the latest in a series of start up misfires that have triggered concern among some area residents.
Velo wrote that the internal investigation found that liquid carryover from an ammonia liquid let-down vessel led to the incident when the ammonia combined with water to form excess levels of aqua-ammonia, triggering the flare events.
"This level resulted in heavy flare events during plant pressure variations. The investigation team  determined that uncertainty in interpreting the fault state of the level indication on D-7 and the subsequent operational response due to this uncertainty were the main root causes of this incident," Velo's letter states.
The plant manager said the investigative team determined that some changes including the replacement of some equipment had to be completed before the plant could be restarted.
He listed a series of actions, including retesting of all let-down vessels "to verify functionality and reliability, and replacement of a pressure valve.
Velo said all recommended steps were taken before start up  and that the plant has operated without incident since the re-start. He did not disclose the date of the start up.
"Several long term actions related to training and operating procedures have been identified and will be completed in the coming months," the letter concludes.
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