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Louisiana Refinery Accident Database

Valero (1238), Meraux

LDEQ Accident Report

Pollutants Released

Accident Classified As: Reportable Quantity

Cause of Problem: Power Failure

On April 5, 2013 at approximately 08:47, Valero experienced excess emissions of Sulfur Dioxide and Hydrogen Sulfide at the South Flare, the #3 Sulfur Recovery Unit (SRU), and several refinery fuel gas fired sources due to a loss of power to the refinery's Distributed Control System (DCS). The DCS is a computerized system used to monitor and control the refinery process units. At the time of the incident, the most refinery units were shutdown for planned maintenance, only the Reformer, Naptha Hydrotreater (NHT), MiddleDistillate Hydrotreater (MDH), #3 SRU, and the four boilers remained in service. In order to perform work on the electrical distribution system, a temporary generator was installed to power vital loads, including the DCS. Additionally, the DCS Uniterruptible Power Supplies (UPSs) were bypassed for protection so that battery backup was not available. This temporary power generator dropped offline due to loss of communications between the generator and the engine driving the generator. The root cause of the loss of communications was a loose termination connection on a communications cable. The loss of the DCS caused the immediate shutdown of the remaining refinery units. Upon shutdown of the #3 SRU, field operators cut stripping steam to the #2 Amine unit to prevent acid gas flaring. This allowed some H2S to enter the refinery fuel gas system which was then combusted to SO2 as the fired sources were returned to service. The bulk of the SO2 emissions came from the actuation of a Pressure Safety Valve in the MDH that vented H2S containing material to the South Flare.

Discharge Preventable - Yes

The release was preventable.

Notes/Remedial Actions

The DCS was restored in less that 25 minutes. Valero restarted all four boilers, the #3 SRU, and the MDH. The Reformer Charge Heater was re-lit as part of a controlled shutdown and the NHT was shutdown. SO2 emissions from the North Flare occurred on 4/5/13 from 08:47 to 4/5/13 22:51 for a duration of 14.1 hours (14 hours and 6 minutes). An estimated 2417 pounds of SO2 and 10 pounds of H2S were released. Power to the DCS was quickly restored and the affected units were shutdown in a controlled manner. The rental company technician for the generator quickly identified the loose termination connection as the issue, corrected the loose termination, and placed the generator back online in approximately ten to fifteen minutes. Power to the DCS was quickly restored and the affected units were shutdown in a controlled manner. Valero requested a backup generator from the rental company as a spare for the one that had tripped, which arrived later that day.