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Louisiana Refinery Accident Database

ExxonMobil Refinery (2638), Baton Rouge

LDEQ Accident Report

Pollutants Released

Accident Classified As: Reportable Quantity

Cause of Problem: Equipment Design

This Tail Gas incident violates a 2005 Consent Decree with the U.S. Environmental Protection Agency. ExxonMobil Refinery has to comply with this consent decree and file special incident summary for any incident releasing a quantity greater than 500 pounds SO2. On May 22, 2013 an operator at the Baton Rouge Refinery (BRRF) observed a leak on the Tail Gas Clean-Up Unit (TGCU) combustor. Areas with elevated skin temperature were found on the combustor with insulation on. The team determined that the combustor would have to be shutdown to safely remove the insulation and determine the necessary repairs. At approximately 4:15 am on May 23, the unit reached reduced rates and began bypassing the TGCU and exceeded 250 ppm sulfur dioxide. All three Claus trains were bypassing the TGCU and being routed to the incinerators by about 7:30 am the next day. The insulation was removed and additional infrared scans were performed on the combustor to establish areas for repair/corrective action. Repairs included installation of a pressurized leak box and nitrogen purge box used to mitigate vessel skin temperature increases. The repairs were complete by 22:30 pm on May 24. At 0:40 AM on May 25, natural gas from Claus 400 began routing through the combustor to bring the tail gas unit up to operating temperature. All Claus tail gas was being routed through the TGCU by approximately 5:35 Am on May 25 and the 12 hour average on the incinerator SO2 CEMs dropped below 250 ppmv SO2 at 19:00 PM on May 25. The combustor design specified a need for personal protection associated with the heat from the combustor outer surface. During the combustor installation in 1996, insulation was installed as a barrier for the vessel outer surface temperature. However, design and installation failed to follow a procedure which specified that insulation should not be utilized for refractory lined vessels. Based on review of vessel integrity failure mechanism, it is believed that the insulation restricted heat transfer across the vessel surface and created isolated areas of elevated temperature leading to metal fatigue. The emission calculations for the Tail Gas Exceedance are as follows: The analyzer associated with the incinerator was reading maximum range, so ExxonMobil used the following calculation to estimate the quantity of sulfur dioxide released: Tons of SO2 = Acid Gas Rate to sulfur plant * SO2 factor based on 2009 turnaround emissions. Where the acid gas rate = mcf/event = 26.57 mcf. SO2 factor based on data from 2009 turnaround = tons/mcf = 2.0. Tons of SO2 = 26/57 * 2.0 tons SO2/mcf = 53.14 tons SO2.

Discharge Preventable - No Information Given

It is important to note that the 2009 turnaround on the combustor noted no major visual equipment degradation after 18 years in service. There were no indications of the potential vessel metallurgy failure at the leak location.

Notes/Remedial Actions

The refinery quickly began reducing rates and maintained reduced rates until the combustor was repaired. Additional ExxonMobil personnel worked to ensure inspections and corrective actions were completed as soon as possible. Contractors and mechanical personnel worked overtime to build and install the leak box. One corrective action that was completed at time of the facility report is the insulation was reoved from the combustor to alleviate metal fatigue mechanism. BRRF determined that the following corrective action is required: develop plan to identify and evaluate other similar refractory lined equipment within the complex for potential for metal fatigue mechanism. The corrective action is scheduled for completion by 3rd quarter of 2014. ExxonMobil will submit a final report within 30 days of the completion of all corrective actions.