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Accident # | 148798 |
State Police # | 13-02180 |
Accident Date | 2013-05-17 |
Report Date | 2013-05-24 |
Follow-up Date | 2013-07-12 |
Follow-up: | Yes |
Pollutant | Duration | Point Source | Greenhouse Gas | Criteria Pollutant | Ozone forming chemical | Amount of Release |
Sulfur Dioxide | 17h 18m | North Flare, #2 and #3 SRU, Heaters, Reboilers | NO | YES | NO | 2,708.0 pounds |
Hydrogen Sulfide | 17h 18m | North Flare, #2 and #3 SRU, Heaters, Reboilers | NO | NO | NO | 10.0 pounds |
Accident Classified As: Reportable Quantity
On May 17, 2013 at approximately 15:43, Valero experienced excess emissions of Sulfur Dioxide at the North Flare, the #2 and #3 Sulfur Recovery Units, and several refinery fuel gas-fired sources due to an unexpected shutdown of the #3 SRU. The #3 SRU shut down on high burner pressure caused by a plugged condenser seal leg. After several unsuccessful attempts to unplug and restart the #3 SRU, Valero determined that the unit could not be restarted and completely shut down the unit. The Gas-Oil Hydrocracker/Hydrotreater was also shut down and refinery charge rates were reduced accordingly. Valero opened up the unit for inspection and discovered that catalyst from one of the reactor beds had migrated into the condenser and caused the plugging in the seal legs. Valero could not definitively identify the exact cause of the catalyst migration, but believes that it was most likely due to improper catalyst loading during the last catalyst replacement in 2010.
Valero immediately initiated its sulfur shedding procedure and attempted to unplug the #3 SRU condenser and restart the #3 SRU. Valero transferred as much of the remaining sulfur load to the #2 SRU as the unit's capacity would allow. Before the sulfur shedding procedure reduced the sulfur load to within the capacity of the #2 SRU, hydrogen sulfide entered the refinery fuel gas system and was combusted to sulfur dioxide in the refinery heaters and boilers. Hydrogen sulfide concentrations in the refinery fuel gas system returned to less than the 162 ppm NSPS Subpart J limit at approximately 05:14 on May 18, 2013. To prevent recurrence, Valero reloaded the #3 SRU with new catalyst and ensured that the catalyst was properly loaded and supported with additional support media. Valero plans to install a smaller mesh screen on top of the existing quarter inch screen that currently supports the catalyst bed and support media.
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