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Valero (1238), Meraux
LDEQ Accident Report
| Accident # | 150231 |
| State Police # | 13-03516 |
| Accident Date | 2013-08-08 |
| Report Date | 2013-08-15 |
| Follow-up Date | 0000-00-00 |
| Follow-up: | No |
Pollutants Released
| Pollutant | Duration | Point Source | Greenhouse Gas | Criteria Pollutant | Ozone forming chemical | Amount of Release |
| Sulfur Dioxide | 9h 30m | #2 SRU | NO | YES | NO | 5,779.0 pounds |
| Hydrogen Sulfide | 9h 30m | #2 SRU | NO | NO | NO | 16.0 pounds |
Accident Classified As: No Information Given
Cause of Problem: Equipment Failure
Valero experienced excess emissions of SO2 and H2S at the #2 Sulfur Recovery Unit (SRU) and several refinery fuel gas-fired sources due to an unexpected shutdown at the #2 SRU. Valero Maintenance personnel were in a satelite equipment building to replace a cooling fan on the Uninterruptable Power Supply (UPS). When an electrician opened the cabinet to identify the cooling fan, the UPS shut down and power was lost to several key fueling-gas valves on the #2 Sulfur Recovery Unit (SRU). The valves moved to their fail safe position (shut) and the #2 SRU shutdown.
Discharge Preventable - Yes
Valero determined the root cause of the UPS shutdown to be the failure of a static switch control card. The card showed clear evidence of damage on one component. Valero also identified the following contributing factors: 1) An intermittently failing cooling fan was first identified on December 2012. Valero received the replacement fan in January 2013, but did not change it out until August 2013, 2) This particular UPS model has been identified as having static switch failures due to design issues 3) Preventative maintenance was performed on this UPS in June 2013, but the fan was not changed out at the time.
Notes/Remedial Actions
The electrician manually restored power to the #2 SRU fuel gas valves via the manual bypass switch on the UPS. After the Shutdown of the #2 SRU, Valero cut stripping to the #1 Ademine Unit to prevent acid gas flaring. This eventually resulted in increased Sulfur Dioxide emissions from heaters due to elevated hydrogen sulfide in the fuel gas system. The static switch control card was replaced and the UPS was returned to service approximately two hours after it had failed. Valero will also evaluate the following actions to further decrease the likelihood of re occurrence: 1) Replacing the UPS with a newer, more reliable model, 2) Changing out the 120 VAC fuel gas valves to 24 VDC valves that are then powered by the more reliable Distributed Control System (DCS) power supplies. Performing a test of the DCS power supply.
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