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Louisiana Refinery Accident Database

Valero (1238), Meraux

LDEQ Accident Report

Pollutants Released

Accident Classified As: Reportable Quantity

Cause of Problem: Equipment Design

Valero experienced excess emissions of SO2 and H2S at the North Flare, South Flare, and #2 Sulfur Recovery Unit (SRU) Incinerator Stack due to a sudden electrical transformer failure that cut power to several process areas within the refinery. Valero determined the root cause to be an electrical failure caused by water intrusion into the air terminal chamber on the 13.8 KV side of the transformer and inadequate insulation on the bus bar and connections. It appears that when the transformer was installed the 13.8KV incoming cables were too short to reach the transformer bushing so a field designed buss work and air terminal chamber was used. This locally designed air terminal chamber proved inadequate to protect the transformer breaker were improperly set and allow too much current to flow to the fault which caused voltage to sag across the reinfery and unnecessary tripped loads that upset other units.

Discharge Preventable - No

This was a sudden, infrequent equipment failure caused by a design flaw previously unknown to exist.

Notes/Remedial Actions

The refinery initiated shutdown procedures for all affected units and followed the MACT UUU SSM Plan to recover the #2 Sulfur Recovery Unit (SRU) and #2 Tail Gas Treater (TGT). The #2 TGT was bypassed during the upset and subsequent startup. All refinery transformers were visually inspected for signs of water intrusion. Water was found in one other transformer of the same design which was removed and the air terminal box was sealed. The damaged transformer was replaced and a new overhead cable was used to replace the underground cable that was too short. Relay trip settings were changed to better coordinate and protect equipment and prevent unnecessarily upsetting other units. Valero has initiated a project to design and install appropriate terminal boxes in place of the locally designed ores for the three remaining transformers of the same design on site. According to the LDEQ's list of reportable quantities, the reportable quantity for SO2 is 500 pounds.