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Valero (26003), Norco

LDEQ Accident Report

Accident #157998
State Police #14-03549
Accident Date2014-08-12
Report Date 2014-10-10
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 Dioxide35m3700 SRUNOYESNO590.2 pounds
Hydrogen Sulfide35m3700 SRUNONONO0.3 pounds

Accident Classified As: Reportable Quantity

Cause of Problem: Process Upset

On 8/12/14 at approximately 10:30 hrs, the 3700 SRU reaction furnace tripped, which led to a reportable quantity of sulfur dioxide (SO2) from the 3700 TOX. The cause of the trip as a controller logic script that auto initiated and propagated an incorrect flow measurement to the Combustion Air Blowers (K-37-391 A and B). The incorrect flow measurement caused the blower control scheme to falsely assume surge operating conditions and correspondingly the atmospheric discharge vent opened. When the discharge vent opened, it significantly reduced the combustion air flow to the reaction furnace which initiated a Safety Instrumented System trip of the unit.

Discharge Preventable - No

The incident is not considered reasonably preventable. The anti-surge scripts that ran were located on the host server machine during an alarm rationalization project. The scripts ran without being manually executed and the contractor used to investigate the incident could not replicate the automated script execution.

Notes/Remedial Actions

Emissions were minimized by transferring SRU feed to other operating trains, until the 3700 SRU was restarted. The following corrective actions were taken: 1) Review the incident with all affected personnel 2) Determine if a two second delay to blower anti-surge logic to accommodate bad flow indication should be programmed into the logic 3) Remove all custom scripts from host computers 4) Update the CSE Change Approval Matrix to include additional QA/QC procedures.