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Accident # | 157998 |
State Police # | 14-03549 |
Accident Date | 2014-08-12 |
Report Date | 2014-10-10 |
Follow-up Date | 0000-00-00 |
Follow-up: | No |
Pollutant | Duration | Point Source | Greenhouse Gas | Criteria Pollutant | Ozone forming chemical | Amount of Release |
Sulfur Dioxide | 35m | 3700 SRU | NO | YES | NO | 590.2 pounds |
Hydrogen Sulfide | 35m | 3700 SRU | NO | NO | NO | 0.3 pounds |
Accident Classified As: Reportable Quantity
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.
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.
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.
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