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|State Police #||14-00615|
|Pollutant||Duration||Point Source||Greenhouse Gas||Criteria Pollutant||Ozone forming chemical||Amount of Release|
|Sulfur Dioxide||12h 30m||North Falre, #2 SRU Incinerator, & Area 2 Fuel Drum||NO||YES||NO||731.0 pounds|
|Hydrogen Sulfide||12h 30m||North Falre, #2 SRU Incinerator, & Area 2 Fuel Drum||NO||NO||NO||6.0 pounds|
Accident Classified As: Reportable Quantity
On 2/7/2014, Valero exceeded the reporting threshold for sulfur dioxide (SO2). While attempting to identify the source of the increased odor in the North Flare header, the #2 sulfur recovery unit (SRU) shutdown. Valero determined the root cause of the elevated sulfur in the North Flare and the unexpected shutdown of the #2 Sulfur Recovery Unit (SRU) to be open block valve(s) on the Flare Knockout Blowcase [i.e. operator error]. This blowcase is used to periodically drain liquids from either a nearby flare knockout pot or the sour water offgas line feeding the #2 SRU. Liquids are drained into the blowcase and are then pressurized out with natural gas to the #1 Sour Water Stripper. With one or more of the block valves out of position, H2S passed from the sour water offgas line into the North Flare header. Later, to remove the accumulate liquids, the blowcase was pressurized with the block valve(s) still open causing a surge in pressure and flow and possibly entraining liquids through the sour water offgas line to the #2 SRU main burner. The resulting disturbance in the flame pattern was detected by the SRU fire eyes and the unit shutdown.
The blowcase block valves were left open due to operator error.
Valero conducted a search for the source of sulfur in the North Flare as soon as it was detected. Valero initiated the refinery's sulfer shedding procedure and shifted sulfur loads to the #3 SRU after the #2 SRU shutdown. This incident is similar to an incident that occurred on 5/7/12. Valero discovered that one corrective action from this earlier event has not yet been completed. This action was to install check valve(s) on the lines that drain the sour water offgas line to the blowcase. These check valve(s) could have prevented the shutdown of the #2 SRU, but not the elevated H2S in the North Flare. In addition to installed these check valves, Valero will review the procedure for operating the blowcase and conduct refresher training with the operators. Valero will also modify the current piping configuration that allows water to accumulate in the sour waster offgas line, thereby eliminating the need to periodically drain this line using the blowcase. This work will occur during the next turnaround.
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