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|State Police #||12-06210|
|Pollutant||Duration||Point Source||Greenhouse Gas||Criteria Pollutant||Ozone forming chemical||Amount of Release|
|Carbon Monoxide||33m||Wet Gas Compressor||NO||YES||NO||951.0 pounds|
|NOx||33m||Wet Gas Compressor||NO||NO||YES||102.0 pounds|
|Particulate Matter||33m||Wet Gas Compressor||NO||YES||NO||3.0 pounds|
|Volatile Organic Compounds (VOCs)||33m||Wet Gas Compressor||NO||NO||YES||4.0 pounds|
|Sulfur Dioxide||33m||Wet Gas Compressor||NO||YES||NO||12,643.0 pounds|
|Hydrogen Sulfide||33m||Wet Gas Compressor||NO||NO||NO||33.0 pounds|
Accident Classified As: Reportable Quantity
The Wet Gas Compressor (WGC) in the delayed coking unit had malfunctioned resulting in excess SO2 emissions at Flares 1 and 2. The WGC malfunction was caused by a loss of power to the Bentley Nevada (B/N) Control Panel. The B/N Panel is powered by two separate supply feeders, each having a breaker. Maintenance personnel who were investigating the WGC malfunction found that both power source breakers to the B/N panel had tripped causing the WGC to lose power, which resulted in flaring. It could not be determined if both breakers tripped at the same time or if one had failed earlier eliminating the redundancy. Maintenance personnel could not find any issues inside the B/N panel so they reset the breakers and restored the power to the panel. The WGC compressor was reset and restarted without further issue. This event is considered reasonably unforeseeable and therefore qualifies as an "upset."
According to the follow up letter sent by Valero, this incident was not preventable as there was no clear cause for the release attributable to operation or or maintenance of the WGC.
Gas from the coker was combusted in Flare 1 and 2 and the resulting combustion byproducts rapidly dispersed. Emissions were minimized by restarting the wet gas compressor. In the future, the facility will communicate the incident to all affected personnel. They will install a power monitoring system that will trigger an alarm on the Distributed Control System (DCS) if one of the power system fails. They will also install breakers separated by a physical gap on the power supply. Finally, they will review other Bentley Nevada systems in the refinery for similar issues. The reportable quantity for SO2 was exceeded.
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