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|State Police #||11-05467|
|Pollutant||Duration||Point Source||Greenhouse Gas||Criteria Pollutant||Ozone forming chemical||Amount of Release|
|Sulfur Dioxide||19 h 36 m||Flare||NO||YES||NO||1,695.0 pounds|
Accident Classified As: Reportable Quantity
On 9/3/11 at 12 noon the Coker Unit was reduced to minimal operating dates due to approaching Tropical Storm Lee. This was done in an effort to extend the Coke Drum cycle time by several hours so that refinery personnel would be out of danger and not located on the tail Coke Drum structure during the highest winds of Tropical Storm Lee. The reduction in Coker feed caused the Coker compressor's surge controller kick back valve to rapidly open several times almost tripping the compressor off-line because of this surging affect. During another surge event, the compressor's kickback valve opened rapidly subsequently increasing pressure at the compressor's suction drum above its set point. When this occurred, the console board operator changed the flare valve from automatic control to manual control in an effort to prevent the flare valve from suddenly opening during future compressor surging events. When the board operator put the flare valve in manual control, the valve was already opened at 8% output and the console board operator thought he had placed the valve in manual control when the computer graphic display showed the flare valve at 0% open. When the flare valve opens, the compressor's suction steam is automatically diverted to the Low Pressure Flare (308F-D-1). The Coker compressor did not surge any further after the flare valve's control scheme was changed. The console board operator was unaware that the flare valve remained opened for hours, and when it was discovered opened, the flare valve was immediately closed and returned to automatic control status. A root cause investigation of this flaring event revealed the from the archive history of the Distributed Control System (DCS) that at the same time that the flare valve was put in manual mode it was inadvertently opened to 8% even though the control board operator and his supervisor both reported seeing the DCS Screen display 0% on the valve when it was placed in manual. It was also discovered that ie old DCS system the flare valve had an "output" alarm anytime the valve was at or above 1% open. However during the cutover from the old to the new control system the alarm was not picked up in the migration documental. Had the alarm been in place, it would have benefited the board operator to recognize the flare valve had opened and must be closed immediately. A contributing cause in preventing the board operator from recognizing the flare valve had opened 8% was the fact the board operator, for the next hour, was in a "Major Alarm Flood" (>30 alarms per 10 min period) due to major upsets at the Alkylation Unit (part of the board operator's additional responsibilities) which was enhanced because of very low unit operational rates and ever changing weather conditions from Tropical Storm Lee.
Report indicates that the board operator could have recognized the flare valve was open, but had extra responsibilities due to the weather conditions during the storm. Also, the alarm may have gone unnoticed or may have been faulty.
The compressor's suction drum flare valve was closed and its controller was removed from manual control and returned to automatic control. Corrective actions to address the investigation findings are the following: - Review all control valves to the flare for missing output alarm configurations - Establish the compressor's flare valve with a reoccurring high output alarm at its previous set point of 1% open - Alarm Rationalization team shall review and analyze the alarm flood period surrounding this event for possible alarm improvement opportunities. These tasks have been assigned and are scheduled to be completed before the end of 2011. Weather at the time of the event was rainy and cloudy. Wind direction: 197 degrees SSW Wind speed: 20 mph