No violations found in refinery outage
A report released by Solano County environmental health investigators found that Valero Benicia Refinery did not violate any Certified Unified Program Agencies regulations when more than 74,000 pounds of sulfur dioxide were released into the air following a flareup back in May and at least two other release incidents. However, the Environmental Health Division is waiting to go over a root cause analysis with Valero to make recommendations to prevent another shutdown in the vein of the May 5 incident from happening again.
The report, released at the end of August, details the incident on May 5 as well as a coker unit release on May 8 and a coker relief valve release on May 15. It also includes notes of the multiple meetings that took place with Valero staff in subsequent months.
On May 5, the Valero refinery underwent an emergency shutdown as Pacific Gas & Electric was doing maintenance on power lines.
“With the electrical power off all equipment was down, except for system controllers and computers and computers, which are fed from a 500 kilowatt backup electrical generator and UPS system,” the report said.
With the steam boilers not operating, the flare stack does not work as usual, resulting in incomplete combustion that forms soot, the report said. The report also noted that the lack of a cooling water system enabled process equipment to heat up and triggered a variety of safety systems, including a pressure dump stack. The dump stack ignited, but was extinguished within the first hour of the incident and vented for approximately two hours.
Afterward, the Industrial Park was evacuated and closed off, nearby Robert Semple and Matthew Turner elementary schools established shelters-in-place and the city activated its Emergency Operations Centers, where staff are reassigned from their normal duties. The city also coordinated with a variety of local, regional and state agencies, including the California Air Resources Board, the Bay Area Air Quality Management District and the U.S. Environmental Protection Agency. After conducting an environmental evaluation of the school areas, Solano County’s health officer lifted the shelter in place at the two schools and the Fire Department gave the all-clear notice around 6:45 p.m., the report said.
Three days later during the refinery’s restart, there was an additional release from the flue gas scrubber with occurred from around 3:30 to 9 p.m. The emergency shutdown charged the coker unit with unburned hydrocarbon fines that overloaded the scrubber, releasing the fines, the report said.
On May 15, the coker’s pressure relief and control valves vented, resulting in flaring. The Environmental Health Department attributed the release to trapped condensate water in the piping system as a result of the May 5 shutdown.
The Environmental Health Department and California Occupational Safety and Health Administration (CalOSHA) requested Valero staff hold an informational review meeting, which they did on five dates. At the May 9 meeting, Valero staff provided a site tour. The report noted that the dump stack had darkened paint areas from the fire at the top, but Valero staff did not identify any other damage.
At the May 10 meeting, the Environmental Health Department reviewed the co-generation unit.
“Even though the steam is produced in a Cogen Unit that could be considered to operate independently from the electrical grid, the Cogen Unit cannot operate independently from the grid,” the report said. “The Cogen Unit must have PG&E power to start up and continue to operate.”
The report also noted that the lack of electrical power led to a drop in steam pressure, resulting in the flare stack flume changing its color from a “white, nearly smokeless discharge” to an “orange flume and black soot formation” rising from both flare tops.
“Without adequate steam to properly atomize the unburned hydrocarbons flowing to the flare stack, the flare stack did not properly burn the petroleum hydrocarbons, which resulted in a release of soot to the atmosphere,” the report said. “Without continued production of steam, the existing steam condensed in the steam supply lines.”
After the boilers restarted, Valero increased steam pressure until the color of the flume changed back to normal.
At the May 26 meeting, Valero staff said they had inspected both flare stacks and they were running normally. They also said they would continue to investigate the May 8 release.
At the June 19 meeting, a coker subject matter expert explained that unburned hydrocarbons from the May 5 shutdown were still in the coker unit on May 8. The new flue gas scrubber quickly became overloaded, resulting in unburned hydrocarbons being sent out into the atmosphere.
At the July 26 meeting, the subject matter expert explained that the May 15 release was due to trapped condensate water in the piping system from the May 5 shutdown.
“The Coker system must be maintained at elevated temperatures to avoid piping pluggage problems,” the report said.
After several days, the blockage cleared and the condensate water turned to steam causing the system to become overpressured and valves to vent to the flares stack, which resulted in flaring.
The Environmental Health Department recommended that Valero conduct a root cause analysis of the three flaring incidents by Oct. 15. Environmental Health manager Jagjinder Sahota said Valero completed the analysis and have scheduled a meeting for the department in early November to go over the root causes and receive further recommendations.