Shell California refinery restarted flexicoker Wednesday: filings

(Reuters) - Royal Dutch Shell Plc's 156,400-barrel-per-day Martinez, California, refinery restarted a flexicoker unit on Wednesday, according to notices filed with the Contra Costa Health Department Hazardous Materials Program.

A pressure relief valve failed on the debutanizer column on the flexicoker, which is a type of coking unit, on Tuesday, according to filings with the Contra Costa County Hazardous Materials Program. A coking unit increases the amount of refinabale material in a barrel of oil and converts residual crude to petroleum coke, a coal substitute.

The pressure valve failure released mercaptin and hydrogen sulfide off-site.

Mercaptin is the foul-smelling substance placed in natural gas before it is sent to retail customers to make it possible to easily detect leaks. In its original state, natural gas is odorless.

A fire at the refinery on Monday was caused by a leak of lubricating oil from a compressor on the hydrocracking unit, according to the filings.

The compressor involved in the fire was in normal operation at the time the fire started, according to a report filed with Contra Costa County by the refinery.

When the fire was discovered, workers were evacuated from the area, firefighters began suppressing the blaze and the unit was shut down, according to the report.

The hydrocracker blaze was the second at an area refinery in two weeks. On August 6 a six-hour blaze shut the crude distillation unit at Chevron Corp's 245,000 bpd Richmond, California, refinery, located 22 miles west of the Shell Martinez refinery.

The Chevron fire has triggered widespread concern about refinery reliability and safety among residents in the San Francisco Bay area.

(Reporting by Erwin Seba in Houston; Editing by Lisa Von Ahn and Phil Berlowitz)