UPDATE 1-Steam loss shuts Petro-Canada Alberta refinery

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CALGARY, Alberta, July 10 (Reuters) - Petro-Canada said on Thursday it has shut down its 135,000 barrel per day refinery in Edmonton, Alberta, after an unspecified incident forced the company to depressurize some units after steam boilers lost water.

Kelli Stevens, a spokeswoman for the company, said Petro-Canada can't yet say when the facility will return to normal operation.

"We want to bring it back safely and as quickly as possible," she said.

With the boilers down, the refinery could not produce the steam that is crucial to its operations. Lack of steam also caused smoky flaring at the facility, which was quickly brought under control, Stevens said

She said she does not expect supply shortages because of the shutdown

Petro-Canada is close to wrapping up a C$2.2 billion ($2.2 billion) project at the Edmonton refinery that will enable it to process the tar-like bitumen produced at its northern Alberta oil sands operations.

The company has scheduled a 60-day maintenance closure at the site beginning in mid-August to tie in the new equipment. ($1=$1.01 Canadian) (Reporting by Scott Haggett; editing by Rob Wilson)