UPDATE 1-Shell restarts Martinez hydrocracker - source

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HOUSTON, May 16 (Reuters) - Shell's 156,000-barrel-per-day San Francisco Bay-area refinery in Martinez, California, restarted a hydrocracker on Thursday, according to a source familiar with refinery operations.

A Shell representative was not available to discuss refinery operations.

The refinery reported a compressor upset to California pollution regulators on May 8, but had not said to which unit the compressor belonged.

Trade sources said on Friday the hydrocracker was shut on May 8.

On May 9, Shell had said everything was operating normally at the refinery after the compressor returned to service.

According to U.S. Energy Information Administration, the Martinez refinery has a 42,000 bpd distillate catalytic hydrocracker.

A distillate catalytic hydrocracker uses a catalyst, often a very fine powder that behaves almost like a liquid, and hydrogen to further refine diesels and jet fuel made from crude oil. (Reporting by Erwin Seba; Editing by Christian Wiessner)