Exxon has begun to restart some units at its refinery in Joliet, Illinois, after a three-week outage. The 251,800-bpd facility was shut down in the middle of July following a power outage caused by a storm. The refinery produces about 9 million gallons daily of gasoline and diesel. “Situations like this take time to recover as they will have to see if the sudden shutdown did damage to any of the units,” an unnamed source close to the company told Reuters at the time. It later emerged that the power outage had affected 16 units at the…