Valero has shut down its Port Arthur refinery after an explosion late on Monday set a diesel processing unit on fire, Reuters has reported, citing unnamed sources. Other reports say that emergency services have been sent to the site, and a shelter-in-place order has been issued for the western parts of Port Arthur. Al Jazeera said police sources had told local media that the cause of the fire was an industrial heater. Valero’s Port Arthur refinery is one of the largest in the United States, with a daily capacity of 380,000 barrels. Its diesel…