HOUSTON - BP Plc’s 413,500 barrel per day (bpd) Whiting, Indiana, refinery returned to normal operations by late Wednesday morning following a malfunction on a diesel hydrotreating unit (HTU), sources familiar with plant operations said. A BP spokesman declined on Wednesday to discuss operations at the Whiting refinery. The upset had a minor impact on production at the refinery, the sources said. They did not identify which of two hydrotreaters removing sulfur from distillates had the malfunction. The two hydrotreaters are of similar size with a 36,000 bpd HTU used in ultra-low-sulfur diesel production and at 40,000 bpd HTU used for distillate production. Energy industry intelligence service Genscape reported the refinery used its safety flare for three hours on Wednesday morning. Refineries operate their flare system when hydrocarbon feedstocks cannot be processed normally.