SEOUL: South Korea's top refiner SK Energy has shut a residue hydrodesulfurization unit (RHDS) following a small fire at its Ulsan site, a spokeswoman from SK Innovation said on Wednesday.

SK Innovation is the parent company of SK Energy, which operates two refineries, one in Incheon and another in Ulsan.

The restart dates of the 40,000 barrels per day (bpd) RHDS -- a unit which processes feedstock from a crude unit for gasoline-making unit residue fluid catalytic cracker (RFCC) -- was not immediately clear, she said.

One of SK Energy's RFCC, a 57,000 bpd unit, is currently under maintenance since late May. The unit is to restart in mid-July.