More than 20 firefighters battled to put out an early hours fire at the Essar refinery in Stanlow.
Crews from Ellesmere Port and Chester were called out to the blaze, which broke out in the early hours of Thursday (November 14).
It is believed to have involved crude oil.
Water jets and foam were used to put out the fire, and firefighters checked there were no further areas of fire before handing the incident back to the company.
A spokesman for Essar said: "At 2.15am this morning, November 14, a furnace fire broke out on a vacuum unit at the Stanlow refinery in Ellesmere Port.
"The incident was dealt with by the site’s emergency response team with support from the Cheshire Fire and Rescue Service. The fire was extinguished within 20 minutes.
“No one was injured during the incident. A full investigation has now begun into the cause of the fire."