LyondellBasell began restarting a crude distillation unit at its 270,600 barrel-per-day (bpd) Houston refinery on Wednesday, said a company spokesman.

"We began start-up today on the CDU not impacted by the fire," said Lyondell's David Harpole.

The refinery's other CDU was shut by a Monday afternoon fire. Lyondell expects the restarting CDU, which does the initial refining of crude oil coming into the refinery, will be operational by the end of the week, Harpole said. The unit restarting on Wednesday had been shut for unplanned repairs.

Without the CDUs, Lyondell was running partially refined products, called intermediate feedstocks, already on hand through other units still operating at the Houston refinery. If both units had remained shut for long, the company would have been forced to buy intermediate feedstocks to finish at the refinery or finished products to supply their customers.

Crews were carrying out a damage assesement on the CDU hit by the fire. No timeline was available on Wednesday for returning the unit to service. Lyondell, which is primarily a producer of chemicals, relies on the Houston refinery to make feedstocks for downstream chemical plants.

Lyondell emerged from 16 months in bankruptcy on April 30. The company filed for bankruptcy protection due to a drop in refining returns.