HOUSTON: Citgo Petroleum Corp shut the coker at its 167,500 barrel-per-day (bpd) Corpus Christi, Texas, refinery on Sunday because heater tubes ruptured during a restart attempt, said two sources familiar with plant operations.

The 44,000-bpd coker was shut along with the rest of the refinery as freezing temperatures caused a power outage on Feb. 15.

Citgo said on Monday three employees were taken to a Corpus Christi hospital after sustaining non-life-threatening injuries from a heater tube leak during a planned unit restart in the refinery's West Plant on Sunday night.

Citgo did not identify the unit on which the three employees were working.

The sources said the three were working on the coker restart when they were injured. The coker is located in the West Plant.

Citgo filed a notice on Feb. 22 with the Texas Commission on Environmental Quality (TCEQ) that it planned to complete the restart of the refinery by March 4.

The coker did not fully restart before the heater tubes ruptured, the sources said.

The heater provides the need high temperature to convert residual crude oil into feedstocks for motor fuels or petroleum coke, a substitute for coal.