A fire broke out on an atmospheric distillation unit in a refinery. The fire was started when a leak caught fire on the outlet of a safety valve installed on a gasoline stabiliser (debutaniser). This stabiliser unit is designed to separate gasoline / gases. The internal contingency plan was put into action at 6.56 pm.
The refinery’s firefighting resources were mobilised 7.49 pm to combat the fire. The public firefighters called did not have to intervene. The south-easterly wind dissipated the cloud of fumes. The firefighting water was directed to the refinery’s internal water treatment facility. The unit was shut down according to the emergency procedures. Property damage was limited; the heat lagging on the atmospheric distillation tower was damaged and electric wiring was burned. Repair work was conducted in compliance with API 579: particularly, the valve on the stabilisation tower was changed, and the valves on the atmospheric distillation tower were removed and inspected.
The atmospheric distillation unit had been restarted a few days earlier. Operation had not completely stabilised. A few hours prior to the incident, the console operators and the technicians encountered operating difficulties with the vacuum distillation pump. The stabliser has a reboiler at the base by an exchanger on which the tower’s bottom level control is installed. Starting at 3.30 pm, a shift appeared on the corresponding measurement causing the progressive then complete closure of the bottom valve and thus the tower to fill with gasoline. A gasoline and gas mixture then flowed from the main valve, trickled down and ignited on a hot point at the base of the tower. The flames climbed up to the smoke vent, creating a flame above the main atmospheric distillation tower. The pressure sensor was slaved to allow heating to be stopped and avoid a lack of condensation at the installation head, which is a common cause of excess pressure.
The incident shed light on the need for new control of the sensor on the tower by-pass in order to ensure adequate safety regarding the risks associated with overfilling of the tower.
