Explosions and fire in a refinery

Several explosions occurred in one of the catalytic reforming units of the refinery, followed by a fire in the same unit. The fire derived from the explosions lasted for almost one day. The complexity of the event was determined by the various domino effects which took place.
The accident chronology was as follows:
A) rupture of a 3/4 inch tapping (connection) on the suction pipe of pump;
B) after 30 s, ignition of the cloud (about 200 kg of the substance) and creation of a (combustible) fed torch fire;
C) after additional 30 s, rupture of a 3-inch mineral oil pipe which was exposed to the torch fire, creating another fire jet of larger size;
C) after 5 minutes, by domino effect, rupture of the collector of a cooling tower and ignition of the released substances used in the process;
C) after 5 minutes, by domino effect, rupture of the 8-inch head pipe of a reformer column, ignition of the release, rupture of column valves collector, which is connected to the site's flare system, and ignition of the released gas. This caused a partial release to the atmosphere from the site's flare system.
The ignited releases kept on burning until the material being processed in the unit was exhausted and the flare system could be isolated without risk. The accident caused minor injuries to one person. There was no significant environmental impact. Fire extinguishing water was stored in a 60.000 m3 buffer tank designed this purpose. The accident caused a 7-month shutdown of the unit.

The causes of the accident are related to a system constituted of "steam turbine + pump" (Ref. P3B). Actually, the accident occurred during a periodical test phase carried out with this equipment, which constitutes an emergency relief unit for the P3A pump. Various investigations carried out after the accident, have led to the identification of a complex of factors which may have caused the accident itself.

The INITIATING cause was related to a system constituted of a "steam turbine + pump". The accident occurred during a periodical test phase carried out with this equipment, which constitutes an emergency relief unit for another pump.

Various investigations carried out after the accident, have led to the identification of a complex of factors which may have caused the accident itself, such as Presence of condensates in the turbine, Inadequate design of the pump (foundation, lubrication rotor, cavitation, etc.)

These factors caused strong vibrations followed by fatigue stress to and the rupture of the connection placed just above the pump. The vibration caused as well a misalignment of the turbine and the pump, which caused a fracture of the shaft and a deterioration of the coupling.

A contributing cause which worsened the consequence of he INITIATING cause was an anomalous delay of about 10 min in closing the block valve of the feeding pipe of the pump. If the closing of this valve had been completed within the normal time of about one minute, the domino effects involving the other pipe networks could have been avoided.

catalytic reforming reactor, cracker, steam turbine, pump

The accident occurred during a periodical test phase of the unit which failed first.

DESCRIPTION OF THE PLANT
The plant is a very large refinery with a crude oil distillation capacity of 17 millions tons/year. The plant is classified as Seveso Upper Class.
The unit involved in the accident is a catalytic reforming unit used to produce high-octane gasoline fractions. This unit can process 4200 t/day of product.
The unit consists of 3 successive sections: a de-sulphurisation section, a catalytic reforming section, and a fractionation section.
The substances used in the process are mainly flammable substances (mineral oils, hydrogen), and gases like hydrogen and H2S hydrogen sulphide.

The accident caused minor injuries to two fire fighters.
There was no significant environmental impact, and the extinguishing water has been stored in a 60.000 m3 buffer tank designed this purpose.
The accident has caused a 7-month shutdown of the unit. The material damage amounts to about 13.72 MEuro for repairs and 68.6 MEuro for production loss.

Considering the high material damage, the criterion in Annex VI of the so-called Seveso Regulation was exceeded: the accident had to be notified to the European database (MARS).

Following the approval of the modifications proposed by the operator, the Department's prefect authorised the new start-up of the unit.

Various investigations carried out after the accident, have led to the identification of the complex factors which may have caused the accident itself.

From the KBS News video it appears that the driver was able to detach the tractor from the trailer before the hydrogen ignited.
The fire brigades were able to extinguish the file in 30 minutes. The images suggest also that the fire brigade strategy was to extinguish the fire. The distance of the fire brigade from the vehicle was very small ,and also the safety area for the car was much less than the usual hundreds of metres advised by guidelines.

According to the eMARS report (see references), the following corrective measures were proposed by the operator:
1) Change of pump type and modification of the vertical alignment of the column, in order to avoid cavitation phenomena;
2) Replacement of the motor-driven valves placed in the pipes feeding the pumps, in order to reduce the shutting delay;
3) Modification of the turbine's speed regulation system into an "isochronous" regulation system;
4) Replacement of the 3/4 inch tapping (connection) of the involved pumps by 1 inch tapping (connection), provided with reinforcement gussets;
5) Modification of the drainage system of the turbines involved;
6) Implementation of a campaign aiming to increase worker's awareness of the importance of a strict application of operating procedures during the heat-up phase of turbines.
These proposals were approved by the third-party expert, who has independently prepared some additional recommendations.