Fuels fire in a refinery

A fire broke out affecting the heavy fuel purification plant of the refinery.
The incident could have originated by the failure of one of the following plant components:
- pipes leading to the pressure gauges of the reactor
- recycled gas pipe at the bottom of the reactor having a quench function,
- diatermic oil pipe (hot oil) entering or exiting the exchanger
- flanged joints exchanger and connection lines.

On the base of and data logging and video evidences, the company excludes a release from the hot oil circuit as the triggering factor of the fire. The release started 30 minutes before the fire. Also a release from the hydrogen pipes is not considered likely, as the records demonstrate that the hydrogen pipe failed 7 min after fire began. Concerning the flange joints of exchangers, after dismounting the exchanger flanged joints, the gaskets resulted not to be damaged.
The company concluded that the failure of a pipe from the pressure measurement gauges of reactor is the most likely accident triggering factor.

This assumption is supported by the following facts:
1) this part is located in the area corresponding to the epicentre of the fire,
2) the area corresponds to the area visually identified by the witnesses,
3) the product release (hydrogen and fuel oil) from one of these pipes can cause a 6 m long jet flame as occurred.
4) the product supposedly released would have had a high enough temperature and pressure to self-ignite or ignite against a hot spot of the plant, like the hot oil circuit.
5) the damages recorded were caused by overheating (flame exposition) and were not caused by overpressure or explosion - the pressure measurement records confirm significant pressure changes at the beginning of the event. The company does not have any element allowing to identify the failure that caused the pipe to rupture.

The INITIATING CAUSE of the accident is the release and ignition of fuels from a pipe.
The incident then escalated to other systems, among which a hydrogen pipe.
The root cause is unknown.

catalytic hydro-treatment plant, pipes, heat exchanger

DESCRIPTION OF THE FACILITY
Capacity of 1650 t/d (light fuel treatment section) and 1450 t/d (heavy fuel treatment section)

The goal of the unit is to improve the characteristics of light and heavy fuel oil produced in the refinery by treating them with high pressure hydrogen on a specific catalyst, to eliminate the sulphur in the fuel oil, produce hydrogen sulphide, hydrogenate the hydrocarbons and improve other characteristics. The plant was designed with two heating - reaction - fractionating sections, one for light fuel oil mixtures (the unit affected) and one for the heavy fuel oil mixtures, while foreseeing one single gas purification and compression section for the recycled gas to be reintegrated in the circuit.

The fire caused damage to the structures of the unit and has not affected other units of the refinery.
There have not been any damages to persons or the environment reported.
Material damage has been estimated in 5 million Euro for the structures and 7,6 million Euro for the reconstruction, the remediation measures, materials and other related costs.

The alarm was given by the hissing sounds. The production of hydrogen was then stopped and all shut-off valves were closed automatically. The report does not says if the production stop was the action of an operator, or was triggered by an automatic system. it is highly probably that the 'hissing sound' did not triggered any of the preventing/mitigating automatic system in place.

The operator decided to rebuild the plant with a new executive project, in consideration of the damage caused to the plant. The new executive project foresees essentially:
- the complete separation of the light fuel oil section and the heavy fuel section such to avoid for example the possibility of domino effects,
- lowering the maximum height for the installation to facilitate fire extinguishing operations- reconstruction of the plant in compliance with the PED directive,
- rationalising the piping system to minimise adjacencies, relocate valves on the hydrogen quench line to maintain the line depressurised, reduce the number of measurement gauges and insertion of valves in a safe area for depressurising the hot oil circuit.