Fire at a hydrotreater of a refinery

A fire developed at a unit converting heavy oil residues into refined products. It involved a fluidised bed reactor and the related hydrogen supply system serving the catalytic conversion insider the reactor.
The fire was due to the rupture of a supply line providing the reactor with hydrogen gas at 160 bar and 500 °C ruptured, causing hydrogen to leak and immediately ignite. The resulting horizontal jet flame affected nearby equipment containing other flammable products. The steel structures in the vacuum residue conversion facility were caught up in the fire. The plant own firefighting teams and equipment were used to fight the fire and bring it under control.

[Note: there are two versions of the events. eMARS and MARSH (see references). They agree in identifying as triggering event the trip of a hydrogen compressor. They diverge however about the following steps and their causes. The version presented here is the one provided by the European eMARS database, because based on the results of an investigation.]

The INITIATING/direct cause was a mechanical failure, which caused a series of additional failures.

The rupture occurred close to a valve with clamp connectors, in the vicinity of the reactors. A loss of flow in that pipe occurred because of a compressor becoming blocked and a second compressor reducing to minimal flow. The reduced or non-existent hydrogen flow in the pipe led to its cooling by natural convection, inducing thermal stress.
The escalation which brought to the rupture of other components was also the result of the malfunctioning of a cut-off valve when operated manually, probably because of a power cut owing to the power supply panel being affected by the fire. There was also a fire near the air coolers that broke out when the facility was depressurised rapidly because of stresses exceeding their design values.

Two sources diverge on the exact reasons of these failures, but both point at the same type of ROOT CASUES: procedures had not been followed, and incorrect mitigating operations were undertaking on a series of failing components.

hydrogen compressor, flidised bed reactor

The hydrogen supply line was at 160 bar and 500 °C.

DESCRIPTION OF THE INDUSTRIAL PROCESS
The hydrocracker was a prototype, aiming at refining crude oil rest. It was of the type 'ebullated bed reactor' , i.e. a type of fluidized bed reactor that utilizes ebullition, or bubbling, to achieve appropriate distribution of reactants and catalysts. Hydrogen and feedstock enter at the bottom of the reactor, thereby expanding the catalyst bed.

The facility suffered such major damage that it had to be rebuilt. Material losses resulted for more than €2 million, and the costs of the emergency response, cleanup and restoration were more than €2 million

There is no record that the event had consequences for human health, the environment or non-company property. The data recorded by the air quality monitoring network did not reveal significant increases in the concentration of the pollutants measured.
Substanced released:
70 t hydrocarbons
0.3 t hydrogen.

Two managers were found guilty of contributing to the incident through negligent and imprudent conduct.

At 3:40 p.m. a worker on the spot noticed a leak in the structure behind the reactor and reported it to the control room. The operational staff who went to the location found white smoke leaking from the hydrogen supply line followed by the outbreak of a fire with a light-coloured, horizontal flame. The alarm was raised and the order given for the unit to be rapidly depressurised and cut off.
The firefighting team attended an air cooler where a fire was clearly breaking out and in the vicinity of the reactor using the necessary firefighting vehicles and equipment to contain the incipient fire and cool the surrounding metal structures.
The local fire brigade was called at 4:05 p.m. once it had become clear how serious the situation was. When the firefighters arrived, they continued the containment and cooling activities with the help of refinery personnel. Operations continued through the night until 7:50 a.m. on 2 December, with cooling and control activities going on until the afternoon of 2 December.
As per the IEP, the local authorities were kept constantly abreast of how the accident was developing, both by the company and by fire brigade representatives present on site. Based on how the situation developed, the local authorities did not deem it necessary to trigger the External Emergency Plan (EEP).

Following the analysis of the causes of the accident, the plant operator proposed measures concerning both redesigning parts of the facilities and implementing additional management measures to monitor critical equipment. Unfortunately, the sources do not provide details.