Fire broke out on the furnace of a hydrodesulphurisation (HDS) unit for refinery diesel. Flames and thick black smoke, containing CO2 and SO2, were visible at the smokestack. The site was locked down 5 min after detection of the accident. The internal emergency plan was not activated. Notified by neighbours, 60 fire-fighters and 15 emergency vehicles were dispatched to the site without having to respond. The fire was contained within a half hour by internal teams, once incoming loads and H2 were shut down, as the strategy called for the fire to burn itself out: reactor decompression downstream fed the fire inside the furnace for several hours.
Out of precaution and lacking precise information from the operator, the A7 motorway was closed for an hour. City police evacuated 600 residents. During the evening, the site director issued a press release: 2 members of the in-house fire crew were slightly injured. The quantity of burnt hydrocarbon was estimated at 45 tonnes, while 1 tonne of SO2 was released. According to atmospheric pollution records, the SO2 concentration never exceeded the threshold required to issue a public statement.
At the suggestion of the inspection of classified facilities, the Prefect ordered that any resumption of HDS unit operations be conditional upon submission of a report on: the smokestack condition, state of continued unit safety, and evacuation/elimination of all waste and effluent stemming from the fire. The furnace (T = 420°C, P = 40 bar), fitted with austenitic stainless steel tubes (diam.: 6”), contained a convection zone in the upper part (not accessible to inspection) and a radiation zone (tubes in contact with the flame, accessible and considered as the most heavily exposed) below. During the accident, the upper part underwent the greatest heat flux: in some spots, metal exposed to red heat, melted tubes, fired refractory material. An appraisal of the responsible tube (not melted) revealed a lack of thickness due to a former attack exacerbated by oxidation/sulphuration and slight creep due to the presence of coke on the walls. An analysis of operating parameters showed no evidence of a drift. The operator replaced the furnace along with other equipment, depending on the temperatures actually reached. The smokestack, shared by the HDS and atmospheric distillation (AD) units, was thoroughly inspected (for thermography and verticality), yielding no noteworthy anomaly. The furnace flue and connection were renovated (with new refractory bricks). AD unit operations, shut down during the accident, were allowed to resume. The HDS unit was down for a total of 3 months. The cost of property damage was estimated at €6 million, while operating losses amounted to €22 million.
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