Syngas fire in in a chemical plant

The event occurred while re-starting the ammonia production unit after a technical stop, a synthesis gas (50% hydrogen, 17% ammonia, methane and nitrogen) leak ignited on a flange located just after the synthesis reactor.
Emergency shutdown of the unit was executed and the fire was extinguished in a bit less than 1 hour.

The leaking at the flange was caused by a tightening torques of the bolt which were not adapted to the exceptional conditions prevailing during the accident. The short technical breakdown had induced a very quick temperature evolution with significant temperature gradients between the bolts and the flange.

The INITIATING CAUSE was loss of tightness of the flange due to the temperature gradient occurred during the technical shutdown. flange were not adapted to the situation.

The ROOT CAUSE (or at least an intermediate cause) is related to the fact that these temperature excursions had not been taken into account in the design of the reactor. Assuming that the operation of tightening had been executed by a contractor during the last inspection and maintenance works, another factor of the ROOT CAUSE could be the management of the contractor's operation by the site operator.

flange

The ammonia producing unit had to be shut down rapidly due to a technical issue. At the moment of the re-start, the reactor had been shut down for 1h30.

The material damage was estimated at 60 K Euros and concerned the thermal insulation of pipes, louvers protecting the reactor against atmospheric action, fire-proof concrete of the reactor frame and the instrumentation cables within a radius of 3 m. The blaze did not damage the reactor that was protected by a deflector. Operating losses stood at 300 k Euros.

The unit’s automatic alarms were triggered and the operator started the emergency shutdown, which isolated and depressurised the synthesis cycle.
Steam was sprayed on to the leak using mobile fire nozzles to extinguish the fire that was brought under control 55 minutes following its start.

The following was implemented as corrective measures from the lesson learnt :
i) modification of tightening torque.
ii) improvement of leak collector on flange.
iii) nitrogen injection system in leak collector
iv) installation of vapour injectors to protect the reactor.