Syngas fire at an ammonia production plant

The leak occurred at the ammonia reactor after a technical shutdown of 4 days. When the production was resumed and the syngas compressor restarted 14 hours later, a jet-fire occurred.
The Internal Operation Plan was launched and the fire immediately extinguished.

The cause of the gas release was a thermal dilatation difference between the joint and the reactor body. While the latter was still hot, the joint was cooled by the gas upon starting up the synthesis process. The high hydrogen concentration of the synthesis gas explains probably its spontaneous ignition.
An additional cause was the procedure of quickly and completely exposing synthesis loop components to air by systematically opening all sectional valves, even in the event of short-term shutdowns, increased the unit’s vulnerability to this type of incident.

The INITIATING cause was the loss of containment of the syngas due to thermal gradients between joint and reactor, and the spontaneous ignition of the gas.

Contributing cause was the shutdown procedure which opens all the valves, which exposes to air the whole ammonia synthesis loop.

In conclusion, root cause would be probably a deficiency in the design of the operation procedures

Joint, inlect pipe, ammonia reactor

The ammonia production unit was stopped 4 days due to a technical incident. A syngas jet fire occurs when restarting the unit.
The shutdown prior to the accident stemmed from an incident on the turbo air compressor lubrication circuit of the NH3 unit that stopped the machine and nearly the entire unit.

The dispenser hose/nozzle was disconnected, and the leak location was quickly isolated to the tank/valve interface. A 30-foot boundary around the lift truck was cleared of personnel and equipment. The combustible gas detector mounted on the wall above the hydrogen dispenser did detect an increase concenrtation of hydrogen, due to the action the facility ventilation system which was providing enough air flow to disperse the leaking hydrogen throughout the event.

A rapid and total opening to the atmosphere of the reactor and of all the valves even for a short stop of the unit increase the likeliness of an incident.

The procedure was modified, by keeping the reactor pressurised by injecting nitrogen (80-100 bar) during short down periods and automatically closing the synthesis compressor connection in order to reduce the pressure decrease rate.