Fire on a hydrotreater of a refinery

The incident occurred at an oil refinery hydrotreater used to de-sulphurise naphtha. A small leak developed in one of the finned tubes of the heater pre-heating the naphtha-hydrogen mixture before the reactor. The leak resulted in a 0.6 m long torch flame noticed by an employee. The hydrotreater was then shut down by cutting off the flow of naphtha and the flow of fuel to the burners in the heater. The hydrogen flow was maintained to cool and sweep the reactor during the shutdown operation.

The torch flame appeared to diminish significantly while only the hydrogen was flowing. However, molten metal dripping from the heater indicated that a much more severe fire was still in progress. The fire was eventually controlled by reducing the hydrogen flow and injecting steam into the heater. The fire caused significant damage to several tubes.

The INITIATING CAUSE was the cracking of a tube, with release and ignition of a hydrogen-naphtha mixture.
The measure taken to fight the emergency were effective in (1) reducing the amount of total flammable substance, and (2) avoiding the further damage to the heater due to further hating with reduced flow in the tubes of the heat exchanger. However, the plant operator failed to assess properly the severity of the flame and to avoid continued damage of the hydrogen flame.

heater, heat exchanger tubes

. Inspection of the damaged heater revealed that the fire had completely melted 3.5 m long sections of 32 finned tubes.

The flame was estinguished after cutting off the process gas flows (both naphtha's and hydrogen's) and stpping the fuel to the fired heater.

The event showed that naked eye observation of hydrogen flame does not provide a reliable assessment of the severity of the incident. This and other early cases, such as those reported by NASA (Ordin, 1974) brought later to the adoption of more sophisticated inspection tool, such as infrared cameras.