(135f) Furnace Incident during Decoking Operation

In ethylene furnaces, coke forms in radiant tubes and decoking operations need to be performed regularly. During decoking, the upper convection section is at higher temperatures than during normal operation. The upper hydrocarbon preheat tubes are protected by dilution steam during decoking. In one of Lyondell Chemical Company's ethylene furnaces, a small amount of water was added to the dilution steam to prevent the hydrocarbon preheat tube outlets from exceeding the temperature limit of the piping. During a regular decoking operation, a convection shock bank tube ruptured resulting in positive pressure in the firebox. The excursion damaged the arch area refractory, a few adjacent convection tubes, and the convection header box. This paper will review the details of this incident and the changes implemented to prevent occurrence of similar incidents.