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author

Kelly Thomas

published on

April 2004

This case history illustrates an explosion at a plant powerhouse in which a number of large air compressors were operating. A fire was initiated in the demister for a set of these compressors. The demister element fire most likely resulted from the ignition of compressor exhaust valve deposits due to the formation of a hot spot on an exhaust valve. The demister element fire heated the demister vessel to the point that it failed at system pressure. The demister vessel rupture resulted in the catastrophic failure of a valve in the line to an air receiver tank holding a considerable inventory of lubricating oil. Oil entrained in the flow of air from the receiver tank through the broken line produced a flammable mixture of oil mist and air, which subsequently exploded. The oil mist explosion toppled a nearby masonry wall and caused damage to other portions of the powerhouse. The oil mist explosion (i.e., the secondary explosion) produced blast loads that were more severe than the demister vessel failure (i.e., the initial explosion). Fortunately, due primarily to the distribution of personnel in the area at the time of the event, there were no significant injuries.

This event demonstrates that demister fires have the potential to initiate a serious accident. While it may be difficult to completely eliminate demister fires, there are a number of design options that can be employed to prevent a demister fire from triggering an explosion. One approach to prevent such an event is to install a safety interlock to shut down the compressors and isolate the air treatment system upon detection of a high temperature at the demister discharge.

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Kelly Thomas