Auto-Ignition and Combustion Properties of Iron/Steel Micro-Particles in Oxygen Atmospheres Heated by Rapid Compression

摘要

Accumulated deposits of metal particles contaminating high-pressure oxygen piping systems represent a strongly reactive and highly adiabatic medium. They are prone to ignition following an initial thermal perturbation or heat confinement and then will apply an extremely high temperature pulse to adjacent surfaces, thus becoming a factor enhancing the severity of accidental fires. In order to investigate metal powder layers' ignit-ability and burning, a rapid compression machine was used for generating, at a given time-origin, heated oxygen atmospheres at programmed pressures of 0.5 to 28 MPa and temperatures of 550 to 1100 K. Critical conditions for auto-ignition were determined as a function of particle size for two commercial iron powders with particle sizes ranging from 1 to 5 μm and three real residual powders from industrial installations. A first major finding is that iron/ steel particle deposits can be easily ignited in rapidly heated oxygen atmospheres at temperatures considerably lower than the iron melting point. Moreover, this critical temperature diminishes significantly with increasing oxygen pressure. The temperature of burning particles was measured with a time resolution of 4 μs by means of a novel photoemission technique. It was seen that the temperature can quickly rise up to 3100 K and then fall to 1850 ± 50 K. An extensive database is available for the development and validation of models describing fires in various piping elements with specified particulate contamination, to be used in order to identify circumstances for especially severe accidents.