A fire broke out at around 7:15 a.m. in the flue-gas cleaning system of a melting furnace in operation at a metallurgy plant. The system comprises two cyclone pre-separators; one chamber for injecting a mixture of slaked lime, clay, and activated carbon and intended to adsorb organic micropollutants (dioxins and furans in particular); and two bag filter boxes (1255 bags per filter). At 7:23 a.m., a visual and audible alarm sounded when sparks were detected downstream of a box. The public firefighters were alerted at 7:43 a.m. The fire spread to two door seals and the lip seal of the passage channel of the cleaning trolley of one filter. Two fire extinguishers were used to put out the fire on the lip seal and trolley. The box was doused with water. The flue-gas cleaning system was turned off at 7:59 a.m. (furnace at end of casting) and the firefighters, who arrived five minutes later, brought the fire under control. All the bags and one filter box were destroyed. The second box was damaged. The extinguishing water was drained to the site’s pits, then disposed of appropriately. No health effects from the atmospheric releases were reported.
The two possible causes of the fire are either incandescent particles that were drawn in from the melting furnace or overheating of self-combustible materials due to friction in the dust extraction augers or of the mixture of adsorbents. In the days before the fire, several incidents had occurred on the flue-gas cleaning system. The bag filters had shut down and the dust could not be cleaned out, a dust extraction auger overheated, and a smouldering fire was discovered in the super sacks used to remove the adsorbents and dust. The flue-gas cleaning system had been extensively damaged by a fire in March 2010 (see 44535).
To prevent a fire recurring, the operator fitted an impingement filter in the fume extraction system in order to trap incandescent particles and restarted the thermal safety damper (bypass) in the melting furnace’s roof stack. The operator also intends to lower the activated carbon content in the adsorbent and fit a bypass in the melting furnace’s fume suction duct.
