An explosion occurred at around 1:40 a.m. in a remelt furnace during a sintering operation in a metallurgical plant. Just before the explosion, significant smoke and flames emanating from the furnace were observed during the installation’s inspection rounds. The order to evacuate was issued at 1:34 when the phenomenon appeared to be getting out of control. The explosions ejected the molten iron contained in the furnace (500 kg) and the furnace cover. The fallout created scattered fires in the nearby storage areas (packaging, pallets). The power was disconnected at the site’s general high voltage power cell. The fire brigade was alerted at 1:45 a.m. and managed to extinguish the fire using multi-purpose powder. The power was restored at around 3:30 a.m., except for the furnace installations, as the high-voltage feeder remained locked. One of the two technicians, who had observed the furnace runaway, showed symptoms of post-traumatic stress. The furnace and related equipment were damaged. Operating losses were limited to the production of remelted chromium.
The OCP (Optical Coil Protection) device allows temperature reached at the induction coil of the furnace to be monitored, the triggering of alarms and the shutdown of the furnace in case of significant deviations.
During the first part of the sintering process, the furnace is operated in automatic mode and then in manual mode. Automatic mode is controlled by a thermocouple placed in the furnace pot. During sintering, the temperature is gradually increased to 1,700 °C after 12 hours by increasing the power supplied to the induction coil. In this instance, the thermocouple had failed. The measured temperature did not increase, leading to an abnormal increase in the power injected. The molten iron began overheating. This malfunction was not observed by the operators because, during the automatic sintering phase, there is no human supervision in place, nor by the OCP (Optical Coil Protection) device as their alarm thresholds had been reached too late. The movement of the molten iron eventually ended up piercing the refractory material. The iron had come into contact with the cooling water of the coil solenoid. The sudden vaporisation of the water caused the furnace to explode.
Following the accident, the operator planned to install a second thermocouple for the sintering operations to compensate for possible equipment failure. Plans were also formulated to position an operator during the entire sintering cycle. Adjustments were also made to the OCP system’s alarm thresholds and personnel training was reinforced and expanded. Finally, a thermocouple control instruction was also implemented.
