Citrofeed is the fraction of maize after the extraction of glucose and fermentation retentate, part of which consists of the residual substrate of rapeseed cake consumed during fermentation. It is dried and then stored in silos.
The flow of citrofeed stopped while it was being loaded from its storage silo into a dry bulk truck inside a building adjoining the silo. A technician opened the silo’s inspection hatch to see what was causing the blockage. That was when the explosion occurred. Fire spread in two directions: first via the loading system to the truck, igniting its tarpaulin and some of its equipment, and then via the silo, causing its explosion vents to burst open. The silo, which had a capacity of 500 m³ and stood 30 m tall, contained 65 t of maize fibres, or 23% of its filling capacity. It was made of glass fibre with polyurethane insulation. The internal emergency plan was implemented. The firefighters were alerted. When they arrived, the operator moved the truck out of the loading bay and extinguished the fire there. The information he gave to the firefighters indicated that the surface fire was under control. After locating hot spots on the surface of the silo surface using a thermal imaging camera, the firefighters decided to empty the silo and cool it by spraying water on its top. At 8:45 p.m., after 4 t of meal had been removed, embers were seen from the inspection hatch. Another explosion occurred, setting fire to the entire silo. The silo and meal burned together like a candle and threatened to collapse. The firefighters had difficulties extinguishing it because the water could not penetrate into the flames and it caused the meal to become compacted. After multiple attempts, they decided at 6:00 a.m. to let the fire burn itself out. At around 9:00 a.m., a specialist firm began dismantling the silo. This caused the meal to reignite. At 2:50 p.m., the silo was dismantled and the fire was out. The combustion residues were picked up mechanically across an area of 0.1 hectare. In all, the fire produced 60 t of solid waste. Such an accident scenario had not been considered in the site’s safety report. Material damage amounted to €330,000 and €100,000 was required to return the silo to service.
The maize self-heated due to the accumulation, over several weeks, of meal along the silo’s inner walls coupled with moisture in the meal. This caused a plug to form while the truck was being loaded. The opening of the hatch by the technician created a draught that sparked a flame.
The operator added the scenario to the site’s safety report. This includes temperature checks of the cooling system and silo and humidity checks in the dryer with alarms. Instructions to visually check for residues in the silo after emptying have been introduced. The new silo is fitted with vents and is 10 m shorter than the previous one.
