This article describes an incident that occurred on 12th March 2019 in the Solvay factory at Rheinberg in Germany. It caused the explosion of circulating fluidized bed furnace for coal and biomass.
The investigation showed that corrosion and erosion of a tube in the heat exchanger section led to the entry of 25 metric tons of water into the furnace. The operators shut down the furnace and tried to eliminate the water by circulating air, following the standard procedure detailed in the operating manual. Due to an unforeseen combination of circumstances, the furnace exploded. It was shown that the explosion was not caused by the presence of flammable gas. It was rather a physical explosion, linked to the presence of about 12 tons of water at 100 °C, suspended above the ash bed at 850 °C. The explosion occurred when the hot bed of ashes was suddenly suspended by the circulating air and came into contact with the suspended water, generating up to about 15,000 m3 of steam instantaneously inside the furnace (free volume 380 m3).
The article details the construction and other measures which are necessary to avoid this type of accident.