Study on Suppression of the Reaction between Incineration Ash and Water Using Heating Temperature and Cooling Temperature Variations

Explosion incidents have been reported in waste incineration plants, particularly in ash extractors, ash conveyors, and ash pits. These incidents are believed to be caused by hydrogen generation resulting from the reaction between cooling water and metallic aluminum contained in the ash.
The authors have been investigating methods to suppress hydrogen generation by controlling temperature changes in the ash–water reaction. In this study, to simulate temperature variations during conveyor transport, actual incineration ash and aluminum powder were immersed in water in a container and heated to a target temperature. After reaching the target heating temperature, the system was allowed to cool naturally. Once the target cooling temperature was reached, the sample was reheated to the target temperature. This heating–cooling cycle was repeated until a predetermined experimental duration was achieved to confirm reproducibility.
The experimental results revealed that higher heating temperatures and lower cooling temperatures lead to reduced hydrogen gas generation. Specifically, when the cooling temperature was 30°C, the reaction was suppressed at heating temperatures of 70°C or higher. When the cooling temperature was 60°C, suppression occurred at heating temperatures of 90°C or higher.
These findings suggest that hydrogen explosions in conveyors and ash pits may be mitigated by heating the high-temperature incineration ash discharged from the furnace together with the cooling water, followed by natural cooling during conveyor transport. In addition, preventing explosion accidents at municipal solid waste incineration plants and improving operational safety can also contribute to reducing environmental impact.