Dioxin evolution from recycled fly ash sent back to municipal solid waste grate furnace

Dioxins in fly ash constitute significant pollutants during solid waste treatment in grate furnaces. Recycling this fly ash back into the furnace serves as an effective thermal treatment method for dioxin removal. This study establishes a numerical model integrating FLIC, Fluent, and MATLAB to simulate dioxin evolution from recycled fly ash reintroduced into a grate furnace. It addresses key research limitations, including underdeveloped kinetics for dioxin decomposition and formation in fly ash, insufficient understanding of in-furnace thermal decomposition behaviors, and unclear factors influencing treatment effectiveness for circulating fly ash. While the model accurately predicts dioxin behavior for original fly ash using existing kinetics, kinetic parameters required modification for pelletized fly ash due to internal diffusion effects complicating removal. The modified model, validated through laboratory experiments and field tests, enabled a detailed investigation of dioxin evolution. Simulations yielded a 99.0% final decomposition rate at the furnace outlet, matching field measurements. Feeding fly ash from the top of the bed optimizes dioxin decomposition compared to uniform mixing with waste. Higher furnace temperatures reduce solid-phase dioxins while increasing gas-phase dioxins. Given solid-phase dominance, elevated temperatures enhance overall removal. This model provides a reliable foundation for further research and industrial application of in-furnace thermal decomposition for dioxin-laden fly ash.