Heterogeneities of fly ash particles generated from a fluidized bed combustor of municipal solid waste incineration

Although municipal solid waste incineration fly ash are fine particles and a priori considered as homogeneous, they have complicated structures inside their bodies. This study quantitatively investigated two categories of heterogeneity of fly ash produced from a fluidized bed combustor. They are the heterogeneity of a single fly ash particle body (intra-particle heterogeneity) and heterogeneity among fly ash particles (inter-particle heterogeneity). In the surface and semi-soluble components, Ca has smaller intra-particle heterogeneity than Al and Si. These results and ternary diagram analysis suggest that semi-soluble components consisted of mainly Ca-based matrices such as CaCO₃ and unreacted Ca(OH)₂ in which aluminosilicate domains. All major elements, excluding Fe and Ti, are 3–66% higher inter-particle heterogeneities on the surface than semi-soluble and insoluble core components. It shows that the surface component of the fly ash is more heterogeneous than other components of fly ash particles. Fly ash from fluidized bed combustor has intra- and inter-particle heterogeneity similar to stoker combustor. Besides, heterogeneity analysis can explain the fly ash formation process. Heterogeneity analysis suggests that Si plays more critical roles in the fly ash formation process of the fluidized bed combustor than that of the stoker combustor. Fly ash has heterogeneous bodies, and it might give non-negligible impacts on the leaching of metals included in fly ash components.