Mechanism of Na2O/CaO Ratio Affecting Ash Fusing Characteristics During Ash Deposition and Slagging in Municipal Solid Waste Incinerator

Municipal solid waste (MSW) incineration is a highly efficient way of utilizing waste resources. The problem of ash deposition and slagging in MSW incinerators is closely related to the fusion characteristics of MSW ash. In this study, the effect of Na2O/CaO ratio on the fusion properties of MSW ash was investigated and specific mechanisms were summarised. The ash fusion temperature (AFT) of synthetic ash was minimum when Na2O/ CaO = 10/0, and gradually increased as Na2O/CaO ratio decreased. At high temperatures, low fusing temperature minerals such as albite and nepheline appeared in synthetic ash with high Na2O/CaO ratios, decreasing the AFT, while high fusing temperature minerals such as anorthite, gehlenite, wollastonite and Ca3Si2O7 appeared in synthetic ash with low Na2O/CaO ratios, increasing the AFT. In synthetic ash melts, both Na+ and Ca2+ had the network modification and charge compensating effect. Q could indicate the degree of aggregation of the silicaaluminium network structure of MSW ash melt. The higher content of Q in melts with low Na2O/CaO ratios indicated that high concentrations of Ca2+ strengthened the network structure of synthetic ash under the effect of charge compensation and inhibited the network modification effect, which led to high AFT.