Basic Research on Co-treatment of Municipal Solid Waste Incineration Fly Ash and Municipal Sludge for Energy-Saving Melting

Abstract

MSWI fly ash and municipal sludge are solid wastes. Melting vitrification treatment was a resource utilization method. However, the flow temperature of grate furnace MSWI fly ash and municipal sludge was high (>1325 °C), which increased the energy consumption in the melting process. MSWI fly ash contained a large amount of CaO, and municipal sludge contained a large amount of SiO₂, Al₂O₃, and Fe₂O_3. The temperature of melting vitrification can be reduced using these two kinds of CITY garbage as raw materials to change the proportion of ingredients. The eutectic characteristics of MSWI fly ash and municipal sludge and the phase diagrams of CaO-SiO₂-Al₂O₃ (C-S-A) and CaO-SiO₂-Al₂O₃-Fe₂O₃ (C-S-A-F) were analyzed in this paper. It established a low melting point mixing system. The results showed that when the amount of municipal sludge was 50-70%, the flow temperature of the mixtures was <1215 °C, which was significantly lower than that of MSWI fly ash (1490 °C) and municipal sludge (1325 °C). The optimal range of low melting point components was 14.1-36.3% CaO, 21.6-40.4% SiO₂, 6.7-12.6% Al₂O₃, and 6.3-11.4% Fe₂O₃. At 400-1400 °C, the minerals in the mixtures mainly changed as follows: CaCO₃ + SiO₂ + Al₂O₃ → Ca₂SiO₄ + Ca₃SiO₅ + Ca₂Al₂SiO₇ + Ca₃Al₂O₆ + Ca₁₂Al₁₄O₃₃ → CaAl₂Si₂O₈. In the melting experiment, with the increase in temperature, most of the phases in the mixtures might become amorphous. Therefore, the low melting point phase anorthite (CaAl₂Si₂O₈) only accounted for a small part of the final molten product.