Characterization of Grate Sifting Deposition Ash, Unquenched Bottom Ash and Water-Quenched Bottom Ash from Mass-Burn Moving Grate Waste to Energy Plant

Abstract

This studyinvestigates grate sifting deposition ash, unquenched bottom ash, and water-quenched bottom ash from a mass burn waste-to-energy plant. Various methods were used to determine the characteristics of these ash types and to evaluate the influence of water quenching on bottom ash characteristics, namely visual observation, analysis of particle size distribution, particle thin section analysis, measurement of pH, moisture content, and loss on ignition, bulk chemical analysis, and mineral composition analysis. Results showed that the pH of all samples was in the range of 11.7-12.7. Approximately 70-80 % of samples consisted of CaO, SiO2, Al2O3, and Fe2O3. All samples were also enriched with Zn, Cu, Ba, Pb, and Cr, with concentrations higher than 500 mg/kg. Major minerals found in all samples included calcite, quartz, gehlenite, hematite and mayenite. However, physical, chemical, and mineral characteristics of the samples were heterogeneous. There were various indicators of the influence of water quenching on bottom ash characteristics, including differences in particle size distribution, the existence of an unidentified outer layer in water-quenched bottom ash, the decrease in pH, concentrations of CaO, Al2O3, Fe2O3, Cl, Cu, Ba Pb, Sr and As, and the presence of Friedel's salt in water-quenched bottom ash. Further research on the transformation of bottom ash during the quenching process is needed, as also further study of the mechanisms and functions of the unidentified outer layer.