Unraveling the Factors Governing Ash Deposition on Heating Surfaces in Municipal Solid Waste Incineration: A Multi-Plant Investigation

Ash deposition on heating surfaces can lead to clogging and corrosion of the incinerator and pipelines and heavy metal accumulation, significantly hindering the clean and stable running of municipal solid waste incineration (MSWI) systems. Relating deposit characteristics to operating descriptors is essential for developing evidence-based monitoring and mitigation strategies for heating surface deposition. In this study, ash samples were collected from heating surfaces along the flue gas path of seven full-scale MSWI plants. The correspondence between sampling conditions (location, temperature, aspect ratio, diagonal length, and flow rate) and the ash characteristics was discussed. According to the results, across all samples, the aspect ratio showed the clearest association with deposit roughness, while CaSO4 was the most frequently detected crystalline phase. The energy-dispersive spectroscopy data revealed a chloride-rich compositional pattern, although its strength varied across the sensitivity analyses. Pb showed the clearest decline with increasing temperature, whereas Cu, Zn, and As showed distinct associations with the flow rate or geometry. Integrated analysis separated carbonate- and chloride-rich patterns from sulfate- and metal-enriched patterns. Some of these overall relationships weakened when differences among plants were considered, highlighting the importance of the plant-specific conditions. Overall, geometry was more closely associated with deposit texture and capture-related patterns, whereas temperature was more closely associated with chemical evolution and volatile metal redistribution. This work provides an empirical framework for targeted deposit monitoring and corrosion risk assessment in full-scale MSWI systems.