In-situ sampling investigation of deposition and corrosion of convective heating surfaces in a grate type municipal solid waste incineration plant:a case study

Metal corrosion and ash deposition are two common issues in municipal solid waste incineration(MSWI)plants.An in-situ sampling investigation was conducted in an MSWI plant in Jiangsu,China.The deposit samples were collected from 6 convective heating surfaces including the reheaters,superheaters,and economizer.The corrosion samples were obtained from a ruptured tube cut from the tertiary superheater.The element composition,crystal phases,and morphology of deposit and corrosion samples were characterized and analyzed.The results show that S contents of these deposits are 32-45 wt%,considerable Cl(10.63 wt%)was only detected in the deposits of the tertiary superheater.The composition of the deposits varies with the location because the flue gas temperature determines the thermodynamic trend of the sulfation reactions of different chlorides and the SO_(2)equilibrium partial pressure required in these reactions.Ca sulfates mainly exist in deposits at high temperatures(above approximately 500℃).Whereas alkali metal sulfates are the main component of deposits at low temperatures(below approximately 500℃).A multi-layer structure is exhibited on the cross-section of the corrosion samples.The discovery of Cl in the interface between the matrix and the oxide layer confirms that Cl can penetrate the outer oxide film.Besides,polysulfate components were observed inside the metal oxide layers,which indicates that a melt has occurred there.This study has provided a better understanding of ash deposition and corrosion phenomena in MSWI systems and more emphasis should be placed on the research of ash deposition and corrosion mechanisms.