Mechanisms of ash deposition and corrosion in wall-mounted gas boilers: Compositional analysis and thermal efficiency impacts

This research systematically investigates ash deposition and corrosion mechanisms in four types of 24 KW wall-mounted gas boilers. Quantitative analysis reveals that corrosive components constitute approximately 90 wt% of condensing boiler ash deposits, predominantly comprising Fe/Cr/Ni metal oxides, SiO₂ and CaSO₄. Si, Ca, and S have a significant impact on the ash deposition and corrosion of wall-mounted gas boilers. SiO₂ particles mainly come from air dust and were prone to ash deposition on the surface of heat exchange coils. S mainly comes from sulfur-containing components in natural gas, such as H₂S and thiols. When inorganic mineral such as aluminosilicate, CaSO₄, and alkali salts deposit on the surface of the heat exchange coil, corrosive media such as S and sulfate further intensify the corrosion of the heating surface material. A nonlinear deterioration of thermal efficiency was observed with progressive ash accumulation. Under typical operating conditions (0.8 mm nominal coil spacing), the heat transfer efficiency experiences a severe 75 % reduction when ash layer thickness reaches the critical threshold of 0.35 mm. Appropriately increasing the gap between heat exchanger coils can effectively mitigate the impact of surface ash on thermal efficiency.