High-Temperature Corrosion in Biomass and Waste-to-Energy Boilers: Mechanisms, Materials and Mitigation Strategies

Biomass and waste contain elevated concentrations of chlorine and alkali metals that promote the problem of high-temperature chlorine corrosion in power boilers. The results are rapid metal loss, increased maintenance costs, and reduced operational availability. This review paper provides a comprehensive overview of the high-temperature chlorine corrosion in biomass- and waste-fired boilers. The occurrence and chemical speciation of chlorine in these fuels are discussed together with its transformation during thermal conversion. Particular attention is devoted to the mechanisms of active oxidation, the role of ash deposits and their chemistry. The corrosion performance of conventional boiler steels, nickel-based alloys, and protective coatings is evaluated. Laboratory investigation methods, including gravimetric measurement and microstructural characterization are reviewed alongside recent advances in computational modelling, such as thermodynamic equilibrium calculations and computational fluid dynamics. The review shows that corrosion severity is governed by the coupled effects of chlorine speciation, alkali metals, deposit chemistry, temperature, combustion conditions, and material properties. Advanced alloys and protective coatings can substantially improve corrosion resistance, but cannot completely eliminate degradation under prolonged exposure. The analysis also indicates that effective corrosion mitigation requires a combination of fuel modification, combustion optimization, deposit control, appropriate material selection, and surface engineering.