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• Effect of NaCl, HCl, and SO 2 on corrosion of Ni 59.08 Cr 24.31 Al 10.74 W 5.3 B 0.57 was studied. • NaCl salt deposits and HCl gas have a complementary effect on corrosion impact than NaCl salt or HCl gas only. • In the absence of NaCl, SO 2 helped in the formation of the protective oxide layer. • In the presence of NaCl, SO 2 promoted sulfation and reduced corrosion impact by 1.71 times. • Corrosion mechanisms of Ni 59.08 Cr 24.31 Al 10.74 W 5.3 B 0.57 alloy in distinct corrosive environments were elaborated. Due to the new trend of co-incinerating municipal solid waste (MSW) with sewage sludge, medical waste, or industrial organic waste to attain a "waste-free" status, mixing of multi-source organic wastes (MSOW) increases the complexity of solid waste, which fluctuates the composition of corrosive species in the boiler. The fluctuation of corrosive species alters the alkali metals/S/Cl ratios and increases the uncertainties of high-temperature corrosion of boiler key components. The corrosion behaviors and mechanisms in varying compositions of corrosive species are complex and remain elusive. To investigate the corrosion characteristics during the co-incineration of MSOW, this study examined the corrosion mechanisms of a nickel-based Ni 59.08 Cr 24.31 Al 10.74 W 5.3 B 0.57 alloy in simulated co-incineration environments of MSOW. The environment contained either HCl, NaCl, or SO 2 in wet oxygen at 600 °C. For each case experiment, the maximum possible value of each corrosive species expected in the actual incinerator and/or its absence was considered. HCl of either 0 or 1500 ppm, SO 2 of 0 or 300 ppm, and NaCl of 0 or 50 mg/cm2 were systematically used in each experiment. The influence of each corrosive condition on the corrosion of the alloy was evaluated by mass gain measurements, and the corrosion mechanisms were elucidated through SEM, EDS mapping, XRD, XPS analyses, and thermodynamic equilibrium calculations. The results revealed that NaCl salt and HCl gas in wet oxygen have complementary effects, which accelerated the corrosion of alloy, reaching ∼ 65.6 mg/cm2 over one week. HCl enhanced the corrosion by affecting the chemical reactions that regenerated NaCl, which participated in prolonged corrosion processes. SO 2 reduced the mass gain of the alloy to 38.4 mg/cm2. SO 2 participated in the sulfation of NaCl, forming a mixed layer of Na 2 SO 4 and (Al/Cr) 2 O 3 , reducing the mass gain by 1.71 times. In the environment without NaCl, SO 2 helped in the formation of a protective oxide layer, which prevented HCl from reaching the alloy, reducing the corrosion impact by 23.5 times. [ABSTRACT FROM AUTHOR]

• A gas-Fe surface reaction kinetic mechanism was developed. • Corrosion behaviour of pure Fe metal was simulated and experimentally investigated. • Different concentrations of KCl, SO 2 , H 2 O, and HCl were tested for corrosion of Fe. • 10 vol% H 2 O and 300–500 ppm SO 2 were the concentrations for lowest corrosion rate. Combustion of municipal solid waste (MSW) in waste-to-energy plants have an advantage of energy recovery. However, corrosion of super-heaters induced by KCl, H 2 O, and S in MSW is the major problem limiting the efficient utilisation of MSW. Corrosion reactions of metals are not well understood at molecular/atomic levels, regarding how they evolve. This situation emphasizes the need to understand the reaction pathways and their reaction rates in order to identify operating conditions that reduces the corrosion rates. In this study, a novel kinetic model for the gas-surface reactions of KCl, S, and H 2 O with Fe was developed. The rate constants for the elementary reactions were estimated based on density functional theory and conventional transition state theory computations. Fe-clusters (Fe n , n = 2–4) were used in estimating the kinetic constants of the surface reactions. Reaction model was used to predict the corrosion behaviour of Fe in simulated flue-gas of combustion of MSW at 500 °C and 4 bars. A perfectly stirred reactor code of chemkin-PRO was employed for the predictions. Due to the novel nature of the mechanism, independent experimental results from the literature and experimental results from well-controlled conditions at 500 °C and 4 bars for 50 h were used to validate model predictions. Comparison of model predictions and all experimental results showed good agreement. The concentration of KCl accelerated the corrosion of Fe by a parabolic behaviour while SO 2 between 300–500 ppm showed the lowest mass loss. Water vapour of ∼10 vol% was the critical point at which above corrosion rate was accelerated. [ABSTRACT FROM AUTHOR]

• Fate of chlorine and interrelationship with alkalis, Zn, Pb and S was reviewed. • Chlorine-initiated corrosion mechanisms were explained. • The roadmap for chlorine during combustion of MSW was presented. • Combustion optimization to mitigate deposition and corrosion was highlighted. Municipal solid waste (MSW) incineration plays an important role in waste treatment systems throughout the world, due to the advantages of fast volume reduction by 80–90%, heat recovery, and power generation. However, waste-to-energy (WtE) plants have low electrical efficiency of 15–25%, due to the low steam temperature and pressure used in order to minimize boiler deposition and corrosion problems. Undoubtedly, the high Cl-content in MSW is the reason for the severe corrosion problem. Chlorine also forms volatile compounds with trace metals (e.g., Zn, Pb), and, influences the fate of other key elements, e.g., Na, K, and S. Different from alkali metals in biomass, which have been thoroughly investigated, the behavior of chlorine during MSW incineration has not been systematically and comprehensively studied. Up until now, there are few in-depth studies that have been conducted on the thermal behavior of chlorine or on the remedial measures against Cl-induced problems. An up-to-date review on the behavior of chlorine from incineration via freeboard chemistry to corrosive attack is therefore needed, in order to provide knowledge on process optimization and reactor design, thereby enabling high-efficient energy utilization and safe operation of large-scale WtE units. This review provides a critical summary of the progress of research on chlorine in MSW (origins, species, and analytical methods); the thermal behavior of chlorine, including chlorine vaporization, aerosol formation and transformation (freeboard chemistry), deposit formation, and Cl-initiated corrosion mechanisms. In addition, the interrelationship of chlorine with other key elements (S, Na, K, Zn, Pb), and, the chlorine roadmap in the incineration process is presented, along with the influence of feedstock composition and the temperature of both the flue gas and boiler tube metal on chlorine-induced deposition and corrosion. Mitigation measures against Cl-initiated problems such as Segher boiler prisms, mixed secondary air injection, and eco-tube systems, are also thoroughly discussed. Finally, challenges and further research questions, are identified. [ABSTRACT FROM AUTHOR]

• Oxygen-enriched combustion was conducted in a full scale waste to energy plant. • Oxygen-enriched combustion decreases SO 2 and HCl, but increases NO X. • Dioxins in flue gas and fly ash increase in oxygen-enriched combustion. • Thermal efficiency was improved by 0.62% as O 2 concentration increased. This paper describes the effect of oxygen-enriched combustion (OEC) on the flue gas emission and combustion performance of municipal solid waste (MSW) in a full-scale waste incineration plant without flue gas recirculation. Input gas with different oxygen concentrations (21%, 24%, 27%) were supplied into the MSW grating furnace with a capacity of 150 t/d to evaluate the effect of inlet oxygen content on the emissions of NO X , NO, SO 2 , HCl as well as dioxins (PCDDs and PCDFs). Combustion temperature in the incinerator, unburnt rate and thermal efficiency were also examined to assess the combustion performance under OEC condition. Results showed that the amount of SO 2 and HCl decreased to lower levels during OEC condition, while the average concentrations of NO X and NO increased with increase in oxygen content of input gas. Dioxins (PCDDs and PCDFs) in both flue gas and fly ash were highly increased elevated by the oxygen intake, especially for PeCDFs and HxCDFs. The average temperature in three grates of incinerator increased as oxygen concentration increased, while the unburnt rate gradually decreased, indicating a slight improvement of MSW thermal efficiency and more complete combustion under OEC condition. [ABSTRACT FROM AUTHOR]