A thermodynamic analysis of chloride corrosion in biomass-fired boilers for Fe-O-Cl-S system

Abstract

The paper presents a thermodynamic analysis of chlorideinduced corrosion in the Fe-O-Cl-S system. The influence of steam concentration in the gas phase on chloride-induced corrosion process was presented. Based on the parametric equations the equilibrium concentration of the gas phase was determined. The effect of alkali metals chlorides in gas phase (Na,K)Cl on formation of (Na,K)FeO2 in the passive oxide scale layer (FeO/Fe3O4/Fe2O3) was analysed. Condensation of (Na,K)Cl vapors, formation of low-melting eutectic mixtures in deposits and consequences of this process on corrosion process were examined. Additionally, the role of SO2 in chlorination and oxidation process of steel in melted ash deposits was discussed as well. The results were correlated with available in the literature laboratory experimental data and industrial corrosion process observations. Presented thermodynamic analysis was compared with assumptions of an "active oxidation" model. The results may be used for experimental research planning and a corrosion process prevention in the industry.