A twofold study using thermodynamic equilibrium calculations was carried out to study corrosion in MSW incinerators. Corrosion was associated with the amount of alkalis and trace metals gaseous chlorides. Firstly, a two-level factorial experimental design combined with a data analysis were used to determine the main and interaction effects for various alkalis and trace metals gaseous chlorides responses. The factors studied were Na, K, S and Cl concentrations. The results provided a picture of the controlling parameters and insight about the processes taking place. Secondly, the efficiency of two corrosion-fighting additives (ammonium sulphate and silica) was investigated. Calculations confirmed experimental results and brought further insight on differentiated results for Na, K, Pb and Zn but also on capture mechanisms.