Formation of Sodium Sulfate in Gas Turbine Combustors

Sodium sulfate is a useful model compound of those substances which cause hot corrosion of gas turbine parts. Possible mechanisms of formation of this compound from sodium chloride and sulfur oxides from fuel combustion are considered for conditions prevailing in the gas turbine engine. Thermodynamic equilibria are computed when the fuel contains sulfur, and the air sodium chloride. Published data on the kinetics of the reaction SO2 + 1/2O2 → SO3 show this reaction is too slow to reach equilibrium under the conditions prevailing in a gas turbine. Published data on the liquid-vapor equilibria of NaCl and Na2SO4 are reviewed; those on Na2SO4 are probably in error due to dissociation of the vapor at high temperatures. Various possibilities of the equilibrium between Na2SO4 vapor and its dissociation products in the presence of O2 and H2O under engine conditions are compared. From these considerations, it appears condensation of Na2SO4 to a liquid or a solid could occur over a relatively narrow range of engine conditions.