Abstract
Recent vapour pressure measurements and calculations of thermodynamic equilibrium conditions suggest that, in gases obtained by pressurised coal combustion, only a few percent of the sodium and potassium should remain as vapour phase chlorides. The bulk of the alkalis are predicted to form sulphate, condensed onto entrained fly ash or present as an aerosol. Filtration of the condensed sulphates may suffice to reduce alkalis to levels acceptable to a gas turbine. Alumino-silicate materials appear to be potential filter media, because collected aerosol should be retained by reaction with the filter medium.