The limitation of fossil fuel resources and the necessity of reducing CO2 emission require an increase of the efficiency of power plants by using combined cycle power systems. The pressurized pulverized coal combustion (PPCC) combined cycle is a coal fired combined cycle concept which is able to achieve efficiencies in excess of 53%. The direct use of the hot flue gas for driving a gas turbine requires a hot gas cleanup to achieve corrosion prevention of the turbine blading. One of the main problems is the release of alkalies during the coal combustion process. Therefore, the thermodynamic basics for the control of alkali vapor pressures in the hot flue gas of PPCC have been investigated by thermodynamic equilibrium calculations and Knudsen effusion mass spectrometric measurements on alkali oxide activities in and alkali partial pressures over coal ash slags with and without additives and alkali laden model sorbents. The obtained results reveal that the requirements of the gas turbine manufacturers regarding alkali concentration in the hot flue gas should be satisfiable by certain aluminosilicate sorbents. On the basis of these results, a concept for alkali vapor removal is proposed.