Estimation of risk of hot corrosion in gas turbines by thermodynamic modelling

Abstract

Different types of coal fired combined cycle power systems are currently under development. However, the use of hot flue gases, originating from coal combustion or gasification, to directly drive a gas turbine may pose a problem in terms of corrosion. Cleanup of the hot gas is required in order to prevent corrosion of the turbine blading. One of the main problems associated with hot flue gases is their high alkali concentration, as alkalis are released during the coal conversion process. During the development of a hot gas cleanup protocol it is necessary to repeatedly check the effectiveness of the method in preventing hot corrosion. In the present study, thermodynamic modelling was used to estimate the risk of hot corrosion and therefore reduce the timescale and cost of the testing process. The coexistence of alkali sulphates and NiSO4, or the formation of liquid alkali sulphates were taken as the criterion for a risk of hot corrosion. In addition, the results from coal based processes were compared to thermodynamic calculations for a well characterised gas turbine, burning fuel oil. The calculations were performed for second generation circulating pressurised fluidised bed combustion and pressurised pulverised coal combustion. In both processes, the corrosion risk, if there is any, should be much lower than the risk in a gas turbine, burning fuel oil.