The overall objective is the development of new coatings for supercritical steam power plants for efficient and clean coal utilization. A significant reduction of emissions is expected by increasing efficiencies to ŋ > 50%. Currently, an efficiencies of 45% have been achieved in the last 30 years from subcritical 180 bar/540ºC to ultra-supercritical 300 bar/600-620ºC corresponding to a specific reduction of 20% of CO2 emissions. Efficiencies of 50% and more can be achieved by further raising the temperature, but conventional ferritic steels are not sufficiently oxidation resistant, since the temperature designed for operation was 550º C. From the mechanical properties perspective, ferritic steels can be used at temperatures up to 650º C and for higher temperatures austenic steels and Ni base alloys are being considered.
One of the main objectives of this project is therefore to develop advanced coatings for steam environments which can resist the chemical attack of steam and fireside corrosion at temperatures higher than 620ºC employing materials with the required high temperature mechanical properties in particular creep strength. Ferritic–martensitic steels will be considered as substrate materials for up to 650º C whereas, austenitic steels will be explored for higher temperatures.
In general higher temperatures mean higher oxidation rates, in particular when the oxidant is water vapour instead of oxygen. The introduction of carbon capture and sequestration (CCS) technologies also aiming to reduce emissions in power generation has also increased the interest in developing new material solutions able to reduce the economical and environmental penalty associated to energy production systems when CO2 is generated. For instance oxy-fuel combustion takes place in a N2 free atmosphere so oxygen is burned in near stoichiometric conditions with the fuel (pulverized carbon) producing and exhaust gases mainly composed of CO2 and H2O.