MATERIALS ISSUES FOR TURBINES FOR OPERATION IN ULTRA-SUPERCRITICAL STEAM

Coal-fired supercritical-steam power plants are currently operating with steam temperatures at the inlet to the high-pressure turbine close to or slightly above 600°C. The use of recently-developed martensitic-ferritic steels is expected to allow this temperature to be raised to 620°C, which probably represents the inherent limit of capability of these advanced steels. Further increases in temperature capability will require the use of Ni-base alloys, and efforts in this direction have been pioneered in Europe where there are plans to build a plant operating on steam at 700°C. In the U.S., there is a significant effort aimed at qualifying alloys that could be used for tubing and piping to deliver steam at 720/760°C. In this paper, the technical and business considerations involved in determining and prioritizing the materials needs for turbines operating under these ultra-supercritical steam conditions are discussed. BACKGROUND It is widely recognized that, because of the very large role that coal plays in power generation, efforts to reduce overall CO2 emissions will, of necessity, involve efforts to find cleaner ways in which to use coal. Removing carbon from coal before or after combustion introduces costs that seriously detract from the competitiveness of that power generation process. If the efficiency of the overall cycle were to b