Efficiency improvement of thermal power plants is one of the key technologies to protect the global environment because of lower emission gas. There are many approaches in this regard, which are investigated and developed around the world. Thermal efficiency of fossil power plants has been improved by raising steam temperature as high as 620 C in a realization of Ultra Super Critical (USC) steam turbine system. In order to enhance the thermal efficiency further, we are developing the Advanced Ultra Super Critical (A-USC) steam turbine system using high pressure and high temperature steam of 700 C or over 700 C. The main focus of the Research & Development of A-USC steam turbine is the verification of the alloys for the large rotor, casing and valve components, and the main issue for application to the power plant is an economical aspect and field of technology for the realization of such steam conditions with cost-effectiveness, for instance, optimization of cycle heat balance, turbine design, welding technology and so on. This paper describes briefly about R.&D results of A-USC steam turbine and suggests an economical strategy in order to make it possible to be realized sooner.
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