Metallography of CB2 Steel Used for Cast Turbine Components

Steel CB2 developed in frame of the COST actions belongs to the most promising steel for production of cast turbine components working at ultra-supercritical steam conditions. VZÚ Plzeň has participated on assessment of original trial melt CB2 as well as on testing of samples coming from one of pilot valves produced of steel CB2 in full scale. Recently VZÚ Plzeň has cooperated with Doosan Škoda Power in development of weld processes of advanced power energy steels including steel CB2. This contribution deals with a comparison of properties of the steel CB2 produced by four various steelmakers from point of view of their microstructure in relation with their mechanical and creep resistant properties. Evaluation is focused on chemical heterogeneity, porosity, content of non-metallic inclusions, in particular on an occurrence of coarse NB, microstructure and substructure using methods of light and electron microscopy.

Steam Oxidation of TP 347H FG in Power Plants

The long term oxidation behaviour of TP 347H FG at ultra supercritical steam conditions was assessed by exposing the steel in test superheater loops in a Danish coal-fired power plant. The steamside oxide layer was investigated with scanning electron microscopy and energy dispersive X-ray diffraction in order to reveal the effect of oxidation time and temperature on the microstructure. A double layered oxide formed during steam oxidation. The morphology of the inner Cr-containing layer was influenced by the oxidation temperature. At temperatures below approx. 585oC, it consisted of regions of Fe-Ni-Cr spinel surrounded by Fe-Cr oxide. At higher temperatures almost the entire inner oxide layer was composed of Fe-Cr oxide. Possible mechanisms for the oxide growth are discussed and it is suggested that faster Cr transport within the alloy at higher temperatures explains the change in morphology. This hypothesis is supported by thermodynamic calculations and kinetic data. The thickness of the inner oxide layer did not change significantly with oxidation time and temperature for exposures less than 30000 h; however after 57554 h the thickness had increased significantly at the lowest temperatures.

Bundling Advanced Technologies to Achieve Maximum Efficiency and Environmental Acceptability in a Modern Coal-Fired Power Plant

Fifteen municipal electric utilities are jointly studying the feasibility of developing a 500 MW to 1,000 MW coal-fired generation project. The project will combine advanced technologies seeking maximum performance, minimal risk and outstanding environmental acceptability. This paper describes engineering and financial studies comparing coal-firing technology alternatives such as Pulverized Coal (PC), Circulating Fluidized Bed and Integrated Gasifier Combined Cycle, and PC refinements including supercritical steam conditions and innovative use of gas turbine feedwater heating. The paper also examines options to minimize environmental impact. Use of high-efficiency steam plant technologies is found to be an environmental advantage. A prudent combination of sophisticated technologies is found to be cost-effective. Finally, the paper describes the project’s innovative joint development process.

Once-Through Heat Recovery Steam Generators Working With Sub- and Supercritical Steam Conditions for Combined Cycles

This paper characterizes the performances of once-through heat recovery steam generators in combined cycle applications. Although the concept of once-through boilers has been extensively used for fired boilers, this circulation mode is rather new in combined cycles. Once-through circulation is required at very high pressures, including supercritical conditions, for which there is a possible advantage in terms of the plant efficiency. The concept is also certainly the best solution for high subcritical pressures, such as those required by repowering applications. In addition to cycle performance, this paper describes the advantages and disadvantages of the once-through in heat recovery applications. The operational behaviour of such heat recovery steam generators is discussed, together with the main design implications. A prototype plant running in supercritical steam conditions is also described, as well as some of its possible applications.