Introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore research and development work at Graz University of Technology since the nineties has led to the Graz Cycle, a zero emission power cycle of highest efficiency. It burns fossil fuels with pure oxygen which enables the cost-effective separation of the combustion CO2 by condensation. The efforts for the oxygen supply in an air separation plant are partly compensated by cycle efficiencies far higher than for modern combined cycle plants. At the ASME IGTI conference 2004 in Vienna a high steam content S-Graz Cycle power plant was presented showing efficiencies for syngas firing up to 70% and a net efficiency of 57% considering oxygen supply and CO2 compression. A first economic analysis gave CO2 mitigation costs of about 10 $/ton CO2 avoided. These favourable data induced the Norwegian oil and gas company Statoil ASA to order a techno-economic evaluation study of the Graz Cycle. In order to allow a benchmarking of the Graz Cycle and a comparison with other CO2 capture concepts, the assumptions of component efficiency and losses are modified to values agreed with Statoil. In this work the new assumptions made and the resulting power cycle for natural gas firing, which is the most likely fuel of a first demonstration plant, are presented. Further modifications of the cycle scheme are discussed and their potential is analyzed. Finally, an economic analysis of the Graz Cycle power plant is performed showing low CO2 mitigation costs in the range of 20 $/ton CO2 avoided, but also the strong dependence of the economics on the investment costs.

Since the Kyoto conference, there is a broad consensus that the human emission of greenhouse gases, mainly CO2, has to be reduced. In the power generation sector, there are three main alternatives that are currently studied worldwide. Among them oxy-fuel cycles with internal combustion with pure oxygen are a very promising technology. Within the European project ENCAP (enhanced CO2 capture) the benchmarking of a number of novel power cycles with CO2 capture was carried out. Within the category oxy-fuel cycles, the Graz Cycle and the semiclosed oxy-fuel combustion combined cycle (SCOC-CC) both achieved a net efficiency of nearly 50%. In a second step, a qualitative comparison of the critical components was performed according to their technical maturity. In contrast to the Graz Cycle, the study authors claimed that no major technical barriers would exist for the SCOC-CC. In this work, the ENCAP study is repeated for the SCOC-CC and for a modified Graz Cycle variant as presented at the ASME IGTI Conference 2006. Both oxy-fuel cycles are thermodynamically investigated based on common assumptions agreed upon with the industry in previous work. The calculations showed that the high-temperature turbine of the SCOC-CC plant needs a much higher cooling flow supply due to the less favorable properties of the working fluid. A layout of the main components of both cycles is further presented, which shows that both cycles rely on the new designs of the high-temperature turbine and the compressors. The SCOC-CC compressor needs more stages due to a lower rotational speed but has a more favorable operating temperature. In general, all turbomachines of both cycles show similar technical challenges and are regarded as feasible.

Introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. The use of well established gas turbine technology enhanced by recent research results enables designers even today to present proposals for prototype plants. Research and development work of TTM Institute of Graz University of Technology since the 90’s has lead to the Graz Cycle, a zero emission power cycle of highest efficiency and with most positive features. In this work the design for a prototype plant based on current technology as well as cutting-edge turbomachinery is presented. The object of such a plant shall be the demonstration of operational capabilities and shall lead to the planning and design of much larger units of highest reliability and thermal efficiency.

This paper identifies and analyzes the propagation of aerodynamic deterministic stresses through a two-spool counter-rotating transonic facility representative of modern and future turbine aeroengine sections. The test setup consists of a high-pressure stage, a diffusing turning midturbine frame with turning struts, and a counter-rotating low-pressure rotor. The flowfield downstream of the high-pressure stage is strongly influenced by the stator-rotor interaction. Such a mechanism interacts again with the downstream turning midturbine frame leading to a vanerotor-vane interaction, which affects the behavior of the low-pressure stage. The results presented were obtained using a fast-response aerodynamic pressure probe for unsteady measurements as well as three-dimensional unsteady Reynolds-averaged Navier-Stokes calculations. The work is presented in two parts. This first part focuses on the explanation of the flow physics that governs the convection of unsteady three-dimensional flow through the midturbine duct. Viscous and inviscid mechanisms are discussed as main drivers for the convection of wakes, secondary vortices, and shocks. The flowfield in the duct is characterized by three superimposed effects: 1) duct diffusion and radial pressure gradient together with turning strut potential field, 2) rotor unsteady work source, and 3) vane/blade interaction phenomena. The understanding of these mechanisms will eventually help to control the unsteadiness content in future architectures where reduced engine component length will enhance the interaction effects.

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