Thermodynamic and Economic Investigation of an Improved Graz Cycle Power Plant for CO₂ Capture

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 at Graz University of Technology since the 90’s has lead 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 60%. In this work a further development, the S-Graz Cycle is presented, which works with a cycle fluid of high steam content. Thermodynamic investigations show efficiencies up to 70% and a net efficiency of 60% including the oxygen supply. For a 100 MW prototype plant the layout of the main turbo-machinery is performed to show the feasibility of all components. Finally, an economic analysis of a S-Graz Cycle power plant is performed showing very low CO₂ mitigation costs in the range of 10 $/ton CO₂ captured, making this zero emission power plant a promising technology in the case of a future CO₂ tax.