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 1990s 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, which works with a cycle fluid of high steam content, is presented. 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 turbomachinery 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.