A Comparative Analysis of Two Competing Mid-Size Oxy-Fuel Combustion Cycles

Conceptual turbine and compressor designs have been established for the semi-closed oxy-fuel combustion combined cycle and the Graz cycle. Real gas effects are addressed by extending cycle and conceptual design tools with a fluid thermo-dynamic and transport property database. Maximum compressor efficiencies are established by determining optimal values for stage loading, degree of reaction and number of compressor stages. Turbine designs are established based on estimates on achievable blade root stress levels and state of the art design parameters. The work indicates that a twin shaft geared compressor is needed to keep stage numbers to a feasible level. The Graz cycle is expected to be able to deliver around 3% net efficiency benefit over the semi-closed oxy-fuel combustion combined cycle at the expense of a more complex realization of the cycle.