Performance Optimization of Semi-Closed Oxy-Combustion Combined Cycle for Current and Future Blade Materials

Abstract

Among the technologies for carbon capture and storage (CCS) from natural gas, oxy-turbine plants are a very promising solution thanks to the high efficiency, absence of stack, and nearly 100% capture rate. This paper investigates the efficiency which can be achieved by the semi-closed oxy-combustion combined cycle (SCOC-CC) with state-of-the-art and future blade materials. In particular, the analysis considers class-H turbine superalloys with a maximum blade wall temperature of 900 °C and ceramic matrix composites with blade wall temperatures of 1300 °C. Sensitivity analyses are performed to determine the optimal pressure ratio and turbine inlet temperature. The results indicate that state-of-the-art superalloys allow the SCOC-CC to achieve 54% net electric efficiency with a 96% carbon capture rate, while ceramic matrix composite (CMC) blades boost the efficiency up to 60%. For both cases, critical factors are the high temperature gradients across the blade coatings (thermal barrier coating (TBC) for superalloy, environmental barrier coating (EBC) for CMC) and the blade thickness caused by the large heat flux exchanged between hot gases and cooling flows.