Session: 06-01 Innovative Combined Cycle

Paper Number: 82693

82693 - Performance Optimization of Semi-Closed Oxy-Combustion Combined Cycle (SCOC-CC) for Current and Future Blade Materials 

Among the possible CO₂ capture technologies, oxy-combustion turbine cycles are attracting increase attention due to the favorable economics and near-zero emissions. According to the techno-economic analysis reported in [1], the most promising cycles appear to be the Allam cycle and the Semi Closed OxyCombustion combined cycle (SCOC-CC). The report indicates that the SCOC-CC has an estimated net electric efficiency of 49.3% (LHV basis), about 5% lower than the NET power cycle, and a 11% higher cost of electricity (92.8 vs. 83.6 Euro/MWh). On the other hand, it is important to notice that: (i) the SCOC-CC cycle relies on more conventional components and cycle operating conditions (turbine inlet pressures in the range 40-70 bar vs. 300 bar of the Allam cycle, standard HRSG for heat recovery vs. Inconel multiflow printed-circuit recuperator), (ii) similarly to standard combined cycles, the efficiency of the SCOC-CC is expected to benefit from the continuous progresses in turbine blade materials and turbine inlet temperatures.

The purpose of this work is to assess the performance of the SCOC-CC considering the turbine technological level of today’s class-H heavy duty gas turbines (i.e., blade metal temperatures up to 900 °C with thermal barrier coating and film cooling, capable of allowing turbine inlet temperatures in the range 1400°C-1700°C) and the level of future gas turbines employing Ceramic Matrix Composite (CMC) materials [2]. Steady-state models of the cycle and cooled turbine are developed using the GS simulation software and the cooled expander model developed by Chiesa and Macchi in [3]. The model is used to investigate the optimal cycle minimum pressure, pressure ratio and turbine inlet temperature for fixed blade wall temperatures (900 °C for Nickel-based superalloys, 1100-1500 °C for CMC blades). Results indicate that the temperature gradient across the thermal barrier coating (or Environmental barrier coating for CMC) is the primary concern: due to the high heat transfer coefficient of CO₂, the temperature difference across the TBC/EBC can be as high as 300 °C also at relatively mild turbine inlet temperatures. Thus, the effect of the maximum allowable temperature difference across the coating has been assessed by considering a range of values (200 °C, 300°C and > 300 °C). The results indicate that the optimized SCOC-CC can reach net electric efficiency (including CO2 purification unit) up to 54% (LHV basis) with today’s superalloys and close to 60% with future CMC blades. Also the CO2 capture level is outstandingly high, above 96%.

 

References:

[1] IEAGHG, Oxy-combustion turbine power plants. 2015. Report 2015/5, August 2015, IEAGHG, Cheltenham, UK.

[2] James A. DiCarlo, Advances in SiC/SiC Composites for Aero-Propulsion, NASA/TM—2013-217889

[3] Chiesa, P., and Macchi, E., 2004, “A Thermodynamic Analysis of Different Options to Break 60% Electric Efficiency in Combined Cycle Power Plants,” ASME J. Eng. Gas Turbines Power, 126(4), pp. 770–785.

Presenting Author: Matteo Martinelli Politecnico di Milano

Presenting Author Biography: Matteo Martinelli graduated in Energy Engineering (MS) in Politecnico di Milano and currently is pursuing the PhD in Energy. His research focuses on the development, modelling and optimization of oxyturbine cycles (Allam cycle, SCOC-CC, etc).

Authors:

Gabriele Pio Risimini Politecnico di Milano
Matteo Martinelli Politecnico di Milano
Paolo Chiesa Politecnico di Milano
Emanuele Martelli Politecnico di Milano