Optimization of turbine pressures in a net-zero supercritical Allam cycle

The Allam cycle is an innovative clean power cycle that reduces environmental pollution associated with fossil fuel-based power production by capturing the generated carbon dioxide. Numerical simulation of the cycle performance has been reported in past studies. This article develops a new method to predict and optimize the thermal efficiency of the cycle. Optimization of the cycle efficiency is performed with a thermodynamic model with respect to the turbine inlet and exhaust pressures at a fixed turbine inlet temperature (TIT). A criterion is established for the maximum efficiency which subsequently relates the turbine inlet and outlet pressures, exit pressure of the CO₂ compressor, and minimum cycle temperature. Using a previously developed process model, it is shown that the turbine cooling flow rate has a negligible impact on the optimum turbine pressures although it reduces the cycle efficiency by 2–3%. The process model is also used to assess the accuracy of the present method over a wide range of turbine inlet pressures and a CO₂ compressor exhaust pressure (p_CO2^e) of 60 and 80 bar. The average percentage error is found to be −1.6 ± 0.3% for TIT = 1431 K, p_CO2^e = 80 bar and 1.3 ± 0.3% for TIT = 1331 K, p_CO2^e = 60 bar. The methodology developed in this paper improves the understanding of relationships between the key process parameters of the Allam cycle at the condition of maximum efficiency.