Optimization of Supercritical CO₂ Brayton Cycle for Simple Cycle Gas Turbines Exhaust Heat Recovery Using Genetic Algorithm

For the application of waste heat recovery (WHR), supercritical CO₂ (S-CO₂) Brayton power cycles offer significant suitable advantages such as compactness, low capital cost, and applicability to a broad range of heat source temperatures. The current study is focused on thermodynamic modeling and optimization of recuperated (RC) and recuperated recompression (RRC) configurations of S-CO₂ Brayton cycles for exhaust heat recovery from a next generation heavy duty simple cycle gas turbine using genetic algorithm (GA). This nongradient based algorithm yields a simultaneous optimization of key S-CO₂ Brayton cycle decision variables such as turbine inlet temperature, pinch point temperature difference, compressor pressure ratio, and mass flow rate of CO₂. The main goal of the optimization is to maximize power out of the exhaust stream which makes it single objective optimization. The optimization is based on thermodynamic analysis with suitable practical assumptions which can be varied according to the need of user. The optimal cycle design points are presented for both RC and RRC configurations and comparison of net power output is established for WHR. For the chosen exhaust gas mass flow rate, RRC cycle yields more power output than RC cycle. The main conclusion drawn from the current study is that the choice of best cycle for WHR actually depends heavily on mass flow rate of the exhaust gas. Further, the economic analysis of the more power producing RRC cycle is performed and cost comparison between the optimized RRC cycle and steam Rankine bottoming cycle is presented.