Design method for s-CO2 gas turbine power plants: Integration of thermodynamic analysis and components design for advanced applications

Supercritical CO2 (s-CO2) Brayton power plants present advantages like the possibility of using external thermal energy sources (concentrated solar radiation or biomass combustion), high conversion efficiency at moderate temperatures, and possibly low operational and investment costs. This work stemmed from the observation that the optimization of the thermodynamic cycle and the design of the system components can be integrated into a single calculation procedure, which can be subjected to an automated constrained optimization process. The objective of this work is therefore to perform a preliminary assessment of the envisaged methodology. First, the thermodynamic analysis is performed and consists in the study of three s-CO2 power cycle configurations. The thermal efficiency is prescribed to 50% with a power output of 18.7 MW respectively. The effect of the components operation on the turbine inlet temperature (TIT) and regeneration load is studied. The recompression Brayton cycle configuration allows to comply with the specified performance with the lowest turbine inlet temperature (787 C) and at moderate maximum pressure (272 bar). The operating conditions given by this analysis are used as inputs for the design of the regenerator and the cooler. The models of these heat exchangers are validated against the design and performance data of an existing s-CO2 heat exchanger, and well-known commercial design code. The methodology that combines the thermodynamic analysis and the components design is tested with two study cases. The first one is aimed as a first assessment of the adoption of a s-CO2 closed Brayton gas turbine for aircraft propulsion. The s-CO2 power system is designed such that it exceeds the performance rating of a cutting-edge turbofan, and at the same time the weight of the system is decreased as much as possible. The calculations show that the regenerators have a weight of minimum 5 tonne, which is almost the weight of the reference engine. The second study case regards the design of a power plant using a solar tower power as the heater, with the same power output and efficiency as the ones adopted for the thermodynamic analysis (18.7 MW, 50%). This exercise provides key characteristics of the power plant: 636 heliostats that occupy an area of 300 m2, the regenerators weigh 17 tonne, the dry cooler also 17 tonne, TIT is 647 C, and the compressor discharge pressure is 245 bar.Energy Technology (SPET)Process & EnergyMechanical, Maritime and Materials Engineerin