Conception and optimization of supercritical CO2 Brayton cycles for coal-fired power plant application

Overview & Synopsis

Efficiency enhancement in power plant can be seen as a key lever in front of increasing energy demand. Nowadays, both the attention and the emphasis are directed to reliable alternatives, i.e., enhancing the energy conversion systems. The supercritical CO2 (SC-CO2) Brayton cycle has recently emerged as a promising solution for high efficiency power production in nuclear, fossil-thermal and solar-thermal applications. Currently, studies on such a thermodynamic power cycle are directed towards the demonstration of its reliability and viability before the possible building of an industrial-scale unit. The objectives of this PhD can be divided in two main parts: • A rigorous selection procedure of an equation of state (EoS) for SC-CO2 which permits to assess influences of thermodynamic model on the performance and design of a SC-CO2 Brayton cycle. • A framework of optimization-based synthesis of energy systems which enables optimizing both system structure and the process parameters. The performed investigations demonstrate that the Span-Wagner EoS is recommended for evaluating the performances of a SC-CO2 Brayton cycle in order to avoid inaccurate predictions in terms of equipment sizing and optimization. By combining a commercial process simulator and an evolutionary algorithm (MIDACO), this dissertation has identified a global feasible optimum design –or at least competitive solutions– for a given process superstructure under different industrial constraints. The carried out optimization firstly base on cycle energy aspects, but the decision making for practical systems necessitates techno-economic optimizations. The establishment of associated techno-economic cost functions in the last part of this dissertation enables to assess the levelized cost of electricity (LCOE). The carried out multi-objective optimization reflects the trade-off between economic and energy criteria, but also reveal the potential of this technology in economic performance