Title: Multi-objective optimisation of supercritical CO2 combined cycles based on energy-exergy-economy balanced analysis
Authors: Chunlei Li; Qitai Eri
Addresses: School of Energy and Power Engineering, Beihang University, No. 37, Xueyuan Rd., Haidian District, Beijing, China ' School of Energy and Power Engineering, Beihang University, No. 37, Xueyuan Rd., Haidian District, Beijing, China
Abstract: In this paper, the supercritical CO2 (sCO2) recompression cycle combined cycles are analysed, where the bottom cycles include transcritical CO2 (tCO2), organic Rankine cycle (ORC) or trilateral flash cycle (TFC). The working fluid for the ORC and the TFC can be R123, R245fa, or n-Pentane. We implemented four sub-models in our calculation: 1) thermodynamic model; 2) heat transfer model; 3) economic model; 4) exergoeconomic model. The specific exergy costing (SPECO) method is utilised in the exergoeconomic model, and the multi-objective genetic algorithm is adopted to give the Pareto front of total unit exergy cost of the product (cPtot) and the thermal efficiency. Our model has been validated with the existing literature. The results show that the thermal efficiency standalone CO2 achieved 41.66% while attaching the tCO2, ORC, or TFC bottom cycle could improve the thermal efficiency by 1.1%, 1.68%, or 0.05%, respectively. In the meantime, the (cPtot, which is the representation of the cost, decreased by 0.2$/GJ for ORC and increased by 0.06$/GJ and 1.05$/GJ for tCO2 and TFC respectively. The influence of different working fluids for ORC and TFC is not obvious. Therefore, attaching the ORC as the bottom cycle will bring about the best performance and lowest cost.
Keywords: supercritical CO2; combined cycle; multi-objective-optimisation; specific exergy costing; SPECO.
International Journal of Exergy, 2022 Vol.38 No.1, pp.85 - 109
Received: 04 Feb 2021
Accepted: 22 Jul 2021
Published online: 19 Apr 2022 *