Supercritical CO2 (sCO2) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to CSP and waste heat recovery (WHR). To evaluate the competitiveness of sCO2 cycles relative to other competing technologies, mainly steam and ORC, a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO2 plants, compared to the existing steam and ORC solutions. In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO2 cycle configuration shows competitive performance, while in the second case, the simpler sCO2 cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately -130 €/kW compared to the steam cycle). In general, while traditional technologies confirmed a good trade-off between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation.
Electrical power production from CSP is worldwide still limited in its diffusion by a higher LCOE with respect to other renewable sources, nevertheless it offers some unique features such as the possibility of a reliable energy storage capability. Among the most interesting, emerging-to-industrial ready technologies, CO2 power cycles seem to have the potential to provide a major step toward the average plant efficiency and equipment cost levels needed to achieve the marketability. Today, in most cases, supercritical CO2 power loops are seen as an opportunity to achieve a major step in thermodynamic efficiencies if applied in supercritical condition and with a quite complicated cycle configurations (e.g. Recompressed and ReHeated, or other combined solutions), with cycle maximum temperature above 650°C. Current cycle configurations are affected by a relative complexity of the power block, including non-negligible technological uncertainties with respect to simpler Brayton cycle solutions, possibly causing delay in the commercial application of the CO2 power block, at least for CSP applications. The aim of this article is to present some possible CO2 power closed cycle solutions, including supercritical as well as transcritical options, in order to propose cost-effective alternatives to current state-of-the-art steam power block of CSPs, highlighting that relatively simple CO2 cycle arrangements can enhance CSP competitiveness, representing a valid intermediate step towards next more advanced sCO2 cycles.
Supercritical CO2 (sCO2) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to CSP and waste heat recovery (WHR). To evaluate the competitiveness of sCO2 cycles relative to other competing technologies, mainly steam and ORC, a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO2 plants, compared to the existing steam and ORC solutions. In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO2 cycle configuration shows competitive performance, while in the second case, the simpler sCO2 cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately −130 €/kW compared to the steam cycle). In general, while traditional technologies confirmed a good trade-off between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation.
High efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and a few projects in the EU Horizon 2020 program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures. The H2020 SOLARSCO2OL project1, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. This paper presents the first off-design analysis of such a demonstrator, which is based on a simply recuperated sCO2 cycle. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. The whole system dynamic model has been developed in TRANSEO MATLAB® environment. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet. The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely mass flow rate, total mass in the loop, and available heat source. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected.
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