Supercritical CO~2~ (sCO~2~) power cycles are largely considered for CSP, nuclear and waste heat recovery applications owing to its higher efficiency and compact footprint. There are several sCO~2~ cycle configurations proposed for different heat sources and Crespi et al. \[1\] reviewed forty-two of them. The comparison of different cycles is often performed by their design point performance such as efficiency and specific power (kW/kg-s). Although this gives an indication of the capital expenditure (from the specific power) and operational expenditure (from the efficiency) to screen the potential power cycle configuration from many possibilities, it doesn’t give a complete picture as it is not clear what weightage needs to be considered in order to minimise the total cost of the power block. The Levelized Cost of Electricity (LCOE) of a CSP plant is not only the function of power block efficiency and net power but also a function of the annual solar irradiance profile, annual ambient temperature profile, solar multiple, storage hours, to name a few. Thus, the corresponding power cycle off-design performance has to be considered in order to select an optimal cycle for a given plant geographic location.

A flexible MATLAB code has been developed to evaluate the design and off-design performance of different sCO~2~ cycle configurations that uses REFPROP library to calculate the thermal physical properties. This paper describes the design and off-design code architecture along-with the validation. Besides, this study designs a 10MW~e~ CSP plant for three highly potential sCO~2~ cycle configurations for CSP applications: 1) simple recuperative 2) recompression 3) partial-cooling cycles and analyse their design point and off-design performances. Multi-objective optimisation is performed for these cycles with the objective to maximise the specific power and efficiency for different plant off-design conditions using NSGA-II algorithm and the corresponding Pareto fronts are compared. This provides the basis for the plant designer how the plant off-design performance of these cycles varies for different boundary conditions such as ambient temperature, molten salt mass flow rate, and molten salt inlet temperature. The plant annual simulation results are also presented by integrating the sCO~2~ cycle with a molten-salt based solar tower and two-tank TES system. Finally, the LCOE is compared for all the cycles studied and this could support selecting the optimal sCO~2~ cycle for a CSP application.

 

References

\[1\]        Crespi F, Gavagnin G, Sánchez D, Martínez GS. Supercritical carbon dioxide cycles for power generation: A review. Appl Energy 2017;195:152–83. doi:10.1016/j.apenergy.2017.02.048.


Analysis of Design, Off-Design and Annual Performance of Supercritical CO2 Cycles for CSP Applications

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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