Development of a Modelica Dynamic Model of Solar Supercritical CO2 Brayton Cycle Power Plants for Control Studies

by Francesco Casella1 & Piero Colonna2
1Dipartimento di Elettronica e Informazione, Politecnico di Milano
2Process and Energy Department, Delft University of Technology

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The supercritical CO2 (scCO2) Brayton cycle power plant is one of the most promising options for the efficient and cost-effective thermodynamic conversion of solar radiation into electricity. The control of the system is one of the challenges that must be overcome in order to bring the technology to the market. On the one hand, the system must be able to cope with large and fast perturbations induced by rapid variation of solar radiation due to changing weather conditions. On the other, the behavior of the system is highly nonlinear. A reliable and flexible dynamic simulation tool based on the solution of first-principle physical equations is mandatory in order to design and optimize the control system of the power conversion unit. A dynamic simulation tool can also be used to study issues related to the strong thermal gradients affecting the high-temperature section of the plant, namely metal creep of the primary heat exchanger and of the turbine stator and first rotor, possibly with the goal of designing optimal controllers that maximize the components’ lifetime. This paper describes the implementation of a dynamic 1D model of a system implementing the recompression-cycle configuration using the Modelica modeling language. This approach allows for a large degree of flexibility, along with the re-use of existing models where possible. The features of the language make it easy to model different plant configurations, as well as to integrate the model of the power unit with that of the receiver, the storage system, etc. Thermophysical properties are computed with the CO2 model implemented in the FluidProp library, which has been interfaced to Modelica. Results of preliminary simulations of open-loop transients are reported, in order to assess the potential of the adopted methodology.