Optimization of S-CO power conversion layouts with energy storage for the pulsed DEMO reactor
Introduction
Suitability of power conversion cycles using supercritical carbon dioxide (S-CO) was proven for a wide range of applications and there are potential areas in e.g., GenIV nuclear reactors [1], fossil fuel power plants, waste heat recovery [2], renewable heat sources [3], solar thermal power plants [4] and fusion power plants [5].
S-CO as an energy conversion system brings many advantages such as significantly more compact turbine island against Rankine steam cycle, which, besides, positively affects a power plant economic [6].
In comparison with earlier research of S-CO power cycles for the pulsed DEMO in [7], this article solves the optimization of power cycles for the latest DEMO design, focusing on reducing the difference between gross power during pulse and dwell periods. This approach is suitable due to lower oscillations in the electrical output and relatively stable thermophysical conditions of the cooling medium. The elimination of this phenomenon is done using energy storage for the main heat source and using electrical heating to keep steady temperature at the turbine inlet during both periods. This approach requires deep study of power cycles and optimization of the input parameters.
Section snippets
Pulsed DEMO description
Unlike DEMO2, which is assumed to work in steady-state operation mode, the predecessor (pulsed DEMO) will work in the pulsed operation mode. In this study, there were involved two operation modes: pulse with length of h and dwell min [8].
Physical parameters and input data for the power cycles optimization of the pulsed DEMO fusion power plant were obtained from the EUROfusion DEMO balance of the plant for helium cooled pebble bed BB concept [8]. Necessary characteristics of
S-CO power cycles for the pulsed DEMO
This study assumes a parallel connection of the low potential heat sources (DIV-Cas and VV). This connection is visible in Fig. 1. Heat exchangers of the low potential heat sources (DE, VVE, DCE) are connected to the low temperature recuperator (LTR) in parallel. This layout is advantageous thanks to using similar input and output temperature levels of DIV-Cas and VV in comparison with the serial connection of all components used in earlier research [7], [9], [10], [11]. Mass flow is split in
Optimization method
The optimization was done in CCOCS (Cooling Cycles Optimization Software), which was upgraded to include initial and border conditions and calculate a large number of combinations. For this reason, multiprocessing methods were used. This software is written in Python 3 [14] and thermodynamic properties were gained from CoolProp C++ thermodynamic libraries [15].
The objective of the optimization is to find a combination of input parameters that give the highest gross efficiency. This study also
Optimization procedure
The optimization is based on the initial conditions described in Table 1 and on the times of pulse and dwell periods. Efficiencies of components of the power cycle are described in Table 2.
Parametric ranges were set as follows:
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Inlet temperature of the medium to the compressor = 33 C.
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Maximum turbine admission temperature =470 C.
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Main compressor inlet pressure MPa;9.0 MPa.
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Ratio of outlet and inlet main compressor pressure .
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Power diverted from BB and used for BBES
Discussion
Simple Brayton cycle with recuperation gain higher efficiency than re-compression power cycle by 1 . This result is given mainly by the low potential heat sources, which strongly limit the outlet temperature of the auxiliary compressor. Due to this issue, it is more difficult to optimize the re-compression cycle. In Fig. 6 it is visible that there are less results than in the case of simple layout. The number of successful combinations is by 35 lower for re-compression cycle. In comparison
Conclusion
This article describes two S-CO layouts in connection with electrical heating. This study showed that simple Brayton cycle with recuperation has many advantages to re-compression cycle. It is given by the higher total gross efficiency of both cycles, which directly influences the total gross power behind generator. The auxiliary compressor in re-compression layout is barely used and its power is suppressed by optimization. Moreover, the mass flow is lower in the case of simple layout and
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The work was supported by European Regional Development Fund - Project “Center for Advanced Applied Science” (No.CZ 02.1.01/0.0/0.0/16-019/0000778) and by the Strategy AV21 of the Czech Academy of Sciences within the research program “Systems for Nuclear Energy”.
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Techno-economic comparison of DEMO power conversion systems
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2022, EnergyCitation Excerpt :One of the potential application of sCO2 is PCS of fusion power plants. The sCO2 cycles applied to the DEMO fusion power plants have been studied in several publications, where the research topic was the difference between the optimization of simple and re-compression sCO2 Brayton cycles for DEMO pulse mode [7] and DEMO with stable electricity generation [31]. Another studies focused on the difference in efficiency between basic Rankine steam cycle design and sCO2 cycles and influence of low potential heat sources connection to the PCS [32], complex comparison of Rankine steam cycles and various sCO2 Brayton cycles [14], sizing of sCO2 HXs in the overall PCS design [33] and various modifications of sCO2 based re-compression PCS [34].
Constructing a novel supercritical carbon dioxide power cycle with the capacity of process switching for the waste heat recovery
2022, International Journal of Energy Research