Optimization of S-CO2 power conversion layouts with energy storage for the pulsed DEMO reactor

doi:10.1016/j.fusengdes.2021.112609

Fusion Engineering and Design

Volume 169, August 2021, 112609

https://doi.org/10.1016/j.fusengdes.2021.112609 Get rights and content

Abstract

Nowadays, the technology of fusion power reactors faces various engineering obstacles. One of the most discussed topics is the pulse and dwell period of the fusion power reactor, which may be the most challenging for material engineering, electrical power grid, energy storage systems, etc. The main goal of this research is to calculate the optimized parameters for power cycles to gain the highest efficiency. This article also describes the optimization method of a possible supercritical CO $_{2}$ power conversion cycle in DEMO. For comparison, there were chosen two Brayton power cycle layouts using S-CO $_{2}$ . The calculation focuses on the optimization due to the difference between the gained electrical power for these two periods, which lowers the oscillations in the power output. Besides, the approach of calculation via upgraded software for the power conversion cycles optimization is described. The optimization of this specific DEMO design points to the simple Brayton cycle as a better choice due to simplicity, higher flexibility and slightly higher gross efficiency.

Introduction

Suitability of power conversion cycles using supercritical carbon dioxide (S-CO $_{2}$ ) 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 $_{2}$ 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 $_{2}$ 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 $t^{p u l s e} = 2$ h and dwell $t^{d w e l l} = 10$ 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 $_{2}$ 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:

•
Inlet temperature of the medium to the compressor $T_{1}$ = 33 $^{\circ}$ C.
•
Maximum turbine admission temperature $T_{T}$ =470 $^{\circ}$ C.
•
Main compressor inlet pressure $p_{1} \in 〈 7.5$ MPa;9.0 MPa $〉$ .
•
Ratio of outlet and inlet main compressor pressure $r a$ $\in 〈 2; 4 〉$ .
•
Power diverted from BB and used for BBES $P_{s t o r} \in 〈 100$

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 $_{2}$ 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
2023, Energy Reports
The transition to low-carbon technologies lies in the support of modern energy sources, which are also represented by fusion power plants. One of the first fusion power plants will be the European Union DEMOnstration fusion power plant. Among the key attributes that influence the entire design of this power plant, belongs the power conversion system. In addition to the classic Rankine steam cycle, it is possible to use different cooling media, such as supercritical CO $_{2}$ in the Brayton cycle. The advantages of supercritical CO $_{2}$ are mainly in the compactness of the power conversion system, that is, lower investment costs for the entire power plant while maintaining the high efficiency of the entire power plant. The key question that can influence the choice of the power conversion system is the levelized cost of electricity. The direct cost of the supercritical CO $_{2}$ cycles is lower compared to the Rankine steam cycles, in general. On the other hand, supercritical CO $_{2}$ cycles for the DEMOnstration fusion power plant offer slightly lower efficiency (by approximately 1.5 percentage points), which negatively influences supercritical CO $_{2}$ cycles levelized cost of electricity by 10 %–20 % against Rankine steam cycles.
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Citation 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].
Nuclear fusion is a promising low-carbon and low-emission source of energy. One of the first fusion power plants will be the European Union's demonstration fusion power plant DEMO. Among the key attributes that influence the whole DEMO design is the fusion reactor pulse operation. Due to the power fluctuations of the power source, there will be a significant impact on the power plant technology, turbine, etc. Therefore, a power conversion system based on a supercritical CO₂ capable of operating in two nominal power levels is proposed. The system operates in nominal parameters during the entire power cycle without the need for thermal power pulses balancing. Unlike other designs, instead of connecting the energy storage system directly to the heat transfer system, this article proposes a layout with an energy storage system behind the generator. Power pulses are balanced using a battery farm, compensating the fluctuations in the gross power and power plant self-consumption. Power conversion system is based on a sCO₂ Brayton simple cycle with regeneration and includes technology for nominal operation at two levels of thermal power. Optimization of the proposed layout shows thermodynamic net efficiency of 24 %.
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

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Optimization of S-CO2 power conversion layouts with energy storage for the pulsed DEMO reactor

Abstract

Introduction

Section snippets

Pulsed DEMO description

S-CO2 power cycles for the pulsed DEMO

Optimization method

Optimization procedure

Discussion

Conclusion

Declaration of Competing Interest

Acknowledgment

Fusion Eng. Des.

Fusion Eng. Des.

Appl Therm Eng

Fusion Eng. Des.

Assessment of gas cooled fast reactor with indirect supercritical CO2 cycle

Nucl. Eng. Technol.

Design performance simulation of a supercritical CO2 cycle coupling with a steam cycle for gas turbine waste heat recovery

J. Energy Resour. Technol.

Review of supercritical CO2 power cycle technology and current status of research and development

Nucl. Eng. Technol.

Optimization of S-CO $_{2}$ power conversion layouts with energy storage for the pulsed DEMO reactor

S-CO $_{2}$ power cycles for the pulsed DEMO