Research PaperExperimental and numerical investigation of supercritical CO2 test loop transient behavior near the critical point operation
Introduction
A supercritical CO2 (S-CO2) Brayton cycle is receiving attention as a promising power conversion system for various heat sources because of its high thermal efficiency, simplicity of the cycle configuration and compact turbomachinery compared to other power cycles: air, water, helium [1], [2], [3], [4], [5], [6], [7]. The main reason why the S-CO2 Brayton cycle can achieve high efficiency is because the compressor work is lower than other gas Brayton cycles due to its high density and low compressibility near the critical point [1]. However, most of the existing property databases are not proven to be accurate near the critical point [8], [9]. Moreover, in case of the S-CO2 Brayton cycle, it is not appropriate to use the ideal gas assumption for predicting the cycle performance. Therefore, controlling the compressor operating near the critical point of CO2 is one of the key technical issues for operating the S-CO2 Brayton cycle with a high thermal efficiency.
Due to the growing interest on the S-CO2 Brayton cycle, research on the transient analysis of the S-CO2 system has been conducted by a few researchers previously [10], [11], [12]. However, previous studies showed some limitations in the modeled experimental facility, and the experiment was not performed to observe specific scenario.
To accumulate experiences in control by obtaining experimental data of the CO2 compressing system, KAIST research team has constructed and operated the CO2 compressing test facility, SCO2PE (Supercritical CO2 Pressurizing Experiment). The SCO2PE can be divided into two systems: a primary CO2 system and a secondary water system. The CO2 loop consists of a canned motor type compressor, a spiral type heat exchanger, a globe valve, some control valves, etc. Using the SCO2PE, a compressor under various operating conditions can be tested.
The GAs Multidimensional Multicomponent mixture Analysis (GAMMA) code is a transient analysis code for analyzing hypothetical transient cases in a high temperature gas-cooled reactor system [13], [14], [15]. To simulate the SCO2PE with the GAMMA code, some updates in the code were necessary. A transient scenario was selected to compare the transient analysis code performance and the experimental data. The selected transient scenario is the reduction of cooling event, which the test was conducted in SCO2PE by decreasing the mass flow rate of the cooling water loop. The selected transient is of interest since the compressor inlet conditions start to move away from the critical point of CO2. This can cause degradation in the compressor and heat exchanger performances as well as the system performance. The transient analysis code is to predict the overall system behavior while the event is taking place. Major components, the compressor and the heat exchanger, are separately modeled before the whole SCO2PE loop was simulated, and then the transient simulation is finally conducted with the updated GAMMA code.
Section snippets
The S-CO2 system test facility review
The S-CO2 Brayton cycle benefits from small compression work than other gas Brayton cycles by operating the compressor near the critical point of CO2. However, properties of CO2 near the critical point vary substantially and also it is not appropriate to utilize the ideal gas assumption for predicting the cycle performance unlike other gas Brayton cycles. Therefore, the CO2 compressor data from the S-CO2 compressor test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment) are
The system transient analysis code review
It is known that the testing and modeling of the S-CO2 Brayton cycle require a great deal of technique because the compressing process is conducted near the critical point featuring a large uncertainty [8], [9], [18]. Especially, modeling a S-CO2 compressor is a challenging issue due to the significant gradients in the fluid properties near the critical point and significant windage and other parasitic losses in the compressor which are difficult to model [17], [18], [19]. This issue was well
Validation of GAMMA code with SCO2PE data
Prior to the simulation of whole SCO2PE loop, the major components, the compressor and heat exchanger, were separately modeled and simulated with the GAMMA code.
Conclusions
The main reason why the S-CO2 Brayton cycle can be expected to show high performance is because it consumes smaller compression work than other Brayton cycles due to high density and low compressibility near the critical point of CO2. However, it is difficult to clarify fluid characteristics near the critical point and also it is not appropriate to use the ideal gas assumption for predicting the cycle performance unlike other gas Brayton cycles. Therefore, a S-CO2 pressurizing experiment loop,
Acknowledgements
The authors gratefully acknowledge the support from the National Research Foundation (NRF) (NRF-2013M2A8A1041508) and funded by the Ministry of Science, ICT and Future Planning (MSIP) of the Republic of Korea.
References (26)
- et al.
Potential advantages of coupling supercritical CO2 Brayton cycle to water cooled small and medium size reactor
Nucl. Eng. Des
(2012) - et al.
Study of various Brayton cycle design for small modular sodium-cooled fast reactor
Nucl. Eng. Des
(2014) - et al.
Study of various Brayton designs for small modular sodium-cooled fast reactor
Nucl. Eng. Des
(2014) - et al.
Modelling and simulation of CO2 (carbon dioxide) bottoming cycles for offshore oil and gas installations at design and off-design conditions
Energy
(2013) - et al.
Potential improvements of supercritical recompression CO2 Brayton cycle by mixing other gases for power conversion system of a SFR
Nucl. Eng. Des
(2011) - et al.
Supercritical carbon dioxide turbomachinery design for water-cooled small modular reactor application
Nucl. Eng. Des
(2014) - et al.
A numerical investigation of the sCO2 recompression cycle off-design behavior, coupled to a sodium cooled fast reactor, for seasonal variation in the heat sink temperature
Nucl. Eng. Des
(2013) - et al.
CFD investigation of a centrifugal compressor derived from pump technology for supercritical carbon dioxide as a working fluid
J. Supercrit. Fluids
(2014) - et al.
A supercritical carbon dioxide cycle for next generation nuclear reactors
(2004) Conceptual study of a high efficiency coal-fired power plant with CO2 capture using a supercritical CO2 Brayton cycle
Energy
(2013)
Aerodynamic design of turbomachinery for 300 MWe supercritical carbon dioxide Brayton power conversion system
Supercritical CO2 Brayton recompression cycle design and control features to support startup and operation
S-CO2 Brayton loop transient modeling
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