System modification and thermal efficiency study on the semi-closed cycle of supercritical carbon dioxide

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including high cycle efficiencies, reduced component sizing, and potential for the dry cooling option. More research is involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems for CSP applications. In this study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced, up to 50%, compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the simple recuperated and recompression Brayton cycle layouts using s-CO2 as a working fluid are evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the recompression Brayton cycle using an isothermal compressor has 0.2–1.0% point higher cycle thermal efficiency compared to its reference cycle. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency for a wider range of CIT than the reference cycle. Adopting an isothermal compressor in the s-CO2 layout can imply larger heat exchange area for the compressor which requires further development.

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High Flux Microscale Solar Thermal Receiver for Supercritical Carbon Dioxide Cycles

ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2015-48233 ◽

2015 ◽

Cited By ~ 6

Author(s):

Thomas L’Estrange ◽

Eric Truong ◽

Charles Rymal ◽

Erfan Rasouli ◽

Vinod Narayanan ◽

...

Keyword(s):

Heat Transfer ◽

Carbon Dioxide ◽

Heat Flux ◽

Supercritical Carbon Dioxide ◽

Surface Temperature ◽

Thermal Efficiency ◽

Solar Thermal ◽

Fluid Temperature ◽

Thermal Receiver ◽

Supercritical Carbon

Characterization of a microchannel solar thermal receiver for a supercritical carbon dioxide (sCO2) is presented. The receiver design is based on conjugate computational fluid dynamics and heat transfer simulations as well as thermo-mechanical stress analysis. Two receivers are fabricated and experimentally characterized — a parallel microchannel design and a microscale pin fin array design. Lab-scale experiments have been used to demonstrate the receiver integrity at the design pressure of 125 bar at 750°C surface temperature. A concentrated solar simulator was designed and assembled to characterize the thermal performance of the lab scale receiver test articles. Results indicate that, for a fixed exit fluid temperature of 650°C, increase in incident heat flux results in an increase in receiver and thermal efficiency. At a fixed heat flux, efficiency decreased with an increase in receiver surface temperature. The ability to absorb flux of up to 100 W/cm2 at thermal efficiency in excess of 90 percent and exit fluid temperature of 650°C using the microchannel receiver is demonstrated. Pressure drop for the pin array at the maximum flow rate for heat transfer experiments is less than 0.64 percent of line pressure.

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Design Considerations for Supercritical Carbon Dioxide Brayton Cycles With Recompression

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4027936 ◽

2014 ◽

Vol 136 (10) ◽

Cited By ~ 68

Author(s):

John Dyreby ◽

Sanford Klein ◽

Gregory Nellis ◽

Douglas Reindl

Keyword(s):

Carbon Dioxide ◽

Heat Exchanger ◽

Supercritical Carbon Dioxide ◽

Thermal Efficiency ◽

Electricity Production ◽

Design Parameters ◽

Computationally Efficient ◽

Heat Rejection ◽

Outlet Pressure ◽

Supercritical Carbon

Supercritical carbon dioxide (SCO2) Brayton cycles have the potential to offer improved thermal-to-electric conversion efficiency for utility scale electricity production. These cycles have generated considerable interest in recent years because of this potential and are being considered for a range of applications, including nuclear and concentrating solar power (CSP). Two promising SCO2 power cycle variations are the simple Brayton cycle with recuperation and the recompression cycle. The models described in this paper are appropriate for the analysis and optimization of both cycle configurations under a range of design conditions. The recuperators in the cycle are modeled assuming a constant heat exchanger conductance value, which allows for computationally efficient optimization of the cycle's design parameters while accounting for the rapidly varying fluid properties of carbon dioxide near its critical point. Representing the recuperators using conductance, rather than effectiveness, allows for a more appropriate comparison among design-point conditions because a larger conductance typically corresponds more directly to a physically larger and higher capital cost heat exchanger. The model is used to explore the relationship between recuperator size and heat rejection temperature of the cycle, specifically in regard to maximizing thermal efficiency. The results presented in this paper are normalized by net power output and may be applied to cycles of any size. Under the design conditions considered for this analysis, results indicate that increasing the design high-side (compressor outlet) pressure does not always correspond to higher cycle thermal efficiency. Rather, there is an optimal compressor outlet pressure that is dependent on the recuperator size and operating temperatures of the cycle and is typically in the range of 30–35 MPa. Model results also indicate that the efficiency degradation associated with warmer heat rejection temperatures (e.g., in dry-cooled applications) are reduced by increasing the compressor inlet pressure. Because the optimal design of a cycle depends upon a number of application-specific variables, the model presented in this paper is available online and is envisioned as a building block for more complex and specific simulations.

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Hybrid System of Supercritical Carbon Dioxide Brayton Cycle and Carbon Dioxide Rankine Cycle Combined Fuel Cell

Volume 3B: Oil and Gas Applications; Organic Rankine Cycle Power Systems; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2014-25238 ◽

2014 ◽

Cited By ~ 1

Author(s):

Seong Jun Bae ◽

Yoonhan Ahn ◽

Jekyoung Lee ◽

Jeong Ik Lee

Keyword(s):

Carbon Dioxide ◽

Fuel Cell ◽

Supercritical Carbon Dioxide ◽

Hybrid System ◽

Thermal Efficiency ◽

Rankine Cycle ◽

High Mass ◽

Brayton Cycle ◽

Heat Sources ◽

Supercritical Carbon

The Supercritical Carbon Dioxide (S-CO2) Brayton cycle has been receiving a lot of attention because it can achieve compact configuration and high thermal efficiency at relatively low temperature (450∼750 °C). However, to achieve high thermal efficiency of S-CO2 Brayton cycle, it requires a highly effective recuperator. Moreover, the temperature difference in the heat receiving section is limited for the S-CO2 Brayton cycle to achieve high thermal efficiency results in high mass flow rate and potentially high pressure drop in the cycle. Thus, to resolve these problems while providing flexibility to match with various heat sources, authors suggest a hybrid system of S-CO2 Brayton and Rankine cycle. This hybrid system utilizes the waste heat of the S-CO2 Brayton cycle as the heat input to the Carbon Dioxide (CO2) Rankine cycle. Thus, the recuperator effectiveness does not always have to be high to achieve high efficiency, which results in reduction of the recuperator volume reduction. By controlling amount of the heat transfer from the cooler of the S-CO2 Brayton cycle to the Rankine cycle, the total system can be compact and can achieve wider operating range. Thus, the hybrid system of S-CO2 Brayton cycle and CO2 Rankine cycle can be coupled to various heat sources with more flexibility without trading off the performance. In this paper, Molten Carbonate Fuel Cell (MCFC) system is selected to demonstrate the feasibility of the proposed hybrid cycle system while comparing the proposed system’s performance to that of other cycle layouts as well.

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A Design of Parameters with Supercritical Carbon Dioxide Brayton Cycle for CiADS

Science and Technology of Nuclear Installations ◽

10.1155/2018/3245604 ◽

2018 ◽

Vol 2018 ◽

pp. 1-9

Author(s):

Yichuan He ◽

Aihua Dong ◽

Min Xie ◽

Yang Liu

Keyword(s):

Carbon Dioxide ◽

Genetic Algorithm ◽

Supercritical Carbon Dioxide ◽

Thermal Efficiency ◽

Search Algorithm ◽

Pattern Search ◽

Outlet Temperature ◽

Brayton Cycle ◽

Pattern Search Algorithm ◽

Supercritical Carbon

Recompression supercritical carbon dioxide (SCO2) Brayton Cycle for the Chinese Initiative Accelerator Driven System (CiADS) is taken into account, and flexible thermodynamic modeling method is presented. The influences of the key parameters on thermodynamic properties of SCO2 Brayton Cycle are discussed and the comparative analyses on genetic algorithm and pattern search algorithm are conducted. It is shown that the cycle parameters such as turbine inlet temperature, pressure ratio, outlet temperature at the hot end of condenser, and terminal temperature difference of regenerator 1 and regenerator 2 have significant effects on the cycle thermal efficiency. The calculation results indicate that pattern search algorithm has better optimization performance and quicker calculating speed than genetic algorithm. The result of optimization of the parameters for CiADS with supercritical carbon dioxide Brayton Cycle is 35.97%. Compared with other nuclear power plants of SCO2 Brayton Cycle, CiADS with SCO2 Brayton Cycle does not have the best thermal efficiency, but the thermal efficiency can be improved with the reactor outlet temperature increases.

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Design optimization of supercritical carbon dioxide (s-CO2) cycles for waste heat recovery from marine engines

Journal of Energy Resources Technology ◽

10.1115/1.4050006 ◽

2021 ◽

pp. 1-44

Author(s):

Md. J. Hossain ◽

Jahedul Islam Chowdhury ◽

Nazmiye Balta-Ozkan ◽

Faisal Asfand ◽

Syamimi Saadon ◽

...

Keyword(s):

Carbon Dioxide ◽

Supercritical Carbon Dioxide ◽

Thermal Efficiency ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Waste Heat ◽

Recovery System ◽

Heat Recovery System ◽

State Models ◽

Supercritical Carbon

Abstract The global climate change challenge and the international commitment to reduce carbon emission can be addressed by improving energy conversion efficiency and adopting efficient waste heat recovery technologies. Supercritical carbon dioxide (s-CO2) cycles that offer a compact footprint and higher cycle efficiency are investigated in this study to utilize the waste heat of the exhaust gas from a marine diesel engine (Wärtsilä-18V50DF, 17.55 MW). Steady-state models of basic, recuperated and reheated s-CO2 Brayton cycles are developed and optimised for net work and thermal efficiency in Aspen Plus to simulate and compare their performances. Results show that the reheated cycle performs marginally better than the recuperated cycle accounting for the highest optimised net-work and thermal efficiency. For the reheated and recuperated cycle, the optimized net-work ranges from 648–2860 kW and 628–2852 kW respectively, while optimized thermal efficiency ranges are 15.2–36.3% and 14.8–35.6% respectively. Besides, an energy efficiency improvement of 6.3% is achievable when the engine is integrated with an s-CO2 waste heat recovery system which is operated by flue gas with a temperature of 373 °C and mass flow rate of 28.2 kg/s, compared to the engine without a heat recovery system.

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