Synthesis, design and operation optimisation of a marine supercritical CO2 cycle for nuclear propulsion

Supercritical carbon dioxide (sCO2) cycles are studied as the next-generation power cycles in order to reduce the cost of Concentrating Solar Power (CSP) plants. The design performance of numerous cycles has been investigated, nevertheless, the off-design and annual performance of these cycles are seldom studied. This plays a critical role in selecting an optimal cycle for CSP application, as an efficient power cycle influences the solar field size, consequently affecting the Levelised cost of electricity (LCOE). In this study, the design, off-design and annual performance of three sCO2 cycles; simple recuperative, recompression and partial-cooling cycles are studied. Multi-objective optimisation was performed and the off-design Pareto fronts were compared for the changes in the power cycle boundary conditions. Annual performance simulation was carried out, and the performance of the three cycles was compared when the power cycle is operated in maximum efficiency mode, which facilitates selecting the optimal cycle. The LCOE of the simple recuperated cycle was higher by roughly 1.7¢/kWh than recompression cycle when maximising the power cycle efficiency and the partial cooling cycle is higher by 0.2¢/kWh. However, operating the power cycle in the maximum efficiency mode significantly lowers the plant capacity factor (around 10–20%).

The supercritical carbon dioxide (sCO2) Brayton cycle has been regarded as a promising technique for future energy conversion systems. sCO2 recompression cycle configuration has been widely studied for nuclear reactors with the temperature difference between the reactor inlet and outlet restricted to 200°C. However, this cycle configuration may be not suitable for high temperature gas-cooled reactors (HTGR) with a temperature difference up to 500°C. Herein, we aim to develop an optimal sCO2 cycle configuration for HTGR with a broad temperature span, which has both high cycle efficiency and sufficient mechanical security guaranteed by energy cascade utilization. We propose a recompression cycle combined with reheat and expansion technologies, and perform a parameter optimization in Fortran platform. First, the thermodynamic models of the system are established. Then, the parametric analysis is conducted about the effects of split ratio, temperature difference of the heat exchangers, inlet parameters of turbines and compressors, and isentropic efficiencies on the cycle performance. The sCO2 cycle tailored for HTGR can achieve a cycle efficiency of 44.98%. Our work not only highlights the design criteria of temperature-match between the HTGR and sCO2 cycle but also guides the numerical assessment of the steady-state performance.

Effect of flue gas cooler and overlap energy utilization on supercritical carbon dioxide coal fired power plant

Comprehensive comparison of various working media and corresponding power cycle layouts for the helium-cooled DEMO reactor

The supercritical carbon dioxide (S-CO2) recompression cycle is a power conversion cycle compatible with intermediate-temperature nuclear reactors. The main advantage of the S-CO2 cycle is relatively high efficiency (∼47% at the turbine inlet temperature of 650°C). The dynamic characteristics and control of this cycle remain areas of active research because of the cycle’s unique features, in particular, large fluid property changes near the critical point. This paper reports the conceptual development of a dynamic S-CO2 recompression cycle controller designed to efficiently respond to a demand for reduction of generator electric power. The S-CO2 cycle generator electric power production can be controlled using either turbine bypass (TB) or mass inventory (MI) controllers. Turbine bypass is a fast response controller, which reduces generator power by opening the TB valve. Mass inventory is a slow response controller, with a time constant an order of magnitude larger than that of the TB controller. The MI controller reduces generator electric power through decreasing the inventory of CO2 gas in the cycle by pumping some of the gas into a storage reservoir. Both TB and MI controllers operate in conjunction with a precooler temperature controller, which maintains compressor inlet conditions near the critical point. Although using a TB controller allows for quick reduction of the generator electric power, S-CO2 cycle thermal efficiency is reduced during the steady-state operation. Cycle efficiency can be improved if cycle control is transitioned from the TB to the MI controller. However, directly switching from the TB to the MI controller would result in a spike in generator power because of the large discrepancy between the time constants of the two cycle control modes. To address this deficiency, we have designed a mixed-mode (MM) controller to transfer cycle control to MI mode after steady state has been reached in TB mode. In the MM controller, both TB and MI controllers operate simultaneously, thus maintaining nearly constant generator electric power during S-CO2 cycle control transitioning. Design of an MM controller for the S-CO2 cycle does not appear to have been previously reported in literature. To test our controller design, we have performed proof-of-concept numerical experiments. All controllers in this study were implemented as proportional-integral controllers using the System Control Module (SCM) language. Gain coefficients for all controllers were determined via numerical experiments, in which response of the S-CO2 cycle was calculated with the GPASS (General Plant Analyzer and System Simulator) software package. Gain coefficients and cycle timescales were calculated under idealized conditions of instantaneous measurement response.

Supercritical carbon dioxide (sCO2) cycles are compact, cost-effective and widely adaptable to various heat sources, including the waste heat from gas turbine (GT) exhaust gases. While the addition of a steam cycle enhances the typical 40%-efficiency of GTs up to 60%, their substantial investments render them less appealing for smaller GTs. This creates an opportunity for sCO2 cycles, but a comprehensive comparison of their performance with that of steam across a range of applications remains lacking. Moreover, their applicability to various industrial scenarios based on existing installations is missing from a techno-economic standpoint. To address these needs, four promising sCO2 cycles are evaluated and optimized using Aspen, and compared with the simple steam cycle. Their techno-economic performances are then investigated for 20 industrial GTs of different size up to the larger CCGT units incorporating amine-based carbon capture systems. Due to the significant investments required by the carbon capture unit, the implementation of a CC unit is only investigated for the largest CCGT units. The analysis yielded performance maps demonstrating comparable performances for sCO2 and steam cycles, as well as significant techno-economic advantages for sCO2 bottoming cycles for smaller GTs. However, when it comes to larger GTs combined with reheats and expansions steam cycles, sCO2 cannot outperform them in current technological standards. Nevertheless sCO2 cycles offers an attractive alternative, facilitating cogeneration. Among the different approaches designed to integrate the heat requirements of amine-based capture, steam cycles have always proved more suitable because of the thermal stability of amines. In conclusion, the research underscores the cost-effectiveness and adaptability of sCO2 cycles for heat recovery applications, particularly as bottoming cycles for smaller GTs, while larger GTs present a challenge. The work conducted sheds light on the substantial promise of sCO2 cycles, encouraging further exploration and implementation of these systems in the energy sector.

Supercritical carbon dioxide (sCO2) cycles are compact, cost-effective and widely adaptable to various heat sources, including the waste heat from gas turbine (GT) exhaust gases. While the addition of a steam cycle enhances the typical 40% efficiency of GTs up to 60%, their substantial investments render them less appealing for smaller GTs. This creates an opportunity for sCO2 cycles, but a comprehensive comparison of their performance with that of steam across a range of applications remains lacking. Moreover, their applicability to various industrial scenarios based on existing installations is missing from a techno-economic standpoint. To address these needs, four promising sCO2 cycles are evaluated and optimized using Aspen, and compared with the simple steam cycle. Their techno-economic performances are then investigated for 20 industrial GTs of different size up to the larger combined cycle gas turbine (CCGT) units incorporating amine-based carbon capture systems. Due to the significant investments required by the carbon capture unit, the implementation of a CC unit is only investigated for the largest CCGT units. The analysis yielded performance maps demonstrating comparable performances for sCO2 and steam cycles, as well as significant techno-economic advantages for sCO2 bottoming cycles for smaller GTs. However, when it comes to larger GTs combined with reheats and expansions steam cycles, sCO2 cannot outperform them in current technological standards. Nevertheless sCO2 cycles offers an attractive alternative, facilitating cogeneration. Among the different approaches designed to integrate the heat requirements of amine-based capture, steam cycles have always proved more suitable because of the thermal stability of amines. In conclusion, the research underscores the cost-effectiveness and adaptability of sCO2 cycles for heat recovery applications, particularly as bottoming cycles for smaller GTs, while larger GTs present a challenge. The work conducted sheds light on the substantial promise of sCO2 cycles, encouraging further exploration and implementation of these systems in the energy sector.

Thermodynamic study of supercritical CO2 Brayton cycle using an isothermal compressor

Study on the supercritical CO2 power cycles for landfill gas firing gas turbine bottoming cycle

Advanced oxy-combustion coupled with supercritical carbon dioxide (sCO2) power cycles offers a path to achieve efficient power generation with integrated carbon capture for base load power generation. One commonality among high efficiency sCO2 cycles is the extensive use of recuperation within the cycle. This high degree of recuperation results in high temperatures at the thermal input device and a smaller temperature rise to the turbine inlet. When combined with typical high side pressures ranging from 150 to 300 bar, these conditions pose a non-trivial challenge for fossil fired sCO2 cycles with respect to cycle layout and thermal integration. A narrow thermal input window can be tolerated for indirect cycles such as those used for nuclear power generation and concentrating solar power plants, however, it is at odds with traditional coal or natural gas fired Rankine cycles where the working fluid has been condensed and cooled to near ambient temperatures. Coal fired sCO2 cycles using oxy-combustion have been examined by Southwest Research Institute and Thar Energy L.L.C. under DOE award DE-FE0009593. Under this project, an indirect supercritical oxy-combustion cycle was developed that provides 99% carbon capture with a 37.9% HHV plant efficiency. This cycle achieves a predicted COE of $121/MWe with no credits taken for the additional 9% of carbon capture, and represents a 21% reduction in cost as compared to supercritical steam with 90% carbon capture ($137/MWe). Direct fired sCO2 cycles for natural gas or syngas are currently being evaluated by Southwest Research Institute and Thar Energy L.L.C. under DOE award DE-FE0024041. Initial evaluations of direct fired supercritical oxy-combustion cycles indicate that plant efficiencies on the order of 51% to 54% can be achieved with direct fired natural gas oxy-combustion when paired with the recompression cycle with 1,200 °C firing temperatures at 200 bar. Direct fired natural gas or syngas sCO2 cycles still face significant technology development needs, with the pressurized oxy-combustor a significant component with a low Technology Readiness Level, (TRL) as defined by the DOE. In addition to the combustion system, significant work will be required to prepare the sCO2 turbomachinery for the turbine inlet temperatures required to achieve plant efficiencies greater than 50%.

The supercritical CO2 (sCO2) is regarded as the good working fluid for multiple energy applications. It has advantages on high energy flux density, compact equipment, higher cycle efficiency, product modularization. This paper discusses the sCO2 application with sodium-cooled fast reactor (SFR) on offshore scenes. Numerical models are built for the thermo-dynamic process of the recuperation, the recompression, and the partial cooling sCO2-SFR cycle. Energetic analysis, exergetic analysis, and genetic algorithm are used to find the optimal solution. The sCO2 cycle is well matched with SFR on temperature and pressure ranges. Higher cycle and exergy efficiencies could be achieved with both of the recompression and the partial cooling cycles. The structure improvements make more energy/exergy from the working fluid after the sCO2 turbine be re-used. The recompression cycle could get the highest cycle and exergy efficiencies as 37.85% and 67.15% with 27.17 MW net power. For offshore scenes, both of the recompression and the recuperation cycle are recommended. The recompression cycle owns highest efficiencies, moderately simple structure, similar power class of compressors. And the recuperation cycle has edges on simple structure, less control strategies, the potential realization on Turbine-Alternator-Compressor integration.

Waste Heat Recuperation in Advanced Supercritical CO2 Power Cycles with Organic Rankine Cycle Integration & Optimization Using Machine Learning Methods

Thermo-economic optimization and part-load analysis of the combined supercritical CO2 and Kalina cycle

Research on the applicability of isothermal compressors to supercritical carbon dioxide recompression cycle for nuclear energy

Feasibility of Using sCO2 Turbines to Balance Load in Power Grids with a High Deployment of Solar Generation