Search

Supercritical CO 2 is recognized as a promising working fluid for next-generation of high temperature power cycles. Nevertheless, the use of CO 2 mixtures with heavier dopants is emerging as a promising alternative to supercritical CO 2 cycles in the recent years for air-cooled systems in hot environments. Accordingly, this work presents an experimental campaign to assess the thermodynamic behaviour of the CO 2 +SiCl 4 mixture to be used as working fluid for high-temperature applications, conducted in the laboratories of CTP Mines Paris PSL. At first, bubble conditions of the mixture are measured in a variable volume cell (PVT technique), then liquid densities are measured with a vibrating tube densimeter, for molar composition in the range between 70 % and 90 % of CO 2. The Peng Robinson EoS was fine-tuned on the bubble points obtained, resulting in a satisfactory accuracy level. Finally, a non-conventional methodology has been developed to measure bubble points with the vibrating tube densimeter, whose results are consistent with the VLE data obtained with the standard PVT technique. Thermodynamic analysis in next-generation concentrated solar power plant, at 700 °C turbine inlet, confirms the mixture overcomes 50 % thermal efficiency, providing +4.2 % net electrical output over pure supercritical CO 2 at equal thermal power from the solar field. • Carbon dioxide/Silicon Tetrachloride mixture is proposed as innovative working fluid. • Bubble points and liquid densities of the mixture are experimentally obtained. • The experimental data are used for the fine-tuning of the equation of state. • The thermodynamic efficiency of the mixture is simulated in next-generation CSP plant. • The mixture enables +2 % electric efficiency gain compared to pure sCO2. [ABSTRACT FROM AUTHOR]

The present study explores the integration of supercritical CO 2 (sCO 2) power cycles into Concentrating Solar Power (CSP) plants using molten salt, and the hybridization of these plants with solar photovoltaic (PV) systems through electric heaters. Techno-economic evaluations determined the optimal power cycle configuration and subsystem designs for two different scales and locations and then compared them with state-of-the-art solar power plants. The results show that hybridizing PV with state-of-the-art CSP can lead up to a 22% reduction in the Levelized Cost of Electricity (LCOE) compared to standalone CSP systems. This hybridization and the use of electric heaters are particularly beneficial for small-scale installations and locations with low DNI/GHI ratios. By replacing the steam Rankine cycle with a sCO 2 power block, a further 42% reduction in LCOE can be achieved at small scales, even with a simple recuperated cycle. In conclusion, the hybridization with PV and the integration of sCO 2 power blocks provide cost benefits despite the temperature limitations imposed by the molten salt. Hybrid PV-CSP plants with sCO 2 power blocks prove to be a cost-effective solution for capacity factors exceeding 60%. For lower capacity factors, configurations combining PV with battery energy storage or PV with electric heaters, thermal energy storage, and sCO 2 power blocks are preferable options. • Hybrid PV-CSP plants with sCO 2 cycles can be a cost-effective solution for CF exceeding 60%, both at small and large scale. • Hybridizing PV with CSP reduces LCOE by up to 22% compared to CSP standalone. • Hybridizing PV and CSP with electric heaters is beneficial mainly at small-scale and in locations with low DNI/GHI ratios. • By replacing steam Rankine cycles with sCO 2 ones lowers the LCOE by 42% in small-scale PV-CSP plants with molten salt. • A simple recuperated Brayton cycle is the suggested Brayton cycle to be integrated into CSP plants with molten salt. [ABSTRACT FROM AUTHOR]

A hybrid power cycle is designed based on the Allam cycle configuration. The system utilizes solar power as its primary heat source and natural gas oxy-combustion as a complementing heat source. The purpose of the complimenting heat source is continual production when the sun is not available and to ensure the reliability, responsiveness, and availability of the cycle for power generation with minimal adverse effects on the environment. This study is divided into three major steps. The first and second are energy and exergy analyses. The third step is exergoeconomic analysis to obtain the cost contribution of cycle components relative to its final product. Both configurations brought similar power output and second law efficiency. However, the energy efficiency was higher for the oxy-combustion configuration. The total product cost ($/GJ) for the oxy-combustion configuration was 50% less for the concentrated solar power configuration. The unit cost of electricity in (Cent/kWh) for the concentrated solar power configuration is approximately 60% higher than for the oxy-combustion configuration. The results showed potential reduction and cost-saving for both configurations; reducing exergy destruction in the main heat exchanger and the recuperator (concentrated solar power) or replacing the air separation unit (oxy-combustion configuration). •Design of novel hybrid power cycle with two different heat sources: oxy-combustion and concentrated solar power. •The sCO 2 power cycle has similar power output and exergy efficiency for both heat sources. •The PHX and the recuperator have significant effect on the overall cost of the CSP heat source. •The combustor and ASU are the most critical components to reduce the cost of the Oxy-combustion heat source. •Higher the turbine inlet temperature and pressure improve thermodynamic and exergoeconomic performance. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (SCO 2) Brayton cycle has been widely used in a variety of industrial settings. In this work, three commonly used SCO 2 Brayton cycle dynamic numerical models at different heat source temperatures are built with MATLAB and Simulink software, and the key parameters of three commonly used Brayton cycle models (recompression, reheating and intermediate cooling) are compared when the heat source temperature changes from 813 K to 2,113 K. And The steady-state values of the simulation system and experimental values are verified. Under the same component parameter setting, the recompression of the model cycle efficiency at different heat source temperature is generally the highest, followed the reheating mode, and the lowest in the intercooling model. With the increase of heat source temperature, the efficiency of the recompression model gradually improve. Under 5 % leakage condition, the recycling efficiency of the recompression model increases by 2.58 %, while the efficiency of the reheating model and the intercooling model decreases. Sinusoidal disturbance with the amplitude of 12.5 K and period of 8 s is added at the inlet of HTR hot side, compared with intercooling model and reheating model. The efficiency fluctuation amplitude of the recompression model is large, but the power generation is more stable. • Three SCO 2 dynamic Brayton cycle simulation models are established and validated. • Steady-state key parameters of the system are compared among three different models. • The responses of three Brayton cycle models under the leakage condition are compared. • The sine wave amplitude of temperature of the key points in system are compared. [ABSTRACT FROM AUTHOR]

To provide a higher energy conversion efficiency, an organic Rankine cycle (ORC) is coupled to a supercritical carbon dioxide cycle (sCO 2) for energy cascade utilization. However, power cycles often operate during a wide range of loads and the heat sink temperature varies over time. Therefore, the off-design behavior analysis is vital to better define cycle performance and build control systems. In this paper, detailed design and off-design models of the cycle components are developed to evaluate the cycle performance at different operating conditions. The results show that the cycle thermal efficiency can reach up to 44.39% when the inlet pressures of the sCO 2 and ORC turbine equal to 20.77 MPa and 754.04 kPa, respectively. The variable-speed control strategy is used to regulate the maximum pressure, the mass flow rates and the component behaviors to achieve operational goals. Based on this method, the combined sCO 2 -ORC cycle can be matched well with the nuclear reactor during a wide range of power loads (20–110% normalized power load) and heat sink temperatures (10–40 °C). The cycle performance decreases with plant loads, and an opposite trend is observed when the heat sink temperature changes. Compared with the stand-alone recompression sCO 2 cycle, the combined sCO 2 -ORC cycle can gain a thermal efficiency improvement of 1.09–3.36%. But the cycle performance deteriorates significantly when the heat sink temperature is high due to the increase in the compression power consumption. From an economical point of view, the recompression sCO 2 cycle can gain a decrement by 2.32% for the levelized cost of electricity by integrating an ORC, and further cost optimization of reactors and turbines can make the cycle more commercially competitive. • Thermo-economic optimization and preliminary designs of the sCO 2 -ORC cycle are performed. • Detailed off-design models of cycle and components are developed. • Effects of power loads and heat sink temperatures on cycle performance are obtained. • Integrating an ORC with the sCO 2 cycle can improve efficiency and reduce cost. • Variable-speed control is suitable for a wide range of operation conditions. [ABSTRACT FROM AUTHOR]

Application of the supercritical carbon dioxide (sCO 2) cycle to advanced nuclear reactors have confirmed a number of benefits. However, abundant low-level cooling heat is wasted in the gas cooler. A combined cooling, heating and power (CCHP) system, which integrates a sCO 2 cycle with an Organic Rankine cycle (ORC) and an ejector refrigeration cycle (ERC), is proposed to realize the energy cascade utilization for nuclear power. The thermodynamic and exergoeconomic models of the novel CCHP system are established for system simulations under steady-state conditions. Parametric analysis results show that the decrease of ORC turbine back pressure or the increase of sCO 2 turbine inlet temperature and ERC evaporation temperature contribute to both design thermodynamic and exergoeconomic performance. In addition, there exist optimal values of the sCO 2 compressor pressure ratio and the bottoming cycle turbine inlet pressure to minimize the total product unit cost and maximize the exergetic efficiency. Furthermore, multi-objective optimization by means of a genetic algorithm is carried out to obtain the optimal design performance. The CCHP system can gain an improvement by 9.17% for the exergetic efficiency and a decrement by 5.05% for the total product unit cost compared with the stand-alone sCO 2 system under the optimal condition. • A novel CCHP system based on supercritical CO 2 cycle is proposed. • Thermodynamic and exergoeconomic models of the system are established. • A parametric analysis is performed to study effects of key parameters on system design performance. • Multi-objective optimization by means of a genetic algorithm is carried out. [ABSTRACT FROM AUTHOR]